"Build to Last" Questions and Answers

Robert Riversong has created his own form of the Larsen Truss building system, and specializes in super-insulated houses. He teaches at the The Yestermorrow School in Vermont, and his classes have included: Efficiency by Design; Plumbing DeMystified; Math for Builders; Engineering for the Homebuilder; Hygro-Thermal Engineering: Moisture Mechanics & Management in Residential Construction; Tricks of the Trade; Thinking Like a Mountain; Foundations: Building the Base for Appropriate Construction; and Rigging, Rolling & Raising. From geodesic domes in the 1970s and a community land trust homestead program in rural Maine in 1981, Robert has worked as a project manager, trainer, and consultant for non-profit building projects from inner-city Boston to the hollers of Tennessee.  He has focused on passive solar super-insulated buildings, with one of his design/build projects receiving a Citation for Excellence in a national energy/resource-efficient design competition. Robert has also worked as an outdoor experiential educator and wilderness guide, a ritual leader and rites-of-passage facilitator, and a spiritual midwife for people in transition. 

Q: I recently had a new home built in northern Wisconsin. SIP panels were used throughout, although I recently learned that the builder ended the SIP roof panels at the walls and then "extended" the roof panel beyond the wall with conventional stick construction to form the eaves. This part of the construction is uninsulated. Last year I complained that I was getting extensive ice dams along the eaves and particularly at the valleys. The builder then installed 2" diameter vents in the soffits every couple of feet. This year the ice dams are back. I wonder if you have any suggestions for resolution? Should for example the entire eave be filled with foam? Otherwise, the house seems very tight and we are pleased with energy consumption.

A: Unless there is a heat loss pathway from the conditioned space into the eaves/soffit area, then uninsulated eaves will have no effect on ice dams, and 2" round vents won't help and may make matters worse. Valleys are always notorious places for the collection of snow and ice and are best avoided at the design stage. Given that your house is complete, and assuming there are no gaps in the thermal envelope to leak heat or warm air to the roof, there are only two ways to prevent ice dams - either use a roof rake to remove the snow every time it accumulates more than about 8", or remove the existing roofing and add sleepers, a secondary roof deck, and new roofing to create a vent channel from soffit to ridge, with continuous (linear) soffit vents and continuous ridge vents with a wind baffle - though that may not be possible with a complex roof geometry.

Ice dams must be addressed at the design stage and then by installing a fully vented "cold" roof. "Hot" roofs will always be vulnerable to ice damming when enough snow accumulates to change the thermal gradient and move the melting point to the roof surface.

Q: I am going to have a 20'x20' cabin (with south side greenhouse, eastside porch) built to live in (been in buses, tents, tipis.. for long time). I am disabled, chemically sensitive, "poor". I have little time. So straw bale is out as it has become unaffordable. I am in northern NM. It will be framed wood, tin roof, wood floor. Not sure of outside materials yet. It will be a lot of scavenged stuff. No plumbing or electric to worry about. I have read a lot about good insulation, but everyone keeps saying I need plastic vapor barriers. I hate plastic; plastic is relatively new. There is surely something healthier for me and my environment. Any other suggestions would be most appreciated.

A: Why do you say that strawbale is unaffordable? If you're not installing electric and plumbing, then SB is one of the least expensive and simplest and both energy- and resource-efficient methods of building shelter, particularly if it's load-bearing and doesn't require an additional frame. A clay-plastered strawbale house is also one of the healthiest of all options, since clay both removes toxins from the air and adds health-giving negative ions. Adding a little lime to the plaster prevents mold and bacterial growth.

Vapor barriers were originally required because most homes were insulated with fiberglass batts, which are nearly worthless if air or vapor moves through them (and nearly impossible to install properly). You don't indicate what kind of insulation you're considering, and that will make a difference in terms of vapor control.

But, with any thermal envelope, what is most needed is an air barrier. If air cannot exfiltrate into the insulated cavities, then neither will moisture, and there should not be issues with either condensation or mold and decay (at least from the inside). Be careful, though, with a greenhouse - if it's really used for growing plants then it will need a very high relative humidity, which could cause problems in the living space if they're connected.

Plastic walls - whether interior vapor barrier, spray form or exterior rigid foam boards - is almost always problematic, since it prevents the walls from breathing, can trap moisture, and can reduce the interior negative ion count. But the interior surfaces of the thermal envelope (walls & ceiling) have to be air-tight. This requires some kind of continuous membrane if drywall is not used (and sealed to the bottom and top plates and around electrical boxes). You cannot, for instance, merely install tongue & groove boards on either walls or ceiling without an additional air barrier. Taped drywall is the best and least expensive air barrier and it can be covered by wood. A vapor retarder primer, like Benjamin Moore Super Spec #260, will take care of any moisture diffusion issues.

Q: As a B&B owner/operator for many years I've had the pleasure of meeting people from around the world - one of them identifying as a master builder from the mid-States (Missouri/Kansas/Nebraska?) so we spoke about concerns around how global warming might affect future building practices. I'm planning a major build in the next 18-20 months. We hear about the march of termites northward. A few have been discovered entering into Montana/N. Dakota state lines, but they are not a problem (yet) in Sask. (Canada) He commented that he ONLY uses BLUE rigid foam insulation in soil work since termites do not damage this product (vs. other colors). Does color have any effect on deterring termite infestations?

A: While there is an understanding among wilderness guides (I used to be one) that mosquitoes are more attracted to blue than to other colors (don't wear blue jeans in the wild), the color of XPS (extruded polystyrene) has absolutely no effect on the voraciousness of termites, which will tunnel through any plastic foam to get to damp wood. There is some EPS (expanded polystyrene, the white "beadboard") foam board which is factory treated with insecticide (if you don't mind having poison around your house).

Q: We're doing an extensive remodel, and our builder is recommending cvpc water pipe. This PVC relative is probably noxious to make, but so is copper pipe, and copper leeches into acidic water. We're told cvpc is very stable, heat effecient (loses less heat from water heater to use), etc. In the long run what are the tradeoffs and comparisons with copper?

A: (Leon) My best recommendation is to contact the manufacturers directly and get case reports to do a comparison between PVC and copper.

Q: I want to use ironwood shingles in an alpine environment, but do not know of even a single example of this having been done before. Do you know of any examples of ironwood shingles being used in alpine (non-humid) environments? I can't use it unless I see that it handles this environment- any help appreciated.

A: (Leon) I'm not aware of any ironwood shingles that have been used in an alpine environment. I was able to contact a source who works with the product and here's his answer: "Greetings, it's interesting to note all of the inquires I've had with this project in NZ. We have been selling and installing this product for almost 20 years and do not have an exact example of every condition on the planet. With the same specific gravity as aluminum you'd think that that alone would be enough to satisfy even the most critical builders/architects. There are different thickness' to stop any curling etc.

Q: Do you know of any examples of people preserving conventional "cracker boxes" with natural materials, such as earthbags, rammed earth or adobe?

A: (Kelly) I don't know of any examples of people retrofitting cracker boxes with rammed earth, adobe, or sand bags, but somebody has probably tried some of this. There would be lot of finicky details to work out (such as details around doors and windows)...I would rather start from scratch myself.

Q: I would much rather start from scratch as well... but, perhaps the bigger concern on a grander scale is not necessarily all of the homes to come that have yet to be built - but the homes that currently exist (there are more of them), many of which have been standing for quite some time (my home 100 years for example), and it is not their fault that efficiency has improved and technology has left them behind, so maybe it wouldn't be right to scrap them and start over, and we can't all go off to the wilderness to set up our dream homes in pristine valleys and remote mountain tops - because if we did they wouldn't be pristine or remote any more... So I guess where I am coming from is how can I best honor this wonderful building which has served the test of time and now serves as my home, and at the same time honor this amazing planet which provided the materials from which the home was built so long ago and heated for so many years in a time when concern over such things as having less of an impact on the planet is most beneficial for all concerned?

A: (Kelly) I didn't want to imply that retrofitting and upgrading existing housing was not a noble effort...it certainly is! It is just not so easily done, or at least each particular dwelling needs to be considered independently as to how best to approach it. For instance, your idea of using earthbags, adobe, or rammed earth in this regard, presents the problem of how to put these thermal mass materials inside an existing dwelling, where they ideally belong. Strawbales, which are best put outside to insulate the walls, need to be put on a substantial foundation and protected from the weather, so they also present challenges. With careful planning, these things can be done, but there is no obvious formula for every house.

Q: There are many homes that currently exist which have been standing for quite some time (my home 100 years for example), and it is not their fault that efficiency has improved and technology has left them behind, so maybe it wouldn't be right to scrape them and start over, and we can't all go off to the wilderness to set up our dream homes in pristine valleys and remote mountain tops - because if we did they wouldn't be pristine or remote any more... So I guess where I am coming from is how can I best honor this wonderful building which has served the test of time and now serves as my home, and at the same time honor this amazing planet which provided the materials from which the home was built so long ago and heated for so many years in a time when concern over such things as having less of an impact on the planet is most beneficial for all concerned?

A: (Kelly) Retrofitting and upgrading an existing housing is just not easily done, or at least each particular dwelling needs to be considered independently as to how best to approach it. For instance, using earthbags, adobe, or cob in this regard, presents the problem of how to put these thermal mass materials inside an exiting dwelling, where they ideally belong. Strawbales, which are best put outside to insulate the walls, need to be put on a substantial foundation and protected from the weather, so they also present challenges. With careful planning, these things can be done, but there is no obvious formula for every house.

C: Michael Reynolds would have us wrap a cracker box in tires. The only problem is most urban settings don't have enough room for what Michael proposes. The stuff that Nadir Khalili does however has the same effect on tempering against the outside elements only it is much thinner (I have never been in a rammed earth building so I cannot comment, but I would imagine it to be similar). So my only concern was tying in the two modalities - the heavy earthen outer wall and the existing building - mainly the foundation, and then how do you sell that to a local building code official? The actual building of the walls would be just like laying brick or adobe (only bigger). Tie the walls into the existing structure as in laying brick, with railroad ties for lintels, and a concrete cap to fasten a sill plate on to for extending the existing roof out a bit. Sealing the existing building side of the wall would depend on the wall material, but generally it could be filled with R7/inch expanding foam like retrofitting empty walls, or perhaps papercrete. Now there is this wonderfully thick outer wall buffering against the outside changes so anything that happens inside won't just go away (assuming we've remembered to take the attic as close to R60 as possible). Most cracker boxes have crawl spaces and some have basements these can become the heat sink later. First lets get the building to stop using so much energy just sitting there - the common formula for any building. If it already exists, what parts of it can be used to environmental advantage, and what needs some tweaking? So again foundation concerns and then selling it to a building code official.

Q: I am a citizen of India and I have built my house two years back in the south part of India in Chennai city. After 1.5 years of completion I have observed many air cracks formed (like a world map)on both the exterior and interior faces of the walls. As I have already spent a lot of money on building the house, now I look for a good, cheap and permanent solution to fill the aircracks without visibility and make my house to be in good shape. Thank you in advance for your best suggestion.

A: (Kelly) It sounds to me like the plaster work was not completed properly; either the original materials were not mixed right, or they were applied improperly. Obviously the plaster has shrunk, leaving the network of cracks. I have seen this happen when a plaster is applied too thickly, or when the plaster has too much lime in it. The solution is likely to re-apply a final coat of plaster over what exists, but the fact that it has been painted could present some difficulties, depending on whether the new plaster will stick or not. I recommend getting the advice of a local specialist in this work.

Q: It would be interesting in hearing your views in building homes resistant to flooding. etc! But I would think your comment would be to avoid building anywhere near areas liable to flooding..lol

A: (Kelly) You are absolutely right that I would advise against building in areas subject to massive flooding, especially along the coast where hurricanes are frequent. If one must build there, then I would design something using materials that would not be damaged by water and in such a way that when water does arrive the building will stand. Earthbags have this potential, as does other masonry materials such as stone, or concrete.

Q: I just bought a house in a flood prone area. The walls are made of bricks and cement.  The foundation has sunk slightly due to poor piling. The interior walls have recently been painted but has turned yellow and brownish at the bottom. Some of the stains are due to past floods.  On top of that, when I scraped off the paint from the walls, it peels off easily and the walls are slightly moist. If I have it repainted, the same problem will crop up. Can you kindly advised me on what can be done?

A: (Kelly) From your description, I would say that your main problem is that with the inadequate foundation, you have moisture wicking up into the masonry wall from the ground. No amount of prep work on the wall prior to painting will solve this problem. I'm not sure what you can do about the moisture, other than digging a French drain around the base of the foundation on the outside and try to direct all moisture away from the wall. You might consider scraping off all of the paint and leaving the wall natural brick. Good luck with this very difficult problem to fix!

Q: We have a brick house on a slight slope. Occasionally rain water collects outside one of the walls and seeps up under the bathroom floor creating a damp area. Should we put a concrete apron around the house or do you suggest something porous? What is your advice?

A: (Kelly) I suggest that you carefully create a French drain around that side of your house that is giving you problems. This means digging a trench, perhaps 1 foot deep and 1 foot wide, laying perferated drain pipe in it, and then surround this with gravel up to the ground level. The pipe is laid in such a way that is will drain any collected water to some "daylight" away from the house.

Q: The cabin is on wood skids...what kind of foundation should we consider/attempt? Want to save the cabin. Ground is wet and muddy year round. 75yds away from riverfront in Washington State.

A: (Kelly) There are several approaches to putting the cabin on a firmer foundation, ranging from a traditional continuous concrete foundation to raising it up on piers. If the skids aren't rotten, you might be able to simply jack the whole cabin up off the ground while you create a substantial rubble trench foundation using local stones underneath where the skids are, and then lowering the cabin back down. This could be done with little cost and could be quite effective.

Q: I live in Northern Vermont and I'm looking to start ASAP cutting down some trees to construct an Adirondack type lean-to. My question is considering the fact that I mostly will be working alone. I'm concerned that the time allowed for me to do most of the cutting peeling and stacking of the logs will cause them to rot. I will be using pine and have read a crazy amount of books that talk about when to cut etc etc. My lean-to will be about 12 x 12. Is there something on the market that's reasonably priced that I can coat my logs with while I continue to cut, peel, stack , inventory the logs before I actually build next year?

Why next year? I again read many things about green wood or seasoned wood and for me I think, or lets say feel, that if I let the logs dry for a year after they were hopefully stacked properly this will help reduce the amount of moisture in the logs which can help me maneuver the logs easier due to the weight reduction, if I'm in fact totally alone while doing this dream of mine. Do I sound confused or mis-informed here? Is using green wood while building the way to go? I would really like to have this structure last as long as possible, but again my help let's say is far and few. I don't want to waste time and efforts just to have this project fall to the wayside due to rotting wood that could have been prevented. I've seen a product called Penetreat, but this also requires another product to be purchased to coat the logs with after you use this. My location is pretty much in the middle of nowhere and I'm really looking for convenience. Time is really not on my side, but being a stay at home father as well as a husband make my weekends limited and when I do get out I want to work efficiently. If I didn't read more up on this I would have just cut, peeled and stacked the wood, without treating the wood thinking that protecting the logs from the elements with a tarp was good enough.

A (Kelly): I suggest that you cut, peel, and stack your logs as you planned. The best way to keep them from rotting is to let them dry out and keep them off the ground with plenty of air circulation around them. It is usually easier to peel the logs when they are still green, since the bark will separate more easily. Pine is a fairly soft wood, which may be more suseptable to rotting than fir perhaps, but still it should not rot if kept dry. I would only tarp it once it has had a chance to dry out completely, which may take a whole year, dependiong on the climate. You can expect the logs to split (or check) lengthwise some, but this does not affect their strength or usefullness in building. It is much better to work with dry wood, because it will have shrunk and should not warp any more after assembly. Once you have built your cabin, then you could give it a coat or two of boiled linseed oil to help preserve the wood. A design that has a good overhanging roof will help keep the logs from rotting over time.

Q: We purchased a doublewide mobile home that is on piers at 4' high. Our lender required a block foundation. Well, the guy put in a footer and then 4' of block and left about 2" between the top block and the bottom of the home. We would like to apply a cementitious polymer overlay, and then we would stamp it with a cement stamp. After it would dry, we would stain the cement to resemble real stone. Not sure if this is a rock question, but you may have come across something like this: Would the fact that the home is on piers affect how we apply the cement? Would the piers cause cracking later? Is there anything we can do first to help prevent cracking?

A (Kelly): I think what you have in mind should work. One way to minimize cracking where the materials may be different would be to attach a stucco netting over the entire area before you apply the plaster.

Q: We're 2 sick retired seniors not able to paint our 36 yr. old split level cedar shake house. Painting again is too expensive as it would have to be painted again in 5 yrs. or so. If we have the house vinyl sided, should the old cedar shakes be removed and replaced with Tyvek and R4 insulation or should they vinyl side over the old cedar shakes. Some of the cedar shakes are wet and blistering, but only in a few places.

A (Kelly): If the cedar shakes are in relatively good condition you might consider blasting the old paint off with a pressure steamer or something and leaving the wood to weather naturally. Cedar will last a good long time, and the fact that they have been painted means that may not have weathered much. Then you wouldn't have to paint them regularly. Those that are blistered or not in good shape could be replaced. If you want to put vinyl over the old shakes they should be absolutley dry, or you can do the Tyvec and insulation route.

Q: I've been looking at a house built in 1888 with a stacked rock foundation. It has a relatively small sag in one section where a small door was put in to shovel in the coal, I imagine. This section has been supporting the house with only a couple of 2X10's. The frame of the house is triple layer thick brick. Do you have any suggestions on how to fix this without making it worse? The sagging is very visible on the exterior of the house and also affects one window

A (Kelly): Repairing foundations is a very tricky business, because the process of repair can have many repercussions on the rest of the structure. Without seeing the exact situation, it is hard to suggest a remedy. There are ways to temporarily jack up the house while you repair the foundation, either by replacing the original stones, or by puting in an adequate lintel across the doorway. I suggest that you seek the advice of a local builder who can access the situation first hand and make suggestions.

Q: I have a one story house in front of the beach in Greece, with hot summers and cold winters with very high humidity. All the beach front houses like mine experience the same problem more or less: The exterior and interior stucco (over brick or concrete) is getting wet and falls out over time due to the humidity from the ocean and the water levels below. Is there a material you would suggest that can prevent this problem? If stucco is an answer, should it be mixed with appropriate materials and in what proportions?

A: (Kelly) This sounds like a difficult problem to deal with. Even if you somehow render the stucco waterproof, there is always the potential that moisture can get behind it and weaken the bonding with the materials supporting it. Obviously, a stucco netting would help keep small pieces from breaking off. And it might be that a more water-proof stucco that uses a high ratio of Portland cement or has liquid latex added might help. It might take some experimenting over time to find the best solution. Maybe just leaving the brickwork exposed would be even better.

Q: Thank you very much for your time and your suggestions which I find very logical and will apply. I just wanted to also ask your opinion about the option of using Styrofoam materials. The idea is to remove the existing stucco, up to the brick surface, then fasten this one inch Styrofoam material by DOW, and then apply a thin coat of stucco. I checked with DOW Company and they suggest that their Styrofoam material can be used in high humidity environments and is considered moisture resistant but they do not provide any warranty other than the thermal warranty on the R value of the foam.

A: I would say that the use of the stuccoed styrofoam might work quite well in your circumstance, since it not only would provide a moisture barrier and a different substrate for the stucco, but it would also provide a layer of exterior insulation which would make the interior masonry act as a thermal mass. Your house would be more stable in temperature, and easier to keep comfortable over all of the seasons.

Q: I live on the Rockaway Peninsula in Queens, NYC which is a long narrow peninsula with the Atlantic on one side and Jamaica Bay on the other. The average altitude is "sea level" and we do get hit often by large storms, high winds, high tides and flooding. What would be the best natural material to use that would be practical in such an area with sandy soil?

A: (Kelly) Certainly building with materials that are not adversely impacted by wind and rain or flooding would be important. So any sort of masonry material, such as stone, brick, or concrete would work. A more alternative approach would be the use of earthbags, which can be filled with gravel (especially on the lower courses). Earthbags can also be fashioned into domes which are especially resistant to winds. With the advance of global warming and likely rise of sea level, you might want to raise the entire house up on piers...

Q: Hello we recently bought a home in middle Tennesse. The home is only 18 months old and has a circular peagravel and concrete driveway, our problem is it is cracking all over, some cracks all the way though. Our question is what may be causing this and is there any way to repair it. I've tried caulk but the cracks just open up again.

A: (Kelly) Once concrete starts to crack there is really nothing that will completely repair this. You can fill any voids with various commercial products that are designed for concrete repair, but this will not keep the crack from enlarging. The only total repair is to either remove the concrete completely and start over again with proper reinforcement, or to raise the level of the existing concrete with a cap of new reinforced concrete. I recommend the use of fiberglass reinforcement strands in any fresh concrete.

Q: I purchased a new townhouse here a year ago and am still having problems fixing small problems. My next door neighbor had a bad crack in her slab that cracked her sheet flooring. Then my other neighbor had a problem with a hardwood floor in her entrance hallway, they lifted up a piece of the wood and she had a crack in the slab more than an eighth of an inch wide. We are all conserned that there might be other cracks throughout the townhouses. Is the builder responsible to lift the carpets to inspect for more cracks as the house is still under warranty.

A: (Kelly) Your question is really a legal one, that we don't have the expertise to answer. I suggest that you take the text of the warranty to get legal counsel locally. It is not unusual for concrete to crack some after it cures, but this should be controlled by proper reinforcement so that such cracks are only cosmetic, not structural. The cracking that you describe is obviously excessive and likely the result of poor planning or workmanship.

Q: I have a cement foundation that is crumbling and I would like to replace it with real stone. I've had a lot of advice from everyone, but would like an expert opinion.

A: (Kelly) Replacing a foundation is a major undertaking and requires a good deal of skill and planning to do it right. Every situation is different, so only general precautions can be sent via the internet. I suggest that you find a local builder with experience in this sort of work to give some advice about your specific situation. The house needs to be adequately supported while the old cement is removed and the new foundation of stone is placed. This stone foundation will need to be seated below frost level. All of this can be done, but very carefully or you can jeopardize the integrity of the house, both immediately and over time.

Q: How can I figure out the depth of footings for house on piers or cinderblocks? Also, I am in south east Texas, so there is potential for flood or hurricane and I am not sure if that will make any difference to the depth.

A: (Kelly) Usually the depth of footings is determined by the frost depth in the area where you live, which I doubt is very deep in south Texas. I would suggest a "toe-in" of a good foot onto undisturbed soil for your piers. This should also give you ample flood and hurricane protection...but you might check this suggestion out with some of your local builders to see what they think.

Q: My wife & I live in Hawaii; our home is a Bali style with an Ironwood or Coconut (not sure which) shingled roof. My question is the wood is starting to show some cupping, bleaching & splitting and we would like to know is there ANY product we can use on it to extend the life of the wood? I forgot to mention that we are about 300ft from the ocean and the weather can be pretty extreme, and we catch our water from the roof to a 14,000gal catchement so the treatment needs to be safe for us to at least bath in. Also the water tends to have a slight rootbear color to it.

A: (Kelly) Unfortunately I am not really familiar with either ironwood or coconut being used as shingles for a roof, so I can't speak from experience. All shingles bear a great deal of hard exposure to the elements and cannot be expected to last beyond a reasonable time (about 35 years for cedar or redwood shingles). As for some product to apply that might extend their life, you might consider an oil (like linseed oil) that would soak in enough to replenish the natural oils. I suggest that you consult some local roof experts who have experience with what you have.

Q: I just want to know if you have any information on building a concrete slab, reinforced with straw?

A: (Kelly) I have heard of using straw as reinforcement in concrete instead of steel mesh. There have been some experiments with this in Canada, but this is not common. A few handfuls of fiberglass reinforcement would likely be much more durable and stronger.

Q: We have an old 70s stucco home. We would like to apply a thin plaster (smooth finish) of some sort to get rid of the old bumpy stucco look. Can you recommend an application for this? We are on a budget of course so Portland cementing over it seems like a waste of money. Thank you in advance for your advice.

A: (Kelly) I suggest that you check with a local stucco company to see what they recommend to smooth this out. It needs to be something that will adhere well to the existing stucco and be be very durable. I wouldn't rule out a cement-based product, since you would not be needing very much to do this job. I would imagine that just a smooth finish (color) coat is all that is needed.

Q: I was wondering how you preserved wood that is in the ground without using chemicals or too much concrete?

A: (Kelly) I don't think there really is a way to preserve wood in the ground, especially without chemicals. It is generally best to keep wood completely out of contact with the soil. There are some species that naturally last quite a long time with ground contact (such as cedar and redwood), but even these will decompose over time. I have heard of people charring the ends of buried logs to delay rot, but I don't know how well this really works.

Q: We will be building our retirement home in southeast Arizona, with very mild winters and only 11-14 inches of rain per year. Our elevation is 4200' where we will be perched, exposed to the 300 sunny days/yr and desert winds. We understand termites are an issue out there. What type of construction material/building would one suggest for this environment. Stick construction is affordable but maybe not the best.

A: (Kelly) I think that you are right that stick construction is not the best, especially when termites are a real concern. Earthen materials, such as adobe, rammed earth, cob and earthbags are good. And masonry materials, such as stone, brick, and concrete are not affected by termites. I would consider going underground in your environment.

Q: My wife and I just bought 3/4 acre in central Michoacan, right on the river [actually wetlands of the river or maybe swamp would be a better word :)]. Local building material is brick or adobe but I question either material's longevity in such a wet environment. Any suggestions for limited available material. in such a wet environment?

A: (Kelly) The main feature to be concerned about in a swampy environment is the foundation. It needs to be substantial enough to protect the walls from any moisture problems, and to eliminate any possible subsidence or shifting over time. The most common foundation here in Mexico is made with mortared stone dug down about a meter into the ground. On such a foundation you can build with adobes or bricks. The other main feature to protect walls from moisture is a good roof that has a substantial eave. This is actually not so common in Mexico, with the boxy building styles and methods used there. A good eave is more important for adobe than for bricks (which are minimally fired here). A whole other route to go would be using earthbags, and these can become part of the foundation as well as the wall. You can start with a shallow rubble trench foundation and then lay a few courses of gravel-filled earthbags before starting courses of bags filled with other materials, such as local soil or crushed volcanic stone. See www.earthbagbuilding.com for more about this technique.

Q: I need  to get a final layer of cement/concrete on the last 2 or 3 entry stairs that  fills in over the rocks that were laid.  I'm thinking I better get it done soon because I don't know how long I can go before it won't adhere to  the previous layer. I know the mix is gray cement and one of the two sands outside on the street.  I also don't know if lime is in it or not.  Do you know the formula and how specific it needs to be?  This mix  has to be the last coating over the rocks to just fill in around them, keeping  them in.  The mix needs to not have much in the way of rocks and be  pretty smooth.

A: (Kelly) Concrete never really adheres very well to other concrete unless it is it still "wet" so there is no hurry on that project. Of the two kinds of sand, you want the river sand, not the yellower, powdery variety, and you want to screen it with at least a quarter-inch mesh. You don't want any lime, just straight sand and cement, in a ratio of about  8 to 1. In order to make this stick better, I suggest that you also add what they call sellador (sealer) which is actually a liquid latex that is water-soluble. You only need about one liter per full sack of cement, so it doesn't take very much...and you mix it with water first and then add this to make the cement when mixing.

Q: I am replacing my cedar fence, which is falling down. I would like to avoid using pressure-treated fence posts, but can find next-to-no alternatives on the web. Would metal brackets embedded in concrete hold up a 6-foot tall post?

A: (Kelly) If you can find cedar posts, these can last up to fifty years in the ground. Your idea of using concrete with metal brackets is also possible, if the brackets are tall enough to be able to bolt them in two places, one above the other by about 6" minimum. There are commercial brackets that are made to support posts resting on concrete piers, and these often raise the post up above the concrete so that moisture does not tend to rot the bottom.

Comment: The roof is the most important system in any building. It seems to my simple way of thinking that the sustainability (and quality) of any building is directly related to the quality of the roofing system. As someone who has been on a building site every day for 30 years I cannot help but observe that members of the lower classes (social economic class) usually are the ones installing what ever roofing system that has been specified. Your web site has huge amounts of information on obscure wall systems, but almost nothing about roofing systems. As a builder I have the usual prejudicet about the architecture profession, however I do not think the sustainable-building movement can afford to ignore the important lessons of thousands of years of architecture.

Response (Kelly): I agree with you about the importance of roofs, and can see your point about making a separate study of the sustainability of various roof systems. When I chose how to build my last house, I decided to make it with earthbag domes, which completely eliminated the need for conventional roof materials.

I would not consider most normal roofing materials particularly ecological, except that some are more durable than others. I often suggest metal roofs because much of the metal used these days is recycled, but there is still a lot of embodied energy there. Those pictures you sent of standing seam roofs are beautiful (I suspect that these are your work), but beyond durability, can you justify these as ecological choices?

It has often confounded me how to get around the need for large amounts of wood, steel, or other industrial materials in fabricating adequate roofs. One possibility that has recently been brought to my attention is yet another industrial material, magnesium cement, but it has the potential for making durable roofs with very little support structure. See this article. +

Q: My husband and I purchased a 100 year old home that is on a small brick flagstone foundation. We only have a very small crawl space under the house, and want to build a second story on top of our house. The city will not allow us to do so unless we reinforce the foundation. I need to know what kind of reinforcements can be done, and what type of worker does this kind of work.

A: You're asking in the wrong place. If the city has imposed structural requirements then you should be asking the city's code enforcement official. Very likely, you'll have to get a licensed engineer to inspect your foundation and draw up a plan for appropriate reinforcement. This typically means digging under the existing foundation to install a spread footing and possibly re-mortaring existing stone or brick joints (though I don't know what you mean by a brick flagstone foundation).

Q: We have a brick wall about 2 feet high around the patio edges that is chipping badly. The wall itself (mortar, soundness) is still very sturdy structurally. I would like to know what kinds of materials I could cover this brick with to make it nice. Would you have any suggestions?

A: (Kelly) Probably the easiest thing to do is cover the brickwork with a cement-based stucco. This can be done in a variety of colors and should provide a durable finish that will keep the bricks from chipping any more.

Q: I have a wood framed, pier & beam home that is covered on the outside with painted wafer board. It will be bricked within the next 2 weeks. I would like to brush on some type of natural, mold resistant paste before the brick is put up. I have a few things in mind but don't know if they will damage the wood over time from humidity. I would like to apply something like salt, borax, or lime. Would these be safe for my health and would they damage the wafer board? Most of the contractors I've asked about this suggest paints or plastic wraps, or they think I'm crazy.

A: Salt attracts water, borax is water-soluble, but lime-wash (white wash) is highly mold-resistant. However, the goal should be to prevent the moisture accumulation that would allow mold growth and rot. There must be a vapor-permeable but water-resistant barrier covering the "wafer board", such as #15 felt or grade D building paper, which also serves as a drainage plane. And there must be an air gap between the brick facade and the sheathing, with weep holes at the bottom of the brick facing.

Q: I have a house built in 1923, sitting on a stone foundation, which was covered and spread flat with mortar or cement. Although the basement in general is pretty straight, there are two portions of the basement that are deviating inward in the middle, about 1-2 inches, even though there is still good mortar completely covering the stone. Someday this will need to be fixed. Looking for a contractor that would be interested in bracing the existing foundation. Seems like no one wants to deal with that issue anymore; most contractors just want to put a new foundation under the house, which is what I am avoiding. Was looking at the possibility of some type of pony wall, possibly placing rebar around the inside perimeter of the basement, putting up wood forms, and then pouring concrete over the existing stone walls, creating a 6-8 inch covering of concrete reinforced by rebar. Is this or another method of reinforcing the existing stone foundation possible? I am looking for a permanent solution that will require little or no maintenance.

A: What you propose is to pour a steel-reinforced concrete wall to stabilize an inadequate and shifting stone foundation, probably with no footing. If you want a "permanent solution that will require little or no maintenance", then you need to follow the advice of the contractors and replace the existing foundation with a reinforced concrete wall on an appropriately-sized footing. It's not just a matter of what the contractors want to do, it's a matter of what the building code requires. Depending on your jurisdiction, you may be required to use an engineer to determine an approved replacement or repair.

Q: We are building a house out of CLT (cross laminated timber). The house must be insulated and clad on the outside, and, because of the incredible tightness of the building envelope, they don't breathe well. Which means that there are some added breathability concerns within the exterior wall assembly, as any water or water vapor that becomes trapped inside the siding will not escape, and is in fact likely to condense against the wood and start to mold.

I have attached a document which shows the suggested detail for the external wall, but I am having an issue with it. The issue is that the insulation suggested is rigid boards of mineral wool, which for a variety of reasons are hellaciously expensive in Atlanta. (our latest estimate was $15,000 to insulate a 1100 square foot space, material cost only).

So we have been exploring some alternative insulation types. The siding we are putting on is smooth HardiePanel, and will be put up in 4x8 sheets. So one proposed solution was to fix furring to the CLT, then fill the void between the CLT and the siding with perlite or vermiculite loose fill. This would add to the thermal mass of the wall, and is very economical, but there doesn't seem to be data on anything like the vapor permeability of aggregate insulation like husks or vermiliculite pellets?

Then of course there is hygroscopicity. We also considered cellulose, but I was concerned about it absorbing too much moisture in our fairly humid climate. I was wondering if you would be willing to venture an opinion about what the most breathable insulation options are, and which might perform best when they need to fill the dual role off adding r-value and allowing water vapor to escape the exterior wall cavity easily.

A: First, I would have to ask why you want to build with such a non-conventional system as cross-laminated lumber rather than conventional stud-wall construction, and thus create these insulation challenges (and probably others). The advantage of insulating on the exterior is that it can provide an uninterrupted thermal boundary (no thermal bridging), but that advantage is lost by applying vertical furring directly to the CLT shell.

Vermiculite (about R-2.13/inch) would require a 6" thickness to meet the modest R-13 minimum wall value for Atlanta (climate zone 3) and perlite (R-2.7/inch) would require 5". They would both create a breathable layer, since their granular nature would create air spaces, but in a hot, humid climate you want a vapor impermeable layer near the outside, with breatheability toward the inside, since the primary vapor drive is outside to in.

I don't like recommending petrochemical foam insulation, but in your application the best exterior insulation would be 2" of foil-faced isocyanurate with foil-taped seams to create an exterior air/vapor barrier. Isocyanurate board has a much smaller global warming impact than polystyrene or polyurethane, as well as higher R per inch (about 7). This would require a vented rainscreen cladding system with vertical furring strips attached to the CLT through the insulation with long screws. And the foam insulation board wouldn't compress like mineral wool as the furring is screwed in place.

The alternative is to go with conventional studwall construction with a cavity insulation like cellulose, air-tight non-permeable sheathing like Huber Zipwall, furring and cladding, and keep the interior wall surfaces breatheable for drying to the interior.

Q: I have read about the life span of shipping containers. Most say between 15 to 20 years, is this correct? I thought they would last longer since they are made of steel. Wouldn't you say that they are better than wood for housing? That they should last longer?

A: (Kelly) If steel is kept from rusting it will last practically forever. Wood does last a long time if kept dry and away from insects, but you can't expect it to last forever. So it all depends on the details of the construction and how it is maintained how long it will last.

Q: I am looking for the best material to use to face the foundation of an older home. What is currently on the house is some sort of concrete aggregate and it is cracking and sloughing off. I am not sure how old this material is, but I suspect 25 or so years. The part of the house it is on is the stone work foundation that is over 200 years old, on the outside of the house, and it needs protection from the elements and to keep the house warmer. I was thinking something on the order of a hyper tufa type material with fiber glass fibers in it and perhaps something to allow for expansion and contraction? I need a good idea and formula from someone more in the know than I who has been there done that. We are in Northern Maryland with fairly wet winters, not too much extreme cold (we will have one to two weeks in an average winter where the temps dip to and stay in the teens at night) and we have extremes of little snow to the occasional 2 or 3 foot snow fall once every three to five years.

A: Most likely what is now cracking and peeling is a coat of Portland cement mortar that has been through too many freeze-thaw cycles and was likely never sealed against water absorption. Hypertufa is a very lightweight, porous cementitious mix designed for potted plants, typically made with sphagnum and perlite.

You need something that is strong and water-resistant. I would recommend a conventional Portland cement mortar, either M or S type ( the mixes are Portland cement, hydrated line, and sand by volume). You can buy these already mixed in bags or in bulk and mixed on site. Type M mortar (3/1/12 mix, 2,500 psi compressive strength) used for below grade load-bearing masonry work and for chimneys and brick manholes. Type S mortar (2/1/9 mix, 1,800 psi compressive strength) used for below grade work and in such areas as masonry foundation walls, brick manholes, retaining walls, sewers, brick walkways, brick pavement and brick patios.

If you want to make it more water-resistant, you could paint it with two coats of UGL Drylok latex masonry sealer after initial curing. If you want it more crack-resistant, you could coat the mortar with 1/8" of surface-bonding cement, which contains fiberglass, and you can make that mix even more water-resistant by substituting acrylic mortar modifier for half of the water. If there is still a lot of mortar intact on the stone, then you could clean off whatever is loose and simply coat everything with surface-bonding cement with acrylic modifier, which increases the bond, the tensile and compressive strength and the water-resistance.

Q: We have built a natural timber frame with larson trusses and straw/clay walls. We are ready to apply a base coat. The question is how do we deal with the detail of the 1 inch thick base coat butting against aluminum windows? This is a double glazed aluminum solar cage/ curtain wall on a natural timber frame. The windows are sealed all around. The house is light clay straw and we are hoping to butt the 1 inch exterior clay base coat right up against the aluminum frame. (There will be wire lath or burlap over the window buck up to the frame.) My worry is: Will the clay plaster base coat adhere to the aluminum?

A: Not only will the clay plaster not adhere to the aluminum frame, but aluminum has a very high coefficient of expansion and, particularly facing south, there will be too much movement for anything that doesn't have a similar ability to stretch. I would recommend installing a wooden plaster stop about 3/16" from the aluminum frame and plastering to that, adding a layer of burlap soaked in clay slip over the outer edge of the stop and embedded into the base coat, then a finish coat over the stops/burlap.

Before any plastering is done, push some 1/4" Closed Cell Backer Rod into the gap between aluminum and wood stops about 1/8" in, and caulk with good quality urethane sealant tooled to form a concave outer surface and an hourglass shape to allow lateral stretching:

Q: We are in the process of building a home insulated with straw bale and cellulose. The south wall of our building is about 14 feet high, and we have decided that rather than going that high with the bales, which seems like it would be potentially unstable and just generally difficult to build, we have decided to insulate the top half of the wall with cellulose. The question we have pertains to how to deal with detailing the junction between the two materials. Since we have to put a vapor barrier on the inside of the cellulose portion of the wall (we live in a cold climate in Quebec), we are wondering whether we should wrap that vapor barrier under the cellulose and over the straw bale in order to create a barrier between the two. My gut is telling me that this will invite condensation problems. The only other alternative I can think of is to create a top plate of plywood over the straw bales as a barrier between them and the cellulose and to then have the vapor barrier from the cellulose lap down vertically to a couple of inches down the bale wall just to allow enough for the plaster to cover it, thereby sealing any potential moisture infiltration points. I think this is a good alternative because the plywood, being full of glue between each ply, should probably provide enough of a moisture barrier that it will not allow moisture to infiltrate into the cellulose portion of the wall. At the same time, since plywood is a cellulose material itself, it has the potential to adsorb any potential humidity that may travel through the wall. Also, since it is a warm material, as opposed to plastic, it may not entrain condensation problems. Any confirmation or correction of my line of thinking would be greatly welcomed.

A: Straw bales and cellulose insulation have very similar hygroscopic properties and, ideally, neither should have a plastic vapor barrier. If the Canadian codes require a warm-in-winter side true vapor barrier, then it will require the same on the straw bale portion of the wall and that is a recipe for disaster, as it will prevent breathing and make plastering problematic. Most cellulose manufacturers recommend against any vapor barrier.

The International Residential Code requires only a 1 perm vapor retarder, which can be accomplished with latex vapor retarder primer, such as Sherwin Williams SuperSpec. If you must use a vapor barrier, I would recommend a "smart" membrane material, such as MemBrain, which becomes more vapor open as the relative humidity increases and will allow the thermal envelope to dry. It is critical to keep exterior water out of a SB wall, with broad roof overhangs and "kickups" to raise the bales 18" off the ground.

Building codes are starting to catch up with the well-established building science, but Canada still requires a vapor barrier. In extremely cold climates, or with uncontrolled indoor humidity, a vapor barrier can make sense. Otherwise it's more likely to create problems than to prevent them.

There is no need to isolate the straw bales from the cellulose, but since it sounds as if you are building a structural SB wall, you will need a compression header at the top. In any case, you will need some way to anchor wood framing in the upper wall section and a 3/4" plywood baseplate may be appropriate if properly detailed.

Q: I want to insulate my house for maximum R-value and don't want to use fiberglass rolls due to fibers getting into environment. I prefer to use board insulation, a natural one rather than poly types. I want to do two sheets with two air spaces. I've been told I could use a cellulose board, but it is not available in my area. I've also been told foil backed is desirable for R-value. Naturally, I want to keep cost down. I'm open to unconventional materials. Much of the insulating will be in steep roof walls. I will be doing most of the work myself, but am pressed for time because I live in a cold climate and need to finish it soon.

A: You don't indicate what area you live in, but the other "natural" batt-type insulations include hemp (in Canada) mineral wool (though high in embodied energy and global warming), sheep's wool (though also difficult to find) and recycled cotton blue-jean batts (a bit more available and nice to work with). There are no natural rigid foam board insulations, but foil-faced polyisocyanurate has the highest R-value per inch and the lowest global warming contribution. For the foil to have any benefit it must face an air space.

I find cellulose board insulation in online search. Is this not a natural material? And when you say the polyisocyanurate board has the lowest global warming contribution, do you mean because it has greatest R value, or because of something to do with its manufacture? How does the R value and expense of the natural materials you suggested compare to the polyisocyanurate board? The blue jean batt-type sounds good, but is there a moisture absorption issue? I'm in Maine.

The only rigid cellulosic board I'm familiar with is Homasote, used mostly for sound deadening. It has too high a density to be as effective an insulation material as batts or densepack cellulose. You don't explain why you want to use a rigid board rather than other types of insulation, but boards are better for covering over studs rather than filling the stud cavities. Of the petrochemical foam insulation boards, polyiso has the lowest embedded global warming contribution due to manufacturing (mostly due to the expansion agents), and the highest R/inch.

Moisture absorption is more a benefit than a problem (except in a flood), as it serves to buffer indoor humidity. But any insulation system requires an effective air barrier to prevent moist air from exfiltrating into the structural envelope. An insulation that readily absorbs moisture protects the wood framing by reducing local concentrations. But any wall system also has to be able to "breathe" to the outside in order to dry.

Q: I am looking to buy a low cost home here in Florida. I have the choice of an older concrete block home which may contain asbestos or newer homes from the post asbestos time period made of wood or also maybe a manufactured home, those are my choices in my price range. I have always been told not to buy a wood house in Florida due to the risk of rot and termites in the humid environment and because they are not as strong in a storm. Is there a way to reinforce a wood house and make it stronger and resistant to termites naturally or using newer building methods ? Or should I stick mainly to the older concrete block homes?

A: (Kelly) Asbestos is only a health hazard when it becomes airborne, so this might a factor in your choice; you would certainly want to know whether any particular house had it as a component though. Any wood house does have the potential for rot, especially in a humid environment, and they are generally more vulnerable to severe storms. Concrete blocks probably hold up better to these two hazards, but it all depends on the detailing and how well built it might be. One approach is to buy a very basic, solidly built house, and then add on to it as time and money allow, making it more energy efficient and comfortable.

Q: We just bought a house in Manhasset, NY that has fiberglass attic insulation and we want to replace it with non-toxic type. Please advise.

A: Loose-fill cellulose with borate-only fire retardants (no ammonium sulfate) is often the most ecologically-responsible and healthiest option.

Q: What has been your experience with roof paint as the slates on the house are losing their colour and there is supposed to be a paint which doesn't wear off for years?

A: (Kelly) I don't put much stock on paint, especially on roofs. Some people swear by Elastomeric, or specially formulated roof paints, but I think they all need to be renewed within a few years. Weather, time and UV take their toll.

Q: Wanted to find out if you can refer me to any books, manuals, websites etc. that can give one insights on the construction techniques used by historic builders that have allowed their structures to last centuries.

A: (Kelly) That is a good question. Most really old buildings are either built of stone or earthen materials that will practically never degrade. You might get some insight from a few books and ideas fromm this website's pages about Building to Last, especially regarding the preservation of historic buildings. For books and information about stonework see the pages about building with Stone. Regarding earthen building, see
rammedearth, adobe, cob, or earthbag.

A: (Owen Geiger) It all boils down to using good building practice on every step. There's no secret to it. Good building practices include making a strong foundation on stable soil (know soil science), good drainage, sloping the grade away from the building, building on high ground, using durable materials, building a good roof, use climate appropriate designs and materials, etc. This can be done even with simple natural materials in many cases. Many ancient rammed earth structures have lasted thousands of years.

Unfortunately, many builders are more focused on profits that durability. We need to get back to the basics. Drive around old neighborhoods in your town and look at how well crafted they tend to be. Obviously, pressed board siding, vinyl siding, asphalt shingles, etc. will not hold up nearly as long as the old ways. Another avenue of research is to learn about building science.

Q: If you have experience with dome houses I would love your opinion. Check it out on zillow.com and tell me what you think. My biggest concern is wood rot in the framing. but short of tearing off shingle and paper or gutting an interior wall not sure how to check.

A: (Kelly) Well, it certainly looks nice on the inside. Geodesic domes are notoriously hard to keep from leaking, with all of the facets exposed to the elements. Judging by the rust on some of the outbuildings, the scene is fairly old. I suggest that you have a thorough inspection focusing on any possible moisture damage in the past. Any sagging or staining could indicate a problem. I recently had a professional evaluation of a house done, and they used a little digital moisture meter that was pressed up against a wall surface to see if there was a problem. Also, another sign is any musty or moldy smell when the space is closed up for awhile. Mainly, you should anticipate being proactive in maintaining the exterior in top shape if you buy this house.

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