Miscellaneous Questions about Cordwood
Rob Roy is Director of the Earthwood Building School, which has specialized in cordwood masonry instruction since 1980. Rob and his wife, Jaki, have built four innovative cordwood homes for themselves since 1975, including the Earthwood home where they have lived for over three decades. Earthwood is a 2400 SF two-story round, load-bearing cordwood home, earth-bermed and earth-roofed. Details of construction are in Rob's Earth-Sheltered Houses (New Society, 2006) and Cordwood Building: The State of the Art (New Society, 2003) two of fourteen books he is written in the alternative building field. Rob and Jaki have taught cordwood masonry in Earthwood Building School all over North America, as well as in Chile, New Zealand, Australia and Hawaii. They have helped scores of owner-builders with their cordwood projects, including homes, saunas and outbuildings. Earthwood has produced a 3.25-hour DVD on cordwood construction, which, with his books, can be accessed through the Earthwood website, or on the Cordwood page here. Rob is considered to be one of the leaders in the field of cordwood construction and earth sheltering. He does individual consultations at a flat rate of $75/hour, but answers questions here without charge. See also Earthwood Facebook.
Questions and Answers
Q: I am about to start building a barn, and three of the walls will be cordwood. I need to know a good method of estimating how much wood I need. Is there a formula or is it just guess work.
A: Here is the formula I use. It seems to work very well.
1. From your plans, determine the square footage of cordwood wall that you want to build.
2. Work in "face cords," which are 4 feet high, 8 feet long and whatever width matches the thickness of your wall (8", 12" 16", 24", whatever). Divide your square footage by 32. For example, if your building has 640 SF of cordwood masonry wall, dividing by 32 yields
20 face cords. (The side of a face cord is 32 SF.)
3. Take 80% of this value to determine how much wood you need, because the wood "swells up" when laid within the mortar matrix. So, in our example, you would need to have 16 face cords at the ready. This will yield enough to eliminate "rejects."
Q: I am thinking seriously about building a cordwood home in West Virginia and am thinking of buying your two books: "Complete Book of Cordwood Masonry Housebuilding: The Earthwood Method" and the newer "Cordwood building the state of the art". I also don't want to be throwing money away. Does the newer copy cover most everything in the older so I shouldn't buy the older one?
A: I have been asked the question about my books a lot during the past nine months, so thanks for the opportunity to clarify this for the vast readership of this website. Complete Book of Cordwood Masonry Housebuilding (Sterling, 1992) was taken out of print by the publisher last year. I have a small number of copies left. Otherwise, you might find it hard to get. Cordwood Building: The State of the Art (New Society, 2003) should be around for many years to come and is the one we now use as a textbook at our workshops.
What's the difference between the books? The 1992 book has two parts. The first half is an overview of cordwood masonry, including all three styles: within a post and beam frame, as a curved wall, and with stackwall (built-up) corners. The second half of the book is the step-by-step construction of our round two-story Earthwood House, which is cordwood masonry above grade (60% of the cylinder's area) and surface-bonded concrete blocks below grade (40% of the cylinder.) The book also describes the floating slab foundation and the earth roof. We provide the book with every set of Earthwood plans that we sell.
The 2003 book has the best 23 or so papers from the 1994 and 1999 cordwood conferences, all redone and re-edited in 2003. This material includes topics such as doing electric with cordwood, the 16-sided post-and-beam frame, bottle-ends, the double-wall technique, Lomax stackwall corners and a lot more. And there is also about 50% additional new material never before in print, about such topics as paper-enhanced mortar, cordwood and cob (cobwood), the use of cement retarder, and new case studies. I am the author of about one-third of the book and the other two-thirds is written by about 25 other cordwood builders. There is an excellent historical chapter by Prof. William Tishler. There really is not very much repetition between the two books. And I still stand behind the information in the earlier book, including the mortar mix.
Concerning cordwood and the code: Most states have adopted (or will soon adopt) the International Building Code, which does not prohibit cordwood. In some ways, it has made things easier, because it allows people to use alternative building methods which meet or exceed code requirements. The onus is on you to make your case with your local building inspector. By the way, the new book (Cordwood Building: The State of the Art) has four papers on cordwood and code issues, something not covered in the earlier book.
I hope this has helped clear the confusion.
Q: We have just purchased a beautiful cordwood masonry home here in northern Saskatchewan, Canada. My wife was concerned with the structure when she discovered (much to my dismay) that the logs appear to be a little loose in the masonry. Will this lead to moisture/rot problems? Should I try to somehow "fill" around the logs before we restain the building?
A: No, the fact that you can move the log-ends within the mortar matrix will not cause rot or moisture problems. The long life of a cordwood wall has to do with the breathability of the wall. Ventilation has been called the best preservative for wood. Wood rot is caused by fungi, which need a steady damp condition, not present on a cordwood wall if basic good building practices are maintained, such as: (1) Keeping the cordwood clear of the ground, (2) Using a good overhang on the building , (3) Debarking the wood, (4) Keep log-ends from touching on the exterior, and (5) Use sound wood in the first place. Now, if there is quite a gap around all the log-ends, you may want to coat the entire mortar joint with a flexible log chinking product such as Perma-Chink or Log Jam(Sashco Industries). This will return a pleasing bright consistent color to the mortar and close off all the gaps, which are causing the movement you describe. Incidentally, I do not advise staining the log-ends. This makes a mess on the mortar and darkens an already dark medium, which is cordwood masonry, particularly on the interior, where you want to do everything you can to maximize light, especially in Northern Sakatchewan in the winter. And why get into a maintenance situation on the exterior? Let it weather.
Q: My wife and I are planning a cordwood wall for our raised bed garden on a slope. The wall will be 2" high and 10" thick topped with local flat rock. We like the esthetics of this idea. Our concern is that the moisture on the soil side of the wall will expand the wood and crack the wall and rot the wood. We have plenty of rot-resistant locust to use and are considering some kind of seal on the inside of the wall. Is this structurally bound to fail in the long run?
A: This project seems like it could be more trouble than it is worth. But, yes, it has been done before, and very attractively, with more traditional woods. As with a building, you need to keep the cordwood off the ground with a concrete or stone masonry foundation. If you are in a frost-free area, maybe 4" solid concrete blocks laid widthwise in the wall, right on the ground, would be sufficient. This would give a 16" wide footing, good enough for a wall width of 10 or 12 inches. Also, as you suggest, the cordwood wall will have to have some kind of "hat" to protect it. This can be tiles, large flat stones, or even a poured concrete cap. Whatever you use must have a good overhang so that the rain is not just running down the wall. It sounds to me like the first step is to try barking the wood. If it is absolutely impossible, you might consider building this wall with the bark on. Enter into this project with the knowledge that you are taking a chance on the success of the wall. Also, it will be a fairly time-consuming way to build a fence or a wall. Let me know how you make out.
Q: I have a neighbor that is very interested in the cordwood designs. I have enough aspen trees to use for the size building that he would like to build. Can you give me a approx. cost for just the wood that would be cut and split when necessary. Perhaps a price on a fire or facecord. (4ft H x 8 ft. L x 16" W). His intention is to purchase the wood only from me, but he would like it already to use and begin construction.
A: I have absolutely no idea what a face cord of poplar (quaking aspen) is worth commercially, even where I live, much less in an unknown part of the country. The wood should be barked, too, best done in the spring, in long lengths, soon after it is cut. With aspen, it is particularly important to store it in single ranks, top of the stack covered, but not the sides.
Q: My husband (handy kind of guy, but age 74 and with severe arthritis in both shoulders plus artificial knee, but still works full time) has taken a wild hare, as we say in Texas, to homestead in the country. I'm 64, but still very healthy and active. All well and good, but I am confronted with problem of building a house on a very tight budget. No choice but do it ourselves. I foresee your website is going to be the answer to a prayer.
A: (Kelly) Building a house, no matter what the technique be, is lots of work...but this can be enjoyable, especially if done so that there is no urgency about moving into the new house. Give yourselves plenty of time to do only as much as you really want to at any given time. And choose a technique that you know will be manageable by the two of you, with some occasional help. I especially like cordwood since it can be done as "infill" under a post and beam roof which will satisfy your local building department and give you protection from the sun and the rain as you proceed. Also you end up with a well-insulated home that requires no maintenance or further finishing inside or out.
Q: Is it ok to chicken wire the outside and stucco the cordwood? I was leaning to the Spanish style appearance. Would there be problems down the road?
A: I recently saw a beautiful cordwood home in Ontario where the inside was plastered. The outside was left as cordwood. I think you could "stucco" the outside, after the wood was dry; that is to say, little or no sap moisture still trapped in the cells. The chicken wire might help with the bond. To be honest, this is an area where I am not experienced, so you have to take responsibility. But I have heard of successful plastering done to cordwood exteriors. I'm just unsure of the best way to do it. We would welcome comments from any readers who have experience in plastering cordwood masonry.
Q: I am interested in building a double stackwall cabin in the North Okanagan of British Columbia. The inside of the cabin would only be 14' X 20'. How much wood am I looking at to need here?
A: There is not enough information in your question to come up with the wood quantity. I need to know whether you are doing stackwall (crisscross) corners or are doing cordwood masonry infilling within a post-and-beam frame (my recommendation). In either case, I need to know the height of the walls. If you are building within a P & B frame, this would be the height to the underside of the girt (or plate beam.) Finally, I need to know the thickness of both the inner and outer walls. In general terms, anyone can figure out how much wood they need if they follow these steps: (1) From the plans, calculate the square footage of the cordwood walls themselves. Don't count windows, doors, and heavy posts and beams that are a part of the wall. (2) Divide the square footage by 32. This yields the number of face cords needed to fill the space earmarked for cordwood masonry, if you were to stack the wood without mortar. A face cord is 4 feet high by 8 feet long by whatever length you are cutting the wood (12", 16", 24", etc.) (3) Take 80% of the figure derived from step (2) and this will be the number of face cords you will need for your project. You will have enough to reject pieces you don't like. This step takes into account the mortar, which tends to "swell" the face cord. Any leftover wood will help to heat you the first winter in your cabin. As an example, if step (2) yields 10 face cords, take 80% of this - or 8 face cords - and you will have plenty.
Q: We would like to build a 14' x 14' cordwood root cellar as a stewardship project for a school in New Hampshire. I know this may sound big but we may be up to 80 students in a few years and need to prepare for this size population. I am told by a long time resident that if the cordwood structure is properly sited on the north side of a hill and in the shade, there will be no need to excavate to maintain a temperature between 40 and 60 degrees year round. I am not so certain that I agree. I believe that even with a living roof there will be a bit too much fluctuation in temperature. I think we probably need to dig it into the hill on three sides. Any wisdom you can give is much appreciated.
A: I agree with you. A cordwood building on the north side of a hill, in the shade, without a source of heat, will not maintain 40 degrees Fahrenheit in the winter, especially in New Hampshire. The interior will freeze, and severely. Similarly, I think the interior will eventually get to ambient temperature in the summer, possibly in the 70's. Your idea of digging it in on three sides is a good one. I am not too wild about using cordwood masonry below grade. It can be done, but must be done very carefully: dry cordwood, parge the outside smooth with two coats of plaster, apply a waterproofing membrane and use good drainage. Frankly, as much as I love cordwood masonry, I would personally use surface-bonded concrete blocks for this root cellar. Use cordwood masonry on the one exposed side. And, no, the earth roof, while helpful, is no panacea, unless it is very thick, placing the whole building, effectively, deeper into the ground. Structurally, that becomes expensive. An extra inch of extruded polystyrene is as effective as an extra foot of earth, in this regard, and a whole lot easier and cheaper to do, because of the high cost of the structure to support an earth roof on a 14-foot span.
Q: I was reading your book about the round cordwood house you built, Earthwood. I'm not asking anything about the cordwood, but I'd really like to know how the sod roof has held up through the years and if any moisture problems or maintenance occurred.
A: We love the earth roof and it has performed very well for 25 years now. We had a small leak in the membrane the first year, the result of bad edge detailing and some tenacious carpenter ants. We had to dig up a section, repair the leak, and improve the drainage detailing. Then, no problems for over 20 years. In December of 2004 we had another leak, this one in the bathroom. Again, ants seemed to be the culprits, eating up from some wane in the 2x6 T&G planking and through the membrane. Christmas Day was warm enough that year to give us a narrow window of opportunity to quickly pull up the earth and the insulation, repair the leak, and rebuild everything before the dark and cold returned. Took us about four hours. No leaks since. Our new Stoneview Guesthouse at Earthwood is an octagonal post and beam frame, with the eight wall panels made of cordwood, a door, and windows. The living roof was a very successful experiment making use of just 3.5" of earth, planted to sedum, chives, and other drought-resistant plants. It is the most beautiful roof on campus. We have improved our drainage detailing, too involved to discuss in this reply, but my new book, Earth Sheltered Houses, covers this thoroughly in a designated chapter. Outside of the two small leaks mentioned, we have had no problems with Earthwood's roof. We agree with Mac Wells that Americans are paving and roofing certain parts of the country to death. The earth roof has energy, environmental, and esthetic advantages and, if done right, is the longest lasting roof you can build, because the substrate is protected from the negative effects of erosion, freeze-thaw cycling and UV deterioration. Earth roofs also provide protection from sound, tornados, fire, and radiation.
Q: Hi, am really excited to start building...but I am in the midst of nay-sayers who are concerned about the problem of termites in the Dallas, TX area. How do we go about building the foundation for the cordwood and leave these little pests hungry and wanting?
A: I know of only one instance where termites attacked a cordwood wall. (There may be others I have not heard of, so, readers, let me know!) In this case, the owner/builder, in southern Georgia, had had no problems with termites for several years. Then he installed an air conditioner in one of the windows. Due to less than ideal detailing, condensate poured down the wall, keeping it constantly wet. Despite being built mostly of cypress and red cedar, fungi began to grow. Termites ran up the wall to harvest the fungi, for there was no metal termite shield built into the concrete slab foundation. After a while, the termites destroyed a fair amount of cordwood under the window, but there was no damage anywhere else.
Keeping the cordwood wall from experiencing constant damp is imperative. This means a good overhang and detailing, such as with an AC unit. Keep the cordwood at least 6 inches clear of the ground in damp climates, more if possible. Use a metal termite shield on the foundation, and walk around the building once in a while and look for evidence of termites, such as their above-grade "tubes." Kick 'em out if you see them. When people ask me about termites in a cordwood wall, I kind of turn the question around and ask, "What about termites in a framed wall?" They get in and you don't even know it until considerable damage is done.
Finally, I have heard (and it makes sense) that termites do not like to enter into the hard end-grain of the log-ends.
By the way, I have problems with this business of poisoning the ground around the home with chemicals against termites, required by some banks, and, perhaps, even some local code jurisdictions. These chemicals (poisons) have got to get into the water table, particularly where the percolation rate of the soil is rapid. I much prefer a termite shield and frequent monitoring around the base of the wall. Don't hide cordwood where you can't see it. Ventilation is our best preservative.
Q: I would like to build a cordwood blacksmith shop in southern WI. It wont be used often, so no heat, no lights,etc. The foundation would be timbers on laid on 4x6 treated wood, with a hard packed floor; walls about 6" thick, and a foot print of 12'x12'with a small porch. I have read all (almost all) the q&a of yours and other types of building. I have apple, pair, oak, walnut, elm, pine & maple. I don't have enough of one to complete the building. I'm not looking for perfection just workable, but I do want it to last about 10 years. By then I hope to move to a more open site not residential. Do you see any major problems?
A: In answering your question, I am keeping in mind your goal of a 10-year structure, with no heat. My suggestion is that you use 6x6s to frame the building, get a roof on it and then start the cordwood. You don't say what kind of pine you've got, but most pines are less troublesome than the other woods you mention, which are all hardwoods. So use the pines on the first course, at least, and then mix the hardwoods in on succeeding courses. With 6" walls, you will need to go with a solid mortar joint as there is no room for insulation and you are not worried about heating the structure, anyway.
Q: How do you correct what Malcome Wells calls an "energy nosebleed", something about not wanting to have direct conduction of heat from the inside of the building to the exterior? What is this thermal break in the framing system to prevent condensation? How do you create this thermal break?
A: Thank you for a good question. Softwood timbers on side grain, such as the posts and girts of a post and beam frame, have an R-value of between R1.0 (red and white pine) and R1.5 (white cedar) per inch of thickness. So an 8x8 post has a total R-value of between R8 and R12, hardly an energy nosebleed. Compare with a thermalpane window at R2. I have never seen condensation on the inner surface of any heavy timber frame building, and I have seen a lot of them.
Q: Could you suggest one or two definitive books for someone looking to build a cordwood home?
A: The basic textbook we use at our cordwood classes at Earthwood is Cordwood Building: The State of the Art. The CoCoCo/05 Collected Papers has the latest developments. Cordwood and the Code is good ammunition if you anticipate a battle with your local code enforcement officer. Richard Flatau's Cordwood Construction: A Log End View is also good, and is the least expensive at $20. All are available from Earthwood at out website, www.cordwoodmasonry.com , although Richard's book is not listed on the order form. Just add it on at $20 and include $2 shipping. We have a 3-1/4 hour Complete Cordwood DVD which we sell at a reduced price of $44 (including First Class Postage).
Q: I'd like to get hands-on experience at building a cordwood house other than attending a workshop. I'd volunteer to learn the skills and trades of cordwood masonry. Is there any green building coop in the US or Canada that would be interested in getting volunteer help?
A: I am not aware of any co-op of the kind that you describe. There is an excellent cordwood forum at www.daycreek.com and you could put your request as a posting on that forum, if you have not already done so. Keep in mind that there is a learning curve to cordwood, so that it is only worth while for builders to train a volunteer if that volunteer is willing to stay on and help for at least a week or two.
Although you indicate that you are not interested in attending a workshop, it is a great place to meet other people in the same situation. Very often, students get together and help each other on their individual projects, a networking benefit of workshops that is often not considered.
Q: I am working on a small cordwood cabin (16 ft internal diameter, circular). It has taken me 4 days to locate, collect, debark, and cut enough wood for one face cord. I am using hardwoods as this is all that is available in my location. I am a novice builder who is new to cordwood building. I have plenty of wood available in my lot, consisting mostly of the scrap from a logging operation, and I'm a student which means I have almost every day of the summer to work on this. My question is about the amount of time I should expect the project to take. I would like to have the building enclosed, including the roof, before November, if possible, and I am wondering if this is a reasonable timeframe?
A: The only "truth" I have managed to come up with in 60 years on this planet is this: "Everybody is different." I have seen people who would do the project you describe in 3 weeks, others would squander away 6 months. It seems to be taking you quite a while to gather the wood. Depending on doors and windows, and height of wall, it seems as if you will need 6 or 7 face cords of wood. At 4 days per, this looks like 24 to 28 days of work just to get the wood prepped. Perhaps you will gain speed with experience. Once you have the wood, it should be possible to do a 16-foot diameter cabin in 30 days of cordwood laying. Then there is the foundation, the roof, and other details which you don't discuss in your letter. I think you could do it by November, but, then again, "Everybody is different!" Go for it! And best of luck to you.
Q: My husband and I live in Nova Scotia, Canada. We have decided to build our dream home using cordwood. Can you tell us what would be the best wood and supplies for this area? What would you use for interior supplies (wiring, plumbing, windows, insulation etc)? What would we have to look into for building permits? And are these types of home easy to get home insurance for?
A: I cannot be familiar with woods available in all the various regions of North America. Please read my past replies to others, wherein I describe the importance of using light and airy woods (which are more stable and have a higher insulation value), as opposed to dense woods with poor insulation value and a greater tendency to swell and shrink.
There really is no difference in "interior supplies" (wiring, plumbing, windows, insulation), to use your words. The wiring of the cordwood walls is a little different from the other non-cordwood interior walls, but this is covered in detail in a couple of articles by Paul Mikalauskas and Michael Abel in my book Cordwood Building: The State of the Art . It is not possible to rehash those comprehensive articles an this type of column. It is rightly said, "A little bit of knowledge is a dangerous thing."
You need to find out what the local jurisdiction to get a building permit. It could be town, county or province. You will apply to the code enforcement officer or the building inspector, two names for the same person. There is an excellent document now available called Cordwood and the Code , which can smooth the way with the code official.
I have never had any trouble insuring cordwood homes, and we have had four of them. In all of the hundreds of cases with which I am familiar, I have only heard of a handful where getting insurance for a cordwood home has been a problem. Some people have had to try several companies, but eventually one comes through.
The books cited are available at our Earthwood website, www.cordwoodmasonry.com
Q: How are cordwood homes affected by termites, or other wood boring insects, or pack rats?
A: I have only once seen a cordwood home attacked by termites, in Georgia. Actually, it was fine for many years. Then the owner installed an air conditioning unit in a window, and it was not detailed properly, so condensate ran down the wall, a constantly damp condition. Fungi began to propagate and, next thing, termites started scrambling up the wall to harvest the fungi. After a while, they had eaten a fairly large hole in the wall.
The best protection against termites a "termite shield." This is a piece of metal, like flashing, that extends out from the foundation, six inches or so off the ground, but below the cordwood. The termites have to build their tunnels around the shield if they want to get to the wall. (And they don't like endgrain of wood, anyway, unless laced with fungi!) You just walk around the building once in a while and look for signs of activity and kick any mound construction down before it reaches the wall. If you live in a termite area, ask the local building inspector or go to the local building supply yard. They should be able to advise you about the termite shield.
It is also a good idea to keep vegetation, including grass, at least two feet back from the wall. I do this with plastic or landscaping cloth, covered with two inches of crushed stone.
If any readers have additional experience with termites in a cordwood wall, please write.
Pack rats? You mean like the Roy family? Can't help you on this one!
Q: I have been wanting to build a cordwood home for 8 years. I live in Sewanee, TN. I am having issues with the bank appraisal, they don't know how to determine it's value. I thought they could use log homes to compare it for value. I keep running into dead ends. Do you have any advise?
A: Your attempt to compare it with log-building was a good idea. Too bad they didn't go for it. My advice to people building of cordwood is to do it within a strong timber frame (post-and-beam) structure. This affords the luxury of working under cover, generally makes the building inspector happy, and you should be able to pass the project off as a timber frame structure. The cordwood infilling, in this case, could be cordwood, straw, light clay, cob, zucchinis, almost anything. (Well, I probably wouldn't use the zucchinis.)
Q: We own a cordwood home in Francy Gap, VA and use it as a second home. The house was completed in 1984 and the walls are 12 to14 inches thick. Two weeks ago, we were checking on the property and found a faucet had frozen during a 5 degree cold snap and it looked like a fire hydrant when we walked into the home. We estimate that water ran for two or three weeks within our home. Overall it is in pretty good shape because the stone fireplace and the concrete slab absorbed most of the water. The remaining water ran out under the logs. The water restoration company has had dehumidifiers and blowers within the house for eight days and the inside of the logs are showing being dry with a moisture reader. The concrete slab and stone fireplace are dry as well. The outside of the logs are still showing higher moisture content and you visually can see the wetness. The logs that are still showing dampness are the bottom section and just where the faucet was located within the inside. I wanted to see if you have any suggestions on how to get the logs dry on the outside during winter or if this is something that will dry in time . My concern is mold or even rotting.
A: Wow, what a nasty surprise to come home to! It is very difficult for me to evaluate the situation from a distance of 800+ miles, so I must issue a disclaimer with my answer: Advice is worth what you pay for it! But, nevertheless, my strong feeling is that the cordwood wall is going to dry out over time and be okay. Fungi will not begin to propagate in the cold, and by the time it gets warm, the wall should be dry. Hopefully, the fungi will not get a foothold. It would not be a bad idea to run an electric fan directed on the very worst area, maybe one inside and out, a few hours a day while you are there. The insulation in the first course - and you don't say what kind - will take the longest to dry out. Let's hope it was sawdust with lime, which will set up with the moisture like a beadboard insulation product.
Q: My husband and I live in Dutch Harbor, Alaska, a windy, treeless, beautiful volcanic island. We want to build with local materials, and have decided that driftwood is the most available "green" resource. After researching a number of options, we are pretty sold on the idea of building a cordwood home, with a Mongolian yurt shape--and have just ordered your book. From what we've read so far, we think this would be a good fit with our climate of high winds, rain, and snow, and almost no sun -- but moderate temperatures. We get 100 or even 170 mph winds, which, of course, can cool a house down quickly. Also, living so far away (800 miles from Anchorage), we want to cut down on or eliminate the cost and energy consumption of shipping materials, and two resources that aren't available locally are the cement (we do have sand, though) and sawdust. With these concerns in mind, do you have any advice for us?
A: Wow, you and your husband are certainly hardy types! Driftwood can be used for cordwood masonry, and has been before, although I would be hard-pressed to locate an example. I remember one being done with driftwood from the Mississippi River.
Make sure your sand is washed and not salty. You want sand that is some distance from the shore, where it has had a good rinsing from rain. Salty sand makes poor mortar. Maybe lime putty mortar would be good for you. The lime bags are lighter, only 50 pounds instead of 94 pounds for Portland. And all you need is lime: no Portland, no sawdust (for the mortar), no cement retarder. The downside might be, for you, that lime putty mortar requires a couple of weeks of frost-free conditions to set without damage, whereas the Portland mix needs to be protected from frost for just a couple of days. For insulation, an absolute necessity for you, you could bring in any sawdust, or bales of cellulose, which fluff up nicely.
You mention a yurt, which requires a tension ring around the outside of the top of the wall. I do a lot of round cordwood buildings, and I always use a center post to support the inner end of a radial rafter system. This prevents outward thrust on the wall, so that you don't need the tension ring. The wind should move quite nicely around your round building, particularly if you don't spoil the aerodynamics by plunking a mudroom or some other appendage onto the side of it. If you must have a mudroom, keep it inside the building, as we have done at Earthwood.
Q: I have read several books on cob/strawbale/cordwood building and would love to build a sauna. I live in Interior AK, so have special building considerations. Most notably earthquakes (we had the world's largest a few years ago), permafrost (my house foundation is telephone poles because of this), need to use vapor barriers/mold worries in walls, and extreme cold (-50 will happen every year). I also live on a creek, but flooding concerns are rare. Because of these needs, I've had a hard time reading between the lines of non-Alaska publications to see if a cordwood (or other natural building type) sauna is appropriate. Many natural buildings seems to have very heavy floors, yet my foundation will have to be elevated due to permafrost. And what is appropriate for sauna, where things will get both wet and hot? What is appropriate for earthquake-proofing (e.g. need timber framing for cordwood walls, and can you still use a living roof)?
A: I do not see why a cordwood sauna will not work for you, just as it does for us in our cold climate. With respect to your special concerns, you do not need or want a vapor barrier; unnecessary with cordwood masonry. Yes, most probably you will need to build off the ground with your permafrost situation. I suggest frequent pillars or posts, using standard building procedures for your area. With cordwood walls, you will want a substantial perimeter girt system joining the tops of your pillars, probably 8 x 8 girts with no more than a six-foot span between them. Yes, you need to do timber framing as protection against earthquake damage, but I do not see why you cannot support a reasonable living roof of 6" of soil or less. The thermal mass in a cordwood sauna works to your advantage in a sauna.
Q: I live in Eastern Tennessee. I have purchased several 40' steel shipping containers with the intent of converting them to a house. I am wondering about building cordwood walls around this strong exterior structure to provide thermal mass, insulation and improved aesthetics. My thought is to build a concrete block footer to get the logs away from the most soil. The container would be on piers, providing an open crawl space underneath. Is there a method you could recommend to anchor the logs to the steel skin and frame that would not require a timber frame?
A (Kelly): I think that what you propose is entirely feasible and practical. Such an external cordwood shell would definitely help insulate the metal container in very aesthetic manner. It would add some thermal mass, but not a whole lot. The cordwood walls would really just need to be self-supporting, since they are not necessarily part of the structural integrity of the building. It would not require much of an attachment to the container, only enough to connect the two together, and this could be accomplished with periodic metal bars (angle iron, etc.) that was welded perpendicular to the container wall and imbedded within the cordwood. You can actually stack cordwood at the corners in such a way that they interlace directions and are self-supporting. Whatever roof structure you devise would obviously need to extend over the cordwood walls.
Q: What about carpenter ants? We do see them quite frequently here on PEI, Canada and in fact had to battle to get rid of an infestation in our white cedar log house.
A: We have twice (in almost 30 years) had to get rid of carpenter ants at our Earthwood home. Both times, they were up in the tongue-in-groove ceiling, but, once, they migrated into the cordwood wall and we had to poison them. The problem only lasted a day or two.
Q: People asked me if can you put electrical in the cordwood wall as you build them, either by using conduit or UF wire, and also possibly plumbing and radiant heat. If this could be done then I would only have to stud the interior walls and save more this way.
A: As for the electrical part, you can use either of the methods you suggest. For duplex receptacles (plugs, required every 12 feet around a room by code), you can run a course of conduit at about 14" or 16" off the floor. (Code does not specify the height of receptacles off the floor, but 14" to 16" is the convention.) Run it right in the insulated space between the inner and outer mortar joints. Boxes can be installed on the sides of posts, laid up in the wall like small log-ends, or - as one friend did - inserted in routed spaces on large log-ends.
By the way, you can legally run Romex conductor itself through the wall without the conduit, as long as it is more than 4" back from the surface of the wall. This 4" distance is easy to maintain with 12-inch walls, or thicker. You can also run surface-mounted wiremold where you want it after the external walls are built. And, of course, you can - and should - run wiring in your framed internal walls in the regular way. There is much much more in Chapter 10 of my book Cordwood Building: The State of the Art. Titled Electrical Wiring in Cordwood Masonry Buildings, it was written by two licensed electricians who each built cordwood houses.
As for your plumbing and radiant heat question, there is absolutely nothing about cordwood masonry which precludes the use of underfloor plumbing or radiant heat. Please see Chapter 4 of my Earth-Sheltered Houses for a lot more on this. We offer both books through www.cordwoodmasonry.com
Q: What steps can be used with cordwood masonry to minimize the growth of mold and onset of rot in the cordwood itself? It's hard to believe that the exposed cordwood ends don't "wick" humidity.
A: You express a common fear in your question, but, in reality, cordwood houses are quite dry, with a fairly low relative humidity. At Log End Cottage, our first cordwood home - all cordwood - we had to keep open topped pans going on the cookstove to maintain good humidity, and that often was not enough. Mold and rot are not a problem at all. Wood rot is caused by fungal growth, which requires a constant damp condition. A cordwood wall will get wet in a driving rainstorm, but will soon dry out because of its breathability. Baby fungi don't get a foothold. Ditto with mold.
Q: I don't know if this is possible, but with the proper water proofing procedures or an additional barrier, can one build an earth-sheltered cordwood home in Alaska? Ideally, I would love to have approximately 1/3 of the home exposed (circular design nestled against an incline and backfilled on the sides with an earth roof).
A: Yes, I believe it is possible to earth-shelter a curved cordwood wall, and Alaska should be no different than the lower 48 in this. We attempted to do it at Earthwood, but had to tear the cordwood wall down because we used very dry hardwood, which swelled and caused an outward tilting to the wall. Before we tore the wall down, we tried our intended method of waterproofing. We put on a scratch coat of cement plaster to the exterior, then a finish coat, returning the wall to a nice smooth cylinder. Then we applied the Bituthene waterproofing membrane. Later, we adopted this method, in a small way, but with good success, at our round cordwood sauna. Having said all that, I would still build below grade with surface-bonded blocks rather than cordwood. See my book Earth Sheltered Houses to learn about that. The blocks (filled with sand) are faster, easier, brighter in interior finish, and more massive than the cordwood.
Q: I was wondering about the chart for how much cordwood is needed in your book "The Complete Book of Cordwood Masonry." In the chart it says that 10 cord of wood will do a 120'x 8' wall and then it has an adjusted amount for what I assume is for windows and doors of 8.33 cord to do a 120' x8' wall. If I am correct about this then I will need a significant amount less wood...I just want to be sure.
A: It is safest to deal in face cords, not full (4' by 4' by 8') cords. A face cord is 4' by 8' (or 32 square feet) by whatever the length of log-ends is (same as the thickness of your wall). Stack your wood in single ranks so that you can measure it easily. Now, as everyone is different with regard to window and door area percentage, it is also safest to deal with actual square feet of cordwood area. (With a round building, you can use interior surface square footage of actual cordwood masonry.) From your elevational plans, measure the square footage of the cordwood portion. You can do a gross square footage of an elevation, then subtract the actual square footage of windows, doors, posts, etc. Let's say, for easy figuring, that this comes out to 640 SF of cordwood wall for a particular example. Divide this number by 32 (the number of SF on the side of a face cord) and you get 20 face cords. (640 divided by 32 = 20). Now, you can safely take 80% of this total to get an adjusted (final) figure of 16 face cords (20 x .80 = 16), because the cordwood "swells up" by the introduction of the mortar between log-ends.
Use the method above in your own case, instead of the rather convoluted information you cited, which was first published in 1981. Pages 24 and 25 of Cordwood Building: The State of the Art, I think, simplifies the earlier discussion from Complete Cordwood.
Q: I see that you mentioned that you lived in southern Colorado and used crushed scoria as infill insulation between two cob walls. We have some land outside of Trinidad, CO and are looking at building a small cordwood building to start. We have contemplated using Cob instead of mortar for the walls, and are trying to figure out what kind of insulation to use in the cordwood/cob walls. Rob Roy recommends sawdust, and I was intrigued by the idea of scoria. What size scoria would you recommend for this type of infill? Also, I think the soil on our property would be great for cob, and plan on doing a few tests, but I was wondering what your experience with southern Colorado soil in cob had been?
A: (Kelly) I see no reason why you couldn't use scoria in place of sawdust as insulation in cordwood construction. I used scoria as fill material for an earthbag house, and it performed very well for this. Scoria is inherently very stable, being insect and rodent resistant and not vulnerable to rot. I used a 3/4" minus aggregate for this purpose.
For those not familiar with scoria, it is light weight volcanic stone, similar to pumice, that is quite abundant in the Western US and other areas of the globe where there has been volcanic activity in the past. It comes in a variety of colors from black to rust to yellowish to white, and is used in decorative landscaping because of this. It is a naturally insulating material because of all the trapped air, and is used for this purpose under floors, in bags, etc. I even used it to insulate a ceiling in Mexico (see http://earthbagbuilding.com/articles/ceilings.htm). Great stuff, but unfortunately not so prevalent in the Eastern US.
The soil where I built in Colorado is basically sand, so it could be the major component of cob, but would require about 1/3 to 1/4 times as much clay added to make good cob. I know that cob has been used successfully for "cobwood" construction.
Q: I am approximately 90 percent completed with a stackwall house on Georgian Bay, Ontario, Canada. I will be taxed by the government based upon the outside dimensions of the house, which are much larger than the living space, as my walls are 2' thick. This issue applies to many alternative structures. I realize there are endless issues. Has this one surfaced anywhere? Alternative building obviously should not cost us more than conventional stick frame when it comes to taxes...
A: This is a huge question, one which I have no answer for, but which needs to be discussed and attended to on sites like this and by cordwood, strawbale, earth-bag, cob and other "thick-walled" builders, shakers and movers. The question of footprint square footage becomes really nebulous in the case of earth-sheltered houses. How thick are the walls of a cave?
This true anecdote may not help in your case, but it is interesting. An acquaintance of mine built a two-story round cordwood house with 16" walls. When the assessor came around to assess, he kind of shook his head at the round shape, thinking "How am I going to get the square footage of this place?"
The owner/builder, seeing the official's distress, said, "Well, if it's any help, the diameter is 36 feet."
"Ah, thanks," said the assessor. "Pi R squared, right?"
"That's right," said the builder.
He had given the correct inside diameter, the space in which he and his lovely wife were to actually live. The assessor could have stretched a rope around the building and divided by pi to get his own diameter, but he did not. And the owner-builder had not lied. The difference, due to the impact of diameter squared, is a whopping 400 SF, about 20%. In a regular stick frame, the difference between inside and outside dimensions in terms of area is only 5% (large houses) to 10% (small houses.)
I have serious doubts about assessments and property taxes in general, having seen owner-builders taxed out of their homes, but, at the least, we should only be assessed on where we can live, and not be penalized for building energy-efficient homes, with extra mass and insulation. The easiest way to do this is to subtract the wall thickness from the house's outer dimensions before calculating area.
Finally, my better half, Jaki, read my reply before I posted it and suggested, rightly, that you should be arguing and fighting this right from the word go. Use common sense arguments, which are all on your side. Be willing to be assessed on your living area plus a conventional wall thickness, and make it sound like a compromise. Basketball coaches know that it pays to "work the refs" a bit to get a call to go your way in the fourth quarter. Maybe, when a reassessment comes up, they'll leave you alone. Jaki and I have fought our valuations several times, thinking it to be a kind of civic duty, and we have had some success in this. Nothing ventured, nothing gained.
(Kelly): I completely agree with you that it is grossly unfair to the builders of natural, energy efficient homes to tax them for the thickness of the walls. I think the issue should be brought forward whenever it surfaces so that officials become aware of the discrepancy and how unfair it is.
Oddly, though I have encountered the opposite advantage with thick walls when building in the property owners association where I live. The covenants and restrictions demand a minimum square footage for all residences, and many conservation minded folks prefer to live in small homes. In this instance, since the square footage is measured from the outside of the building, there is a slight advantage to having the thicker walls.
Q: I'm looking for advice on how to find somewhat experienced people to help build a cordwood home. I'm kind of on my own in terms of building, but want to get this dream home started. Its difficult to find people who can grasp this type of building.
A: I am not aware of any professional cordwood masons. Years ago, there was an outfit in the midwest called Log End Construction (or similar name). They built quite a few cordwood homes for people, but are no longer in business. Most cordwood homes are built by owner-builders. I can only come up with two suggestions for you.
1. To try to find someone with experience to help you, I suggest going to the excellent cordwood masonry website, www.daycreek.com On the top subject menu bar, click on Forums and then look for a forum that will meet your needs. Or, if you can't find an appropriate topic (like Help Wanted!) then create a thread or topic yourself. You will have to sign in, which means creating a user name and a password.
2. Come to one of our cordwood workshops at Earthwood. If you have someone that you want to train to do cordwood with you, bring that person along. You can register as a couple for a discounted rate. For details, go to our Earthwood website at www.cordwoodmasonry.com
Q: We are building a cordwood home. My question is of an aesthetic nature. I love the look of the cordwood, but it can also be a little busy and overwhelming. I'm wondering if I can put a tile backsplash on the kitchen wall, or plaster on one part of the living room wall, just to tone down the polka dot look. Or are there any other wall treatments that people use? Our interior walls will be made of wooden boards, painted white or other light colors, which I think will help brighten it up, too.
A: Sure, you can do the things you suggest. I would not seal both ends of the log-ends until the wood is as dry is it is going to get. You are right to use bright internal walls to reflect light onto the relatively light-absorbing cordwood walls.
Q: I am building a house with insulation in wood shavings. It seems that I have to add Borax or lime for resistance of bugs and fire. Is Borax better then lime? Do you know what is the percentage in volume that I have to add?
A: We mix in one part of lime with 12 parts of sawdust to make our insulation. The lime helps against insects, and I'm sure the Borax would, too. Another benefit of the lime is that if the sawdust gets wet during construction for any reason, the lime will set up with the sawdust, yielding a kind of beadboard product. If it stays dry, it remains like a loose fill insulation. I don't know if either Borax or lime will do anything about fire-proofing wood shavings. We avoid wood shavings in cordwood masonry because it is so hard to place between the mortar joints. We have used it when there has been nothing else, usually at regional workshops, but much prefer sawdust.
Q: In the cordwood book Rob & Jaki recommend using printer's plates to encase bottles when making bottle logs. Here in Australia I cant find out what printer's plates are. Does they go by any other name or are there any alternative's? Like could I use aluminum foil? We're building a Hybrid earthship, i e a recycled steel frame, some fully rammed earth tire walls, infill walls with 2 layers of tires as base to support cordwood infill (Black Cypress pine harvested off our 100 bush block.) Your advice.help or further referral would be greatly appreciated.
A: Offset printing plates are thin aluminum plates used for printing newspapers and pulp advertising weeklies here in the U.S. They are used once and thrown away or recycled. Sometimes we get them free, sometimes we pay a small amount. The large newspapers have switched over to a new process, so do not have the printing plates available any longer. We can still get them from small printers. They are perfect for the job, because they have just the right flexibility. You can also use aluminum flashing (a bit stiffer) and recycled floor vinyl or linoleum. One friend uses a combination of wax paper and aluminum foil, and likes it, although we think it is easier with the printing plates or floor vinyl. We make a "spring-loaded" cylinder about 6 to 8 inches (15 to 20 cm) shorter than the bottle-end we want to make, leaving room on the glass for a 3-inch to 4-inch mortar joint. The "spring loaded" feature is easily accomplished by using two stout rubber or elastic bands, one at each end of the cylinder. Now, plug the neck of the bottles, or glass jars, into the spring-loaded cylinder and - presto - your bottle-end is ready to use. This techniques is appropriate for bottle-ends (wall thickness) of 16 to 24 inches (40 to 60 cm.)
For shorter bottle-ends, like 8 inches (20 cm), it is easier to cut each of two bottles (of the same diameter) to half of the wall thickness, using a slate and tile diamond-tooth table saw. Clean and dry the cut pieces and join them with duct tape.
Whatever the length of bottle-ends you make, it is best to combine a colored bottle with a clear one for better light transfer. We put the colored end to the inside for greater color vibrancy. This means you will be using a lot of clear bottles or jars. It is important to marry up two two pieces of the same diameter, no matter the bottle-end length.
Q: We live on the eastern side of North Carolina near the coast. We are thinking of building a cordwood home here and where we are there is a termite problem and, obviously, hurricanes as well. Should we think of an alternative building material?
A: The only instance of termites in a cordwood home that I know of (in the U.S.) was a home in southern Georgia. The owner-builder had no problem for a few years, and then put an air-conditioning unit in one of the windows. Condensate was dripping down the cordwood walls, keeping them constantly damp. Fungi began to grow on the exterior wall. Then the termites scrambled up the wall - there was no termite shield - to harvest the fungi. Soon, they were eating the soft deteriorated ends of the logs. In general, fungi are a bigger problem than termites. Use a good overhang and good detailing so that water does not constantly run down the walls. It is okay if the wall gets wet from a driving rainstorm, because the log-ends - laid up on end-grain - soon dry out and the fungi don't get a foothold to reproduce. As for termites, they don't normally like end-grain, but I would advise a termite shield around the perimeter of the foundation, and just walk around the completed home once in a while to see if the little varmints are building a way over the shield. If yes, kick their structure down. I did see termite damage on a cordwood home recently in Nicaragua, but the cordwood was right down on the ground. Where it was done properly, no problem. I would not hesitate to build of cordwood in your area because of termites.
With regard to hurricanes, I would advise a timber frame meeting "continuous tie-down" code. That is to say: the posts are mechanically fastened to the foundation; the girts (plate beams) are positively fastened to the posts; and the rafters (or trusses) are also mechanically fastened to the girt system. Check with your local code enforcement officer on this for advice for your area. Also, see my book Timber Framing for the Rest of Us, Chapter 4, particularly pages 75 to 83. I would use a timber frame with continuous tie-down features to address the wind damage question. It may well be required by code in your area anyway, but, even if it isn't, do it anyway!
Q: Can I use muriatic acid to clean off the faces of cordwood that has some mortar on them? If not any suggestions?
A: No need to use muriatic acid to remove mortar from the ends of log-ends. An ordinary wire brush will do a good job. Mortar dries so quickly on the ends of logs that it is weak and there is practically no bond to the wood. The exception might be if the mortar was smeared on the log-ends during construction. Muriatic acid won't help in that circumstance, either. You might need a 4500-rpm 5" disc sander, the kind that Makita makes, in that case. (Use eye protection).. But, please, try the wire brush first. One last thing: Wait at least a week after doing the cordwood masonry to remove any mortar on the ends of logs. It is easier. Finally, a 10% to 20% muriatic acid solution is very good at removing mortar from bottle-ends, where there is a chemical bond, Try 10% first. Use an old toothbrush, eye protection, and acid-proof rubber gloves. Try to keep it off the mortar joints.
Q: I am building a 12' by 10' garden shed using 6" x 6" English Oak. I intend to use western red cedar cordwood in between the frame. Looking at a lot of literature and examples on your site I am not sure if the wall thickness is sufficient to warrant an insulation cavity. What would you recommend for a narrow wall thickness?
A: You're right. a six-inch wall is rather narrow for an insulation cavity. But why would you need insulation on a garden shed? I would just go with a solid 5.5-inch wide mortar joint, with the wood proud of the mortar by a quarter-inch each side.
Q: What king of material would you recommend to be placed between logs to insulate from sun and heat?
A: Pass sawdust through a half-inch (12.7 millimeter) mesh screen and mix it with builder's lime at a ratio of 12 parts sawdust to one part lime until the sawdust is a consistent color. Place this sawdust insulation between the inner and outer mortar joints as you build.
Q: I saw that it said we mix different species, but that we should keep consistent texture. What do you mean by that.
A: You can mix wood species or use all the same kind. "Texture" refers to keeping a constant reveal to the log-ends - we generally keep the log-ends about a quarter inch proud of the mortar - but can also mean keeping a consistent balance between large and small log-ends, splits and rounds.
Q: I was looking to build a surface bonded block wall like you did with Earthwood. Just curious how you laid the block traverse to get the 16inch wall. Did you use wider block so there was more than 4 inches across the seam on the second course of block?
A: We used 910 eight-inch corner blocks at Earthwood, and laid them transversely (widthwise) in the wall tight to one another, giving a 16"-wide wall. Then we surface-bonded both sides. "Eight-inch" blocks are 7-5/8" x 7-5/8" by 15-5/8", allowing for the 3/8' mortar joint normally used, Corner blocks do not have the scalloped ends, like regular blocks, so that, laid up width-wise in the wall, you have all smooth surfaces for surface-bonding. In the case of the round Earthwood house, we had a small gap between blocks on the outside only, less than a half-inch, filled with mortar before surface-bonding.
