Insulation
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Q: My wife and I have been working on plans for a cob home we intend to build in Vermont, hopefully within the next few years, and we've been researching natural insulation. If we go with wool, is a vapor barrier needed, as wool can absorb considerable moisture before loosing insulative properties? Would a living roof provide enough insulation on it's own, or would it also need some other form of insulation?

A: Yes, wool insulation used in Vermont should definitely be installed with an eye for moisture control. Moisture, as you probably know, occurs in building assemblies (roof, wall & floor) as a result of cracks in the assembly and migration right through the materials that the assembly is made up from. My suggestion would be to use a 6mil poly air barrier on the studs, taped at all joints and caulked at all protrusions: ie. outlet boxes, vent stacks, plumbing runs, etc. Keeping the moisture laden air out of the walls will account for almost 90% of the moisture. The other 10% can be controlled with the use of moisture barrier paint. (As an alternative, I use cellulose blown into my stud spaces to the manufacturer's prescribed pressure spec. That way, I don't require a moisture barrier.)

As for your living roof, you should definitely plan on additional insulation. Earth that supports life is usually wet and has very poor insulating characteristics. Vermont is a pretty chilly place. If you're confident that there will never be any leaks (membrane or concrete roof), you might consider wool, cellulose, fiberglas, rice hulls, etc. but if there is a possibility of roof leaks (usually!), then I would suggest looking at the family of foams. They tend to do better at retaining some insulating value even when wet. Hope this helps. Let us know when you start construction so we can bring a bunch of Yestermorrow students over to help.

Q: I have just purchased a 1900's clapboard siding home in Savannah, Georgia. I have been trying to get some answers on cost effective ways to insulate without creating a moisture problem. The house has wood siding in good condition, nailed directly to the studs, balloon framing, with no sheathing or vapor barrier between the exterior sheathing and interior wall board (future). Most of the plaster has been removed on the interior and I will go back with gypsum board. Where there is plaster it will remain. I would like to insulate the walls with R-19 Batt insulation, but there is no vapor barrier. Since in the south, the vapor barrier should be on the exterior side between the siding and stud, I fear potential moisture problems if I install insulation without a vapor barrier; or if I install the vapor barrier (felt paper) to the inside. I thought I could install the felt between the studs to the exterior, with insulation behind, sealed tightly. But I feel this will not drain properly I fear and will only rot the sills as it drops to the bottom of the wall. Since there was never Central HVAC installed, I am sure moisture was never a problem. How can I keep the moisture out, fill in-between the studs with insulation without removing the siding?

A: If I were you I would line or fill the stud bays with an insulation product that is also a vapor barrier - i.e. foam. If your budget can support it and your green values tolerate it, use polyurethane foam blown in with green agents. This is a high R-value, sprayed in place, closed cell foam that will also act as a vapor barrier. It's very expensive and not all that "green" but it will be the best solution for your house. To keep the cost and environmental damage to a minimum, use only 1" on the inside of each stud bay (including the sides of each stud). Same goes for the rafters. Then fill up the rest of the bay with either icynene foam (an open cell foam of slightly lesser R-value but better "green" rating) or dens-pack cellulose. Cellulose, of course, is the most sustainable and
least expensive but in your climate it is susceptible to mold so I only suggest it with this caveat: retain only the most experienced and reliable installer. And when you find him, ask what he would do if not what I suggest above. I am a big believer in listening to the local talent when it comes to anything that has to do with moisture movement. He has
probably seen dozens of houses just like yours.

Q: I've purchased an old farmhouse in Maine, with virtually no insulation. We are trying to find the most energy efficient (and cost effective) option to add insulation. In Maine, R40 walls are recommended, but realistically we will not even approach that level. We currently have 2x4 walls, and are considering removing the sheetrock or plaster/lath (different parts of house built with each), making walls 2x6, then insulating. Or, I've read somewhere about an R7 foam which can be used to fill wall cavities, but can't find any information on it. I like this idea as it might save money and resources by not tearing out perfectly good sheetrock and plaster/lath, but am concerned about offgassing from foam, as well as toxic fumes if there were a fire, and ultimate disposability issues if the house were ever torn down. If we were to tear down the interior walls and build out the studs, I am not sure what insulation we would use - cellulose, cotton, or fiberglass (our builder likes fiberglass, but I am not convinced yet that it is the right choice). What are your thoughts on insulating an old house like this, and the different products available?

A: Indeed, you can produce a VERY tight and well insulated house using polyurethane spray-in foam.  While it has approximately an R7 rating, it's incredibly expensive (around $15,000 for your house, at the very least) and it's not "environmentally enlightened", strictly speaking. The blowing agents used to install polyurethane tend to attack the ozone layer.  Even when the better, greener blowing agents are used (more cost!) you're still stuck with the fact that urethane is a petroleum product and pretty ugly stuff until it's in place.  However, having said all that, it's a FANTASTIC insulator, doesn't off-gas and has an incredible fire rating- I tried to ignite a blob of it once with a brazing torch and couldn't.  It just smoked a little.  If it's covered by drywall or plaster, I wouldn't worry about it.  And if the house is ever torn down, the foam will be the least of your land fill problems.

OK so that's foam.  But if it were MY house: I'd either use icynene foam (more environmentally defensible) or cellulose.  Cellulose is my first choice but it will require that you restructure your walls to get a full 5.5 inches.  If you're up for the effort and fun, I'd use the cellulose.  You'll sleep better and so will the rest of the world!

Q: We will be insulating an addition to our house in Maine with dense pack cellulose. The walls are 10" thick, staggered studs, with Advantek sheathing and Tyvek on the outside. Our insulation contractor is suggesting that we use damp-spray cellulose. Our building contractor believes that we need a vapor barrier. I am a bit concerned about not using a vapor barrier, and also that 10" thick walls may not dry out adequately if we wet spray them. I would love to hear what an expert has to say about this!

A: It seems you already have some experts giving you opinions.  Remember that your insulating contractor should warrantee his work against defect and that includes mold and rot from inadequate drying.  Get it in print!

But just so you can have an expert (as defined by anyone who lives more than half and hour away) opinion, I wouldn't put a vapor barrier in this wall assembly.  I would install my sheet rock using the AirTight Drywall approach and paint it with vapor retarding paint.  The 10” of insulation should put the dew point way outside any possible moisture migration in the wall.  Still, a lot depends on where you live.  Are you on the shore or in the mountains?   In Vermont the winters are so arid that any moisture migration into such a wall assembly would more than dry out during the winter.  But if you live on the coast where it's high humidity all year round, it might be different story.  In that case I'd heat my house with wood in order to dry it out in the winter.   Either way, I put more faith in the moisture coming back out than I do in a vapor barrier keeping it out in the first place.  So use the 10” of damp-spray cellulose, leave the walls open for at least two weeks (longer if possible), forget the vapor barrier and maintain low humidity within the house for a major portion of the year.  That's my advice.

Q: We have a 400 year old stone house in the Cotswolds, England. We are trying to insulate the windows to conserve energy. We aren't allowed to put in storm windows because the local heritage control agents won't give us permission (our house is a listed building of architectural/historical importance). I'm using blinds and heavy curtains. In the bedroom we have terrible condensation on the (leaded) windows which the insulation of course makes worse. We can't have wood burners in the bedrooms-too dangerous (Carbon Monoxide risk). Any ideas for sustainable dehumidification?

A: The humidity really shouldn't be let go below 40% and at that level you will still get condensation on your windows if they aren't insulated.  So how about interior storm windows?  If you can have a local carpenter frame some insulating glass in a nice frame, that will do the most for reducing condensation and reducing energy use.  But keep in mind that the interior storm windows must be air tight or the moisture laden air will simply leak around it and freeze on the window beyond. I don't think dehumidification is the answer.

Q: We have to apply to the Council for Listed Building Consent every time we try to do anything substantial, and we applied last year to put in temporary glazing and were turned down on the grounds that it would spoil the appearance of the insides of the windows ! I have rigged blinds made of rubberized cotton between the windows and our heavy lined curtains.  The condensation remains bad and there is heavy mildew even with monthly attempts at spraying. We would try a dehumidifier powered by a solar panel but the local council have let it be known that they are opposed to any solar panels anywhere on listed buildings.

A: I'm thinking you will never get rid of the bedroom humidity without moving air (sleeping humans are a relentless source of humidity).  So, this can be done either with electricity or thermo-active gravity effect (hot air rising, cold air sinking).  Since the use of electricity defeats the purpose, we need to see if there is a way of circulating the bedroom air with the drier downstairs air (heated by stoves).  I really can't advise in any detail without a set of drawings.  Nevertheless, if the floors are wood and there is space for a few registers, this may be half the battle.  To get the hot dry air to rise into the bedrooms we need to suck the humid air down and out of the bedrooms (or up and out, but that uses more energy).  To evacuate the humid air it will need to be drawn down by the force of the hot air rising (somewhere else).  This is a delicate balancing act which requires sizing of apertures and whatnot.  Still, it's entirely possible if you can find someone with the experience in forced air systems. I'm sorry if this is all about as clear as mud.  It's just so hard to solve this kind of a problem "in general".  Send me some plans or a plane ticket and we'll have it worked out in a jiffy.

Q: I have also been recommended to seal the windows with silicone rubber but having worked with this material in another context I am suspicious of the long-term effect of the solvents in this material on the oolitic limestone which is the material of which the window frames are made.

A: (Kelly) It is my understanding that once the silicone sets up (usually within about an hour) it becomes rather inert and is not likely to negatively affect the stone. Sealing all points of draft within the shell of your home will be essential to control the humidity and to make your home comfortable.