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I would like to build a super-efficient one-story house in the deep South (MS), but do not know of any local contractors using thick walls (2×6 or >), vapor barriers, high density insulation, and the like. Do those typical efficiency methods make sense for the Deep South? Does our high relative humidity cause mildew/rot problems in walls “sealed” with vapor barriers? Has anyone used a “staggered stud” wall in a similar climate and, if so, with what success? My challenge also involves the primary structure being located in a 20-acre open field with brutal Western and Southern exposure. Anybody got good ideas on how to build for efficiency and comfort in such a hot and humid climate?
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Allen
I would check into building with ICF's. Not only will you address the energy effiency issue, far beyond what a 2x6 wall will do for you. You will also deal with huricanes and the such. For info on ICF's go to
http://www.insulatingconcreteform.com
Rob
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I assume you will be using A/C. Beyond wide overhangs to shade the windows, I would make sure that the roof is well vented, ridge and soffits not just gable ends. I would also look into radiant barriers in the attic. Use light colored shingles of a metal roof. Where to place the vapor barrier (retarder) is a good question. One choice is to use an insulation tolerant of no vapor barrier such as Icynene or cellulose. With a double stud wall, You could place the barrier between the two walls keeping its surface above the dew point in both heating and cooling seasons. The insulated concrete forms would also probably not leave a space for condensation to form. Make the house as tight as possible to prevent moist air grom getting into the insulation and to reduce the latent heat load. Minimize ceiling holes and seal them as well as possible.
*Hadn't I read earlier that insulated concrete forms could promote or harbor pests? In the deep South, I'd be very sensitive to termite potential.
*Allen. Youn are going to get a lot of conflicting and wrong advice. Rather than take a half-dozen pages explaining what to do I suggest you call Building Science Corporation in Massachusetts at (978)598-5100. Order a copy of Joe Lstiburek's book _Builder's_ Guide:_ Hot-Dry & Mixed-Dry- Climates. It gives you all the answers, and the correct answers. Joe is too busy travelling, but I'd be happy to answer your questions.Insulated Concrete Forms make a lot of sense. But there is the nagging question of termites. See October 1998 issue of the Journal of Light Construction about termites and foam insulations. Oh yes, you don't ventilate attics in the hot south, anymore than you ventilate cral space in hot humid regions.GeneL.
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What about aerated autoclaved concrete, aka Hebel Block? The insulating value is tremendous, it's impervious to pests, and doesn't cost any more than conventional materials. Hebel makes the stuff in Georgia, so hauling a house worth of it to Mississippi wouldn't be expensive.(Their site is http://www.hebel.com)
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According to Joe Lstiburek's presentation at Thermal VII, it is not just a matter of not venting the roof, but of including the ducts in the building envelope. Therefore, in a cooling situation insulation should occur at the roof and not the attic floor and the attic should not be vented. This was proven in hot, dry climates, but there is no reason it should not be true in any cooling climate.
*Mike - it would seem that keeping all the ducts completely inside the thermal and pressure barriers would make sense in any climate. Was Lstiburek's recommendation only for warm climes?
*This was case studies of homes in Las Vegas and Phoenix, not a generalized evaluation. Identical houses were built with vented and unvented attics. But, the energy loss, in this case cooling, occured mainly from the ducts. Therefore, it would follow that extensive heat loss would also occur from ducts. This is a severe problem as Fred has often pointed out.
*Jon et al. Lstiburek has a section on auticlaved aerated concrete which he calls PAAC, p for precast. He warns readers that PAAC is xtremely water sensitive and must be protected from ground moisture. I mention this only as a reminder that many building material are climate sensitive and must not be used indiscriminately as is too often the case. GeneL.
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I would like to build a super-efficient one-story house in the deep South (MS), but do not know of any local contractors using thick walls (2x6 or >), vapor barriers, high density insulation, and the like. Do those typical efficiency methods make sense for the Deep South? Does our high relative humidity cause mildew/rot problems in walls "sealed" with vapor barriers? Has anyone used a "staggered stud" wall in a similar climate and, if so, with what success? My challenge also involves the primary structure being located in a 20-acre open field with brutal Western and Southern exposure. Anybody got good ideas on how to build for efficiency and comfort in such a hot and humid climate?