I’m getting to break ground this week on my new home just outside of Ann Arbor, Mi. I am considering installing the white 2″ foam board insulation on the exterior of the poured foundation walls prior to back filling. My builder told me is not worth the cost.
I am looking for other input, is it worth it?
thanks
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Replies
I'd go with Superior Walls. However, it's do late for that if you are set on breaking ground this week. It would probably be better to wrap the basement walls with a non-permeable membrane like Polyflex and put the insulation on the inside.
Allow me to disagree on the superior wall suggestion. Looking over the way they make it, I am not impressed. A thin concrete shell on the outside, where it's thermal mass will do you no good and mere steel beams on the inside to support the weight of the house (as best as I can tell).I would follow buildingscience.com's lead in putting the concrete on the inside and the dowfoam (or whatever XPS you want to use) on the outside, if at all possible. Simply design the building to sit on the concrete that is 2" back from the actual exterior wall surface. Cover the exterior of the wall with Rub-R-Wall and apply the XPS (it glues). Protect the foam with stucco or whatever pleases the eye and you have a high-thermal-mass basement that will be very comfortable, dry, and strong. I couldn't do it that way due to historical considerations, so my thermal mass is on the outside also. Having the thermal mass on the inside becomes even more important as you go up beyond the basement as high-thermal mass buildings can flywheel easily through a lot of variable weather w/o the need for heating or cooling.
Superior walls has been in business for over 20 years & they guarantee you a dry basement. They are all over the place where I live for both residential & commercial applications. I spent the better part of the past year & a half researching them for my house trying to find one example of a structural failure & couldn't find any
The support comes from 10" steel reinforced concrete studs with a 10" bond beam on the top & bottom. The entire inside is covered w/ 2" rigid foam insulation..
The only time I'd hesitate to use them is if I lived in a seismic region.
Edited 8/2/2005 3:19 pm ET by Johnny
Johnny,There is no doubt in my mind that a basement built with "Superior Walls" may stay dry, keep the occupants happy, etc. All I am trying to get across is that their solution is not optimal, IMO. If they flipped the XPS to the outside and attached it to the concrete shell, it would make me happier. I also prefer thicker load-bearing surfaces, out of personal experience.I live in an area with wide swings in temperature (-15F to 95F), lots of rain, and a very high clay content in the soil. Such conditions are ideal to destroy basement walls over time. Our previous basement foundation lasted 130 years, which is pretty good considering the terrible water management around the foundation but the basement was always wet, stinky, and full of termites. In other words, it might as well have been a crawlspace in terms of its usefulness to us.Since I didn't want to have to deal with a wet basement again, I elected to go with a rebar-reinforced foundation wall that has XPS on the outside below ground. Allegedly, said foundation will outlast me and several generations to come. Time will tell.
Edited 8/2/2005 4:53 pm ET by Constantin
If you put the insulation on the outside you also need to take care of waterproofing and a drainage plane. Some people recommend foamboard that has been treated with borates for insect protection.
Check here for a detailed explanation of the benefits of foam insulation:
http://www.buildingscience.com
The Building Science website suggests putting foam on the inside of your basement walls in your climate region:
http://www.buildingscience.com/housesthatwork/cold/chicago.htm
Here are more details:
http://www.buildingscience.com/resources/mold/Read_This_Before_You_Design_Build_or_Renovate.pdf
Don't forget to put foam under your slab as well.
Billy
Edited 8/2/2005 11:51 am ET by Billy
Edited 8/2/2005 12:02 pm ET by Billy
Stogman:
If you do put foam in the ground, make sure its's rated for burial (borates?) so that you don't trigger a future termite or whatever "problemo". I've seen some blue XPS panels (with drainage grooves) placed on the exterior foundations here in NE Ohio. A local building supply house should be able to recommend the appropriate foam - Rookie.