I built a 2200 sq. ft. ranch ans put 2" styrofoam on the outside of the block. Since I got 250 studs for free I decided to build the walls in the basement and cover them with 3/16" plywood I also got for free. After it was all done my basement went up 2 degrees. The joist box already had 3" closed cell foam anyway. I'm a bit disapointed it ony went up 2 degrees though. Just in case some want to do their basement walls this is what I got out of it in case anyone cares.
insulating basement walls.
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250 studs! Wow, that is quite a deal. When you say it went up 2 degrees, what do you mean? Is it unheated?
maple1
Minister of Fire
Also, is the basement heated? The insulation is used to retain heat, it won't generate heat
Exactly. If you have no intention of heating the basement, insulating it doesn't add a ton of value. It will still seek equilibrium with whatever ambient temp is on the other side of the insulation, but it will be at a much slower rate. I wouldn't be completely shocked if your basement stayed a few degrees colder when the outside temp rises. Insulating an unheated basement doesn't add a ton of value.
Something else to consider, the basement went up 2 degrees, but what about the upstairs temps and the fuel consumed to heat?
jdp1152
Minister of Fire
If the sill is insulated as stated, likely not much as heat transfer down is negligible in the absence of draft. Energy auditors recommend putting your money/effort elsewhere rather than insulating the living space/basement barrier. The sill is a vastly different story. Uninsulated crawlspaces/garages/basements with exposure to cold temps/air leakage would prove beneficial.
It is unheated and I did insulate with R11 and some r 7.5 (1.5" ) pink foam. I though I'd get more than 2 degrees even if it's unheated. It is 2 degrees though and it feels much more comfortable too. Oh well 300 bucks of insulation isn't the end of the world and it is 2 degrees. Just thought I'd throw it out there for others for refernce in case other wanted to do it. It would have made more difference if there was no insulation on the outside. Also, to northern Ontario , I didn't notice a reduction in heat demand but the floor must be 2 degree warmer so it has to be reducing my btu needs some.
I haven't found that to be quite true. Our insulated crawlspace (should be called a tallspace) stays at 63-60F, even if it's 20 outside. Earth floor with plastic on top.
Insulating the basement walls is only part of the job. With no insulation under the slab, you still have a huge area in contact with typically cool ground. Then there is the matter of air infiltration, introducing cold air at some rate, however slowly.
Yes, it's bone dry down there and every thing looks the same as it did 6 yrs ago when we put it down. I was a little skeptical because this is in a really damp climate. The end result has been better than I expected. We rarely get into the teens here. But it can happen and I was concerned about pipes freezing. A couple winters ago when we did get down to 13F, I had a digital remote thermometer down there and we never went below 60F. I have insulated panels for the crawl space vents that I remove in late spring when temps rise outdoors.
So you basically laid the plastic right down onto the dirt floor, correct? I have a crawlspace with some moisture issues and I'm looking for a temporary fix until I can get time to concrete it (I'd like to eventually put a 2" skim of concrete on it)
Saw this video today. It explains a lot of the intricacies about basement insulation. Don't know if it was already posted on hearth.com somewhere or not. Insulating basement walls/floor may not add too much value to the sale price of a house, but over time the investment will pay off with energy savings. Good work getting it done.
Laszlo
Member
Really informative, thanks! Just got a home energy assessment and the #1 recommendation for my house was to insulate and air seal my basement band joists. Nice to learn about all the possible moisture concerns before going ahead with it.
I sat through that 30 minute video and thought that in general it was quite good. My only comment regards his assertion that the concrete foundation had to be dry. As long as concrete is separated from moisture-sensitive building materials by strong vapor retarder layers and well air-sealed on the interior, it can remain moist without harm. The notion that interior insulation layers had to have some low level inward drying capability has been challenged here: http://www.greenbuildingadvisor.com...usses-basement-insulation-and-vapor-retarders. Reference to this was made in another GBA blog: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-insulate-basement-wall.
Yep, lay 6mil right on the dirt. Crawl down there in a couple mos. and see the moisture buildup on the underside. You should also have some venting at either end of the stem wall.
Also, the assumption appeared to be that the footing would be sitting in wet soil. That is not the case with our footings, even though we live in a damp climate. Our house has generous overhangs and good draining soil which help to keep our crawlspace really dry.
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