How can I resolve air leakage under wall sill plates?

Question

I have a problem with air leakage under the base boards of our new home. I know there will be some temperature difference but how about an 8° to 10° difference? It seems to be all throughout the home. The home is built on a slab.

I have pulled back the carpet in areas and one concern I had was it looked as if the sill plate was bowed and not tight to the slab. I could stick a pocket knife blade between the sill plate and the concrete. The contractor has done a blower test on the house and assures me that we are at the standard for air leakage.

One of the closets can be as low as 49° to 55° on a cold day. This is not normal. At one point they pulled the carpet back in this problem area and you could see daylight from the garage under the base board. They applied caulk in one corner of the closet but still there is a big temperature difference. Any suggestions would be great!

"Flush with" and "tight to" are not synonymous. Which do you mean? — isherwood, Mar 12 '17 at 16:45
I think you're right that there's a problem. There should've been "sill seal" (rolled closed-cell foam) between the slab and the wall plates. If there's nothing, I'd check local codes. Just call your city office and ask to speak to the building inspector. — isherwood, Mar 12 '17 at 16:49
I don't understand how you can pull back the carpet and see the sill plate but if you can do that all around the house get some cans of spray foam insulation and fill the gaps. — OrganicLawnDIY, Mar 13 '17 at 01:57

score 1 · Answer 1 · answered Mar 12 '17 at 17:06

1

This is an easy one. Caulk the gaps with a 100% silicone, polyurethane, or butyl caulk. Then reinstall your baseboards.

answered Mar 12 '17 at 17:06

iLikeDirt

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score 0 · Accepted Answer · answered Mar 12 '17 at 16:53

If the concrete slab is not perfect, and none are, there is always the possibility that there may be a space between the bottom of the lower plate and the slab surface. In the case of a poorly prepared slab this could be more prominent.

Back in the day that I helped build houses we would unroll a narrow strip (about the same width as the lower plate) of this pink colored foam material. The closed cell material was about 1/4 inch thick and would fill the gaps between the lower plate and the concrete slab. It was compressible so that in areas where the plate was a good fit and/or securely fastened to the slab via the anchor bolt it would be squeezed tight.

Yep. "Sill seal". This doesn't really offer the OP a solution, though. — isherwood, Mar 12 '17 at 16:59
There is some type of seal sill but the sill is still lifted from the slab. Peeling back the carpet there is air coming in somehow — Micah Read, Mar 12 '17 at 17:00

How can I resolve air leakage under wall sill plates?

2 Answers2