foam between sill plate & concrete?
cat
| Posted in Energy, Heating & Insulation on
hello all, new workshop/ garage construction on coastal North Carolina (heaven). new slab poured yesterday is beautiful, pressure treated 2×6 are on their way tomorrow. question – should I use these rolls of 5-1/2″ thin open-celled blue foam that Lowes sells under this sill plate? we use 5/8″ threaded rod all the way through top double plates to keep hurricanes from running away with the structure. do I still need a sealant or adhesive? what side of the foam does it go on?
TIA – Cat
Replies
The blue stuff is fine, put the grooved side down. No additional sealant is necessary unless the top of the concrete is unusually rough (or you have to shim to get the sill plates level). If you have to shim and wind up with gaps between the sill plate and concrete, I'd recommend a heavy duty sealant that has good adhesion to both PT and concrete (e.g lexel).
Another good option is a product called protecto wrap, usually used for windows, placed on the outside of the slab to 2x connection.
The foam should be Closed cell.
Called sill sealer around here. Purpose is to seal the interface between the PT sill and concrete against air/moisture infiltration.
It serves two purposes: Prevents air/moisture infiltration into the structure and also prevents moisture wicking from concrete to framing.
If your view never changes you're following the wrong leader
My contractor on our new house placed a GENEROUS amount of PL400 all along where the bottom plate (treated) meets the concrete. When I asked him about this, he said he didn't like the white open cell foam that everyone uses and with the PL400 it assures a airtight/watertight seal. I thought it was a rather novel idea.
Not sure if really was the way to go but I could see his point.
WOW, what is hte presure per square inch compressing that foam at the sill? Hundreds of pounds I wager. Unless the foundation wall is really wavey, that foam is compressed to next to nothing. But if the foundation is wavey then I suppose additonal treatment could be called for.
As to pressure on the sill, you can estimate it. For the side bearing floor and roof, fully loaded, assume say 28 ft front to back, and 40# live load + 10# dead load per sqft each. So for each foot of width, the load on the foundation supporting 14 ft of roof and floor (ignoring wt of ceiling and the framing) is 14x(50+50) or 1400 lb. For a 2x6 sill, that weight is supported by 5.5/12 sq.ft, so the pressure is 3054 lb/sqft. Dividing by 144 gives 21 psi.The sill sealer is just supposed to fill in spaces between high points bearing the higher pressures and the dips bearing little or no load, squishing as needed. The material provides air seal and vapor barrier between the porous concrete and the wood sill.I think it's Protecto that makes a thicker than usual sill sealer. Someone correct this if wrong.
That is what I said. If the wall is not even then a sealer might do you some good.
ended up with construction adhesive in the end, as it turns out. easy enough to return the rolls of foam, I'm using the tried and true method instead. the guy who made such a beautiful slab for me really thought that the foam would not be as waterproof as the sealant from a tube. I've trusted lots of other things he's told me, no reason to stop now. thanks for all your opinions.