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106 Posts
Discussion Starter · #1 ·
Hi all. My basement finishing plans are moving along. I have decided to do spray foam insulation with stud walls, and will be installing laminate flooring with a vapor block and padding from lumber liquidators.

One problem I am still struggling with is what to do with the sole plates of the walls. I'm not comfortable putting pressure treated wood direct on the concrete slab. I have seen various ideas for raising the sole plate off the floor. I was considering going with 1" xps under the sole plate all the way around, but I would like other ideas. I have seen a few posts that address this indirectly, so I have some ideas, just wondering what everyone would recommend. Thanks!

· Registered
37,499 Posts
What's your reasoning for not attach directly to the slab.
If not there's going to be air flow behind the wall.
It's done this way all the time with no issues.
I'd be far more concerned with using laminite below grade.
At a minimum made sure it's warrented for below grade use.
Any moisture and it's trash.

· Registered
106 Posts
Discussion Starter · #3 ·
I think I meant vinyl for flooring. Been looking at so much stuff recently my brain is all crossed. We haven't had any moisture problems, so not putting the wood directly on slab is more preference/overkill on my part than anything else. I think I would just have better peace of mind knowing the wood was raised above the concrete.

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11,730 Posts
You are correct! You don't want/need air flow under the plate to deposit moisture on the fibrous cavity insulation/wood framing to condense/mold/rot. (see #1 below) Similar to all exterior walls above grade require caulk/sealant/gasket under the bottom plate to stop infiltration/exfiltration -- per minimum code. As in the attic;

"N1102.4 Air leakage. N1102.4.1 Building thermal envelope. The building thermal envelope shall be durably sealed to limit infiltration. The sealing methods between dissimilar materials shall allow for differential expansion and contraction. The following shall be caulked, gasketed, weatherstripped or otherwise sealed with an air barrier material, suitable film or solid material.
1. All joints, seams and penetrations.
2. Site-built windows, doors and skylights.
3. Openings between window and door assemblies and their respective jambs and framing.
4. Utility penetrations.
5. Dropped ceilings or chases adjacent to the thermal envelope.
6. Knee walls.
7. Walls and ceilings separating the garage from conditioned spaces.
8. Behind tubs and showers on exterior walls.
9. Common walls between dwelling units.
10. Attic access openings.
11. Rim joists junction.
12. Other sources of infiltration." From:

Since that is your new air/thermal barrier location, you should seal it well. A poly sill sealer will 1. stop air, act as a 2. thermal barrier (from conductive heat loss to the slab, earth below), and a 3.capillary break, if no poly under the slab;
Use something under any wood plate on concrete.

Foam the rims, #11 above;

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