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Zone 5 Basement buildout – any suggestions for my plan?

Sean Cotter | Posted in Energy Efficiency and Durability on

We are in Zone 5 (Spokane, WA). House is 1930 Cape Cod style brick veneer. The basement is concrete and is in good condition (according to the home inspector 4+ years ago…). There is some efflorescence along what I assume is the frost line a foot or so above the cement floor. There are no bulk water issues that I can see. Actually, it’s been raining for 3 days straight and I haven’t had any dampness or bulk water problems. The grading on the exterior is OK, but I am going to improve the situation with some gutters in a couple places. Drainage in the yard is good and the house itself is perched up on a subtle hill with the yard grading away on all four sides.

Previous owners finished about a quarter of the basement with a new full bath and laundry. Concrete floor was cut into and new plumbing/drain was put in for that as well as the kitchen and bathroom on the first floor. The construction in the basement was late 90’s and 2005 from the permits I looked up. They put in 2×4 with kraft backed fiberglass batts, a poly layer then sheetrock. Not ideal, but I decided to sacrifice one portion of the construction and all the material is clean. No mold or dampness. Pink batting wasn’t even discolored. I may end up cutting into it and repairing it but I would rather leave it for now and get he rest of the basement finished to save on heating costs and make that useable before tackle that.

The rest of the basement is (now) bare concrete wall. Around 550sq feet of wall surface (if my math is right…).

I am thinking:
1.5 inches of Dow Cladmate (R7.5) attached with adhesive to the walls then
2×4 framing (24 on center) with Roxul (r15)
followed by drywall.

On the floor I was thinking Delta FL dimple mat (on top of geotextile fabric to reduce noise of the dimple mat) and then laminate flooring or maybe engineered hardwood floor.

In regard to the framing, I had read on a blog where someone was using composite deck material screwed to pressure treated wood as the bottom plate and then used tapcons to attach that to the cement floor – the composite decking would help eliminate any wicking of water up into the pressure treated and regular lumber if there was water issue. Has anyone tried this? is it worth that extra step?

Also, I am a bit confused on the type of adhesive and tape to use on the XPS. Is there a preferred product? I read online about some instances where Tyvek and other tapes were coming off after a short time (weeks/months). Dow seems to suggest this:
http://building.dow.com/na/en/products/specialty/wmtape.htm

As mentioned, the exterior of the house is brick veneer. The floor joists are set into the concrete pour. From what I have read this probably isn’t ideal but a lot of the houses around here are the same configuration. There is no rot or water damage on the joists where they set in the concrete. The sill sitting on either side of the house running parallel with the joists looks good. I am a bit confused on sealing up the rim joists. Is there potential for trapping moisture on the end of the joists if I use foamboard and Great Stuff to seal it up? there isn’t an issue now, but it has been open to the air for 80+ years. Is there a rule for how to deal with joists set in the foundation?

This is a great site, learned a lot so far.

Thanks

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Sean,
    Q. "The composite decking would help eliminate any wicking of water up into the pressure treated and regular lumber if there was water issue. Has anyone tried this? is it worth that extra step?"

    A. I have never heard of it. The step sounds unnecessary to me. I would just use pressure-treated plates.

    Q. "I am a bit confused on the type of adhesive and tape to use on the XPS. Is there a preferred product?"

    A. Most manufacturers of construction adhesive make a product that is compatible with XPS. Two well-know brands are Loctite PL 300 foamboard adhesive and Liquid Nails foamboard adhesive.

    According to my own tests, the best tape for XPS is one of the following: Siga Wigluv, Siga Sicrall, or 3M All Weather Flashing Tape. For more information, see Backyard Tape Test.

    Q. "Is there potential for trapping moisture on the end of the joists if I use foamboard and Great Stuff to seal it up?"

    A. Unfortunately, Sean, the answer to this question is yes. Because the ends of your floor joists are embedded in concrete, the safest way to proceed would be to keep the rigid foam one or two inches away from the ends of the joists, so that some air circulates there, and so that you can keep an eye on the area to make sure it stays dry.

  2. Sean Cotter | | #2

    Thanks for the response Martin!

    I ended up deciding to go with Corning Foamular 150 @ 2" since that's more readily available in my area. I don't think the Dow product I found online is sold in the lower 48 - just in Canada.

    Regarding the tape, I found some Venture Brand sheathing tape online and ordered a roll. If that doesn't seem like best choice when I am looking at it I can try the 3M product. Big box stores seem to have limited options around here. Maybe a lumber mill? There is a Pro Build in town my contractor buddies use - I can try them for the foam and tape as well, perhaps.

    Regarding the joists, do I just cut a loose fitting foam section and adhere that up in the cavity and then put roxul against that? Can I come in 6,7" off the foundation (in the joist cavity, towards the interior) and make a 'wall' with foam board - making an area where moisture can dissipate to? The above surface is plank and then maple floors (original) - I assume any moisture that is wicked in (again, doesn't look like any has in 80 years - not bulk water anyway) would be able to dissipate up through the floor system?

    What about the 4x4 sill running parallel with the joists that sits in either end of the foundation? Stop the foam just shy of that (below) so it has room to breathe?

    Stood in the adhesive section of HD and read the label on 20 different adhesives and grabbed the loctite product because that looked like the best option. Right choice it looked like.

    Thanks for all the help!

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