Advice for insulating basement wall

2 years ago

As you from the attached photo, the basement wall in my 1972 built house was constructed with 4 foot 2x4 framing [A] on a 4 foot high concrete foundation wall.

Now because I want to finish my basement, I installed a 4 foot 2x4 pony wall [B] atop the concrete foundation wall.

And then an 8 foot floor to ceiling 2x4 wall [C] in front.

Notice that I now have Rockwool Comfortboard 80 attached to the concrete foundation wall.

I propose removing the existing fiberglass in the [A] wall, replacing with 2x4 sized Comfortbatts.

And 1 inch foamboard in the 1 inch space between {A] and [B].

Next, I would extend the existing Comfortboard 80 to the top of the ceiling.

Finally, I would finish filling the cavities on the [C] wall with 2x4 sized Comfortbatts.

My house is located in Blind Bay, British Columbia.

Winters are cold ones, temperatures often -20 degrees F and worse.

Summers are hot, temperatures often reach 100 degrees F.

The concrete wall is completely below grade.

But on the 18 foot wall adjoining, the concrete foundation is fully exposed.

What about my insulation plan?

Without considering local code compliances, would it be successful?

Otherwise, what other plan would you go with?

I have not mentioned vapor barrier/retarder but assume it would be required prior to installing drywall.

In lieu of standard poly, would it pay to go with MemBrain by CertainTeed or IntelloPlus by Pro Clima?

Featured Answer

worthy

2 years ago

Here's a build we did in '04 with XPS as sheathing.

And a current one with 2"-3" of XPS on the exterior of the sheathing, to be followed by 1" of spf on the interior followed by fg batts.

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Comments (7)

worthy
2 years ago
You're in Climate Zone 5.

See this section of the B.C. Building Code for information on best practices.

(Been by you every time I've driven to Vancouver from TO. Beautiful!)
zumtobel thanked worthy
zumtobel
Original Author
2 years ago
Appreciate knowing I am in Climate Zone 5 but I think the BC Building Code wouldn't address my specific situation in specific enough detail, e.g. the placement of the 1 inch foam board.
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worthy
2 years ago
last modified: 2 years ago

page 10 of the Province's Illustrated Guide

At least, meet those minimums.

Dont really understand your diagram. But one inch XPS (extruded polystyrene) followed by rockwool batts sounds fine to me. An interior vapour barrier may be required by building code officials. In that case, use Membrain. (See this article from Fine Homebuilding, particularly the last quote from Dr. Straube.)this
zumtobel thanked worthy
zumtobel
Original Author
2 years ago
I am not as concerned about meeting code as I am about doing it right with no air leaks, no water damage and no mold resulting. Interesting that you don't understand my diagram. Not sure I can add more clarity. I concur about installing one inch XPS directly against the sheathing, followed by Rockwool batts. And for sure the Membrain or Intello Plus. Thank you for your reply!
zumtobel
Original Author
2 years ago
Well, what you have with those two places is definitely the way to go! External insulation beats everything you can do on the interior.. Thanks for sharing.
3onthetree
2 years ago
I believe the Comfortboard will work on the concrete wall, but haven't checked perms. The point lacking is turning the rigid board over the top of the concrete. You are guarding against condensation with this detailing. Read BSD-103 Understanding Basements which has your scenarios.