Basement Walls And Insulation

highpeaks

I'm in the process of finishing a basement. Walls are 2x4 wood studs, secured to dricore panels on floor. There will be a 14-"-16" offset from foundation walls due to a french drain system. I want to leave aan air-gap and avoid installing over drains. What is the best insulation method? I'm assuming that Im not insulating the foundation walls directly. I was planning on using 2" rigid foam panels, glued between studs instead of 3.5" batts. I was afrad of the batts picking up moisture from the air space. Would like input from everyone else as to insulation method.

Tom M

I believe gluing 2"inch board to the masonry sounds like a better idea. I personally have never glued such a thick board to masonry but everything I have read say its a better install. You get a more consistant R-value by full boards than pieces and you stop the thermal break at the source so air space to dry vapor condensation is not needed.

highpeaks

I had a concern attaching foam directly to foundation walls. I'm afraid of condensation and other water that may drain through weep holes. Does anyone have any comments on this? Will I get any R-factor if th stud walls themselves are insulated and not the foundation itself?

concretemasonry

Putting the foam between the studs will work much better that fiberglass any day of the week. If the panels betweem the stude you will not need much glue or could even use and expanding foam (from the front or back, if possible). The excess can be trimmed. The expanding foam is very good for holding things in place if you recognize that it will expand (fast at first, but still slower for a while)

You really do not need much insulation, if any, since the space between the wall and foundation is a "semi-conditioned" space and does not have much of a temperature differential. - You could even over heat the finished space at certain times of the year.

As an alternate, you could avoid cutting the foam to fit between the studs by using full or partial sheets attached to the outside of the studs (between the studs and foundation wall), IF you have access and fish larger pieces in. This will keep the void between the studs open for easy electrical. This will also give you a better separation and better insulation (if actually needed or wanted). - Just a though without seeing your situation.

__________________
Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

highpeaks

ConcreteMasory, thanks for the ideas. If I attached the foam from the rear, would you use T&G panels, or 4x8 foil faced rigid?

Also, I'm considering installing a continuous air-flow system, like a humidex behind the walls keeping out moisture. any comments would be appreicated

Dustball

I would go with closed cell spray foam directly on the foundation walls and rim joists. If you put insulation on the framed walls only, condensation will collect on the back side due to the moist air in that 14" dead space.

moldbuster

You could seal the concrete with something like Kryton T1/T2 to cut way back on the moisture intrusion to begin with.