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rgauthier20420 · Jan 15, 2014, 12:57 PM

I'm finishing my basement right now, and I've got a couple questions in regards to insulating it. From what I've read, I know the BEST way is to put up rigid foams boards along the concrete walls from floor to ceiling and then but your interior wall against the foam boards. However, I've already got it halfway framed and left a 2" gap between the rear of the wall and the concrete wall, so that's no longer possible.

It is my understanding that fiber glass insulation is permeable and you don't want it touching the concrete (this was the reason for the gap), so my plan was to use the fiber glass insulation that has the overlapping folds and tape those to the studs (metal studs). As long as there is a small cavity in between the back of the insulation and the concrete, then moisture is able to freely move and dissipate and be vented out. Is that at all right?

ebaines · Jan 15, 2014, 01:29 PM

I think what you're doing is fine, and is precisely how I refurbished my basement last year. However, I was a bit chagrinned to find that to comply with the latest fire code requirements we had to (a) put plywood firestops vertically from the back of every third 2x4 stud to the concrete wall - to minimize the chance of fire spreading behind the wall and, (b) seal the top of the wall so that any fire in the wall can't come forward into the ceiling area. In other words the fire safety requirements are precisely designed to foil our goal of air movement behind the walls. We finished the prohject a year ago and so far have not detected any issues, but who knows what may happen after a number of years. One of the more significant things we did was to install two small ductless heater/AC units. They really help keep the air dry and improve air movement in a way that plain old dehumidiiers can't. So far, having gone through a full year and the extremes of summer and winter weather, we're very pleased with the results.

joypulv · Jan 15, 2014, 06:27 PM

I think your way is best, and with the metal studs, you don't have the problems that go with wood ones. I don't agree that Styrofoam against the concrete is the best at all - studies being done now are showing that bugs absolutely love chewing channels all through the stuff, inside or outside the foundation.
This Old House had an episode on this. They used vast amounts of Great Stuff as connectors across the gap. Seemed expensive.

rgauthier20420 · Jan 16, 2014, 09:40 AM

I'm glad to hear that this will be a good way to insulate the area. I don't see the point in the fire stop plywood section that ebaines posted because it defeats the purpose of having moving air... just like he said. That seems a little odd, but who am I to comment really.

I hadn't heard of issues like that with the insulation attached to the exterior concrete walls. It seems everything I read for insulating a basement tells you to attached 1 1x2" insulation boards to the concrete wall then butt your wall against the insulation. Going a step further would be to still insulate the walls with bats but not 100% needed.

Oh well, thanks for the replies gents!

creahands · Jan 16, 2014, 12:39 PM

I installed the 2' 'foam board insulation between the metal studs, sliding into one side and using duct tape on the flat side. Used spray foam at outlet boxes for tight seal.

Chuck

ebaines · Jan 16, 2014, 12:44 PM

Originally Posted by rgauthier20420

I don't see the point in the fire stop plywood section that ebaines posted because it defeats the purpose of having moving air... just like he said. That seems a little odd, but who am I to comment really.

The purpose of a fire stop is to stop (or at least slow down) the movement of fire. If air can move then so can fire; hence a firestop is designed to prevent the movement of air. It wasn't my choice to put those fire stops in, but our local building code enforement officer insisted.

rgauthier20420 · Jan 16, 2014, 12:47 PM

Ebaines. Sorry miss worded that part. I was meaning to agree with you in that it seems counter effective to have that in a place where air movement is a good thing.

21boat · Jan 18, 2014, 05:32 AM

Ooohh I can't tell you how many Fiberglass basement walls we ripped out because of moisture. I hate to be the bearer of bad news but Foam is the only way to go

Also certain areas have diff codes on what type of foam can be used so check local codes.. I think this could go bad on you down the road.

This is actually what we do when hired to do basement walls
..
Install Rigid Foam Insulation in Basement Video - YouTube

Best way to insulate a basement - YouTube

Regards mark

massplumber2008 · Jan 18, 2014, 06:32 PM

Hi Mark! It is nice to see you! Happy New Year!!

parttime · Jan 19, 2014, 02:54 AM

Also glad to see you back Boat, I hope all is well.