Question re furring strips, XP drywall, and finishing basement over 3″ of polyiso
I have used recycled roofing polyiso panels (1.5″ stuff), staggered them, and going to foam the gaps where I can and use acoustic sealant (“the black death”) on gaps too small for foam.
Here is a big question, I want to put furring strips horizontally and just mount drywall over that:
1. Is it OK to just go with furring strips and not build out full 2X3 or 2X4 framing. Wasn’t planning to fill the gap with anything between drywall and polyiso
2. Is it OK to use XP (purple) drywall, instead of trying to chase down paperless kind? Basement is dry and has been retrofitter with internal drain look and double sump pump setup on separate circuits.
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Certainly not an expert but I recently read an on-line article by This Old House that did what you are proposing. Unfaced XPS or EPS (not sure which) was adhered direct to a basement concrete wall. Then 2 layers of furring were run vertically and horizontally. Furring was screwed to substrate concrete, then wall board fixed to the furring. The cross over furring was done to enable cable runs both vertically and horizontally under the dry wall. Do not have the reference but expect you can find it on-line.
Apollo,
Yes, your approach can work. It's easier to run wiring in 3.5-inch-deep studs than in 1.5-inch-deep cavities between furring, but it's up to you which way you want to go.
The decision on whether to use ordinary drywall, moisture-resistant drywall, paperless drywall, or cement backerboard depends on how damp your basement is and your tolerance for risk. You decision to use moisture-resistant drywall will work
Martin,
My basement apparently was flooded only once in the last dozen or so years. Previous owner did have new perimeter under slab drainage installed and sump has staggered sump pumps in it. So decision is more of what is the best cost vs risk of mold if say small leak developed at some point
In the meantime, is my understanding correct that foiled faced PolyISO is OK to be left undrywalled in crawlspace, but I have to cover it in the basement?
If you're really concerned about flooding issues you need to cut the foam up at least an inch off the floor (or to the high-tide mark, and replace it with EPS).
Fiber faced polyiso needs a thermal barrier against ignition. If you're actually finishing the basement, for a flood resilience you can use fiber-cement siding panels mounted to the furring as a moisture resilient wainscot on the lower half (the faux stucco panels aren't too ugly, or the textured plank-look stuff) and regular drywall above that. It's not cheap, ( ~ 4x the cost of 1/2" wallboard) but when you consider the fact that you'll never have to paint it (pick the colors carefully!) and that it will resist dents & scarring better than painted wallboard it's not as bad as it might seem at first blush.
I don't really want to put up drywall. I haven't figured out yet how I want to use the space.
Spec for THERMAX states that you can put it in the basement without drywall. I wonder if it is true with current code. If I can avoid framing the walls and be done with it by just putting another layer of polyiso with foil face - ideal scenario.
Yes, in most jurisdictions a layer of half-inch (do they make it any thinner than that?) fire-rated Thermax would be sufficient.