I have found this site to be very helpful and informative, and after a considerable amount of searching the archives, I'm still a little confused on what to do...

My walls are 8 inch concrete masonry blocks. No siding or interior facings - just block walls with paint. What I decided to do to help with the insualtion department is to add poly-iso rigid foam boards to the interior surface. (I took the advise from a poster on this board to completely cover the walls with the rigid poly-iso and then put the studs on top of that to create a thermal break. Drywall will be added after the electrical has been upgraded. By the way, the poly-iso is 2 inches thick, and has foil backing on both sides.

 

My question is this:

Would it be of any gain to install a radiant barier on top of the studs prior to drywall? There will be a 1 1/2 inch airspace behind the radiant barrier because of the fact that I installed the kiln dried studs flat to the wall. Or, would if be better to just leave the airspace alone?

 

My climate is mild in summer and winter (West Coast - Oregon) and I am more concerned with heat loss in winter as opposed to heat gain in summer.

 

I also learned here that it would be better to insulate the exterior of the blocks rather than the interior, but I am not ready to re-side the house yet. ($$) I will likely do that after I sell the house I am currently living in (not the block house) in order to budget the project.

 

thanks in advance

Mark

 

 

Use 2x2 furring strips at 16" oc over the 2" foam and fill the 14.5" space between the strips with another 1.5" thick foam. That way for most of the wall you'll have 3.5" thickness of foam. They actually sell foam in 14.5" widths just for this purpose.

I'm assuming the iso board is foil-faced, not fiber?

If yes, the foil facing is already a radiant barrier.

For any radiant barrier to have an effect it needs an air gap between it and the gypsum board, which you already have with your flat-placed stud stock.  In a vertical orientation like this the benefit it's giving you is about ~R1-R2, and only if that cavity is air-tight.  If you cut in sheets of 1.5" of EPS (styrofoam) to fill that gap, it would add another ~R6 to the cavity space, which might be worth it (especially if using scratch & dent, scavenged or recycled material, since you don't need full sheets.)

If the interior iso board is foil-faced, if/when you insulate the exterior, be very careful to use permeable or semi-permeable materials for the insulation & siding or you'll have a moisture trap in the wall.  In the rainy PNW, any siding should have at least 1/2" of air space behind it and the drain-plane materials (housewrap or felt) to keep bulk moisture from finding it's way into the block wall.

I would not use wood framing at all, studs or furring strips. If your iso board is firmly attached to the wall, glue InSoFast to that and you have more insulation and attachment for drywall.

I'm just a homeowner, but from what little I understand, you might want to use XPS against the concrete or put poly between the concrete and ISO.

I think I'm wrong--listen to Dana1!