insulation

[goubeau66]

We have added on new additions to our home and was wanting to know what is the best way to insulate outside walls on new construction? Spray foam or batting or both?

[Robert Jones]

I would say that the use of spray foam would probably be better at filling the cracks, being more green etc..., just not sure if the extra cost is worth it. Check out a system called flash and batt. Which is a combo of both. You also have to factor in the area you live.

[kurt]

Closed cell foam. Hands down, best.

The flash and batt recommendation is OK for saving a few dollars.

The great benefit of foam is air sealing the exterior walls; it's remarkable how much better it is than straight batts.

I'm seeing flash and fill, where you flash an inch or two of foam and then finish it with a spray fiberglass or wet cellulose. I like it better than batts.

[Chad Fabry]

I'm seeing flash and fill, where you flash an inch or two of foam and then finish it with a spray fiberglass or wet cellulose. I like it better than batts.

I've been a proponent of flash and batt in the past, but now I'm beginning to see some issues. It is absolutely imperative that the spray foam is installed thick enough so that the dew point surface lies somewhere in (not on) the spray foam layer.

Around here, it needs to go on a couple inches thick to achieve that and that creates another potential issue: when spray foam is a couple inches thick, it is pretty close to an absolute vapor barrier. At this point, I'm not a believer in flash and batt. I urge you to consider an all foam wall.

[kurt]

Oh, I agree. All foam. I've never understood why anyone would want to do it otherwise.

That said, I've seen enough flash and batts to know they work fine. Minimum 2" foam. The problems come from the batts; it's very hard to get the foam thickness uniform enough so there are no air gaps between the batts and the foam.

That's why I think the flash and fill (w/a spray cellulose) is better.

[Tom Raymond]

If I were going to build new and cost were no object, it would be closed cell sprayed in everywhere. Since cost is always a consideration, I'd be forced into flash and fill-closed cell foam and cellulose is good stuff.

If your bent on batts, you'll need to caulk everything with non-expanding foam, place rigid foam in all the cavities and then finish off with batts. If your paying for labor flash and fill is cheaper.

EDIT: If your really bent on using batts forget fiberglass. I'd be thinking rock wool, recycled cotton, or hemp.

That said, additions are tricky things. You need to balance the new against the performance of the old. Not only will there be no ROI spray foaming a 300 SF family room on the back of '60s split level, you may actually freeze yourself out of the old house.