How to insulate walls thicker than standard batts?

[Chip C]

My walls have been furred out with 2-by's but because the old studs actually measure 4" or more (and in some places were furred out previously, for whatever reason) they are much thicker than the 5.5" R-22 mineral wool batts that are going in them. In some places there's more than an inch of air space between the batt and the vapour barrier.

Manufacturer's instructions say "Ensure the surface of each batt is flush with the interior surface of the studs" but doesn't really say what happens if you don't.

Big problem? Am I decreasing my R-value from the nominal R-22, or am I just losing an opportunity to gain a few more R's?

I presume the only fix is to fillet extra batts to the right thickness and put them in, and that leaving the space at the outer wall is as bad, or worse...

Thanks,

Chip C Toronto

[Steve Barker]

wet sprayed cellulose.

[Tony Hwang]

Hmm, Wet? R-value is all gone then.

[Steve Barker]

LOL! well it doesn't *STAY* wet. hello?

[clare]

Use 2 thin bats - one paper backed and one "open" -corrent combination to fill the gap

[clare]

Not after it dries.

[bob haller]

far better to use closed cell spray foam its R value is near 7 per inch

[Steve Barker]

that's true, and it's cost is about 3x of wet sprayed cellulose. But if you've got the money, it's the way to go.

[bob haller]

to obtain max R value more money spent now pays off forever

[bob haller]

to obtain max R value more money spent now pays off forever about R 7 per inch plus it fills all the holes, for quieter better job

[Jules Richardson]

What's the [estimated?] lifespan of it vs. other types of insulation? I've seen some types of *old* spray/molded insulation turn to powder or goo after a few decades; it would be nice to know that the modern stuff wasn't going to go the same way in 40 years (where the fiber-based types might still be fine)

My guess would be that the modern stuff is engineered to last much longer, but it would be nice to know for sure.

cheers

Jules

[hrhofmann]

Back to the OP, get some unfaced fibreglass bats and split them into a couple/three layers, and use them to fill the extra space due to the thicker walls. A little compression of the material will not hurt, just don't compress them to less than 2/3 their original thickness.

[Steve Barker]

i suppose as with any new product, that has yet to be seen. But you can bet it will outlast the person paying for it.

[Joe]

Might be easiest and most effective to trim and apply extruded foam panels to each bay. Our local source has the styrofoam in thicknesses from 3/8" to 2". it can be cut with nice precision on a table saw.

Joe

[Chip C]

This is actually the option my contractor is going to go with. They're finding the mineral batts just kinda fall apart when they try to slice them thinner.

He says the local bldg inspectors have no trouble with large spaces between the vapour barrier and batts, so this is just some odd thing that I'm requesting.

They gave me the option of closed-cell spray in but the cost was a lot higher and my wife and I are happiest letting someone else get the first few decades of experience with it in their walls. UFFI and all that. Plus we know how to work with mineral wool and styrofoam if we ever want to open the walls up ourselves for any reason.

A lot of great comments in this thread; thanks to all.

Chip C Toronto

[piper]

Whoa, seems you want to put a vapor barrier in there b/4 where it's supposed to go. It's ok if you want it to smell like a moldy diaper.

Going by what the OP posted, you are giving terrible advice, as usual.

[gregz]

Styrofoam has about the worst r value of stuff I have looked at. The white stuff.

Greg

[Twayne]

But based on YOUR post, you've provided absolutely nothing in the way of usable information. If you know what's wrong, then you know what's right, and should say so. And, you should better your readng comprehension, too.

HTH,

Twayne`

[piper]

The useable information is apparently over your head. You _do not_ place a vapor barrier on the wrong side. Get it? Or, do I need to explain it to you?

[clare]

when it comes to BASEMENT insulation there are several schools of thought on vapour barriers. All 3 have valid points.

What I ended up doing was putting 2 inches of Styrofoam SM against the concrete wall with the lap joints all taped, then built the 2X4 wall against it and filled the cavity with straight rock-wool (Roxul) batts with no vapour barrier, and glass surfaced paperless drywall. Waterloo Ontario