Mooney Wall Construction Method

[AC_Hacker]

'Mooney Wall' is a very good way to construct or upgrade an exterior wall to have superior insulation.

Reduces thermal bridging to almost zero.

Shown is using cellulose fiber fill, but could also use chopped fiberglass if you insist on lower R-value, higher cost & higher embodied energy & higher manufacturing CO2 emissions.

-AC_Hacker

[Daox]

Whenever I actually get around to insulating my garage, this is what I'm going to do. I love the idea.

[S-F]

I don't really get the Mooney wall. I guess you can reduce the bridging a pretty good amount, but that's about it. At the most you get an inch or two more wall. Just spending the time air sealing properly will do a lot more for you than 1" of cellulose or blown glass. If I'm going to be tearing my interior walls down I'll be making a proper double stud wall for a full 12" cavity. You can reduce thermal bridging much more effectively, for a lot less money and with a lot less disturbance to the residence by installing XPS to the outside of the sheathing. There you can add 4" for an additional R20 as opposed to an additional 3.7 or maybe less.

[Daox]

I think the whole point of the mooney wall is its cheap and easy to do. It also effectively takes an 2x4 ~R10 wall (R13-14 minus thermal bridging) and makes it an R18 wall, and you only loose 1.5 inches! I completely agree I'd like more than R18 for my house (my personal goal is to have R40 walls), but I think for a garage thats pretty good. Its almost 2x better than most people's houses.

[S-F]

I hear ya on any improvement being good. The point I was trying to make is that for the same money you could ADD R20 to your whole house, almost completely eliminate thermal bridging and not disturb the living space much at all with outsulating the walls. You also can add a rain screen which is great. Of course to really do it right you would need to tear up the inside of the house. I plan to add foam to the outside and then probably do something like a mooney or double wall on the inside when time permits.

[tomboy mom]

I think that's pretty neat actually. Any idea if mylar or some other reflective could be used with that? For those of us that have very little problems heating but lots of struggles cooling this seems like a potential solution.

[Daox]

Sure, you can always add radiant barriers to any wall. You just need to be sure that you have an air barrier next to them.

[GaryGary]

Originally Posted by S-F

I hear ya on any improvement being good. The point I was trying to make is that for the same money you could ADD R20 to your whole house, almost completely eliminate thermal bridging and not disturb the living space much at all with outsulating the walls. You also can add a rain screen which is great. Of course to really do it right you would need to tear up the inside of the house. I plan to add foam to the outside and then probably do something like a mooney or double wall on the inside when time permits.

Hi,
For the regular Mooney wall, the R value improvement would be R3.7 per inch times 1.5 inches is +R5.6. Plus essentially eliminating thermal bridging. You could also go with wider than the 1.5 inch strapping and get more R value.
And dense packed cellulose is a good air sealer -- this could be important on retrofits where its harder to good air sealing after the fact.

If you look at the cost numbers for the Mooney wall example here:
Mooney Wall -- A low cost, high R value wall
and, you take out the cellulose that fills the 2 by 4 part of the wall, then the cost per sqft is about $1071 - ($843)(1.5/5) = $818, or 39 cents a sqft. This includes the cellulose in the 1.5 added inches, the 2 by 2 strapping, glue, and insulweb stuff.

Adding R20 XPS would be about $2.10 a sqft plus a ton of fairly expensive washer screws to hold it down, PU sealing foam, and all the hassle and expense of extending the window and door frames out for the 2 inches -- a pretty big job. It also seems like its pretty much something you have to do when its time to replace your siding -- I don't see how you could put the old siding back on?

Not saying either method is best, but I think the Mooney Wall has its place -- it kind of depends on your situation and what kind of exterior finish you have on the house.


Gary

[S-F]

Right. It's generally assumed that unless you are in need of replacing the siding any way the ROI on outsulating is pretty high. Of course this all gets shot when you do the work yourself and you use recycled foam. I recently calculated the cost of foam needed to put 4.5" on my 1100 sq ft ranch and it only came out to about $1,000. Then lap siding costs about $1,400. HeadLok screws do also cost a small fortune. Probably several hundred for them alone. But you also have to factor in the disturbance to the living space, which to me is a big deal. I don't like living in a construction site. Which reminds me, since I'm up I should probably get to work on my current project.