Fiberglass Bats Installed Backwards?

[danf58]

I've two side of my home the have second floor walls exposed to what amounts to 1st floor attic space. The fiberglass was installed, as perhaps it should be normally, w/the paper backing to the drywall facing side. This would be fine in a typical installation as the fiberglass has a plywood backing, or chamber it sits in. It's pretty hard for hot air to migrate through the fiberglass as its in a my and large closed chamber.

By the two walls in question have maybe 100 sq feet of open area between the open backed fiberglass and the side/roof line. There can be no doubt there is lots of thermal lift and transfer there.

Should this have been installed reversed, w/double sided backing, enclosed w/housewrap, or...

I know this isn't an insulation forum, but I also know you guys get held liable for plenty of poor insulation jobs, so I'm betting there are a few folks w/opinions on this.

Thanks for any thoughts.

dan

[bluestone]

The vapor barrier faces the interior in cold to moderate climates, for our purpose above the mason dixon line. Vapor barriers should never face away in these climates as any number of bad mojo can occur. House wrap is vapor permeable and can be used on the vapor away side of insulation. This is a good idea in that it will help with air washing which is a major drawback with fiberglass insulation. Air washing will greatly impact thermal performance of fiberglass, i.e lower the effective R value sustantially. Not much mention of this cocept is made in insulation info.

[danf58]

Say, I didn't know housewrap was vapor permeable. That's GREAT to know as it perfectly solves the problem.

Heck, it sounds like the construction equivelent of Goretex.

Many many thanks.

[jamesaon]

The other advantage to the housewrap in this application is that it will hold the fiberglass in place.

Good luck,
Jim

[bluestone]

Glad to help, and house wrap is very much like Goretex, it allows vapor transmission but will shed water, at least untill the coating wears off. My perferred brand is Typar.

[mark beiser]

I would take it a step further and install some foam or cellulose sheeting over it so that you get better R-value and have some insulation on the wall studs. I haven't looked in a couple of years, but last time I bought some, it came in thicknesses up to R-8 in 4'x8' and 4'x10' sheets.

Stuff like how your house is insulated just makes me sigh and shake my head.
There is always a big deal made about having R-30 or better insulation in the ceiling, and making sure all the ceiling joists are covered, but when it comes to a wall that has attic on the other side of it, they just toss in R-11 bats and leave the wall studs exposed....

[jamesaon]

I would take it a step further and install some foam or cellulose sheeting over it so that you get better R-value and have some insulation on the wall studs. I haven't looked in a couple of years, but last time I bought some, it came in thicknesses up to R-8 in 4'x8' and 4'x10' sheets.


I would qualify the above by encouraging the use of a "siding backer" foam board that will breathe. A solid foam board will trap moisture in the wall cavity.

Jim

[bluestone]

I agree with Jameson, cold side ridged board must breathe, impermeable insulation board will create double vapor barrier and return you to bad mojo condition. If it were me I would skip the ridged board all together, if you need more insulation roll more 'glass perpendicular to the first layer if possible.

[danf58]

Mark:

You should be in my shoes. I gave the job to the company as a result of discussions about creating a tight house. Celluse in the ceilings, foamed joints, cracks, and etc..

Why in the world I should find open backed fiberglass on those sides is beyond me. But I guarantee they'll charge a fortune to fix it...

Jamesaon: (and Mark)

Nice tip, and installing in boards may even be simplier then trying to manage sheets of "paper".
Can they be glued on? (Speed,+airtight)
Can you give me a few product name suggestions. I didn't see same w/tyvek or typar...

Gracias.
Danke.
Merci.
Bbl (darn russians! How in the HECK do you pronounce THAT)
谢谢 (Oh.. ok, maybe the russkies aren't so bad anyway. Well,,

Maybe just THANKS.

[jamesaon]

Siding backer foam board usually comes in a "fan-fold" configuration, but you should know that it will provide very little "R" value, primary purpose would be to stop the thermals that are affecting your glass negatively. If you want more Rs, add more fglass.

Jim

[cem-bsee]

shop for Styrofoam -- been around for 50+years, as I remember --
I installed some 2inch thick Tongue& Groove in rental house in 1981.
I installed some "Foamboard" = 2" tk in my crawl 4y/a.-- no T&G, so I foamed cracks --
one can use LiquidNails glue for such -- I glued to concrete block walls & concrete ceiling under front porch.

read about vaporbarrier at BUILDINGSCIENCE.com