blown in attic insulation

[jevoy]

Hey there. Just curious if anybody out there has just stapled up 6 mil vapour barrier to the bottom chord of the trusses and then used blown in insulation on top? I know drywalling first is a better idea but its a cost thing right now. I know of one person who has done this and it was fine. Anybody ever have a "cave in"?

Thanks

 

[dreamingmuscle]

I'd at least use some lattice straps to hold the plastic up.

 

[AldeanFan]

My garage was vapour barrier with r12 bats when I bought the house, no drywall. The insulation had dropped significantly in spots and stretched out the plastic. I had to pull a lot of it down and re-do it. Took a few hours extra to get it drywalled.

 

[jevoy]

Aldeanfan. Was it 6 mil or a thinner vapour barrier?

 

[soapii]

I have not seen plastic used, but you can buy vapor barrier that is like a fabric mesh that is used specifically for your application. They did it on my garage prior to drywall to blow insulation under the floor of my attic.

You can see in the attached picture. The center fabric area has 10" of blown cellulose on it with no noticeable sag.

--Joe

 

[AldeanFan]

Aldeanfan. Was it 6 mil or a thinner vapour barrier?

Pretty sure it was 6mil
Any thing thinner would have just torn through the staples.

It probably would have been ok if the ceiling was strapped

 

[MBfreak]

My $0,02 worth.
If at all possible put a rather thick paper cover (( is is called "kraft" paper??) must not be vapor-tight) on top of the insulation. This reduces the air circulation quite a lot inside the insulation and reduces heat loss.

This is a requirement in building codes here in Sweden, so for cold climates I am sure it´s worth the effort.
If you live in a warmer climate where ambient can be above if the space is cooled in the summer, I have no idea what is right.

Best regards
Ola

 

[nolimits76]

FYI, if you guys check at the local contractor supply houses, you can find thicker 11 mil & 16 mil vapor barriers. One popular one around here is called Barrier Bac. The VB250 is only 11 mils, and the VB350 is 16 mils.

http://www.barrierbac.com/

This stuff is much better than the 6 mil visqueen you get at Home Depot and similar. Whatever product, I used roofing nails with the fat plastic washers.

Alternatively, I've used blown-in-blanket (BIB) insulation in a house before. They use a non-woven fabric material to hold the material in-place. It may be a better option. It is similar to a garden fabric material but not identical. Doing some web research it appears that Owens Corning & Certainteed both have a product.

http://www.bibs.com/
http://www2.owenscorning.com/literature/pdfs/10000560.pdf
http://www.certainteed.com/Products/317369

 

[NUTTSGT]

I'd be afraid of it pulling through the staples. If it pulls through, you are going to have a mess. I've dug enough blown-in insulation out of attics to know I wouldn't want that mess in my garage and everything in it.

FWIW, you might want to edit your profile to show a location to help your fellow members answer any future question you might have. You don't have to be specific but just a general location of where you're at in Canada might help.

 

[dreamingmuscle]

Tyvek vapor barrier would work also.

 

[csp]

Tyvek shouldn't be used between an interior space and insulation, only outside of the insulation. Tyvek isn't a vapor barrier, it is permeable to vapor passage which you don't want in the insulation.

 

[Elginz]

Alternatively, I've used blown-in-blanket (BIB) insulation in a house before. They use a non-woven fabric material to hold the material in-place. It may be a better option. It is similar to a garden fabric material but not identical. Doing some web research it appears that Owens Corning & Certainteed both have a product.

http://www.bibs.com/
http://www2.owenscorning.com/literature/pdfs/10000560.pdf
http://www.certainteed.com/Products/317369

I would go this route.

 

[DC73]

Tyvek shouldn't be used between an interior space and insulation, only outside of the insulation. Tyvek isn't a vapor barrier, it is permeable to vapor passage which you don't want in the insulation.

Walls must be able to dry. If there is a vapor barrier anywhere in the wall assembly, then walls must be able to dry to both the exterior of and to the interior of the vapor barrier. Not all climates need vapor barriers and it can create problems if not installed properly. Depending on the climate and how the rest of the wall assembly is constructed, using Tyvek as was suggested would not be a problem at all. IF a vapor barrier is required, then Tyvek should not be used in its place.

DC