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What insulation when using vapor barrier?


Civicminded's Avatar
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01-05-17, 06:32 PM   #1  
What insulation when using vapor barrier?

I have a House built in 1978, 2x6 walls. The house has foil faced insulation with poly stapled over the studs, the drywall or paneling depending on room. the house is sheathed with blackboard and the corners of the house have plywood sheathing. No attempt was made to air seal around outlets, or seal the seams on the poly. There is no evidence of moisture problems in the walls.

In reality the house had a ton of airleaks, which I have slowly been eliminating the best I can. The vapor barrier really let a lot of air through around the outlets so it wasn't tight at all.

I am doing a bathroom renovation and was going to install new vapor barrier and from what I have read it seems I should use unfaced insulation? i am going to put airtight boxes around the outlets and switches and use tuck tape and acoustical sealant to create an airtight barrier.

This seems to me a really tricky topic, but it seems to me I need to air seal everything the best I can.

So do I use unfaced insulation?

Thanks

 
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01-06-17, 03:07 AM   #2  
Use Roxul Safe 'n Sound. It has an R15 rating, needs no vapor barrier, is waterproof, vermin proof, mold proof and fire proof. I would cover the shower area with 6 mil plastic as a vapor barrier and to direct seeped through moisture back down into the shower base rather than letting it get to the framing wood.

 
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01-06-17, 04:57 AM   #3  
I agree with Chandler, but your 2x6 walls can hold the r-21 comfort batts. Unless your code requires it the vapor barrier is not necessary, but does no harm. As you stated air sealing is the most important issue. Although a vb seems to help with air sealing, your drywall is normally your primary air barrier, it's rigid.

Unfaced insulation is fine, just be neat and get a tight fit.

Bud

 
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01-07-17, 06:00 AM   #4  
Thankyou!!! I never knew there was such a product. If its as nice as it looks I cannot figure out why anyone would buy fiberglass insulation. Our local home depot only has 3.5 inch thick roxul for 2x4 walls and could order the stuff I need but the minimum was a pallet of it.

So..... I ordered some from lowes since you only have to order a minimum of 3 packages of it.

I am excited about it.

 
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01-07-17, 06:26 AM   #5  
I think the reason it is used less is the initial cost over fiberglas. I had posted elsewhere I insulated my joist bays at the rims with it doubled in the bays and this morning it was 17 outside and really nice in the basement. I didn't know how much difference it would make.

 
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01-07-17, 07:10 AM   #6  
I tried it several years back when it was just hitting the states (made in Canada at the time) and drew the same conclusion, why fiberglass. Cost is probably the primary reason as Chandler said along with the foothold fg has on the market. Many people still like the staple up flanges as well. But air certainly will not drift right through the Roxul like it does fg.

I use a long bread knife or even a hand saw to cut most. Always give it a little extra to ensure a snug fit.

Bud

 
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01-07-17, 07:26 AM   #7  
Same thing, Bud. I had an old bread knife with a nick in the blade which tore bread. PERFECT 12" long blade, thin and sharp. Cut Roxul like butter with no boogers.

 
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