Old Paper-backed Insulation = Vapour Barrier? - Building & Construction - DIY Chatroom Home Improvement Forum

Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction


Thread Tools Display Modes
Old 03-15-2011, 08:42 AM   #1
Join Date: Mar 2011
Posts: 27
Rewards Points: 25

Old paper-backed insulation = Vapour Barrier?

From what I've heard, on old paper-backed insulation (R8?) the paper acts as a vapour barrier. Here's my dilemma:

I am redoing an old house but I don't want to tear apart the attic because the current insulation (paper-back+blown) is below floor boards in about 1/2 the space.

In the other parts, I had to pull up boards to drop wires and vents. I would like to use a thick vapour barrier rated paint on the ceilings to ensure this barrier is continuous.

Will the paper-backed insulation cause a problem due to a "double-vapour barrrier" or is this not an efficient vapour barrier in the first place?

On another note, when I blow more insulation into the attic when I am done, I know to install the channel vents, but do you also put a small barrier to prevent the blown insulation from falling onto the soffit around the channel vent?

Thank you.


billyh is offline   Reply With Quote
Old 03-15-2011, 11:01 AM   #2
Join Date: Dec 2008
Location: Fairbanks, AK
Posts: 1,893
Rewards Points: 1,092

If the paper is laminated w/ asphalt, it has a perm of 0.3 (Class I vapor retarder), but it is leaky. VR paint has a perm of about 0.45. I don't think you'll have a double vapor barrier problem because of the proximity of each, but I could be wrong. Both should be at the same temp, w/ only sheet rock between them, so they should not condense. Yes, block the blown from escaping.


jklingel is offline   Reply With Quote
The Following User Says Thank You to jklingel For This Useful Post:
billyh (03-15-2011)
Old 03-15-2011, 01:39 PM   #3
Join Date: Mar 2011
Posts: 27
Rewards Points: 25

I think that is what it is. It is paper like a brown paper bag, with the bottom of the lower paper black (doesn't really increase the thickness at all).

Thanks for the help.
billyh is offline   Reply With Quote
Old 03-15-2011, 08:38 PM   #4
Registered User
Join Date: Mar 2009
Posts: 11,730
Rewards Points: 526

Read the % solids content on the v.b. paints, not all are the same; http://www.mde.com/publications/Jan07News.pdf

If any ads are present below my answer or words underlined/colored, I do not condone/support/use the product or services listed/linked to, they are there without my consent.
17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
Gary in WA is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Cape Cod Style House Attic/Crawl Space Insulation Help Danielg Insulation 24 05-21-2012 08:20 AM
Basement insulation / vapor barrier questions deepstuff Building & Construction 16 02-09-2012 09:11 AM
vapour barrier HELP!!!!! 06GT General DIY Discussions 8 02-23-2010 08:01 AM
Installing New Electrical Outlet - Vapour Barrier WhIsKeY Electrical 4 12-31-2009 11:08 AM
moisture behind vapour barrier piperboy General DIY Discussions 9 10-21-2008 12:49 PM

Top of Page | View New Posts


Search Engine Friendly URLs by vBSEO 3.6.1