vaper barrier on insulation

Reply

  #1  
Old 01-02-01, 07:09 PM
Visiting Guest
Posts: n/a
My ranch style home built in 1979 has 12 inches of fiberglass insulation but not vaper barrier. What is the consequences of not having a barrier. Should I attempt to install one or is it not worth the effort? I have a 3 foot over hang, all purforated and pot vents in the roof. I have seen frozen moisture hanging from the shingle nails that have exposed them selves in attic ceiling.
 
Sponsored Links
  #2  
Old 01-03-01, 07:42 PM
Member
Join Date: Aug 2000
Posts: 160
The frost on the inside of the attic is due to not having a vapour barrier. Warm moist air is escaping into the attic. Is it worth rectifying? Given enough condensation and time, you will be replacing sheathing & shingles as well as the insulation. The easiest retrofit solution to restricting air movement is to paint the ceiling of the house with an oil based paint. Three coats minimum. A vapour barrier goes on the warm side of the insulation, therefore you would have to lift existing insulation then lay down the poly, then re-apply the insulation. Not a fun job! You could put down a vapour barrier on top of existing insulation sealing around all protrusions into the attic, blow in 10-12" of cellulose ensuring adequate ventillation is maintained. As long as two thirds of the insulation is on the cold side of the insulation your OK.
 
  #3  
Old 01-04-01, 11:09 AM
Visiting Guest
Posts: n/a
moisture barrier/thread =4522

Thanks for the respones Allen. How heavy does the poly have to be for the barrier, 2 mill, 4 mill? When I cut the ploy to lay in-between th ceiling joist, how wide should they be? Just as wide as the space requires our should they be wider so as to have some excess metarial come up the side of each joist? Would it be exactable to have one continues piece of poly; unrolling it up and than down each joist, there by exposeing the joist to the moisture from below? All my ceilings are textured so painting would provide me with more unwanted obstacles.
 
  #4  
Old 01-04-01, 11:28 AM
Visiting Guest
Posts: n/a
addition to my 1st reply t to thread=45221

Thanks for the respones Allen. How heavy does the poly have to be for the barrier, 2 mill, 4 mill? When I cut the ploy to lay in-between th ceiling joist, how wide should they be? Just as wide as the space requires our should they be wider so as to have some excess metarial come up the side of each joist? Would it be exactable to have one continues piece of poly; unrolling it up and than down each joist, there by exposeing the joist to the moisture from below? All my ceilings are textured so painting would provide me with more unwanted obstacles. The 12 inches of insulation I have is two 6 inch piece's laid on top of each other. When I remove them to install the poly is it any advantage to re-installing them so that the 1st layer, one now closest to the ceiling, becomes the second layer? What are the signs to look for that would tell me that I would have to replace the insulation as you suggested I might have to do? Does fiberglass insulation ever dry out after it has become wet?
 
  #5  
Old 01-04-01, 07:53 PM
Member
Join Date: Aug 2000
Posts: 160
The vapour barrier should be continuous. Keep it as snug to the joist as possible to eliminate air pockets, staple to keep in place. If you cut it & lay it in between joists you are wasting your effort. Over lap seams and caulk to seal. The poly should be 6ml. When re installing the two layers of 6" batts, lay the second layer perpendicular to the first. If the insulation is or was wet replace it.
 
Reply

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


Thread Tools
Search this Thread
Display Modes