using poly iso to insulate ceiling

Reply

  #1  
Old 06-01-06, 07:26 AM
Member
Thread Starter
Join Date: Jun 2006
Location: Denver
Posts: 26
using poly iso to insulate ceiling

Hi all,
I've got a 99 year old house with a poorly finished attic. We're redoing the attic (to make a master bedroom) and discovering that the only insulation is r-11 between the rafters. There is no empty space now, it's drywall (inside ceiling) then r-11, then roof. I have a bunch of 3.25" poly iso that I'd like to put in so we can have some added insulation and make it a little less hot in the summer. I'm aware that I'll need 1/2" drywall over it. Because of ceiling height I don't really want to put the insulation over the rafters (I'd prefer to go between). I have two questions, first, am I really going to lose that much r value to short circuits if I put the insulation between instead of over the rafters? Second, if I put it between, what's the best way to hold it in place and how does it interact with any wiring I need to do?

thanks!
 
Sponsored Links
  #2  
Old 06-02-06, 10:17 AM
Join Date: Mar 2005
Location: USA
Posts: 6,125
using poly iso to insulate ceiling

Cutting and fitting rigid insulation between rafters is not a very effective way to use a superior insulation and infiltration preventing product. Without a perfect fit or foaming the crack, you could have infiltration.

The thermal short-circuiting of a fiberglass and wood stud/rafter situation is well documented. I do not thave the tables in front of me, but for the full 2" rafter you probably have the loss is about 7 to 10% of the indicated value of the R11 insulation. - Its a good thing you do not have steel studs where you could approach a 35% loss.

Dick
 
  #3  
Old 06-02-06, 01:04 PM
Member
Thread Starter
Join Date: Jun 2006
Location: Denver
Posts: 26
so suppose I wanted to put the stuff over the rafters instead of between. How do I then attach it to the rafters and how do I get drywall over that?
 
Reply


Thread Tools
Search this Thread
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 On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 09:04 PM.