Replies

1. 
   ClaysWorld | Feb 26, 2006 01:45am | #1

   Just ran across your post. So Here's what i'm thinking.

    How thick is the iso? Rafters strapping sheetrock, sounds like the ceiling? Outlets? why on the Ceiling? or do you mean for light fixtures?

1. 
   toddinmaine | Feb 26, 2006 04:45am | #2

   I plan to use the 2" ISO... I guess it was late when I wrote about the rafters... the iso will be going there... basically just a sloped wall spanning from the knee wall to the ceiling... although, the plan is outlets on the knee wall and gable end walls... and light fixtures in the ceiling....  and it was my impression from other posts that you "should not cut thru the iso" but, I need to and was looking for the fix.... as mentioned, I thought about the "great stuff" spray foam around the boxes... or possibly even getting a spray foam gun as discussed here.... so, any advice you could give me would be great.... btw, whats your experience in using iso? done it alot? what else do I need to know?  

   thanks again,

   Todd

    

1. 
   BillBrennen | Feb 26, 2006 06:49am | #3

   Todd,You need the outlets, so run your wire and set the boxes to end up flush to the finished wall. Then cut the foamboard slightly oversized where the boxes are and seal the box edges with can foam. Seal the wires coming in the back. Stop worrying! With 2" of polyiso board everywhere, you are gonna be in one tight room, given even normal detailing.Bill

1. 
   toddinmaine | Feb 27, 2006 09:15pm | #5

   thanks bill, I appreciate your reply... just before I read your post I read a reply from "DOW" themselves... they basically say the same thing you said... a little more simply though.... I asked:Customer (todd b.) 02/23/2006 09:14 PM
   I am planning on installing polyisocyanurate rigid foam on the inside of my 2nd floor... I will be sheetrocking over the foam... my question is if you can advise me on what to do to maintain the polyiso effectiveness when I have to cut in electrical boxes? which of course means cutting holes into the polyiso... my thoughts are to use spray foam around the box... any help would be greatly appreciated... thanks in advance, ToddTHEY SAID:Dow-Styrofoam Answer Center <[email protected]>
   Response (Paula De Oliveira) 02/27/2006 08:46 AMYes, spray foam such as Great Stuff can be used for this application.

2. 
   ClaysWorld | Feb 26, 2006 06:59pm | #4

   Hey Todd.

   What is it your gonna do? are your trying to use 2" iso on the surface of the frafters to save space and get as much R as you can?

   I did a house where we had 3.5" and skip sheath on top of that . I used 3" Iso and had to fit every bay cause they varried from 12.5-19" even in the same bay, very old house. This left the airspace on the top to let the roof breath a little.

    But tell me what your woried about by cutting into the iso? Vapor barrier or R value or both?

   If you put a box that's 3" and the iso's 2" well youv'e got 0 R so you need to back insulate.

   If you are doing the work you can cut the Iso and fit the bays, it's slow but if you take your time you can get a nice force fit/no air leaks on side of rafters. I know how on the oder houses sometimes it's very important to not have to make to fat a space for insulation.

   I could dig out some of the pictures to scan and show you the bay insulation. It was before I had the didital stuff so I scan the pict to diggit it.

1. 
   toddinmaine | Feb 27, 2006 09:39pm | #6

   hi clay, thanks for the reply.... no need to dig out the pics... I understand what you did... I am planning to just run the polyiso right along the bottom of the rafters.... completely covering the ends of all the studs.... not going to fit in between.... leaving the space for my soffit to ridge venting.... I was worried about cutting thru the iso, but I am just going to spray foam any gaps... as you can see the previous post to this one, I emailed dow cust svc directly, their response was short and sweet, just as I had hoped.... so, thanks to everyone... I appreciate it.... I will take some pics(once its cleaned up, lots of storage up there now) and try to show you all what my situation is and explain what the plans are based on the pics....