Infrared-blocking roofing material


  #1  
Old 02-06-06, 04:05 PM
A
Member
Thread Starter
Join Date: Oct 2005
Location: Milwaukee WI
Posts: 1,217
Received 1 Upvote on 1 Post
Infrared-blocking roofing material

I need a name, website or whatever for a foil-faced roof decking and some opinions on usefulness for my application. My energy auditor mentioned this but did not know the mfgr. or specifics.

This is a 3-layer tear-off so I am not planning to do this myself but I have an experienced roofer in mind who will supply whatever I specify.

Anyway, we have an unvented, sheetrock-finished cathedral ceiling, icynene-insulated, no vapor barrier, 2x6 rafters 24" OC and four Velux roof windows.

I want to reduce the summer heat penetration. I brought up the idea of adding a roof deck above the current decking, with a 1.5" air space and adding soffit and ridge vents. The auditor said that wouldn't have much payback but I should find out about this other stuff that would presumably just be nailed to the existing decking.

Current deck is 3/4" boards spaced about 1/2" to 1" apart, so they will not support asphalt well on their own anyway. Current roofing is original 1920s cedar shingles then (presumably 1950s or 1960s) asphalt, and on top early 1980s dimensional asphalt still in pretty good shape. Roof pitch is about 9/12.
 
  #2  
Old 02-06-06, 09:18 PM
M
Member
Join Date: Jan 2006
Posts: 135
Upvotes: 0
Received 0 Upvotes on 0 Posts
Think you're looking for this:

http://www.gp.com/build/product.aspx...8&hierarchy=pc


Because of your location don't expect much savings from this material.

Before you go adding anything to your roof have a structural engineer check if for the additional roof loads.

Depending on the current spans and rafter spacing, and because of the cathedral ceiling design...your roof system may already be undersized and not able to have anymore structural plywood or anything else added but shingles.

You'd probably do better to attached rigid foam insulation directly to the roof deck under the shingles and get better energy efficiency and a lower price and less load added to the roof.
 
  #3  
Old 02-07-06, 08:38 AM
A
Member
Thread Starter
Join Date: Oct 2005
Location: Milwaukee WI
Posts: 1,217
Received 1 Upvote on 1 Post
Thanks, Plytanium looks like the stuff. I see that they want 3/4" airspace under these panels anyway, so we would still have to add furring, at which point soffit and ridge venting might be better anyway.

Roof loading is a good point. There's a lot of weight up there now and after consulting the architect and building inspector, we removed collar ties that appeared to have been added in the mid-20th century. The building inspector said that our new interior kneewalls and sidewalls reduced spans enough that the collar ties were not necessary. The longest span is now less than 11', and that is only for a 12-1/2' run encompassing seven rafters.

The rigid foam under shingles sounds interesting, but how would you attach shingles then? Would we just use longer nails to get through the foam? Wouldn't nailing the foam dimple and damage it?
 
  #4  
Old 02-09-06, 01:02 PM
doug thomas's Avatar
Member
Join Date: Jan 2006
Location: Detroit, Michigan
Posts: 101
Upvotes: 0
Received 0 Upvotes on 0 Posts
You're in Milwaukee and you have summer heat penetration issues?

Before you spend all this money on re-roofing, why not evaluate the effect of those roof windows?

Use a 5-day forecast to pick out a hot sunny day well in advance. Cover the windows from the outside or put up heavy duty curtains etc before the day starts. Does the room get as hot during the day when the windows are completely blocked?

It is highly likely that you're going to have to coat the windows with a photochromatic coating to reduce solar heat gain, and that re-roofing wouldn't do anything.
 

Last edited by doug thomas; 02-09-06 at 01:53 PM.
  #5  
Old 02-09-06, 04:07 PM
A
Member
Thread Starter
Join Date: Oct 2005
Location: Milwaukee WI
Posts: 1,217
Received 1 Upvote on 1 Post
Originally Posted by doug thomas
You're in Milwaukee and you have summer heat penetration issues?
Not heat penetration issues per se, just looking for the best economical solution as long as the roof needs to be redone anyway. I never took heat transfer but it seemed to me that having air circulate under and over a surface would be a fairly easy way to cool the surface and whatever was underneath.

Originally Posted by doug thomas
It is highly likely that you're going to have to coat the windows with a photochromatic coating to reduce solar heat gain, and that re-roofing wouldn't do anything.
The roof windows are low-e and the mfgr's coating prevents much of the heat from getting in. I can stand under them in the summer in full sunshine and feel no noticeable heat. We would be much better off replacing our leaded glass windows on the first floor, or coating them as you suggest. It's on the list somewhere above "New copper Roof"!

Thanks for the suggestions.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: