Has anyone used radiant barrier sheathing for a cold roof?
We are adding a cold roof to prevent ice dams on a old house in Wilson, Wyoming. The air gap will be 2.5″ or 3.5″ using 2x3s or 2x4s on edge 16″ O.C. on top of the existing sheathing.
Would we benefit from a radiant barrier using foil faced new sheathing above the air gap?
In theory, the foil would reflect radiant heat back to the existing roof in the winter and reduce the emission of radiant heat into the house in the summer. We have second story rooms that get very hot because they have low ceilings under a shed dormer with no attic.
Sheathing such as LP Techshield is manufactured with vapor vents to allow moisture to escape.
Any suggestions and/or references would be greatly appreciated.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
The radiant barrier adds about R1, so something but not enough to pay any extra money for it. It won't make the assembly any better. Radian barriers make more sense down south in a house with very little attic insulation.
Unless you hare in very heavy snow country, ice dams are usually caused by ceiling air leaks, sealing these will make the biggest difference plus save you a fair bit in heating costs.
Top venting will definitely help with ice dams but won't save you any energy.
I have built this exact roof with LP techshield. Sadly, I haven't built one without it, so I can't say how much it actually helped. The cost is low enough right now to make it a wash though. I'd do it again.