GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Insulating Above a Roof Deck

Andrew808 | Posted in Energy Efficiency and Durability on

We plan to insulate above our roof deck in Hawaii (2:12 pitch over most of the home, low/flat over a 20×15′ section) with Polyiso.
We then planned for a torchdown layer + white reflective coating (silicone – GACO, or acrylic – Western Colloid 720ARC).

However, I recently came across this product — FIRESTONE ULTRAWHITE

Comparing SRI (new/aged), it looks pretty good. Gaco is much higher initially, but does loose this over time (assumes no cleaning):
Ultrawhite Cap Sheet             SRI: 89/77
GACO S-20                               SRI: 111/76
Western Colloid 720 ARC     SRI: 84/75

QUESTION: What are thoughts on using a product like the Firestone Ultrawhite vs coating over this layer (torchdown)?

Thanks for any thoughts and advice as always!

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Andrew808 | | #1

    After more research and talking with local roofing supply, it looks like Polyglass Polyfresco is another reflective capsheet worth looking at.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |