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

Venting Above Cut-and-Cobble Roof Insulation

ben87 | Posted in General Questions on

ventilated cut and cobble?

I’ve got an addition with an EPDM flat roof in climate zone 4a. The main house attic is vented.

I understand that venting low slope roofs generally doesn’t work well, and that unvented cut and cobble roofs are risky b/c it doesn’t stay air-tight over time. So my plan has been to use closed cell spray foam (didn’t use external foam board b/c it was unavailable in my area at the time this project started due to lingering covid shortages).

However, spray foam contractors have been extremely slow getting back to me and cost is high, especially since it’s a pretty small scale job.

My question is whether cut and cobble would work well if I left a ventilation channel above it, running from soffit into existing vented attic? I would think cut and cobble would at least reduce interior air/moisture transfer relative to other insulating materials, so would this offset the poor ventilation performance of the flat roof?

thanks,
Ben

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.

Replies

  1. freyr_design | | #1

    Well personally I wouldn't try and passive ventilate a flat roof and my first choice would be exterior insulation, second would be spray foam. If you do go your route I would suggest also using a membrane like intello and very good air sealing detailing. I would also put a monitor in the ventilation space. If needed you could always power vent it if it became an issue in the future.

  2. Expert Member
    MALCOLM TAYLOR | | #2

    Ben,

    The fairest answer is probably "It might". You have to decide if that is a strategy you will be content with.

  3. ben87 | | #3

    Thanks for the feedback

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |