GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter 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

Ceiling insulation

TomProud | Posted in Energy Efficiency and Durability on

I live in South Florida and have an uninsulated open ceiling in a laundry room that used to be an outdoor laundry, it has since been surrounded by a finished living area. It is open to the roof with 6” trusses on 16” centers. The room has a block wall on one side and stud walls to the ceiling on the others so there is no way to vent the space from eaves to ridge. It gets very hot in there and I want to insulate and drywall the ceiling. Should I fill the joist space with insulation or should I leave a gap between the insulation and the roof deck? The roof is very low slope with asphalt roll roofing.

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. GBA Editor
    Martin Holladay | | #1

    It sounds like you want information on how to insulate a low-slope roof. This article explains everything you need to know: Insulating Low-Slope Residential Roofs.

    The easiest approach is to install closed-cell spray foam on the underside of the roof sheathing, followed by 1/2-inch drywall.

    Another possibility (if you need new roofing) is to install one or more layers of rigid foam insulation above the roof sheathing, followed by a layer of OSB or plywood and new roofing.

  2. Expert Member
    Dana Dorsett | | #2

    A flash-inch of closed cell foam on the underside of the roof deck then filling the rest of the cavity with fiber insulation works. If there's sufficient headroom to install Bonfigilioni edge strips or Mooney Wall style framing for additional depth to get to a code min R30 it would help.

    A CRRC rated mop-on "cool roof" coating over the top of the low-slope roofing with an SRI north of 75 can put a big dent in peak & average roof temperatures too. To find a product use this page:

    Tick the "coating" box under Product type, then type "75" into the solar reflective index row, 3 year column.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |