From commercial pilot to general contractor: (11) Insulation under my flat roof
"I had three basic choices: traditional fibreglass bats plus vapour barrier, blown-in insulation, and spray foam."
August 4, 2014 by Robert Koci
The commitment to an ICF wall structure from footings to roof gave me the basis of a well-insulated home. However, little would be gained unless I also gave serious consideration to the type of insulation under my flat roof.
I had three basic choices:
- Traditional fibreglass bats plus vapour barrier installed immediately above the ceiling with an air space under the roof deck. Cost: Least expensive.
- Blown in insulation (BIBS), somewhat similar to fibreglass, but offering certain performance benefits. Cost: Medium range.
- Spray foam insulation applied to the underside of the roof deck. Cost: Most expensive.
At this point in my project, the plumbing rough-in and mechanical work were almost complete. The windows had not yet been installed because my carpenters had been busy building interior partitions on the main and basement levels. Therefore the open building would permit excellent ventilation of any chemical odours.
I was pretty much sold on the spray foam insulation concept, and after reviewing three bids from well-known local installers, selected Georgian Insulation Systems for the contract.
Georgian’s owner, Ed Brassington, reiterated the benefits of spray foam insulation that a home owner should consider when making their decision. “We use closed cell foam, meaning each cell forms its own cell wall. It’s about twice the initial cost of traditional fibreglass bat insulation but doesn’t require a vapour barrier; the foam acts as it’s own air barrier system. It also adds significantly to the structural strength of the surfaces it is applied to.” These points were of particular interest to me, given my flat roof design.
Ed also explained the performance differences between the two types of spray foam; open cell foam and closed cell foam. Despite its excellent sound insulation qualities, open cell foam has an R-Value of only 3.5 per inch, making it harder to reach required code values in tight locations, whereas closed cell has an R-Value of 6 per inch.
I liked the fact that there would be no gaps in the insulation seal. The foam technician could get the foam into all the nooks and crannies around my roof deck and wall intersections, even coating my roof drainage pipes under the roof deck to prevent condensation falling on the inside of the drywall ceiling. (Be warned! Small particles of overspray are widespread and stick to everything, so there’s good reason beyond chemical odours to use tarps and poly over all walls, windows and floors.)
Ed continued: “Look at the potential longevity of a building with spray foam insulation; you don’t have warm air passing through the insulation. With traditional fibreglass bats, any screw hole, any gap in the vapour barrier, is a path for moist air to travel inside the wall or ceiling cavity to the substrate where it hits cold surfaces, creating condensation and perhaps eventually causing rot to the structure or mold behind the drywall.”
Georgian Insulation’s trained team have their work inspected regularly by the foam manufacturer. “Application is very important. You have to follow a certain pattern. We lay the foam down in 2 inch passes, allowing time for the foam to cool between each pass. After it hardens in 30 minutes or so, we can add another layer” explained Ed.
When Georgian’s work was complete, a neighbour dropped by and commented on the ICF/spray foam insulation combo: “You’ll be able to heat your house with a candle!”
By sealing the deal, I hope I can cool it with an ice cube too.