Unventilated "hot" roofs

[Inspector Gadget]

Last year, our office tweaked its policies to allow for closed-cell foam to be used in unventilated rafters/cathedral ceilings as long as the roof was either clad in metal, or had shingles on a slope of 8:12 or greater. The reason for this is that the Objective and Functional statements that drive the relevant clauses of 9.19 refer to ice-dam issues.

A secondary concern has been the ventilation of vapours in cathedral ceilings/rafters. However, I was made aware of the following research into closed-cell foam and hot roofs, and vapour permeation is part of the evaluation:

https://www.genyk.com/wp-content/uploads/2021/05/Jonathan-Smegal-Ventilation-and-Vapour-Control-for-SPF-insulated-Cathedral-Ceilings.pdf

It's a good read, but the quick notes version is that closed-cell foam isn't a problem in rafter/cathedral ceiling situations.

I'm proposing that our office will allow "hot" roofs for all roofing materials provided closed-cell foam is used *and* there is mechanical means to regulate building humidity.

My interp on this is the language of 9.19.1:



The above study (and it's not the only one, it's just the first I have seen to really look at climates, heating-degree days and internal humidity - and it's adequately shown that venting of closed-cell-foamed roofs is not necessary.

Related BCBC tribunal decisions:
1) https://www2.gov.bc.ca/gov/content/...uilding-code-appeal-board-decisions/bcab-1719

2) https://www2.gov.bc.ca/gov/content/...uilding-code-appeal-board-decisions/bcab-1762

 

[tmurray]

The intent of the wording "except where it can be shown to be unnecessary" is to provide an option to the designer to provide evidence to the building official on why their design should be acceptable. It should be noted that this is similar to, but distinctly different from an alternative solution. All of the code is subject to an alternative solution, so that approach required no other enabling language. Sentences with this wording are intended to be held to a lower threshold for evidence to be submitted by the designer.

The obvious concern about enacting an policy on this is that it would likely be viewed by the courts as an operational policy and thus subject to liability claims. Additionally, it might be wise to have a outside third party review the intended course of action in order to maintain the third party review concept.

 

[Inspector Gadget]

The intent of the wording "except where it can be shown to be unnecessary" is to provide an option to the designer to provide evidence to the building official on why their design should be acceptable. It should be noted that this is similar to, but distinctly different from an alternative solution. The obvious concern about enacting an policy on this is that it would likely be viewed by the courts as an operational policy and thus subject to liability claims. Additionally, it might be wise to have a outside third party review the intended course of action in order to maintain the third party review concept.

I see your point.... that the designer would still have to present the evidence: doing so would then mitigate the liability, presuming the evidence is deemed sufficient.