Roof Recovering Over Wood Shingled Roofing - Combustible Concealed Space? - 2018 IRC

[DCEngr1]

In this 2018 IRC paragraph below, would an attic space be the “concealed combustible space”?

R908.4 Roof recovering. Where the application of a new roof covering over wood shingle or shake roofs creates a combustible concealed space, the entire existing surface shall be covered with gypsum board, mineral fiber, glass fiber of other approved materials securely fastened in place.

This wood shingle roof already has a standing seam metal roof over it. The ss roofing must be replaced because of reported wind damage. If a scuttle hole exists to access the attic, with the space no longer be considered a “concealed combustible space”?

If it is a concealed combustible space, what surface is to be covered with the “approved material”?

Thank you . . . DCEngr1

 

[lexpatrie]

You must consider if the proposed standing seam roof actually wants shingles beneath it versus WSP sheet. That would be a larger concern for as you don't want to recommend doing something that violates the manufacturer's installation instructions (for the new standing seam metal). Even if that's the way they did it before you don't want to reproduce a code violation or a mistake.

To me, the concealed combustible space is above the shingles or wood shakes, below whatever you're putting in, and it is perhaps more intended for something like sleepers and a second set of roof sheathing then you have this air channel and something flammable. I see this more often when folks add on and leave an old roof with shingles/shakes in a new attic.

You may want to look at the Commentary.

I'm not convinced the concealed space applies to your situation, but normal standing seam won't have an approval for throwing it on top of a shake roof. They usually want WSP and at least roofing underlayment. Deviate at your peril as you may create a construction defect.

Regards,
Brian

 

[SWComposites]

Why would a structural engineer need to be involved with what sounds like a residential roof replacement?

 

[DCEngr1]

Brian,

Thank you for responding. 2018 IRC, applicable code in this case, allows installation of metal panel roofing over existing wood shingles; as long as the metal panels are installed according to the mfgr. The deck here is spaced 1x. Wood shingles are supposed to be installed over spaced sheathing to allow the wood shingles to dry. Dilemmas: lay metal directly over wood shingles - condensation from the underside of the metal might wet shingles resulting in mold if there is insufficient ventilation of the roof-framing space; lay roofing paper or other fabric between the wood shingles and the metal panels, or between the spaced sheathing and the metal panels after removing the shingles.

In either case, sufficient ventilation of the roof-framing space is necessary to discharge any vapor from the interior of the residence that enters the roof-framing space. The mfgr. will likely provide information on any roofing paper or other wp/vapor fabric install.

SW,

This involves a request for acceptable repair method to remove damaged ss roofing and install new.

 

[lexpatrie]

Yeah sure the Code allows it, but the Manufacturer's don't.

https://taylormetal.com/wp-content/uploads/2023/04/ESR-5046.pdf

Section 3.2

They also mention that 300 lb roof live load we all forget about. Seems they are okay with the spaced boards, provided they are good enough.