I’ve recently did an inspection in Pasadena C.A. and been doing a lot of research on the roof for my client, This is what was observed, Gypsum board sheathing was installed at the base with “NO wood sheathing over the gypsum board” then a felt membrane installed, then the wood or fire treated cedar or wood shake surfaces. It appears that the roof system inspected was missing " the wood sheathing" although a permissible method as long as it is fire treated and would be considered a class B rating.

Well this is the latest information I have found. It turns out that a roofing company obtained a permit to re-do the roof. The permit states that they were going to install 1/2 gypsum board then the cedar shakes, which is exactly what they did and no indication if it was treated or not with fire retardant. I understand that this would be considered a substandard system now because of 1) No confirmed retardant treatment and 2) Now that moss is on it, any preservative treatment is not permissible :roll:…

Note as per (FEMA libary) that when shingles or shakes are fire-retardant-treated, they cannot be impregnated with preservative treatment,

Anyhow, here is a link to this very practice http://www.gypsum.org/wp/wp-content/uploads/2011/11/GA-276-05.pdf

Any competent input, is well received…

this sounds like an insurability issue

prudent action for client
before end of inspection option would be for their insurer to evaluate and approve or disapprove roof system compliance

the standard as far back as i can recall for assembly protection was/is 5/8" Type X gypsum board
there may be other state or local info i’m not aware of

if you don’t exclude insurability in your pia
consult your attorney and add this or similar
**The inspection does NOT imply insurability or warrantability of the structure or its components. **

sounds like an insurability issue

have client consult their insurer before end of inspection option for any/all insurability requirements

btw: 5/8" Type X gypsum board for roof assembly is all i’ve ever seen industry recommended & approved by any ahj…ymmv

Are you sure that they did not install furring strips as what was once normal for wood shakes. Like what your photo shows from the attic side.

I just keep thinking, IF the roof was to ever leak, the gypsum could end up quite the soggy mess compared to wood.

And as Barry mentioned, getting insurance for Cedar roofs in Southern California can be difficult.

Kind of adds a new dimension. :roll::roll:


Read the PDF the op provided that is its intention. Never seen it myself or even heard of it being done.

How old was that roof? The shakes do not appear to be aging well, even ignoring the moss.

Wood shingles (not shakes) should be installed on spaced sheathing to improve it’s drying ability. Installation on a solid deck without mesh or some other method for allowing airflow beneath the shingles is bad.