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If you'll e-mail your mailing address to me at my office (john.rose(--nospam--at), I'll send you a copy of APA's technical note on installing wood structural panel sheathing over spaced boards; or I can fax it to you if you e-mail your fax no.

The application is intended to upgrade existing roofs where cedar shakes are being replaced (for fire codes or deterioration), and to provide a smooth substrate for installing asphalt shingles or other types of roofing.  Recent reports of hail damage to roofing also present another reason to upgrade the roof deck to a solid deck rather than spaced boards.  The lateral resistance (stiffness and strength) under wind and seismic loads will improve, but diaphragm efficiency is limited by non-diaphragm details such as lack of perimeter nailing and tension/compression chords (double top plates could work if adequately connected to the diaphragm and shear walls), etc. as outlined in my previous e-mail.

There was an old HUD report that showed that the fire endurance of a roof with wood shakes/shingles was improved if the roofing was installed over a solid roof deck rather than spaced boards.  There are some fire-resistive roofing membranes that might further improve the fire endurance of the roof deck if used over the roof sheathing before installing wood roofing (an untested idea).

John Rose/APA, Tacoma, WA

>I would like to receive the technical note on plywood sheathing over spaced
>sheathing you referred to.  Whata is the title?
>Not having read it, it seems as if APA is recommending this practice?  Is
>there a  benefit  other than saviing the cost of spaced sheathing removal?