01 May 1999
provides third party assurance that the products delivered to the construction site are essentially
unchanged from those tested and listed.
I. Seismic Requirements. While membrane roofing materials in general do not affect
seismic stability of a structure, components of the roof system may be important. Roof decks, for
example, usually serve as a diaphragm increasing lateral stability.
(1) Bracing for SSSMRs. Structural metal systems with floating clips require bracing
since the structural standing seam metal panels do not provide diaphragm action. An alternative
to bracing is to use a steel subdeck to serve as the shear diaphragm.
(2) Inertia Effect. Heavy roofing materials such as ballast or pavers may result in an
inertia effect that should be included in the design. This may be beneficial or detrimental.
(3) Lateral Motion of Tiles. In steep roofing, seismic motion may shatter materials such
as cement and clay tile. Correct use of mechanical anchors may prevent damage. Twisted wire
systems are recommended for earthquake zones. The National Tile Roofing Manufacturers
Association requires two nails or a nail and a clip on every tile to resist seismic damage.
(4) Restraining Roof Tiles. IR-32-1 (9/89), a Title 24 California code addresses the
attachment of tile, and allows the combination of wire tie and nose clips (wind locks or tile locks).
Nails or wire ties are to be copper, brass, or stainless steel 11 ga. minimum with two per tile.
Nails are to penetrate roof sheathing, battens, or support members 19 mm (3/4 in.) min. Ring
shanked nails may be used when sheathing thickness is less than 19 mm (3/4 in.).
(5) Parapet Walls.
Parapet walls must be used with care. Through-wall flashings or
cut reglets must be avoided as they reduce the wall's resistance to lateral forces.
(6) Roofing Over Seismic Straps. Seismic straps (heavy metal plates) are sometimes
installed over plywood roof decks and between decks and walls. Where roof insulation is not
used (i.e., west coast capsheet construction), use construction details provided by the Western
States Roofing Contractors Association on how to roof over the straps (figure 2-18).
j. Adequate Design Details. Complete sectional views of every location where the roof
changes plane or there is a roof penetration or attachment should be provided on contract
drawings. Sections and design details should be drawn to a legible scale with each element of the
roofing system identified.