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Substrate failure
When installed as a recover, SPF roofing is applied directly to an existing membrane, such as a built-up or modified bitumen roof. Testing indicates that an installation of SPF over an existing roof will tend to increase the wind uplift resistance of the combined system. However, the increased resistance has not been quantified. If the underlying substrate/membrane did not meet code requirements, there is no guarantee that recovering it with SPF will increase wind resistance.

The typical mode of substrate failure in Florida was a loosening of the windward edge, followed by a peel-back of the membrane. Depending on the security of the underlying insulation, the peel-back may or may not take insulation boards with it. At some point in the peel-back process, the membrane typically ruptures, leaving the remaining substrate and SPF intact.

Substrate failures are due to:

• Insecure edges
• Insufficient adhesion or fastening of the membrane and insulation boards to the deck

Membrane roof systems are highly dependent on the roof edge for their security; yet roof edges are the most exposed detail on the roof. Further-more, the pressure difference across the membrane tends to add extra uplift forces to the edge. Once the edge submits to these forces, a membrane peel-back is almost inevitable.

Roof edges are usually fabricated from metal and fastened to a wooden roof edge nailer with screws, nails and/or cleats. The security of the metal edge is dependent on its stiffness, the quality and quantity of the fasteners, as well as the security of the nailer.

Surface damage of SPF roof systems occurred where wind-borne missiles (such as tree limbs and roof tiles) impact the SPF. Gravel scour occurred at windward roof corners, and in some cases, near roof protrusions and mounted equipment. Little or no loss resulted from surface damage.

General Observations

• There were no SPF failures observed from the hurricanes (no separation of SPF from the substrate.)
• Sloped roofs covered with SPF fared well. Many SPF roofs survived undamaged or with minor surface damage.
• While gravel movement was present at windward corners, little or no gravel loss was observed.
• Failures were limited to deck and substrate failures. Surface damage of SPF roofs occurred but was not a cause of failure or leakage. Substrate failure could be minimized or eliminated by improving edge and membrane security.
• Application of SPF as a repair and patch method was very successful. SPF repairs and patches were more wind resistant that the original roof system.