Glossary

Secondary water resistance

A second layer on the roof deck, such as a self-adhering membrane over the seams, that keeps rain out of the house if the shingles blow off in a storm.

Also called: SWR, sealed roof deck, peel-and-stick roof underlayment, roof deck sealing

Secondary water resistance, or SWR, is a backup barrier against rain. Shingles and tiles are the first line of defense. In a hurricane they can be torn off, and the plywood or OSB deck underneath has gaps at every seam where water can pour into the attic and ceilings. SWR seals those seams so the house stays reasonably dry until you can get a temporary cover on.

Florida's wind mitigation form recognizes two ways to get credit. One is a self-adhering polymer-modified bitumen underlayment, the peel-and-stick membrane roofers apply directly to the deck. The other is a foam adhesive applied to the deck seams from inside the attic. The form is specific that foamed insulation does not count, so a house with spray-foam insulation on the underside of the deck has not earned the credit. FORTIFIED Roof requires a sealed deck too.

The practical points: SWR is usually installed during a re-roof and adds modest cost then, while adding a membrane later means tearing off the roof. If you are replacing a roof in a hurricane state, ask the roofer to price it and have the inspector document it. Rain that enters after wind opens a roof drives a large share of hurricane losses. See secondary water resistance and roof-deck attachment, the wind mitigation inspection entry and FORTIFIED Home.

Last reviewed October 10, 2026

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Related terms

Wind mitigation inspection An inspector's checklist of a house's storm-resistant features, such as roof fastening and window protection, that insurers use to apply wind discounts. FORTIFIED Home A voluntary construction standard from the insurer-funded IBHS that strengthens a house against wind, hail and storm damage, with certified designations. Roof-to-wall connection The hardware that fastens roof rafters or trusses to the top of the walls, which decides whether a high wind can lift the roof off the house. Home hardening Upgrades to a house's roof, openings, vents and materials so it resists a specific hazard such as wind, hail or wildfire embers, not just insures against it. Windstorm The peril of damage from high winds, including hurricanes, tornadoes and thunderstorm gusts, which most policies cover, sometimes with a separate deductible. Mitigation credit A premium discount for building features shown to reduce storm or wildfire damage, such as a reinforced roof, impact windows or defensible space.

Related guides

The FORTIFIED Home standard and insurance discounts What IBHS FORTIFIED Roof, Silver and Gold require, which states mandate discounts, what it costs, how long it lasts, and the 2027 shingle limit. Secondary water resistance and roof-deck attachment What a sealed roof deck and stronger deck nailing do in a hurricane, how Florida re-roof rules and FORTIFIED treat them, and how to document them for a credit. Wind mitigation inspections and discounts What a wind mitigation inspection checks, who may sign Florida's OIR-B1-1802 form, how long it lasts, and how to turn the report into a lower wind premium.