InterNACHI Wind Mitigation key terms

A limited visual survey of specific hurricane-resistance features of a house, documented on a standard form so an insurer can evaluate risk. It is not a general home inspection and does not certify code compliance.

The state-prescribed form, commonly the OIR-B1-1802, on which wind mitigation findings are recorded. It organizes findings into roof covering, deck attachment, roof-to-wall attachment, roof geometry, secondary water resistance, and opening protection sections.

A separate insurance inspection covering roof, electrical, plumbing, and HVAC condition, typically required for older homes. It answers different questions than a wind mitigation report and does not substitute for one.

A premium discount or adjustment an insurer applies when verified features reduce expected hurricane damage. Credits depend on documented features such as roof-to-wall straps, secondary water resistance, and opening protection.

A mapped area, generally within one mile of the coast where design wind speed reaches a defined threshold, in which building codes require impact-resistant glazing or approved shutters. Location affects which opening protection qualifies.

The basic wind speed a structure is engineered to resist, expressed as a three-second gust in miles per hour and mapped by risk category and location. Higher values drive stronger connections and stricter opening requirements.

Upward pressure created as wind flows over a roof, caused by the difference between low pressure above and higher pressure below. Uplift tries to lift the roof off the walls and is resisted by the load path.

An unbroken chain of connected structural elements that carries wind and gravity forces from the roof through walls, floors, and foundation to the ground. Inspectors look for each link: covering, deck, truss-to-wall, wall-to-floor, and floor-to-foundation.

Pressure inside a building that rises when wind enters through a breach such as a broken window or failed garage door. Combined with external suction, it can double the uplift on a roof and trigger progressive failure.

Failure that spreads from one element to adjacent elements, such as a lost roof corner peeling away sheathing and then trusses. Once started, it often destroys far more than the initiating damage.

The triangular wall section filling the space between a sloped roof and the horizontal ceiling line at the end of a building. It is braced to resist out-of-plane wind pressure and is a common failure point when bracing is missing.

Collapse or partial displacement of a gable wall under wind pressure, often followed by roof framing collapse. It is associated with weak or absent bracing and with large unreinforced openings in the gable.

Structural members, such as knee braces, studs, or manufactured truss bracing, that transfer gable wall loads into the ceiling or floor diaphragm. Inspectors document visible bracing in attic spaces when accessible.

Window or door glass manufactured and labeled to resist wind-borne debris impact and subsequent cyclic pressure. It usually requires laminated glass in an approved frame system, and the label must match an approved product.

A permanent marking on a window, door, shutter, or panel identifying the manufacturer, product, and approval or test standard it meets. Inspectors photograph labels because credits depend on verified approval, not appearance.

A removable or permanently mounted protective device installed over an opening before a storm to resist debris impact and pressure. Types include accordion, roll-down, colonial, Bahama, and panel systems, each with different approval evidence.

Any approved system that shields windows, doors, and other openings from wind-borne debris and pressure, including impact glazing, shutters, panels, and rated doors. It prevents internal pressurization that multiplies roof uplift.

The wind-pressure and impact rating of a garage door and its track and hardware, often shown on a label or manufacturer documentation. An unrated garage door is a large unprotected opening that can pressurize the whole house.

The outermost weather-resistant layer of the roof, such as asphalt shingles, tile, metal, or membrane. The form records covering type, and some insurers treat certain coverings differently for wind risk.

The method fastening roof sheathing to the framing, described by fastener type, length, spacing, and panel thickness. Common categories range from staples or 6d nails to 8d nails at closer spacing, with ring-shank and clipped panels rated higher.

The connection tying roof framing to exterior walls, such as toe nails, clips, single wraps, or double wraps. Stronger metal connectors reduce the chance the roof lifts free of the walls during a hurricane.

A nail driven at an angle through the side of a truss or rafter into the wall top plate. It is the weakest common roof-to-wall connection and generally earns little or no mitigation credit.

A metal connector, typically embedded in or wrapped over the wall, that ties a truss or rafter to the top plate. Single wraps cover one side of the member; double wraps engage both sides and are rated higher.

A small metal connector fastened to the side of a truss or rafter and to the wall plate, providing partial uplift resistance. Clips are generally rated below straps in mitigation schedules.

The on-center distance between adjacent roof trusses or rafters, commonly 24 inches but sometimes 16 inches or less. Closer spacing changes the number of fasteners per panel and can affect how deck attachment is classified.

A roof with slopes on all sides that meet at ridges or hips, with no vertical gable ends. Hip shapes generally perform better in wind and are rated more favorably than gable roofs in mitigation schedules.

A roof with two sloping planes meeting at a ridge and vertical triangular walls at the ends. It is more vulnerable to wind uplift and gable end failure than a hip roof of similar construction.

The overall three-dimensional shape of the roof, classified as hip, gable, or other, and used to estimate wind performance. The form records the shape and, where relevant, the proportion of hip versus non-hip perimeter.

A membrane or coating beneath the roof covering that sheds water if the covering and underlayment fail. Examples include self-adhered peel-and-stick membrane and some foam adhesive systems applied directly to the deck.

A self-adhering waterproof sheet applied over the roof deck before covering installation. When installed across the full deck as a sealed layer, it is commonly accepted as secondary water resistance.

Images taken during the inspection that prove observed conditions, such as strap type, nail spacing, and label details. Photos must be clear, dated, and tied to the address and the specific finding they support.

The opening allowing entry to inspect roof framing, deck fasteners, and connections from below. Inspectors document whether access was available, safe, and sufficient to observe the required features.

A close, legible image of a product approval, rating, or manufacturer label on a door, window, shutter, or garage door. It is the primary evidence used to support opening protection credits.

The observed distance between deck fasteners, usually recorded in inches on center and confirmed with a tape or gauge in a photo. Spacing, fastener type, and panel thickness together determine the deck attachment category.

The consistent procedure an inspector follows to locate, measure, and photograph each feature, including when access is limited. Following a repeatable protocol keeps reports defensible and comparable between homes.

A statement describing the limited, visual, non-invasive scope of the inspection and the conditions that could not be observed. It clarifies that findings reflect visible evidence at the time of inspection, not a guarantee of performance.