Why Building Orientation Matters in Window and Roof Losses

Homeowners may only think about the direction their windows and roof slopes face in terms of how much sunlight they’ll get. But adjusters should be aware that the orientation of these building elements can play a role in potential property loss, sometimes in unexpected ways. The effects of sun and wind on roofs and windows can vary greatly depending on exposure to these elements, which is important to consider when seeking an accurate claim resolution.

Roof slopes and windows can react differently to sun exposure and wind depending on their orientation.

The Vulnerability of Windward Roof Slopes and Windows

Asphalt shingles are the most common residential roofing material, as well as among the most likely to incur wind damage. Wind damage to asphalt shingle roofs can take several forms depending on the strength of the wind, the orientation of the building, the condition of the shingles, and the method of installation. Wind can repeatedly lift a shingle over a period of time, fatiguing it, and resulting in creasing and tearing below where the shingle is supported by an overlying shingle. This type of damage occurs most frequently on the windward side of the roof, particularly along the edges of a roof’s surface, including hips, ridges, and valleys, but it can also occur in high-pressure areas on the leeward side of a roof.

Stronger winds can cause entire sections of shingles on the windward side and other vulnerable areas to lift, crease, tear, or detach from the roof. However, various perils can mimic wind damages, so it’s important not to decide a claim based on appearances alone regardless of slope orientation. Experts also reference reliable historical weather data to confirm the presence and direction of wind and factor in the orientation of the roof and surrounding collateral damage.

Wind damage manifests in irregular patterns of creased, missing, torn, or detached shingles, most often on the windward side of the roof.

Roofs are vulnerable because wind is directional and increases with height. This is also the reason that windows on the windward side and on upper stories are more susceptible to wind impacts, as are those on corners where windows are less shielded. Designers and builders should account for the increased pressure.

Displacement due to wind pressure is a possibility. Wind exerts positive pressure on the side facing the wind and negative pressure on the side opposite the wind, meaning wind-damaged windows on the windward side displace inward while those on the leeward side displace outward. Sash displacement and frame distortion are other evidence of wind damage. It is rare that wind alone damages windows. According to the National Weather Service (NWS), hurricane-force winds of more than 75 miles per hour (mph) may result in broken windows. The most common window failure due to wind is impact damage from windborne debris, but other failure modes do occur.

Wind speeds have to be very high to blow out glass, generally only reached during hurricanes and other storms. Impact damage, binding, fogging, and other damages are more likely.

To determine that damage to a window is due to wind, experts must confirm that the collaterals, observed damage, and weather data match up in terms of wind direction. This is vital because wind can blow in different directions during various events depending on several factors, making it less predictable than another factor in many losses: sunlight.

The Effects of Sunlight on Shingles and Glass

Over time, the heat and radiation from sun exposure can weaken the binder within asphalt shingles. As it dries and shrinks, the shingles can curl and crack, which exposes the shingle mat. The shingle mat then rapidly deteriorates and eventually disintegrates.

Shingles on south- and west- facing roof slopes tend to have more exposure to harmful ultraviolet (UV) radiation from the sun and will likely deteriorate more quickly than those on north- and east-facing slopes. Shingles that are over stressed areas, such as on ridges, eaves, and valleys, are even more vulnerable to damage from prolonged sun exposure.

These shingles are on the same house, though the north slope (left) shows significantly less granule loss and fading than the south slope (right) due to less sun exposure.

Less sunlight is also something to consider, as slopes with less sun exposure may take longer to dry out following heavy rains. This can contribute to granule loss as well and may lead to other damaging conditions like moss and lichen growth in shaded areas.

Sunlight is far less likely to damage windows directly than it is roofs, but that doesn’t mean that the orientation of a house’s windows has no bearing on potential damage. The heat from sunlight reflecting off a window can cause damage to nearby structures, specifically vinyl siding. As with the roof slopes, windows facing the south and west get the most sun and are more likely to reflect its beams onto neighboring structures under the right circumstances.

Vinyl siding may start to soften and distort when temperatures reach 160 degrees Fahrenheit, a condition that may be reached when sun reflects off of energy-efficient windows made with low emissivity glass, which reflects more sunlight than standard glass. Double-paned insulating glass can compound these conditions when pressure between the panes differs from the outside environment, according to the Vinyl Siding Institute. This pressure differential causes the glass to distort into a concave shape, and the reflected sunbeams leave patterns of distortion in vinyl siding, wood, and other painted materials.

This distortion pattern is the result of reflected sunlight from a window on a neighboring house.

While this reflected sunlight and other damages aren’t always solely the result of the direction a roof or window faces, their orientation on the house can sometimes affect materials in surprising ways. Donan’s team of licensed forensic engineers considers all the possibilities to provide a full and accurate cause of loss backed by the scientific method.

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