Inspecting pitched roofs

Pitched or steep sloped roofs are best inspected when direct access is gained to all their surfaces.

Use binoculars to inspect roofs that are inaccessible or that cannot be walked on. Look for deteriorated or loose flashing, signs of damage to the roof covering, and valleys and gutters clogged with debris. Carefully examine exterior walls and trim for deterioration beneath the eaves of pitched roofs that have no overhang or gutters.

There are four categories of pitched roof covering materials and their condition should be checked as follows:

Asphalt shingles

Asphalt or composition shingles have a service life of about 20 years for the first layer and about 15 years for a second layer added over the first layer, depending on their weight, quality, and exposure. When they begin to lose their granular covering and start to curl they should be replaced. No more than two layers of asphalt shingles should normally be in place at any one time. If a second layer of asphalt shingles has been applied, check to see if all the flashing materials (galvanized steel, aluminum, rubber) in the first layer were removed and replaced with new flashing at the second layer.

Check the roof slope. A slope of 4 in 12 or steeper is referred to as normal. A slope of between 3 in 12 and 4 in 12 is referred to as low. No asphalt shingle roof should be less steep than 3 in 12. If the roof has a normal slope, check the underlayment if possible. It should be at least a single layer of 15-pound (6.8 kg) asphalt saturated felt.

Low-slope roofs should have at least two such felt layers. If ice dam flashing at overhanging eaves is needed or present, make sure it extends three feet beyond the plane of the interior face of the exterior wall below for a low-slope roof and two feet for a normal-slope roof.

Wood shingles or shakes

This type of covering has a normal life expectancy of 25 to 30 years in climates that are not excessively hot and humid, but durability varies according to wood species, thickness, the slope of the roof, whether shingles are made of heartwood, and whether they have been periodically treated with preservative. Shakes are hand-split on at least one face and either tapered or straight. Shingles are sawn and tapered. Check the roof slope. The minimum slope for wood shingles is 3 in 12 and the minimum slope for shakes is 4 in 12.

As wood shingles and shakes age, they dry, crack, and curl. In damp locations they rot. Replace them when more than one-third show signs of deterioration. These materials are easily broken. They should not be walked on during the inspection.

If the roof is historic or relatively complex, consult a wood roofing specialist.

Metal roofing

Metal can last 50 years or more if properly painted or otherwise maintained. Metal roofs may be made of galvanized iron or steel, aluminum, copper, or lead; each material has its own unique wearing characteristics.

Inspect metal roofs for signs of rusting or pitting, corrosion due to galvanic action, and loose, open, or leaking seams and joints. The slope of metal roofing can be from one-half inch per foot (1:24) to very steep.

The types of metal, seams, and slope determine the construction details.

There are three basic seam types -- batten, standing, and flat -- as well as flat and formed metal panels. Snow guards are needed on steeper slopes and in locations with heavy, long-lasting snow, bracket and pipe snow guards also may be necessary. Low-slope metal roofs that are coated with tarlike material are probably patched or have pin holes and cannot be counted on to be leak-free. If the roof is historic or relatively complex, consult a metal roof specialist.

Slate, clay tile, and asbestos cement shingles

These roof coverings are extremely durable and, if of high quality and properly maintained, may last the life of the structure. Check the roof slope. The minimum slope for roofs of these materials is 4 in 12. Slate shingles should be secured by copper nails except in the very driest of climates; look at the underside of the roof sheathing in the attic or check the nails on broken shingles. Nail heads should be covered with sealant. Nails for tile roofs should be non-corroding.

All of these roof coverings are brittle materials and easily broken, and should not be walked on during the inspection. Use binoculars to look for missing, broken, or slipping pieces. Slate is particularly susceptible to breakage by ice or ice dams in the winter, and should therefore be especially well drained.

Snow guards are needed on steeper slopes, and in locations with heavy, long-lasting snow, snow guards also may be necessary. Moss will sometimes grow on asbestos cement shingles; it should be removed with a cleaner to prevent capillary water leaks.

Slate, clay tile, and asbestos shingles should be repaired or replaced by a qualified roofer. Examine the underside of the roof later during the interior inspection.