Ice dam Gutter
Pitched roofs are usually covered with shingles applied in an overlapping fashion. The shingles are not intended to be watertight; they protect the structure from rain intrusion by shedding water. The more common types of shingles are made of asphaltic material, wood, asbestos-cement, slate, and clay tiles. When inspecting the roof, pay particular attention to a slope that has a southerly or southwesterly exposure. These slopes receive a maximum sun exposure, and it is the sun’s rays that cause the shingles to become brittle and age prematurely. Consequently, the shingles on these exposures will deteriorate more rapidly than the shingles on the other exposures. (See FIG. 2-2.)
Since shingles are intended only to shed water, any water that gets under them will leak into the interior of the structure. Shingles that are lifting, cracked, or broken are vulnerable to this type of water leakage. If you see this problem, it is an indication that some maintenance is needed. In areas where the winter temperature drops below freezing, roof leakage can occur as a result of an ice dam. Because of heat loss through the roof and heat from the sun, snow on a roof can start melting, even in freezing weather. As the water reaches the roof overhang, it often refreezes, forming an ice dam and blocking the melting snow from draining. As the snow continues to melt, the water backs up under the shingles and leaks into the interior. (See FIG. 2-3.)
Water leakage from this type of problem is not an indication of a faulty roof and should not be interpreted as a sign that roof repairs are necessary. It is an indication that adequate precautionary measures were not taken during the installation of the covering to eliminate or minimize the effects of an ice dam. The condition could have been reduced by the installation of eaves flashing. On existing roofs, the condition can be avoided by installing deicing cables along the edge of the roof and in the gutters and downspouts. This may not solve the problem completely, but it is somewhat effective. The deicing cables reduce the ice dam buildup by creating heated channels that allow water to drain into gutters and downspouts. The best method for minimizing an ice dam problem is to maintain what’s called a cold roof. By overinsulating the attic floor and ventilating the attic profusely, the roof deck temperature will be lowered to the point where the snow won’t melt.
When looking at a roof after all the snow has melted, you would never know whether there had been an ice dam and water leakage. Sometimes, however, you can see indications of a past problem—stained or warped sections of soffit trim or water stains on the ceilings of the rooms below, near the exterior walls. I have seen water stains on the ceilings of rooms two levels below the roof that were the result of water leakage because of an ice dam. Ice-dam problems will not necessarily occur every year; they depend on the severity of winter weather conditions.
Portions of the roof particularly vulnerable to leakage are the joints between the roof and roof-mounted structures, such as the chimney; the joint between the roof and a vertical sidewall; and the joint where two sloping sections of the roof intersect. The latter joint is commonly referred to as a valley. To protect the joints from water intrusion, they are normally covered with strips of a thin, impervious material called flashing. Sheet metal is usually used as a flashing material, with copper flashing as the top of the line; however, roll roofing strips are also used. Valley or sidewall flashing might not be visible, which depends on the type of joint construction.
When inspecting the roof, check the condition of the exposed flashing at the various joints. Loose, cracked, and deteriorated sections must be repaired. If there is leakage through any of these joints, it will usually be noted by water stains on the wood framing or roof sheathing in the attic or by stains in the ceilings of the interior rooms. Faulty joints are often resealed with an asphaltic cement rather than reflashed. The cement, however, is not as durable a seal as sheet-metal flashing, and the joint will often require periodic resealing.
Also check to see if the roof needs cleaning. Most pitched roofs need an occasional cleaning to remove an accumulation of debris—seed pods, twigs, pine needles, and leaves. Accumulated debris must be removed, especially from the spaces between the shingle tabs. If the debris is allowed to remain on the roof, it will retain moisture and promote the growth of moss and fungi, which is detrimental to the roofing. In addition, the litter can impede the runoff of rainwater, resulting in leaks.