A roof that is perfectly level or slightly pitched is referred to as a flat roof. Since this type of roof is not visible from the ground, the inspection must be made from the roof itself. As with a pitched roof, a flat roof should be the first item inspected. Safe access to the roof is of prime importance. If the building is higher than one story, the roof should be accessible from the interior. Anything other than an interior means of access is a potential hazard and is considered a deficiency in the struc-ture’s design. If the roof you are inspecting is flat and is more than one story high with no interior access, it is best to have it inspected by a professional roofer.
Ventilation of the area directly below the roof deck is needed to minimize the moisture buildup in this area. An excessive moisture condition can result in deterioration of the roof deck, a lowering of the thermal resistance of the insulation, and, eventually, damage to the interior of the structure. During the cooler months, the moisture trapped in the area between the roof and the upper-level ceiling will condense, drip onto the insulation, and cause random water stains on the ceiling. Adequate ventilation of this area is also important in reducing the summer heat load on the rooms located immediately below the roof.
All too often, provisions for ventilation have been omitted by the builder. Therefore, when inspecting a flat roof, be sure to look for ventilation openings. The openings might be in the form of roof vents (vertical pipes protruding through the roof deck) or open areas in the side of the building just below the roof. Roof vents are often shielded from the rain by a cover and should not be confused with the plumbing vent stacks, which also protrude through the roof deck. The plumbing vent stack is connected to the house sewer line and is easily identified by the odor of the discharging gases. If no ventilation openings are noted, that fact should be marked on your worksheet, and installation of ventilation openings should be considered.
A flat roof must have a watertight covering, rather than one that merely sheds water, to protect the area below the roof from water intrusion. The most common types of flat-roof coverings are built-up, single-ply, roll roofing, and metal. When inspecting a flat roof, look for ponded water. In the past, it was considered desirable to have a roof that was perpetually flooded, because the standing water would reduce the heat load during the summer.
Today, ponded water on a roof is no longer considered desirable, since the disadvantages far outweigh the advantages. Ponded water can become a breeding place for insects and can promote the growth of vegetation and fungi. (See FIG. 2-9.) The roots of plants growing on the roof can puncture an asphalt cover-ing. The freezing of ponded water that has penetrated into the layers of a built-up roof can delaminate the roof covering. The temperature difference of the wet and dry areas on a randomly ponded roof results in differential expansion that might cause warping and cracking of the roof cover. If you see ponded water or signs of past ponding on the roof during your inspection, note the location on your worksheet as an area that should be drained.
A properly designed roof should have provisions for drainage. Two basic drainage designs are used in a flat roof—the perimeter system and the interior drainage system. In the perimeter system, water that drains from the interior portions of the roof collects in gutters or scuppers (openings in a parapet wall) located along the perimeter and then flows into downspouts or merely drips off the roof. In the interior drainage system, drains are located in the roof itself and are connected to downspouts that run through the interior of the structure. Look for one of these drainage systems as you walk around the roof. The interior roof drains are often clogged with debris and are sometimes set higher than the surrounding area, a condition that results in ponding. Look for cracks around the joints between the roof drain and the roof covering.
When inspecting a flat roof, you should also inspect all roof-mounted structures and projections such as skylights, hatch covers, chimneys, vent stacks, and so on. These items are discussed in chapter 3.