Are Flat Roofs Prone to Leaks?

Cold Deck Roof

• There are three kinds of flat roofs: cold deck, warm deck sandwich and warm deck inverted. All feature similar components, but each features them in slightly different configurations. The components include a roof deck, insulation and weatherproofing, and some feature ceilings and vapor barriers as well. A cold deck roof, from the ceiling up, is configured in the following manner: Directly above the ceiling is a grid-like vapor check. Above the vapor check is a layer of insulation topped with a space referred to as a ventilated void. Above the void is the roof deck, and directly above the roof deck is a layer of weatherproofing material meant to seal out rain and snow. Cold deck roofs are easily insulated, but since the roof deck itself is not insulated, it is subject to cold temperature and warm temperature heaving. Heaving displaces and weakens the roof deck and makes it subject to leaks.

Warm Deck Sandwich Roof

• A warm deck sandwich roof begins with the roof deck as the bottom layer. Directly above the roof deck is a vapor barrier topped by an insulation Iayer that is sealed with weatherproofing material. This type of roof is useful in buildings that require a great deal of room for overhead wiring. Without a vapor check of waterproof membrane, this type of roof will leak.

Warm Deck Inverted Roof

• Warm deck inverted roofs feature, from the bottom up, a thick roof deck topped by a waterproof membrane that is covered with insulation. The final layer is a sturdy, weatherproof ballast material. The top ballast layer is an effective barrier against water damage, but only when the roof features a good drainage system. If puddles develop above the ballast, water can leak into insulation materials and cause damaging condensation to build up throughout the layers.

Considerations

• Choose the best roof for your climate, weather conditions and personal use. A cold deck roof will be most effective in regions with consistent warm temperatures. In these conditions, the roof deck is less likely to experience damage and leak. Cold roof deck leaks can go unnoticed because the leaks occur above the vapor check. These roofs are also best suited for overhead traffic. Warm deck inverted roofs can withstand foot traffic. Warm deck sandwich roofs are the least effective roof type for overhead traffic. The insulation layer is directly underfoot, and damage to this layer will cause leaks.