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Low pitch roofing options

Updated July 19, 2017

Low-pitch roofs have a slope less than 2 inches of rise to 12 inches of run. Because of the shallow slope, low-pitch roofs cannot be constructed like standard roofs. Instead, special membranes and treatments must be applied to keep the roof protected from moisture and degradation due to debris collecting on the roof surface. Low-pitch roofs can be chosen from options in roof structure, membrane materials, design and drainage

Roof Structure

The structure for a low-pitch roof is close to that of a floor. However, the roof structure must protect from exterior conditions. So the roof deck must be strong and impervious. The types of roof structure can be divided into two categories: non-nailable and nailable. Non-nailable structures include pre-stressed, precast and cast-in-place concrete, and these cannot be roofed with standard mechanical fasteners, such as nails or certain screws. Nailable structures include steel, lightweight concrete, gypsum concrete and cementitious wood fibre board; these can be roofed with standard mechanical fasteners. Non-nailable roof structures are stronger and offer better thermal resistance but are harder to repair

Membrane Materials

Low-pitch roofs are traditionally sheathed with built-up roofing, which is a series of layers of felts, fabrics and bitumen to provide a flexible, watertight surface. However, more contemporary roofing, such as modified bitumen, single-ply, sprayed polyurethane foam, liquid applied and metal panelling provide better protection from the elements with added insulating properties

These membranes are either fastened with adhesives or fasteners, ballasted with gravel aggregate or held in place by concrete pavers. Each material has its own characteristics, and you should consult a roofing company and the roofing product manufacturer before applying the roofing membrane to a low-pitch roof.

Design

Many aspects of the external environment that will affect the choice of low-pitch roofing. Beyond aesthetics and the colour of the roofing, consider local building codes, geography, material availability, energy efficiency and maintenance. As with all other elements of a building, consider how your roof will perform in your region. In fact, in some cases, you might want to use a traditional roof to avoid problems with leaks, collection of snow and ice, as well as debris and foot traffic.

Drainage

The roof must be able to remove water from its surface. If not, the building will be subject to higher roof loads and leaking. So drainage should be adequate for the roof. Proper drainage can be accomplished with a slight slope to the structure, sloped membrane pours or tapered insulation, in conjunction with roof drains and overflow drains. Overflow drains are a redundant drainage system that halts water from collecting on a roof due to blockage of roof drains. The roof slope should allow the water to drain evenly across the surface with roof drains at regular intervals to avoid excessive build-up of water. Furthermore, the edges and intersections of building elements should be flashed to avoid water infiltration

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About the Author

Ryan Crooks is a licensed architect with 15 years experience in residential, institutional, healthcare and commercial design. Crooks is also an instructor, teaching architecture to high school and college students. He has written hundreds of articles for various websites.