A flat roof may sometimes serve a building's purpose more effectively than a sloped roof. Flat roofs provide ideal space for solar panels and rooftop gardens, for instance. Though flat roofs work the best in locations that receive little snow or rain due to possible drainage issues, they are not off-limits in cities that get the occasional rough winter. If you want to build a flat roof in Cincinnati, you must simply be aware of the potential problems. Does this Spark an idea?
Flat Roofs
Despite the misleading name, flat roofs actually do have some slope to them. In fact, flat roofs may contain a range of angles. Every flat roof should have some slope to ensure that some water drains from the roof, but a more substantial slope provides more effective drainage. Generally, up to a 10 percent angle still provides the benefits of a flat roof, such as space for solar panel arrays, and appears flat from ground level while allowing for better drainage.
Best Uses
Because flat roofs do accumulate more water than roofs with more substantial slope, the roofs do pose some risk to buildings in Cincinnati. Use on sheds, garages and other usually uninhabited buildings proves less hazardous than use on inhabited buildings, such as houses and office buildings. If you do want to use flat roofs on a home or office building, use the maximum amount of slope and be vigilant during the winter months when snow accumulation may pose an issue and ice dams can form in drainage areas.
Minimum Angle
If you want to ensure that some water drains from a flat roof, use a minimum angle of 1 percent. According to both Southern States Roofing and This Old House, however, a slightly less steep angle of approximately 0.7 percent serves as the absolute bare minimum slope for a flat roof. Accomplish this by sloping the roof by 1/8 inch for every foot of roof. Though this provides the flattest surface, however, it may prove too little of a slope in most instances.
Roof Construction
Building a flat roof requires a simpler construction method than sloped roofs. Instead of building a frame for the roof that slopes upward from the perimeter toward a center peak, lay the joists for a flat roof in the same way that you lay normal ceiling and floor joists. Place the joists between the tops of the walls of the building structure so that the joists sit at the angle that you have figured for the roof slope and then lay plywood roof decking on top of the joists. Install rubber or metal roofing to a flat roof to ensure water-resistance.
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