A flat roof is a roof which is level in comparison to the most roof types. The slope of a roof is also known as pitch. A flat roof could have up to 10° pitch, approximately. Flat roofs are based on an ancient form most commonly used in arid climates and allow other uses for the roof space such as a living space or patio. Flat roofs or a "low-slope" roofs, are more commonly found in use on commercial buildings. The National Roofing Contractors Association defines a low-slope roof as having a slope of 3-in-12 or less. Flat roofs are constructed all over the world and each area has its own technique or preference of materials used. In warmer climates where there is less rain and freezing is less of an issue flat roofs can be built of masonry or concrete. This is a good way of keeping out the heat of the sun and it's cheap and easy to build where wood is not available. Areas where the roof could become saturated by rain and leak or where it could sink into the brickwork and freeze to ice. This could lead to 'blowing' (breaking up of the mortar, brick or concrete by the expansion caused by ice formation. In these cases a Flat Roof is not suitable. Flat roofs evolved from the Egyptian, Persian, and Arabian styles of architecture
Any material used to cover a flat or slightly pitched roof is known as a membrane. The primary purpose of the membrane is to waterproof the roof area being covered. Materials use to cover flat roofs usually allow the water to run off from a slight inclination into a gutter system. Water from some flat roofs such as on garden sheds sometimes flow freely straight off the edge of a roof. Using a gutter system provides an advantage, keeping both walls and the foundation dry. Gutters on smaller roofs often channel water directly onto the ground or sometimes into a soak away. A flat roof is designed to collect water in pools, usually the purpose of aesthetics, or sometimes for rainwater buffering.
The majority of flat roofs in North and South America use tar or asphalt more with felt paper applied over roof decking to keep the building watertight. The felt paper is then covered with a coat of bitumen (asphalt or tar) and that this covered with gravel to keep the heat of the sun, UV rays and the elements from weathering it and helps protect it from cracking or blistering. Roof decking is usually constructed with solid wood or a composite, chipboard or oriented strand board (OSB, also known as Sterling board) or it could be steel or concrete. Bitumen is applied sparingly in two or more coats (usually 3 or 4) while it’s a hot liquid.
The main reason for failure of a flat roof is ignorance of installation, lack of maintenance or lack of care. When something or someone move the gravel from the roof membrane exposing it to weather and sun cracking and blistering will occur and eventually water will seep through.
Roofing felts are usually a paper or fiber material mixed in bitumen. Gravel cannot protect a tar paper surface when it rises vertically from the roof, such as on a parapet wall or upstand. The felt is usually coated with bitumen and then a metal flashings creating a gravel stop. The gravel stop finishes the roofing, preventing water from seeping underneath flat roofing material and prevents the gravel from washing during heavy rains.
If a leaks occur on a flat roof, damage can go unnoticed. When this occurs the decking and any insulation and structure underneath will be damaged. The cost of this type of damage from the rot can be very high. It can also cause health risks to people and animals breathing the mould spores that will grow. Once the insulation is wet the “R” value is destroyed. If it’s an organic insulation the most feasible solution is removing and replacing the damaged area. If the problem is detected early enough the insulation may be saved by simply repairing the leak.
There are issues that can arise if water penetrates the barrier covering. The water can travel a long way before visible damage shows itself. It can also be very difficult to find the source of the leak, allowing for proper repair. When underlying roof decking gets soaked, it will often sag and create more room for water to accumulate causing more damage to the building structure.
When gravel, leaves and debris block water outlets it causes a pressure head of water (deeper the water – greater the pressure) which can force water into the a hole or crack in the roof. In a colder climate the water can freeze and break up the surface of the roof due to expanding ice. It’s important to maintain your flat roof to avoid damage and reduced lifespan or otherwise unnecessary repair.
A very common material used for flat roofs in modern times are single factory-made long sheets such as EPDM synthetic rubber, polyvinyl chloride (PVC) or thermoplastic polyolefin (TPO). The quality is usually excellent for one-piece membranes or single plies and it’s currently used for large commercial buildings. Modified bitumen membranes are widely available in one-meter widths that are bonded together using a hot or cold seaming processes.
Metals can also be used for flat roofs. Lead (welded or folded-seamed), tin (folded, soldered or folded-seamed) or copper are expensive options not commonly used now as they were in the past.
Flat roofs are sensitive to human traffic. When work is done on the roof such as: through-roof service pipes, cable installation or when air conditioning units are installed a roofer should be called to inspect the roof and ensure it is still watertight. In high traffic areas proper signage should be put up directing people where they should be walking and walkways of rubber matting, wooden or other method of protection should be installed to protect the roof membrane. In some cases a membrane, stone or concrete paving can be used.
Check out Flat Roof Costs to get an idea of what it might cost you in the state of New Jersey Flat Roof Cost.
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