The primary function of the roof system is to protect against and manage the weather elements, particularly precipitation, thus protecting the interior and structural components of the building.
Roof system also protects the interior elements of the building and because of that its components should also be designed, in conjunction with the gutters and downspouts, to direct rainwater and runoff away from the foundation area, to help reduce the potential for soil erosion, compaction and water entering the basement area.
There are two basic types of roof construction, sloped and flat.
Most sloped roofs are covered with individual pieces of shingling material overlapped to prevent water penetration.
Flat roofs are basically watertight membranes that should have just enough slopes to allow water to run off.
The slope of a roof can be a factor in the life expectancy of the roofing material.
The life expectancy of a roof covering is also dependent upon the type of material used, the quality of workmanship, exposure to sun and wear from tree branches, snow/ice and wind.
For a flat roof that achieves waterproofing and drainage excellence, the use of asphalt and coal tar to achieve the water-resistant combinations is the best choice.
Built up roof (BUR) System
The concept is very basic and viable that it rose to capture more than 90 percent of the flat-roofing market since 1960s.
The key to BUR’s strength and durability lies in the fact that all plies of the roof are fused together into a single, monolithic barrier that applies to the entire surface.
This eliminates numerous problems such as the need for fasteners, which create additional risk of leakage; the need for ballast, which is often laid loose in the form of stones and can be blown off by heavy winds and eliminate movement in the form of expansion and contraction, which leads to buckling, ridges and splits.
Modified Bitumen Roof Systems
Modified Bitumen (MB) is asphalt that has had modifiers added to it to give it plastic or rubber-like properties.
The most common types of modifiers being used are APP (Atactic Polypropylene) and SBS (Styrene Butadiene Styrene).
Modified Bitumen roof systems consist of one, two, or three ply systems.
Single Ply Roof Systems
Single-Ply roof systems have outstanding UV-ray resistance and extraordinary resistance to weather elements.
Their white reflective and ‘cool roof’ characteristics help reduce a building’s energy costs.
The reduction in the surface temperature of the roof reduces the amount of expansion and contraction of the roof deck.
Single-ply membranes also provide the ability to cover very large areas more economically.
Single-ply roof systems are based on several types of products; generally TPO (thermoplastic polyolefin), PVC (polyvinyl chloride) and EPDM (ethylene propylene diene M-class rubber).
These are membrane products that are factory fabricated and installed in the field as a single layer.
Single ply roofing systems can be loose-laid (ballasted), adhered, or mechanically attached to the roof deck.
Single-ply roofing systems offer ease of installation, lighter material weight, and a lower relative labour cost on larger projects.
Tile Roof Systems
Clay tile is produced by baking moulded clay into tile. The density of the clay is determined by the length of time and temperature at which it is heated.
Concrete tiles are made of portland cement, sand and water in varying proportions. The material is mixed and extruded on moulds under high pressure.
They generally have lugs on their undersides for anchoring to batten strips. There are additional waterlocks or interlocking ribs on the longitudinal edges that impede movement and prevent water infiltration.
Asphalt shingles is one of the popular choices for steep-slope roofing construction and can be reinforced with organic or fiberglass materials.
Organic shingles consist of a cellulose-fiber such as wood base that is saturated with asphalt and coated with colour mineral granules.
Fiberglass shingles consist of a fiberglass mat, top-and-bottom layers of asphalt, and mineral granules.
Asphalt shingles’ are fire resistances.
Metal Roof Systems
There are three general categories of metal roof systems used for steep-slope roofing applications which are the architectural metal panel, structural metal panel and metal shingle/shingle panels.
Generally, architectural metal panel roof systems are watershedding and are intended for use on steep slope roofs.
Structural metal panel roof systems are used on low and steep slope roofs.
Structural metal panel roof systems can be used on low slope roofs as their have hydrostatic, or water barrier, characteristics.
Most structural metal panel roof systems are designed to resist the passage of water at laps and other joints, as sealant or anti capillary designs can be used in the seams.
Structural metal panel roof systems possess strength characteristics that allow them to span supporting members.
Metal shingles and shingle panels are available in numerous varieties for use as steep-slope roof coverings.
Most of the metal shingles are press-formed during the manufacturing process to provide a variety of shapes.
The component of roofs that is most vulnerable to early deterioration is the area around the flashings (plumbing stacks, the intersection of two or more roofs, skylights, et cetera.)
It is not uncommon for these areas to develop a leak well before the rest of the roof material has aged significantly.
Also, because these areas are frequently made of metal they can be more susceptible than the rest of the roof coverings to damage from wind and expansion/contraction from freeze/thaw cycles.
While flashings may appear fine on the day of an inspection and the roof may be relatively young in age, the flashings should be monitored on a regular basis (at least semi-annually) to detect any changes in condition that may indicate maintenance or repair is necessary.
Leaks left unattended can cause serious damage to other parts of the roof and structure.
Source : All Around The House; Vergola Roof System; Buildings.com and IRC South Florida.com
(this article written for 1BINA.my)