Supplement:
Evolution of Flat Roof Designs
A flat roof is a type of covering over a building. Though they are named flat roofs they are not actually completely flat. In contrast to the sloped form of a roof, a flat roof is horizontal or nearly horizontal. They have a slight unnoticeable slope that helps to drain away the water that accumulates during rains. Yet for historic modern-style buildings, flat roofs are at the core of architecture, meant to reflect the broad horizontal lines of the natural landscape. The flat roof is a popular choice in Africa, where the climate does not tend toward snow or very heavy rainfall.
Flat roof designs in Africa are often constructed from corrugated metal, concrete or fiberglass, which incorporate enough of a slope to allow water to run off. It is important to remember though that standing water can lead to flat roof leaks, and that, if possible, it is advisable to make sure that your flat roof is waterproof by using one of the many available methods that we featured in our February 2010 issue. To add to the waterproofing methods that we featured is the Thermoplastic Polyolefin Roofing Membrane also known as TPO.TPO is becoming one of the popular and latest materials used and available in the market. It consists of three layers that make the roof strong and durable to survive in any condition.
Roofs must meet resistance requirements to mechanical action, thermal insulating, waterproofing and acoustic, fire resistance, durability, economy and aesthetics. Construction Review looks at factors to consider on flat roof designs.
TPO systems
These include ultraply TPO Roofing Systems which are best for low slope commercial roofing applications. The system also offers design options with membranes available in reflective white, tan or gray, which help reduce a building’s cooling requirements. Platinum TPO Roofing Systems comprises of a durable, 80-mil-thick scrim-reinforced membrane, and is best for warm climates. ReflexEON TPO Roofing Systems is the first thermoplastic roofing membrane to greatly reduce the effects of microbial growth, and the subsequent staining and loss of reflectivity.
By reducing microbial growth commonly seen on white roofing systems, ReflexEON TPO remains cleaner and extends the membrane’s ability to reflect heat and improve a building’s energy efficiency.
Kinds of flat roofs
Homeowners can choose among four kinds of flat roofs. All four types cost US$250 to US$350 per "square" (100 square feet), but prices vary according to region and size of the roof. Flat roofs usually come with a 10- to 20-year warranty but the roofs can last 25 years if properly installed and maintained.
Built-Up Roof (BUR)
The traditional hot-tar-and-gravel roof is built from three or more plies of waterproof material alternated with hot tar and ballasted by a layer of smooth river stone. Once made of tar paper, these types of roofs gradually are using more-advanced materials such as fiberglass membranes.
Modified Bitumen
A single-ply rolled roof similar to ice-and-water shield, but impregnated with a mineral-based wear surface. Torch-down systems involve heating the adhesive as the material is unrolled. Newer peel-and-stick systems are safer and easier.
Rubber Membrane
EPDM (short for ethylene propylene diene monomer) is a true rubber. The durable material resembles an inner tube, but it is engineered to resist damage from sunlight. EPDM can be mechanically anchored with fasteners, ballasted with stone, or glued.
Design of Flat Roof
Roofs must meet resistance requirements to mechanical action, thermal insulating, waterproofing and acoustic, fire resistance, durability, economy and aesthetics. Roof structures are set in relation to these functions taking into account the partitioning of the building, its structural strength and general conditions to be provided in the last level rooms.
To fulfill these functions, structural elements (resistance) and nonstructural elements of the roofs must meet several performance requirements: stability and strength, durability, fire safety, tightness, hygrothermic and acoustic comfort.
- The roof unit contains the following main elements differentiated by the functions they fulfill:
- Wrapping, with waterproof protective role – can be wooden, card¬board bituminous slate, ceramic, metal, galvanised sheet metal, galvanised, aluminum, lead or copper, plastic materials;
- Insulation, with thermal protective role against heat input, due to strong summer heat and heat loss in winter time;
- Vapour barrier, layers or diffusion channels, to avoid penetration of water vapour, through migration, in thermal insulation;
- Accessory elements, associated to roof, with role to collect and dispose the rain water, perimeter closure, evacuation of water vapour in the atmosphere, lighting.
Benefits of Flat Roofs over other Roofs
One of the major advantages of a flat roof is the fact that no space is lost below it. With traditional sloping roofs you lose a lot of room because of the way they are structured and because of all the wooden beams. Homeowners do not have this problem with flat roofs which means that there is very limited dead space and more room in their home.
A flat roof is typically cheaper than a sloped one for several different reasons. Firstly, they require fewer materials and secondly they are a lot quicker to construct. The flat roof construction is also less demanding than normal roofs which are another contributing factor towards them being cheaper than what the homeowner would normally expect to pay.
Another big advantage of flat roofs is its accessibility. As compared to the usual types of roofs, flats roofs are easily accessible, as they do not have much of a slope. There is a very rare chance that you would ever slip from a flat roof and that is a big advantage as compared to sloping roofs. A flat roof provides you with many options to utilise it as well as to enjoy. Because of the same reason, flat roofs can also be used as terraces, a personal space where you can carry on a lot of home activities, which you could not do earlier on the sloping roofs.
Ease of construction
The surface area of a flat roof is less than that of a slanting roof. Again, less surface area also means less amount of raw material to be used, which in turn means that you need to spend less amount of money as compared to the construction of sloping roof. For a flat roof, you must consider that the roof provides a water-proof casing for the building. Generally in flat roofs there are one or two layers of materials for water resistance. The flat roof should be designed in such a way that the accumulated water can be directed into gutters, downspouts and drains to avoid accumulation of water. The materials that are used in flat roofs should not only be long lasting but also cost effective.
Roof Slope
The slope of your roof system plays an important role in how effectively your roof sheds water. The biggest problem with most commercial or flat roofing systems is caused by poor roof slope. Imagine a roof that has very little slope and many areas of pounding water. The pounding water is caused by a roof slope that is inadequate to overcome irregularities in the roof surface. When this roof begins to develop leaks, the leaks will be much more severe than they would on a roof that is shedding water quicker and has minimal pounding water.
Simply put, a roof should shed water not retain it. While many older flat roofs have performed satisfactorily with slopes of barely ⅛" per foot, it is typically recommended that the roof slope be a minimum of ¼" per foot. Most roof slope deficiencies can be easily corrected with the addition of tapered insulation. Not only can existing roof slope be increased, but it is also possible to change slope direction completely.
Roof Drainage
The drainage system on your roof plays an important role in how your roof eliminates water. As roof slope pertains to "shedding water", roof drainage pertains to "water disposal". The performance of the roof drainage system needs to be properly matched to the size and slope of the roof. As the roof slope increases, the volume of water (in a given timeframe) that is routed to the drainage system will increase.
Evolution of flat roofs has depended largely on the environment in which the building was built (climate zone), but also on the materials and technologies used. So they evolved from the first roof made of earth to those made of wood or stone. The first envelopes (“skin” of the building) were made from sheet of copper or zinc and then lead, after that it past to covers made of bituminous membranes. Lately it has more and more developed the concept of roof garden or green roof, which is a flat roof covered with a layer of topsoil.
The life expectancy of a flat roof is relative to the amount of maintenance it receives. However, this can also be influenced by the kind of material your flat roof is made of. All flat roofs should be inspected once a year. Overall, a flat roof can prove to be a valuable addition to any home and is cheaper than a normal sloped roof. This many advantages have led to flat roofs being a popular trend.
List of Contributors
1.Ruberoid Building Products
www.ruberoid.co.uk
Pat Caron
pcaron@kogroup.co.uk
2. Nuralite Waterproofing Systems
53A Victoria Street
Onehunga, Auckland
Ak Phone: +64 (9) 579 2046 or 0800 Nuralite (0800 68725483)
Ak Fax: +64 (9) 579 5136
john@nuralite.co.nz
www.nuralite.co.nz
3. Visable Improvement
316 Corlett Drive
Kew,South Africa
2090
www.visroof.co.za
sales @ visroof.co.za
info @ visroof.co.za
