Flat Roof Systems
Flat roof systems cover the structure horizontally (or almost horizontally).
The idea of flat roof originated as a lifestyle rather then necessity.
Roofs, which can be used as terraces provide inspiration to many architects.
A lot of expensive houses and villas follow this pattern of flat roof design.
Another, very important aspect of the flat roof systems is the low cost of the supporting structure.
This is the reason why many African and Mediterranean countries with low rain fall adopted this structure.
The disadvantage is the leakage. Flat roof systems do not drain water easily.
Therefore, many terraces are slightly inclined to direct excess water into gutters.
This, however, is not always sufficient and often extra precautions are needed which add to the cost.
Types of Flat Roof Systems
There are various types of the flat roof systems. The examples discussed deal with heavier structures rather than the simple patios or verandahs.
- Polyurethane Foam Roofing is the most energy efficient material used for flat roofs. It is naturally waterproof and lasts 30-50 years.
- Asphalt is the old water proofing material which has been used for decades. As the by product of oil industry, it is cheap but does not last long. In addition the material is prone to aging and mechanical defects.
- Ethylene Propylene Diene Monomer is a synthetic rubber-like material commonly used because of simplicity in its installation.
- Turbo Seal, CSP and Modified Bitumen are add-ons to the existing materials, which improve the overall performance of a sealing, insulation and thermal mass.
Benefits of Flat Roof Systems
Flat roofs provide great outdoor life-style in areas where ground is either expensive or not available. These structures are also an inspiration for green house designs because they help to create roof-top gardens. The other benefit is in the space efficiency. Flat roof systems fully allow to use the covered space, while pitched roof often compromise that aspect. The cost is also lower for simple flat structures. Both materials and the installation is cheaper for designs, which do not require the specialised labour.
Design of Flat Roof Systems
Paradoxically, flat roofs are not exactly flat. If they were completely horizontal then water would accumulate and eventually cause damage.
Generally, there should be a small incline of +/-1/4 of centimetre per 0.3 meters of length.
However, steeper incline will provide more drainage and improve the performance of materials.
Next, the plywood is added on top of the frame. This fills the spaces between joists and wedges.
Finally, the underlayment is added to completely seal the roof. This prevents leaking.
Sometimes a crashed rock or a roof-top garden helps to absorb the moistures.
However, care has to be taken not to overload or scratch the delicate insulation membrane.
Flat Roof Systems Costs
For patios and verandahs it is the most cost effective system.
Nobody is stepping on top of the structure and there are no heavy loads in the design.
The cost (labour and installation) is between $3000 - $5000 to cover the area of 30 square meters.
The pitched roof for the same verandah or a patio is about $3000 more expensive.
However, for heavier and bigger structures the flat roof may cost more.
The design itself is cheaper but the insulation may substantially add to the cost.
Generally, you should not attempt to build flat (or semi-flat) roofs.
However, in low rainfall areas and with proper design it is a definitely a beautiful structure.