Module 9: Engineering and Design in ASEAN
Table of Contents
Reading Text & Presentation
9.1 Foundations of engineering projects
9.1.3 Construction: topping off
Once the floors are completed the roof has to be constructed.
Roof characteristics depend on the building that it covers. The availability of roofing materials, local traditions, and architectural designs also have to be considered. There may be legislation covering some aspects, too. One would not usually expect to see straw or banana leaves as roofing for a 72-storey building. The biggest consideration is usually rainfall, as draining excess water from the roof would be desirable. The 3 basic elements are; material, construction, durability.
Nowadays, most new buildings will have roofs of precast concrete, tiles, laminated glass, aluminum sheeting, or copper. The basic shapes are flat, arched, domed, skillion, gabled, and hipped. Flat roofs are often slightly sloped to drain the excess rainwater. Sloped roofs are referred to as pitched if the angle exceeds 10 degrees. Domestic houses usually have pitched roofs, including gabled, hipped and skillion.
The roof support and any space underneath the roof will determine the construction. For pitched roofs the angle from the lowest to highest points is all-important. Drainpipes and guttering are often used in conjunction with pitched roofs.
As the roof is often the least accessible part of a building, durability is a matter of concern regarding repair and renewal. Any damage or destruction could be extremely costly. Usually, the roof has its supporting structure and its outer ‘skin’.
Parts of a pitched roof showing cutaway support materials
(Source: See References)
Tiled roofs typically have some of the features indicated above. This one shows a ‘gable end’ shown. The ‘rake’ is the angle of the roof, and the ‘ridge’ and ‘hips’ the names given to the two types of top roof joining parts. The ‘valley’ is the name given to an ‘inner’ roof joint. ‘Flashing’ is what is used to seal any added parts (a chimney in this case) to the roof to prevent leakage. ‘Drip edge’ is the overhanging part of the roof and ‘eave’ the space underneath. The inner linings of plywood and felt underlay are fixed to the (wooden) rafters. The ‘soffit’ is the space between the rafters and the outside wall to which the rafters are attached. Guttering and drainpipes would usually be attached to the fascia.
Flat roof features
(Source: See References)
As suggested by many names in the picture the flat roof isn’t flat. It looks horizontal but has a slight slope to allow water drain off. The parapet is the raised part, which gives housing for the other parts and can protect from falling of when higher. Scuppers, drip caps and downspouts take away excess rainfall, and the decking will be the part of the roof between the top floors. The roofing materials used to cover the decking will usually be waterproof and extremely durable.
