Flat Roof Leaks

If a leak does occur on a flat roof then damage often goes unnoticed for long periods of time during which water penetrates and soaks the decking and any insulation and/or structure beneath it. This can lead to expensive damage from the rot which often develops and if left can weaken the roof structure. There are also various health risks to people and animals breathing the mould spores: the severity of this health risk remains a debated point.

One problem with maintaining flat roofs is that if water does penetrate the barrier covering (be it traditional or a modern membrane) it can travel a long way before causing visible damage or leaking into a building where it can be seen. Thus it is not easy to see where it is leaking in order to repair it. Once underlying roof decking is soaked it often sags causing a further collection or puddling of water in that area and the problem worsens.

Another common reason for failure of flat roofs is lack of maintenance of drains whereby gravel, leaves and debris block water outlets (be they spiggots, drains, downpipes or gutters), thus water cannot drain away and builds up. This causes a pressure head of water (the deeper the water the greater the pressure) which can 'push' more water into the smallest hole or crack. In colder climates, puddling water can freeze into ice which breaks up the roof surface as it expands whilst it freezes.

An important consideration in tarred flat roof quality is differentiating what many call simply 'tar' into rather different products: tar or pitch (which is derived from wood resins), coal tar, asphalt and bitumen. Some of these products appear to have been interchanged in their use and are sometimes used inappropriately, as each has different characteristics, for example their ability or not soak into wood/boards, their anti-funghal properties and their reaction to exposure to sun and weather and varying temperatures.

Modern flat roofs can use single large factory made sheets (e.g. EPDM synthetic rubber) and these are usually of excellent quality, though unfortunately one-piece membranes are seldom seen used in practice. Rather, strips of EPDM, PVC, tar paper etc. which are widely available in rolls (typically of 900 mm or 1200mm width) are bonded together in either hot or cold seaming processes on the roof during the fitting process where labour skill and training play a large part in determining the quality of roof protection attained. Reasons for not using excellent one-piece membranes include practicality and cost-saving:- on all but the smallest of roofs it can be difficult to lift a huge and heavy membrane to the roof (a crane or lift is required) and if there is any wind at all it can be difficult to control and bond the membrane smoothly and properly to the roof.Detailing of these various systems also plays a part in success or failure: In some systems ready-made details (such as internal and external corners, through-roof pipe flashings, cable or rooflight flashings etc.) are available from the membrane manufacturer and can be expediently and well bonded to the main sheet, whereas with materials such as tar papers this is usually not the case - a fitter has to make these shapes up on-site or on the roof and success depends largely on their levels of skill, enthusiasm and training - results can vary hugely.

Metals are also used for flat roofs, these can be made from lead (welded or folded-seamed), tin (folded, soldered or folded-seamed) or copper. These are often expensive options and vulnerable to being stolen and sold as scrap metal.

Flat roofs tend to be sensitive to human traffic. Anything which produces a crack or puncture in the waterproofing membrane can quite readily lead to leaks. Flat roofs can fail, for example; when subsequent work is carried out on the roof, when new through-roof service pipes/cables are installed or when plant such as Air Conditioning Units are installed. A good roofer should be called to make sure the roof is left properly watertight before it is left. In trafficked areas, proper advisory/warning signs should be put up and walkways of rubber matting, wooden or plastic duck-boarding etc. should be installed to protect the roof membrane. On some membranes even stone or concrete paving can be fitted. For one-off works, old carpet or smooth wooden planks for workers to walk or stand on will usually provide reasonable protection.