If you suspect the roof is leaking it will probably be obvious in the room below. The leak in the top layer, which you will be able to see up on the roof, will probably not be directly above where the leak appears in the room below. This is because water will find its way under this top layer and run between any subsequent layers before finding a way through the boarding in your ceiling. |
Leaks are caused by a number of factors and it is important to determine what is causing the leaks before taking any action to rectify the problem. Begin by inspecting the roof covering and check that no ‘ponding’ is occurring. Ponds in excess of 25mm will be a problem and regular ponding can be detected by obvious water stains as well as plant growth.
It may be that bad design is leading to a leaking flat roof, so check for cracks at joints and corners, around chimneys, ventilation slits or tacks, where the roofing may have moved, and around rooflights too. Commonly, roof nail heads are missing or have rusted and cause leaks, or gutters may be obstructed or punctured. Carefully inspect seams and other joins and be sure to look out for problems around junctures with other roofs as these are prime areas for cracks to appear.
If the roof has a gravel covering, pay attention to areas where the gravel has lost colour. This is usually a sign that water is filtering through and leaking, discolouring the stones. Also check for blisters. This is a common problem caused by moisture finding a way between the deck of the roof and the membrane and is a common cause of leaks if not treated.
It should also be noted that the reason many flat roofs failed in the past was not just down to faulty membranes, but due to rotting and failure of the structure beneath, caused by condensation. To avoid this the outer roofing membrane should be placed on top of external insulation with a void beneath the timber decking and the ceiling beneath. This is not only ideal for containing services and lighting but also vital for roof ventilation.
If there are no obvious problems but leaks are occurring, a specialist will be able to use other methods of detection, such as infrared thermography, endoscopes or electronic detection methods.
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