Preventing leaks in your Flat Roof

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Posted 20 Apr 2017 10:05

The best way to prevent roof leaks in the wetter seasons is to be proactive with your roof maintenance in the months before the winter period. 

Around this time of year in Autumn is when home owners should begin a through clean of their gutters, outlets and leaf catchers. One of the main reasons for roofs leaking is a build-up of organic matter causing water ponding and the blockage of water channels.

For all types of low-slope roofs, note areas of ponded water, as standing water on a roof can accelerate deterioration of the roofing membrane. Even if there is not water on the roof at the time of the inspection, there may be stains that indicate previous ponding. Walk the roof and note any areas that feel spongy.

Remove any debris on the roof, such as branches, as it could potentially puncture the roofing membrane. Check the roof drains and remove debris from the drains if necessary.

Have a look at the roof perimeter where the roof membrane turns up onto the parapet, which is the extension of the walls above the roof level. A metal flashing is used to protect the membrane at the parapet. With a low parapet, the flashing may extend over the top of the parapet. With a high parapet, the membrane flashing may terminate in a reglet and there will be separate flashing for the top of the parapet. Check the sealant at the reglet to ensure it remains flexible and fully adhered. Check the flashing to ensure it is not rusted or damaged.

Flat roofs are designed to a specific fall and naturally they are supposed to dispel water, but when they aren’t maintained, problems may arise. The size and location of the roof will determine the drainage design requirements as each home is unique.

Nuralite’s membrane systems have all achieved CodeMark certification recently. The scope and limitations of the Nuraply 3PM CodeMark state the minimum finished fall for a roof shall be 1:80 (0.73 degrees). Due to inconsistences and tolerances in construction, Nuralite recommend that the design falls are 1:40 (1.5 degree) for plywood and 1:60 (1 degree) on concrete.

The scope and limitations of the Nuraply 3PM CodeMark for timber substrate is: 17mm plywood for roofs, 21mm plywood for decks, supported at 600mm centres each way.

With steeper pitches increasing the speed in which the rainwater drains into the gutter and downpipe system, architects need to consider relevant slopes to ensure flat roofs are pitched appropriately to cope with heavy rainfall.

Regions across New Zealand are subjected to varying levels of rainfall intensity which in turn affects the capacity required and the appropriate number of downpipes or outlets. The New Zealand Building Code requires that a rainwater system design be able to cope with the level of rainfall intensity that has a 10% chance of occurring once a year for 10 minutes.

Cleaning gutters and downpipes before problems arise is the advice we give to those with flat roofs or homes in general, especially in Autumn when the weather starts to change. With yearly maintenance and a correctly designed sloped roof, there shouldn’t be any issues with leakages.

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