Common flat roofing questions

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water pooling on flat roof
If you’ve seen water gathering on top of the roof you might think there is an issue with the waterproof layer, this is not necessarily the case. Pools of water occur because of the shape/angle of the roof surface itself, bowing of the sub structure or roofing membrane or issues with drainage channels or gutters.
A roof inspection from an experienced flat roofer can help identify the exact cause and proper action to remedy the problem. However if you look at the surface of the roof and its condition and the lay of the surface you many be able to work out why water isn’t draining off. Solutions can include replacing, as necessary, the decking beneath the membrane, or if the decking cannot be removed it’s possible to put tapered insulation in a warm roof to create drainage falls on the roof surface.

flat roof terrace in liverpool
Over the past decade we’ve seen an increase in interest around the subject of alternative uses of flat roofs. We think it’s fantastic and enjoy working on these projects.

The first things you’ve got to consider is the structure below the flat roof in question. Only a survey from a qualified roofer or builder can give you the ironclad answer you need about whether the structure is suitable for your project. Structural enhancements are often required if the roof is to safely become an area you can use.
The type of flat roof and the materials it’s made of will have a bearing on how best to approach your conversion project. For example rubber roofing, whilst extremely durable, is not a suitable surface for people to walk on regularly and any decking laid on top of it would have to be done so with great care to avoid a puncture.

Garden projects are not as simple as they might seem, to plant extensively on top of a roof you must consider a great many things. As with roof terraces and balconies you must not underestimate the load on the roof structure and a proper survey is required for a roof garden also. In addition to this you must consider drainage and the effect of subsiding organic matter on your drainage as the seasons progress. The damage gnawing roots and Mother Nature in general will slowly deal out to the structure below and of course all the horticultural concerns about sunlight, shelter, soil pH and any minerals or metals that may drain into your soil from the structures around your flat roof. A roof garden is more than just a roofing challenge but with proper planning is a fantastic venture and we are always happy when working on these projects.

an old flat roof
This is an excellent question to ask, confiding the long term health of your roof when it’s still in good shape opens the door to a range of cost effective preventative measures which would not be an option were your roof to have already fallen into a state of disrepair.
If the waterproofing has held fast and the structure below remains sound a flat roof getting towards the end of its life can be given decades more with the correct roof overlay system. Roof overlay systems are available in a range of materials and can be used in conjunction with a range of insulative layers. Using that he right materials and matching insulation is essential and usually requires some help from an experienced flat roofer. Why not read a little more about roof overlay systems (anchor link to roof overlay systems).

an old flat roof
Ensuring your flat roof is basically sound is a matter of checking a great many details. These include inspection of the under structure, checking for leaks, issues with the frame/timbers (like leaning, bowing or cracking) and checks for humidity. It also involves checks on the outer roof for pooling, punctures/damage, bad drainage and malformations (such as blistering). If your roof has issues in these areas it’s going to reduce its life even in moderate weather conditions and as always prevention is better than cure so issues like this should be dealt with quickly. If your flat roof must stand up to severe weather it may not be suitable to withstand it effectively in the long term. Heavy rain and especially heavy snow fall puts significant additional strain on a flat roof and so additional measures are required for that roof to last as long as it should.

For example, the minimum fall required in the roof is 1:80 to ensure rainwater drains effectively towards the gutters and outlets at the edge of the roof. However, if your roof is likely to encounter heavy snow a larger drop would be advisable to ensure snow slides off rather than builds up.

Another consideration is the type of drainage outlets, we find conventional gutters often perform better than internal outlets for a few reasons. Debris build up is a problem to both gutters and internal outlets but internal outlets tend to get blocked more easily. As they’re only in a fixed point on a roof whereas gutters span the length they’re also more affected by slight malformations in the flatness of the roof membrane. Deflection of water by a beam of structural decking away from the outlet could encourage excessive pooling in prolonged rain. Where internal outlets are used they should be fitted with leaf and gravel guards and be big enough to deal with storm conditions.

The top edge of the waterproof membrane should also be protected with cover flashing, to ensure the seam between the membrane and underlying roof layers is properly sealed to prevent the inlet of water.

These are just some of the questions we get asked about flat roofing, we’ll be adding more soon but if you have any you’d like us to answer let us know!