Flat Roof Waterproofing Options

20December 2017

Find the various methods of waterproofing your roof

Flat Roof Waterproofing Options

Flat roofing is something that is common in small outhouses, bathrooms and extensions. It is usually made with two or more layers of bituminous felt, that is laid on top of a flat surface for weatherproofing. More modern flat roofs often have liquid applied glass fibre, which is typically stronger. Mastic asphalt is also sometimes chosen as a roofing material, however not for large roofs, because it is so heavy.

The waterproofing of the roof is typically supported by the roof deck, which is usually a form of timber boarding, which is supported using joists, and the ceiling is affixed to the underside of those joists. There should be insulation on the roofing surface, as modern Building Regulations require this.

Waterproofing a flat roof requires some careful design decisions. The finished roof should have a slope that works out to at least 1 in 80, and roofs are usually designed with a steeper slope than this. The slope is to allow rain and snow to slide off. It is best to make sure that there is drainage to two areas, but one is OK. Ideally, the roof should have a gutter, but an internal outlet can be used, as long as it has guards to stop leafs and gravel from accumulating in them. The waterproofing for the roof surface should cover not just the roof, but also adjacent walls, extending up by at least six inches. There should be some cover flashing at the top edge of the waterproofing, that is suitable for the type of membrane in question.

To prevent the covering from coming away, it’s important that the roofs have adequate ventilation and a vapour control layer that is bonded to the deck. This will stop condensation from accumulating and damaging the lining.

Make sure that the roofing materials are suitable for the intended use of the surface. If the roof is going to be used as a roof terrace, then the structure should be strong enough to take the weight of people, and the surface must be protected to prevent the covering from tearing.

You should inspect the roof regularly, to make sure that there are no puddles or blisters forming on it. Even with new roofing, some small puddles may form, and these are not always anything to be concerned about. However, if a puddle is getting bigger or deeper over time this could be something to worry about. Bigger blisters and puddles should be repaired as quickly as possible, and you should look at flat roof waterproofing options. This may mean adding an extra protective finish, repairing flashing and trip, or fixing a sagging joist to keep the surface sound. Sadly, patch repairs are typically only short term, and while they are inexpensive, it is often a better long-term investment to purchase a new roof covering. Talk to a qualified contractor before you make any major decisions, but be aware that split membranes, punctured membranes and sagging decks can often require a full re-roofing rather than simple flat roof waterproofing options for repair.