The main problem with flat-roof repairs is not usually choosing the material for the weatherproof
covering, but diagnosing why it leaked in the first place. Many British flat roofs are too flat and built with inadequate structural materials, so they sag in the middle, allowing rainwater to pond, which then finds its way through any pinprick imperfection.
A “flat” roof should actually have a gradient of at least 1-in-80, to allow rainwater run-off, and have a decking of OSB or WBP plywood. If your roof is shallower than this or decked with chipboard, then it doesn’t matter what you cover it with — it will eventually leak again.
The traditional flat roof covering material, the current incarnation of which is reinforced
torch-on felt. Properly applied, it has a life expectancy of 20 years.
The latest Building Regulations dictate that any flat roof being re-covered must simultaneously
be insulated to the current standard. This means you must notify your local authority’s building-control department to inspect and approve the work.
Insulating a flat roof is clearly a good idea, but has to be done with care so as not to cause problems with condensation and wood rot in the structure.
The best solution is usually to lay rigid foam insulation boards on top of the weatherproof covering, as this keeps the whole roof structure above dew-point temperature. Paving slabs
can be laid on top of the insulation as a weighting layer and to allow access as a roof garden. However, this adds weight and height to the existing roof so cannot always be achieved.
There are two other ways to insulate which both consist of having the insulation beneath the
The first of these is called a "warm roof" which has a vapour barrier on top of the timber boarding, then a rigid foam insulation board adhered to the vapour barrier , then the chosen waterproof coverings.
The second is called a "cold roof" that has the insulation between the ceiling & timber boarding.
Most properties have this design but the roof must be ventilated above the insulation so a
dew-point cannot occur that would result in the timbers decaying.
We can advise on what insulation would suit your property and recommend what waterproof
covering would be the most cost effective to suit your needs.
We install various coverings from reinforced torch on felt, mastic asphalt, fibre glass (GRP)
and metal roof coverings such as zinc, lead and copper.