Q My flat roof is leaking and needs to be repaired. It is about 3m x 5m and is presently felt and tile construction. I have received several estimates from various firms, some of whom seem keen to carry out the repair using EPDM rubber membrane. Is this advisable? Also, one contractor has informed me that building controls apply to the work and I must employ a surveyor for pre-inspection and completion in order to obtain a certificate from the local authority. Is this correct? MS, by email
A 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 marine 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.
Personally, I prefer a “traditional” covering material, the current incarnation of which is reinforced torch-on felt. Properly applied, it has a life expectancy of 50 years. EPDM rubber might or might not last this long — it hasn’t been used long enough to judge. Like fibreglass, it is often used as a sticking-plaster remedy on top of existing failed flat-roof coverings – which is asking for trouble, as explained above.
The latest Building Regulations dictate that any flat roof being re-covered must simultaneously be insulated to the current standard. This means you must either notify your local authority’s building-control department to inspect and approve the work or employ a roofing contractor registered with one of the government’s “self-certification” schemes. 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. You refer to your roof as being of “felt and tile construction”, which sounds as though this might be a possibility in your case.
Solving a smelly situation
Q We live in a five-year-old, three-storey house with the second (top) floor being mainly under the eaves in the attic space (bedroom and en-suite WC and shower).
The problem is that when the prevailing wind is from a certain direction, there is an unpleasant smell coming from the shower outlet and it is even possible to feel a draught. I cannot understand how this can happen as I thought that any outlet would require an S-bend or similar, thereby creating a seal. Why is this happening and what is the solution please? MB, north Wales
A You are quite right – all waste outlets should be fitted with a trap or “U-bend” to prevent sewer smells entering the home. However, modern shower trays are sometimes so thin that there is no room beneath them for a traditional S or P-shaped trap, and they are instead installed with a shallow “shower trap”. If the pipe leading away from this is too long or too steep, then the negative pressure created by the water running away can sometimes draw the water out of the trap, leaving it dry. Try running a little water into the shower to see if this solves the problem.