Flat Roof FAQ's

My flat roof is leaking. Can it be repaired, or do I need a whole new roof?

If it is obvious what has caused the leak, and the remainder of the roof is in reasonable condition, then a localised repair may be adequate. Such random repairs will not be guaranteed.
However, if the whole roof has aged and is in poor condition, or you require a warranty, then a full replacement (or possibly an ‘overlay’ – see below) will be the best course of action.

How do I find a reputable contractor?

One way is by good reputation in the area. A more reliable way is to ensure that they are members of the appropriate trade association. For flat roofing works, we (the Flat Roofing Alliance) have stringently vetted all of our contractor members, both for their business proceedings and for their technical ability to install flat roofs.
Hence, although they may not be the most local to you, they will be reliable.

There seem to be a lot of materials available – how do I choose the best?

Reinforced Bitumen Membranes or RBMs (roofing felts) have been greatly improved over the last 20 years, and the ‘High Performance’ products will provide much longer service than older types. They are thicker, with greater strength, but still flexible, and hence continue to dominate the market.
Look in the material description for the words ‘polyester, high performance, HP, high tensile, HT, polymer-modified, or elastomeric’.

Rubber/EPDM/ etc. These are very flexible and weather-resistant, but rather thin (1.5mm) and they can be very difficult to joint reliably. Ask for a system with a BBA certificate, and check that it is laid in accordance with that.

Fibreglass/GRP/ etc. These are applied as a liquid resin, with a thin reinforcement between coats. Again, ask for a system with a BBA certificate, and check it is laid in strict accordance with that.

I have several quotes, some mentioning ‘Pour-and-Roll’, others suggesting ‘Torching-on’. What is the difference?

Pour-and Roll is the traditional method of laying bitumen membranes, using hot bitumen from a boiler poured onto the layer below as an adhesive for the membrane, which is rolled onto it.
Products designed for Torching-on have special bitumen on the lower surface of the membrane, which is heat-activated and melted using a large & powerful gas torch, and the membrane is then rolled onto the softened bitumen.
Note: It is not good (or indeed safe) practice to apply a torch flame to any flammable surface (e.g. plywood, timber edgings, below the edge of a pitched tiled roof, etc.) The torch flame can reach 1000 degrees C.
Please be aware that the contractor's insurance will not cover fires caused in this fashion - and neither will your own home insurance.

The contractor wants me to put Insulation onto my roof – DO I NEED TO?
If so, where does it go?

Thermal Insulation is designed to reduce heat loss through the roof, and so conserve energy during the winter, and to reduce heat gain, making the area more comfortable during the summer. This is now a requirement of Building Regulations (Part L:2006).

If you are constructing a new building or a new extension, or repairing or replacing more than 25% of an existing flat roof area, then YES – you do need to upgrade by including a layer of thermal insulation.

Once you have selected your quote for renewing the roof, you should contact your local Building Control to confirm that your work meets Part L (i.e. gives a 'U'-value of 0.25 W/m2k or better).

Ideally, the insulation boards should be placed onto a vapour control layer (VCL) above the roof decking, and before the main membrane system is installed. This forms what is known as a Warm (or Warm-decked) Roof.
- This is shown in Sketch 1 in the Householder’s Guide to Flat Roofing.
- See also page 12 of the Guide for suitable model specifications.

To meet the Regulations, approximately 90mm of Urethane insulation will be required. Other types of insulant will need greater thicknesses. Where this is simply not practicable, discuss with the contractor and your local Building Control department.

I have got ponding on my existing roof. Do I need to replace the roof?

Not unless it is leaking, or showing other signs of deterioration.
If and when you do have it replaced, you should tell the contractor so that he can check the cause of the ponding, and itemise the cost of dealing with it in his estimate.

I have just had my roof replaced, and it is still ponding (where it did before).

Unless the contractor was told about the ponding he is unlikely to have quoted for changing the falls, which would have meant removing the decking, placing firring pieces (wedge-shaped timber strips) upon the joists, and re-fixing the old deck or a brand new one, prior to installing the new waterproofing system. This could have doubled the cost of the works.
It may be that the decking had deteriorated and sagged between the joists, in which case it should ideally have been replaced.
See Householders Guide to Flat Roofing pages 5, 6 & 7.

I have just had my roof replaced, and it is now ponding (when it did not before).

If the contractor has simply followed your instructions and overlaid the existing roof, or stripped down to the deck and applied new weatherproofing, he will not have not done anything to change or improve the falls.
It may be that previously there were stone chippings and possibly moss on the roof, which hid the standing water, whereas the new system is finished with mineral-surfaced felt that is smoother and shows the water.
Alternatively, it may be that the new system uses more robust, thicker materials that hold a thin layer of water behind the laps.
In either case, assuming that High Performance modified reinforced bitumen membranes have been installed, and that the water does not lay there all the time, the manufacturers are happy that this will not be detrimental to the life expectancy of the membranes.

I have had a new roof put on and I am not happy with it.

Your first point of contact should be with the contractor, who may well be able to explain what he has done, and why. If this is not satisfactory, then you will need to talk to an independent expert who will be able to advise you.
We operate a technical advisory service and would be pleased to assist.

My contractor insists on quoting for a scaffold to my roof - is this necessary?

Usually, yes. The contractor is legally liable for the safety of his operatives, and must provide protection against them falling from the roof. If he is quoting for a scaffold handrail system, then this is likely to be the best way of providing that protection.

Other contractors, who do not propose a handrail or other safety equipment, should be viewed with caution.

My quotation contains a reference to re-decking.
Can you tell me what this means?

The deck of your roof is the layer of plywood or similar, which goes over the joists to support the insulation and membranes. See Sketch 1 in the Householder’s Guide to Flat Roofing. In cases where this has deteriorated, it will need to be replaced; this is known as re-decking. The contractor should give you a price per square metre to replace with new. For types of deck, see pages 7 & 8 of the Guide.
It is important for the contractor to establish why the deck needs replacing, as further work may be required to prevent a reccurrence.

I am told the contractor can ‘overlay’ my roof.
What does this entail, and is it advisable?

In many cases the existing roof is sound, and the membrane is simply getting old.
If this is so, the contractor may well advise you not to expose the building structure to the elements while he strips off the old membranes, but to leave them in place to act as a base layer for a new system. This is known as overlaying the roof, and providing there are no other problems such as condensation or damaged decking that need to be attended to, then the process is perfectly acceptable.
- See also our Information Sheet #24, downloadable from this site.

What guarantee/warranty should I expect?

Material warranties usually come from membrane manufacturers, and are handed over by the contractor upon final payment. Dependant on the materials used, this could be for 5, 10, 15 or 20 years. If the contractor is on the manufacturer’s select list, this could also cover the workmanship element.
Always read the small print to see what is included.
FRA members can also offer Latent Defect Insurance at minimal extra cost.

Contacting the FRA

You can contact the FRA directly via this website, email, telephone or post. If you want to contact an FRA approved contractor, click here.