top of page

Flat Roofs - Felt, Fibreglass GRP or Rubber?

Updated: Nov 1, 2023

If you are planning an extension that includes the construction of a flat roof then you will need to choose a covering material for that flat roof. There are lots of different products to choose from and different builders have their own preferences but generally they are one of three types of product. Here we try to give you a broad idea of what these are:

Felt Flat Roofs

A felt flat roof would look something like this. It consists of sheets of felt which are fused to a plywood deck using a naked flame (a method known as 'torch on'). It's been the most common type of flat roof covering for a long time so it's pretty easy to find people to install it. Builders often favour felt because they know it and are comfortable working with it. However, installing 'torch on' felt does involve a certain risk because of the use of fire, gas etc. Also it is not seamless, there are visible edges where the sheets overlap.


GRP / Fibre Glass Flat Roofs

Fibreglass or GRP as it is also known (Glass Reinforced Plastic) would look something like this. Fibreglass/GRP has become more and more popular as a flat roof covering. Unlike felt it is seamless so there should be no visible joint lines because it is applied in liquid form (usually brushed on). Also it cures as part of a chemical process that does not require flames or heat guns etc so it is safer to apply. As a finished product it is very hard and it looks neat around the edges and details, although critics may say it appears a little plasticized. The downside is really to do with requirements for reasonable weather to be able to install it. It must be done in dry weather and whilst the temperature is within a specific range. For that reason many builders will only offer to install it on jobs where you have paid for a "tin hat" temporary roof. Also, from the installer's point of view it is quite messy to handle and has a very strong odour which makes it unpleasant to work with.


Rubber Sheet Flat Roofs

A rubber sheet covering for the flat roof would probably look something like this. Essentially a great big rubber sheet is specially ordered which will cover the whole roof in one piece. It gets glued to the plywood deck of the roof. Having one big sheet cover the entire roof avoids having lots of joint lines. However, just like wrapping a Christmas present, there will always be awkward corners that require cuts, joints etc and that is where some saggy unsightly details occur. On the plus side it is pretty easy to install, no flames are required and the edge trims usually look nice and neat.

3 views0 comments

Recent Posts

See All


bottom of page