The best flat roof roofing material is without a doubt a single sheet of rubber custom made for weather-proofing flat roofs, such as Firestone’s EPDM product.
That is laid directly onto roof boarding, itself supported by the roof rafters and nagging. Insulating roof lifespan is generally laid in the space between your two, and if you are renewing your flat roof anyway you may as well take the opportunity of renewing that simultaneously.
This will almost certainly be the recommendation you receive from any reputable builder or roofer advising you on replacing your existing flat roof.
Until recently the most used material for a new flat roof was bituminous felt laid in three layers, the first layer nailed down and the upper two bonded to the one beneath with mastic bitumen. Depending on material used, this may mean heating a good bitumen-based compound to make it liquid, and then pouring it onto the underlying felt and spreading it evenly on the whole section of the roof.
Then you had to hold back for the compound to cool before applying the next layer, and at the end spreading a layer of stone chippings on the roof and bonding it with a chipping compound, this being to reflect natural sunlight and stop the felt and bitumen degrading quickly.
This was altogether a rather messy, complicated and time-consuming job best left to the experts. In addition, there have been several stages where it was very easy to fail to make the roof weather-proof, e.g. where the edge of the felt met the prevailing tile or slate roofing of the pitch roof.
On top of that, if, or rather when, there developed a leak in the flat roof, it could be very difficult and messy to learn exactly where the rain was getting back in. Seldom would the manifestation of the leak on the ceiling of the room below be directly below the source of it. Water could easily get through a weakness in the bitumen felt and travel along a rafter before descending to the ceiling board below.
The new generation of rubber-based flat roofing systems are far superior. Assuming you have reasonable DIY abilities then you can probably do it yourself, with one other person to aid. You can easily find a local supplier of rubber flat roof roofing material online, and the existing price is around �6.65 per square metre.
Most suppliers slice the material to the exact size and shape that you require so are there no unnecessary joins, meaning no weaknesses and an extremely long-lasting, leak-proof roof.
The vital the main whole process is to ensure that there are no gaps between your rubber roof and any existing pitch roof where rain could possibly penetrate. To ensure there are no problems it is vital to run the rubber material up and beneath the tiles or slates of the adjoining pitch roof so that any rain dripping from the lower-most row falls onto the rubber, with no chance for it over-lapping the edge and getting underneath the pitch roof.
Also, make sure that the existing slope of the flat roof towards the guttering or other means of water escape is maintained. The rubber is merely glued onto the roof boards and sealed where appropriate with metal brackets or bitumen so that rain penetration is impossible. Mind that the glue covers the entire underneath of the rubber in order to avoid bumps in the top which could obstruct the drainage of the water away.
Rubber roofs have been proven to last for well over 50 years under all weathers, so that it really is the only flat roof roofing material that you should consider when deciding on a new flat roof.