Here is an overview of how felt roof applications can differ and how we are able to offer a longer warranty for new flat roofing systems than most other roofing companies:
There are three types of deck boards in use by various roof companies:
This is the cheapest from of 18mm sheeting you can buy and is not generally used by any decent roofing contractor. These sheets were all that were used many years ago, but unfortunately when the boards are wet, they will break down very quickly and make the roof extremely unsafe.
Oriental Strand Board (OSB)
This product seems to be favoured by the majority of roofing companies although is harder to obtain recently. This is still basically a chipboard, but instead of fine chips like the standard boards, this is larger ply chippings all pressed together with one side lacquered.
This is by far the most expensive of the three products. It can last years, even if it is allowed to get wet. If we are replacing a flat roof that already has ply laid, chances are it can be left and felted straight over.
We ONLY ever use 18mm sheets of 18mm Ply wood as standard.
Felts & the Application
Your new flat roof if laid to the correct standards, will have two 3B under layers and a coloured mineral layer. Very rarely(if at all) is the loose granite version used which would have been applied instead of the green mineral layer.
Flat roofers may differ from one another by applying the felts in different ways
- 1. One Layer of Underlay – It has been known that the occasional rouge roofer will only lay one layer of underlay to save time and costs, this will severely reduce the life expectancy of your roof.
- 2. Nailing the First Layer – This is the most commonly used way of applying the first layer. The second layer is normally fixed down using a pour and roll method, with bitumen. The third is torched on polyester Mineral.
- 3. Two Layers of Bitumen Fixed underlay -This option makes the job take longer and adds the additional cost of twice as much Bitumen. This would mean though that you will have three watertight layers including the polyester mineral coating.
- 4. Torch on Underlay – There is available on the market a torch on underlay which eliminates the need for a bitumen pot during the entire job. Some roofers favour this but having tried and tested it we found that in certain weather conditions it wouldn’t bond to the walls well enough that we were happy. Bitumen when hot and in liquid form, like water will get everywhere and a water tight roof is guaranteed.