Summary: Learn how to cover a flat roof, lay a felt roof, install gutter drips, fit the top sheet of felt and fit the verge edges.
This project describes the traditional method of covering a flat roof using Bitumen-based roof felt.
The two materials most widely used to cover flat roofs are traditional Bitumen-based roof felt and a tough Butyl rubber based material, which is more flexible than roof felt and will not degrade following long exposure to sunlight. Another advantage Butyl rubber has over felt is that it can be laid over an old felt roof. Despite this, felt roof coverings still remain popular as they can now be applied with a cold adhesive.
Coldseal self-adhesive roofing felt is made up of a polyester base, saturated and coated with SBS modified bitumen. The reverse side is treated with a self-adhesive coating and protected with a removable release sheet. Applied in two layers (underlay and cap sheet), both layers are bonded by removing the release sheet on the back. Coldseal self-adhesive roofing felts offer excellent performance and are ideally suited for use on domestic garages and extensions.
Before you start work on any flat roof, make sure that it is safe to go ahead. In particular check the timber deck of the roof is not rotten and will take your weight. And if possible get someone to help you.
If replacing old felt with new you will first need to remove the old felt. It is best to start this job in dry weather. Use a tool with a sharp blade, such as a wallpaper scraper or garden spade, to get under the bonded joins to allow you to strip away the old roof covering.
However, if you are laying a Butyl rubber roof covering it is not necessary to remove the old felt.
Do not attempt to lay roof felt in cold or wet weather. Unroll the felt 30 minutes before starting the job. This is easier to do when you have the rolls on the roof.
The first layer to fix to the roof is the underlay and should be laid at right angles to the direction of the fall of the roof.
The underlay should be laid at right angles to the fall of the roof.
Roll out the second layer overlapping the first section along the un-nailed edge by at least 50mm.
Cut lengths of top sheet about 350mm wide and nail these lengths to the timber batten that runs along the edge of the roof.
Fold back the felt on to the top of the roof and stick it down with its edge finishing 175mm from the edge of the roof.
Verge edges stop the rainwater spilling over the side of the roof, allowing it to follow the fall of the roof until it reaches the gutter. Verge edges should only be fitted when the top sheet has been laid.
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