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Replacing a felt roof

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First layer of felt

Make sure the decking is in a good condition before starting to cover with felt. If any boards are found to be in a poor condition or rotten, remove and replace with new boards. The new boards should be coated with preservative before fitting into their positions. It is important to use a preservative other than creosote on the timber, as creosote will not work well with the bitumen material used with the felt roof.

Using galvanised clout nails with large heads, start to nail the first layer of felt onto the decking. Use 20mm (0.75inch) nails and space them about every 150mm (6inches) along the planks.

Start at the centre of the sheet and smooth and nail the felt to the surface in the direction of the edge of the roof. When you start using the second sheets of felt, it is important to allow an overlap of 50mm (2inches) and use bitumen mastic along the seams to aid waterproofing.

Second layer of felt

Work on the first nailed layer of felt a section at a time. Paint bitumen mastic onto the surface, a length at a time. Take half a sheet of felt and place it flat on top of the first layer. Use a soft broom to help you remove any pockets of air between the two layers of felt or press the surface into place.

If the surface is strong enough, walking over the second layer can help remove air pockets and help the two layers bond together. Repeat this process along the surface of the first layer of felt, remembering to allow an overlap of 50mm (2inches) when joining second layer felt to other second level pieces and use bitumen mastic along the seams to aid waterproofing.

Top layer of felt

Before laying this surface, cover the roof edges with welted aprons - strips of felt which cover the timbers at the edge of the roof. Then use the same method as securing the second layer of felt. When the roof is completed covered with a third layer of felt, apply a coat of mastic or chipping compound to the whole surface. Once again it is advisable to apply it in workable lengths along the surface, starting furthest from your ladder or point of exit.

Finish the surface by applying extra loose chipping to the surface by scattering over the completed surface. Using a layer of proprietary chipping compound, such as limestone, gravel or granite on top of the layers of felt, strengthens the surface further. The idea is for the surface to reflect rather than absorb sunlight, thus helping to protect the felt.

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