How to lay a roofing felt or underlay

How to lay a roofing felt or underlay

Roofing felts or underlays are fixed before laying roofing tiles or shingles. They are used underneath the final roof covers. Felts or underlays can be polythene or bituminous in nature. The reason for using them is to prevent any rain water from passing through to the ceiling as the tiles or shingle roof covers may allow water to seep through when broken. The placing of the felt or underlay should be done by a qualified carpenter and with due diligence the ceiling and entire house is protected from any roof leaks.

The roofing felt should be free from any punctures as these are likely points that water may pass through to the ceiling of the house. Sometimes when people want to adjust aerials on the roof they have to climb up the roof. This also applies when fixing digital satellite dishes or solar water systems and this increases the likelihood of disturbing the mortar on ridges or breaking a tile. It is essential that after works on the roof covers, a thorough inspection is done to check on damages. Any broken tiles should be replaced. The ridge tile and mortar should also be checked after any work is done on the roof surface.

The roof underlay or felt is purchased in rolls. When using polythene, it should be heavy gauge and preferably laid in two sheets. This is because the temperature in the roof space may rise thus leading to damages on the felt. The bituminous felt should preferably be the sand blasted type. This is able to take higher temperatures without breaking within the roof space. The felts should be laid smooth from the ridge to the eaves. This prevent them breaking after they become brittle during the cold season.

When laying a roofing felt, ensure the surface is horizontal and level. The roof structure is first completed then polythene is laid using plastic straps. The straps are nailed first on the purlins. They should be tight to prevent sagging under water weight. They are laid in a mesh pattern. After completion the polythene or felt is laid on top. The roof battens are then nailed onto the purlins and they are laid according to the tile specifications. The laying of tiles is then done after testing for sagging or any leaks within the felt.

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