Covering Roof with Asphalt

Filed Under: DIY Outdoor, Do it yourself, Home repair    by: ITC

The method used for constructing a flat roof is outlined in the following way; the joists usually being laid along the length of the extension from the house to the end wall. At the house end, the joists may either rest on top of a wooden wall plate, being toe-nailed in place, or be nailed to metal hangers which are also nailed to the wall plate. The ends of the wall plate are set in sockets built into the extension side walls.

At the end of the extension, the joists can simply rest on top of the end wall and be nailed in place or, if there is a window in the end wall, a second wooden beam can be fitted to span the opening and support the joists.

Tapered furring pieces are nailed to the tops of the joists to create the right fall. For felt covering the fall should be 1 in 60, but for asphalt it should be 1 in 80.

Sheets of exterior grade plywood are used to provide a roof decking and are nailed down through the furring pieces into the joists. The sheets should be staggered so the joints between their short edges do not coincide.

Although a felt-covered roof is the cheapest and easiest to construct, a much more durable finish can be obtained by having it covered with asphalt. This material is heated until it melts and is then spread over the roof to provide a solid, impervious layer when it cools. It is a job that requires a great deal of skill and is one that you should get a building, contractor to do for you.

Flat roofs can often suffer from condensation when moist air passes through the ceiling from the rooms below and cools on contact with the underside of the roof — particularly with bathrooms and kitchens and when the atmosphere is damp.

Leaving ventilation gaps behind the fascia and insulating the roof will help, but the best idea is to either use foil-back gN,:psumboard for the ceiling – which will stop the moist air passing through – or staple a separate polyethelene vapor barrier to the underside of the joists before nailing the gypsum- board in place. Once the extension has been weatherproofed by glazing the windows and fitting the doors, the room can be finished. Before plastering the walls and ceiling, lay in the necessary electrical cables, mount accessory boxes and run in any pipe work for hot and cold water or central heating.


1 Nailing the roof joists into hangers attached to the main beam; toe-nail through the top of the roof joists into the main beam also.

2 Nailing furring pieces (narrow end over the front wall) to the tops of the roof joists to set a 1 in 80 fall for the roof

3 Nailing the plywood roofing sheets over the furrings: stagger the joints between the short edges.

4 After pouring hot asphalt onto the roof. smoothing it out to a layer about 3/8in thick.

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