Roof drainage

Press, 27 June 1983, Page 27

Roof drainage

The efficiency of a roof drainage system depends on the quality of its installation and maintenance. Guttering needs to be sloped away from the roof valleys towards the downpipes with a drop of at least 26mm for every 6m. With a lesser slope, the guttering is unable to move run-off satisfactorily in heavy rain, and water may lie in corners, breeding mosquitoes and corroding metal. Besides an adequate slope, there should be one downpipe for every 6m of guttering, plus one at each end if the stretch is longer than 10.5 m. Water from the downpipe is usually led by underground pipes to a dry well several metres from the house and at least 45cm underground. Even a correctly fitted system is unable to function adequately if it is clogged with debris. Reviving a basically sound system may involve simply unplugging downpipes and resealing a few joints in the guttering. Wear gloves to remove leaves and twigs from the guttering, then loosen caked dirt with a stiff brush and a

garden hose. Mesh screens can be fitted over the troughs to prevent new litter from accumulating, and downpipes can be fitted with wire filters at the top. Small leaks at joins in the guttering can be patched with silicone sealant. If poking around with a screw-driver reveals soft spots in the fascia boards, either carve out the rotten bit and fill it with a plastic putty, or replace the damaged board, or part of it, with new but well-seasoned timber. A fresh coat of paint every few years extends the life of most metal guttering, and there are special paints available for this. Use a wire brush or sandpaper to prepare corroded areas, and areas where the old paint has begun to chip or peel. It is also worthwhile to take the time to apply extra sealant on potential leak spots.