Builders Tips - Flat Roof Repair

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Published: 23rd December 2010
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Repairing flat roofs
By their very nature, flat roofs tend to present more troubles than pitched ones. Although they should have been built with a slight fall to allow water to run off, pools of water tend to form on the surface. The wide variation in temperature to which a flat roof is subjected will generally separate the covering layers and crack them. Inevitably, leaks will occur.
You can reduce this expansion and contraction by topping the roof with a layer of white solar-reflective stone chippings. In time, though, these tend to be washed away.

Missing chippings
Where chippings are sparse or missing altogether, coat the roof with bitumen chipping compound and scatter fresh chippings over the surface, pressing them into the bitumen with a light wooden roller. This ought to give the roof a couple of years' extra life.

Leaking roof
With a water leak, keep in mind that the point at which you notice the stain inside the roof may perhaps be some distance from the problem region. Since it's common for the felt layers to separate, water trickling through the top layer might travel some distance under the felt before appearing on the ceiling below.

Inspect the roof
Whenever you inspect a flat roof, you will find some general signs of prospective difficulties to watch out for. If the top layer of felt has started to wrinkle or looks mottled, these are sure signs the covering is reaching the end of its useful life. Watch too for any signs of springiness in the roof decking, this indicates that the chipboard decking has begun to break up. Also check the upstands where the roof meets an abutment, like the wall of an adjacent building or a parapet wall.
This initial inspection should give you a good idea of what needs doing and how to proceed. You may be able to carry out a patch repair to the damaged region or apply an all-over treatment to the surface, or stripping off and replacing the roof.

Minor roof repairs
If the problem demands only a patch repair over a hole, it is best to use metal-backed self-adhesive flashing strip, although a piece of roofing felt coated with cold bitumen would be a suitable alternative. Scrape away any stones from the damaged area, then apply the liquid bitumen primer supplied with the flashing strip. When this has dried, peel the backing paper away from the flashing strip, which ought to be cut wide enough to enable a lot of overlay, and press it into place, rolling it down with a wooden wallpaper seam roller.

Roof blistering
Your problem may perhaps just be blistering on the surface. In this case, make a star-shaped cut through the blister with a sharp trimming knife. Then peel back the edges of the blister to expose the underfelt. Coat the area with bitumen roofing compound and fold the flaps back in place, pressing them down with the roller.

Checking for troubles
When you are up on the roof, check for any other existing or imminent issues. Obviously, when you notice a leak inside, you'll not wait for a general inspection prior to carrying out necessary repairs.
To repair little splits and blisters in felted roofs, open up the top layer of the felt with two knife cuts at right angles. Peel back the tongues and spread some bituminous mastic over the repair region. Then fix the tongues back down securely with galvanised clout nails and cover the repair with a felt patch, bedded on a lot more mastic and rolled down with a wallpaper seam roller or comparable tool.

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