Repairs: roofs and rainwater goods

Asbestos cement sheet covering probably lasts about 40 years. Many estates where it has been used will now be either due for demolition or ready for the roof to be re-covered.

Note: Given the problems of handling and disposal of asbestos-based materials, any re-roofing operation can no longer be considered cheap, and use of a licensed contractor may be required if the material is in particularly poor condition and likely to lead to excess fibre and dust release.

The Control of Asbestos at Work Regulations stipulate fibre release limits, which will govern the appropriate protocol for stripping off this type of material, and you then have the problem of considering what is the appropriate replacement.

Both asbestos cement sheets and sheet metal roofing are prone to leakage around the fixings.

'J' bolts were commonly used for asbestos cement sheets, and either J bolts or self-tapping roofing sheet screws commonly used for profiled metal sheet roofing are prone to failures, especially when the neoprene seating washers give way (or are omitted).

All of these rely on the correct tension/torsion being applied to the fixing screw. Over-tightening will rapidly rip through the neoprene washer that provides the water seal under the nut head on the top surface of the roof. Over-tightening can either fracture the sheet covering (fibre cement materials) or buckle the sheet covering (metal sheeting), all leading to increased risk of localised water penetration.

Solution 1

The fixing methodology and workmanship is critical for any sort of sheet roof material. There are no shortcuts here. Check to confirm that the self-tapping or other fixings have been properly secured and that neoprene washers are intact.

Solution 2

There are modern fibre-reinforced cement replacement products that replicate many of the profiles of the corrugated asbestos cement sheet roofing, although the longevity of these materials has yet to be established.

Re-covering will often be carried out using a substitute profiled sheet metal with a plastic polymer coating. Again these are relatively lightweight sheets and should not adversely affect roof loading significantly where they replace an asbestos fibre cement product, but it would always be prudent to have the loading characteristics of the roof checked prior to re-covering.