What it costs: roof coverings | Features

Pitched roof coverings	Capital cost £/m2	Net present value for 60 years £/m2	Life expectancy in years
Plain clay tiles to BS EN 1304. Flexural strength 600N minimum. Frost resistance: pass frost test D to BS EN 539-2; 265 × 165mm	67	81	50-70
Concrete interlocking tiles to BS EN 490, interlocking tiles;420 × 330mm	30	43	50-60
Concrete plain tiles to BS EN 490, double lap; 265 × 165mm	53	70	50-60
Fibre cement slates to BS EN 492 with third-party approval; 600 × 300mm	43	71	20-30
Natural slate to BS EN 12326-1; 500 × 250mm	87	92	75-100
Western red cedar shingles Grade no 1 “blue label”, preservative treated; 400 × 75 – 350mm	65	88	30-50
Notes: Service lives represent average lives. In practice there is evidence of clay tiles with more than 100 years of service life and natural slates extant after 250 years. There are also examples of premature failures. Capital costs are based on an inclusive rate for a simple 35° duo-pitched roof area of 250m² for a row of terraced houses with gable ends, no protrusions through the roof. Costs include tiles and detailing at eaves, verge and ridge; fixings, underlay and battens. Lap suited to a sheltered environment. A discount rate of 3.5% is used to calculate net present values. A cost analysis based on project specific information is essential for a realistic best value appraisal. BLP provides latent defect warranties for buildings (www.blpinsurance.com).