Pitched roof coverings
Capital cost £/m2Net present value for 60-year life £/m2Service life in years
Specification options   
Clay tiles    
Plain clay roofing tiles to BS EN 1304. Category 1 impermeability. Mean impermeability factor for all test pieces: 0.5 cm3/cm2/day maximum or a mean impermeability coefficient for all test pieces: 0.8 maximum. Flexural strength 600N minimum. Frost resistance: pass frost test D to BS EN 539–2 48 55 60
Concrete tiles    
Concrete interlocking tiles, single lap to BS EN 490 26 31 60
Concrete plain tiles, double lap to BS EN 490. Smooth or granular finish 44 51 60
Artificial slates    
Fibre cement slates to BS EN 492, type NT — non–asbestos. Class B minimum average bending moment for length of slate. Minimum thickness 2.8 mm. Smooth or riven and coated both sides with a coloured acrylic paint 44 72 30
Resin-based slates with third-party approval. Manufactured by embedding and compacting slate dust with a resin binder. Test data required indicating performance for freeze–thaw resistance and wet–dry cycling, water absorption, sulphuric acid immersion and strength 45 73 30
Natural slates    
Natural slate to BS 680–2. With special reference to achieving the water absorption, wetting and drying and sulphuric acid immersion test criteria. Maximum size 610 mm × 335 mm 56 65 60
Metal multi-tiles    
Mild steel sheet 0.5 mm–1 mm thick. Zinc galvanizing 275 g/m2 both sides minimum. Acrylic base coat on both sides, minimum 75 microns thick. Acrylic weathering coat with embedded natural cleaned and graded silica granules then sprayed with acrylic glaze, minimum 250 microns thick 29 49 30
Bituminous shingles    
Glass-fibre reinforced modified bituminous roof shingles to BS EN 544; class 1. Atactic polypropylene (APP) modified bitumen, minimum 3 mm thick34 52 30
Table notes
Costs are discounted to net present values at a discount rate of 3.5%
Service lives are typical average lives to enable comparison of whole-life costs.
Capital costs are based on a simple 35° duo–pitched roof design for a row of five two-storey terraced houses with gable ends; a cold roof system is envisaged
Only the roof coverings are costed.
The durability classes are for typical specifications.
Replacement costs include an allowance for replacement of underlay, battens or boarding and roof coverings but no temporary over-roofing.
Maintenance costs include five-yearly inspection, replacement of eaves drape at year 20 where exposed.
Ridge tiles and verges for clay and concrete roof coverings are set in mortar.
In the latter half of the life cycle an allowance is made for replacing fixing of individual cracked or loose tiles or slates.
The 60-year period reflects a typical design life to BS ISO 15686–1:2000 Buildings and Constructed Assets. Service Life Planning. General Principles.