David Holmes of AECOM looks at roofing costs
Choosing the right type of roof is more difficult than most people think. Roofs do more than simply offer shelter. They can make the building more energy efficient, bring in natural light and help define the overall style of the property.
The complexity of design and shape of the roof, including junctions with other building parts, will add to the labour needed for the finish. Also consider the height of the roof to the ground, its location, style or steepness and of course, the labour that will require.
Overall perimeter length can be a significant cost driver, particularly on flat roofs. The ratio between the perimeter and the roof area is an important measure when pricing. Relatively more perimeter can significantly increase the overall rate per m2. Green roofs have higher capital costs than traditional ones, particularly when allowance is made for the additional structural loads. Maintenance costs are also higher.
Many factors influence both the design and choice of roof coverings.
- What weather needs to be accounted for
- Level of exposure – more nailing and larger laps may be needed. Western and northern locations generally face greater exposure
- The amount and type of insulation required – both thermal and acoustic
- Whether any bending of roofing is required
- Generally the shallower the pitch the more lapping will be needed to maintain weather tightness, so more material will be required to cover the same area
- Platter pitches take time to dry out after rain or snow, increasing possible maintenance
- Planning requirements may insist that certain materials, design or colours are used
Good design, particularly details around junctions and openings is very important.
Modern roof design on industrial and commercial roofs tend to have a low pitch to minimise heating costs. This has seen the rise in secret fix systems with no exposed through fasteners and minimal end laps (preferably none), which allow pitches down to 1°.
The following rates are based on the UK average and represent typical prices at 2016 Q3. Please note prices can vary significantly depending on specifications.
Flat Roof: Membrane and built-up systems
Includes insulation (U-value = 0.25W/m2K) and vapour barriers as necessary; excludes decking
Single layer polymer roofing membrane; insulation £75-95/m2
Bitumen three-layer polymer modified bitumen system £83-120/m2
Bitumen two-layer modified bitumen system £65-100/m2
Bitumen felt roofing system, laid flat, with solar reflective paint finish £90-150/m2
Mastic asphalt; applied flat; to concrete substrate £25-60/m2
Single layer sheet roof; composite system; warm roof covering; vapour control layer; insulation and water proof membrane £75-110/m2
Polymeric waterproof membrane; 1.2mm thick fleece backed membrane; cold roof £50-75/m2
Air cushion roof (ETFE type membrane) supported on lightweight metal structure (included) £850-1100/m2
Roof walkways; 600mm x 600mm x 50mm precast concrete slabs on support system £45-65/m2
Pitched roof: Tiles or slates
Includes reinforced underlay and battens as necessary; excludes roof structure
Natural Welsh slate tiles £115-140/m2
Natural Spanish slate tiles £70-110/m2
Synthetic slate tiles £65-90/m2
Reconstituted stone slate tiles; random slates £60-80/m2
Clay pantiles £38-45/m2
Clay tiles; handmade; sand-faced plain tiles £85-110/m2
Concrete tiles; interlocking; troughed / bold rolled £33-50/m2
Concrete tiles; plain £33-50/m2
Fibre cement slates £40-55/m2
Red cedar sawn shingles; preservative treated; uniform length £60-85/m2
Pitched roof: sheet metal
Includes breather membrane, underlay or vapour barrier as necessary; excludes roof structure
Copper sheet; mill finish; flat seam or wood rolled £140-170/m2
Copper standing seam roof; mill finish £150-200/m2
Extra for pre-patinated copper finish £40-70/m2
Aluminium sheet; mill finish; wood roll; insulation (U-value = 0.25W/m2K) £80-125/m2
Aluminium sheet; standing seam; mill finish; insulation (U-value = 0.25W/m2K) £80-90/m2
Extra for Pvf2 aluminium finish £10-20/m2
Stainless steel; terne coated sheet £115-140/m2
Lead roof covering; code 7; welded seam; milled lead; laid flat £125-150/m2
Lead roof covering; code 7; welded seam; milled lead, pitched roof £150-155/m2
Zinc; Natural Bright Rheinzink; pitched £95-140/m2
Extra for pre-weathered zinc £20-30/m2
Pitched Roof: Fibre-cement sheet
Excludes roof structure
Profile 6 fibre cement; single skin; natural grey finish £28-40/m2
Insulated system (U-value = 0.25W/m2K); Profile 6 fibre cement external skin; metal lining panel internally £55-70/m2
Extra for coloured fibre cement £1.75-2.25/m2
Double skin GRP translucent sheeting £55-66/m2
Triple skin GRP translucent sheeting £60-75/m2
Landscape roof
Excludes decking
Extensive sedum type flat roof; growing medium; waterproof layer; separation layer; low maintenance £180-250/m2
Extensive rockery type green flat roof for planting; growing medium; waterproof layer; separation layer; low maintenance £190-275/m2