Costs: Flat roofs | Features

Built–up bitumen waterproofing systemsCapital cost £/m2Net present value for 60 years £/m2Service life years
Modified bitumen
Three-layer SBS modified bitumen system, top layer 4 mm thick, polyester fibre base 250 g/m2	51	92	20-30
Two-layer APP modified bitumen system, top layer 4.5 mm thick, polyester fibre base weight 180 g/m2	42	77	20-30
BS 747 bitumen
Three-layer system, BS 747 type 3E top layer, weight 2.8 kg/m2, glass fibre base weight 55 g/m2	16	53	Jul-15
Two-layer system to insulation sub-base, BS 747 type 5E top layer, 4.5 kg/m2, polyester fibre base 330 g/m2 30 70 15-25
Two-layer system to insulation sub-base, BS 747 type 5B top layer, 4.0 kg/m2, polyester fibre base 330g/m2, with solar reflective paint coating	36	82	15-25
Three-layer system, BS 747 type 5E top layer, weight 4.5 kg/m2, polyester fibre base 330 g/m2	40	80	15-25
Three-layer system, BS 747 type 5B top layer, weight 4.0kg/m2, polyester fibre base 330 g/m2, with solar reflective paint coating 429015-25
Table notes
A discount rate of 3.5% is used to calculate net present values. Costs are based on covering a simple rectangular 500 m2 concrete flat roof. Covering system, eaves, verges and abutments only are included. Service lives based on average life expectancy. Whole-life costs include allowance for inspections, cleaning, minor repairs and repainting solar coating where applicable.
A cost analysis based on project specific information is essential for a realistic best value appraisal.
Further information
Building LifePlans provides latent defects warranty for buildings. Log on to www.componentlife.com for building component durability information, email peter.mayer@buildinglifeplans.com or telephone 020-7204 2441