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Single-ply membrane roof coverings
Capital cost Net present value for 60 years £/m 2Life expectancy (Years)
Polyvinylchloride (PVC)ÌýÌýÌý
PVC-based single-ply membrane with third-party assurance for 30 years’ life expectancy457530
PVC-based single-ply membrane with third-party assurance for 25 years’ life expectancy407325
PVC-based single-ply membrane with third-party assurance for 20 years’ life expectancy357720
Thermoplastic polyolefin (TPO)ÌýÌýÌý
TPO-based single-ply membrane with third-party assurance for 20 years’ life expectancy408620
Ethylene propylene diene terpolymer (EPDM)ÌýÌýÌý
EPDM-based single-ply membrane with third-party assurance for 25 years’ life expectancy37.506925
EPDM-based single-ply membrane with third-party assurance for 20 years’ life expectancy357720
Table notes
Life expectancies as defined by third-party assessments. Longer service lives are feasible and would alter the net present value outcomes. Expected service-life criteriainclude a detailed understanding of the molecular chemistry of the plastics, additives such as plasticizers and production methods.
Life-cycle costs are based on a concrete warm roof construction with simple rectangular plan. Costs include: single ply membranes 1.2-1.5 mm thick, perimeter upstands, gutter, outlets and protrusions, insulation and vapour control layer. No allowance for walkways or access. In-use costs include inspections, minor repairs and occasional cleaning.
Costs used are averages. Best value should be determined from a whol- life assessment of roof covering options which satisfy project specific criteria, as much of the cost lies in the detailing and relative costs between options is marginal. A discount rate of 3.5% is used to calculate net present values.