Costs: Single-ply membranes for flat roofs | Features

Single-ply membrane roof coverings
	Capital cost	Net present value for 60 years £/m 2	Life expectancy (Years)
Polyvinylchloride (PVC)
PVC-based single-ply membrane with third-party assurance for 30 years’ life expectancy	45	75	30
PVC-based single-ply membrane with third-party assurance for 25 years’ life expectancy	40	73	25
PVC-based single-ply membrane with third-party assurance for 20 years’ life expectancy	35	77	20
Thermoplastic polyolefin (TPO)
TPO-based single-ply membrane with third-party assurance for 20 years’ life expectancy	40	86	20
Ethylene propylene diene terpolymer (EPDM)
EPDM-based single-ply membrane with third-party assurance for 25 years’ life expectancy	37.50	69	25
EPDM-based single-ply membrane with third-party assurance for 20 years’ life expectancy	35	77	20
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.