Flat roofing materials compared

Key issues

• Flat roofs should be only used where pitched roofs can't be.

• Durability - experience has shown that flat roofs are prone to maintenance problems and failure - though many problems can be eliminated by attention to detailing.

• Short life span membranes requiring frequent replacement will incur a higher environmental cost than other methods.

• The re-use potential of single-ply membranes can be compromised by fixing directly to the decking below.

Types of roofing materials:

TPO (Thermoplastic Polyolefin)
	TPO membranes are thermoplastic single-ply roof membranes constructed from ethylene propylene rubber. The roofing differs from EPDM in its welded joints and its improved resistance to chemical and biological attack.
	Reusable if mechanically fixed or better still ballasted with water or pebbles
	High material efficiency
	Durable
	Low toxicity
	Non-renewable resources (petrochemical)
	Accelerated testing accepted by the BBA shows a life span of circa 25 years

EPDM (Elastomeric membranes)
	EPDM membranes are elastometric single-ply roof membranes constructed from ethylene propylene rubber. The roofing is jointed using either a taped or adhesive seamed systems.
	Reusable if mechanically fixed or better still ballasted with water or pebbles
	High material efficiency
	Durable (but see below)
	Non-renewable resources (petrochemical)
	Membranes have been known to shrink. Careful perimeter detailing is required.
	20+ years

PVC membranes
	High material efficiency
	Unrecyclable& unreuseable
	Non-renewable resources (petrochemical)
	High toxicity
	25+ years

Mastic Asphalt
	Recyclable
	Seamless and flexible in application
	Durable where used appropriately (see below)
	Non-renewable resources (petrochemical)
	Medium / High embodied energy
	Brittle when set requiring heavy decking beneath
	Needs chippings laid over for thermal protection
	60 years

Built-up felt
	Multiple layers of roof felts laminated together with bitumen. Built-up roof material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate (gravel or slag), emulsion or a granule-surfaced cap sheet.
	High material efficiency
	Unrecyclable& unreuseable
	High embodied energy
	Non-renewable resources (petrochemical)
	Low durability
	15 - 20 years

We would specify:

First choice: • Pitched roof
Second choice: • EPDM • TPO
Think about: 'Green roofs'
Avoid: • Bitumen based felt roofing • PVC

Membrane products:

• L524 Roof membranes

Further information:

- Guide to the fundamentals of built-up roofing: irc.nrc-cnrc.gc.ca/cbd/cbd024e.html
- Single Ply Roofing Association: www.spra.co.uk
- Flat Roofing Alliance: www.fra.org.uk/