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 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 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 |
| High material efficiency | |
| Unrecyclable& unreuseable | |
| Non-renewable resources (petrochemical) | |
| High toxicity | |
| 25+ years |
| 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 |
| 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:
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/