Plastic is a material made up of polymers: long chains of repeating molecules, usually derived from crude oil or natural gas. In construction plastic is not one material but a whole family, with widely differing properties: from rigid PVC pipe to stretchy EPDM roofing membrane.
Two main groups
- Thermoplastics — soften when heated and harden again when cooled, over and over. PVC, PE, PP and PMMA belong here. They can be welded and reshaped
- Thermosets — cure chemically once and never soften again. Epoxy, polyurethane and polyester belong here. They cannot be reformed
Plastics in construction
| Abbreviation | Name | Typical use |
|---|---|---|
| PVC | polyvinyl chloride | Drainage, rainwater pipe, window frames, gutters |
| PE | polyethylene | Water supply pipe, vapour control layer, building film |
| PP | polypropylene | Above-ground drainage, geotextile, inspection chambers |
| EPS/XPS | expanded/extruded polystyrene | Floor, wall and roof insulation |
| PUR/PIR | polyurethane/polyisocyanurate | Insulation boards and expanding foam |
| EPDM | synthetic rubber membrane | Flat roof waterproofing |
| PMMA | acrylic | Rooflights and glazing |
What to watch out for
- Thermal movement — plastic expands far more than timber, masonry or steel. Always allow expansion gaps in long runs of pipe and in sheet materials
- UV resistance — not every plastic can be left exposed to sunlight. Unprotected EPS and PUR break down at the surface; outdoors choose a UV-stable grade or cover the material
- Fire performance — plastics differ greatly in reaction to fire and smoke production. Check what the building regulations require for the application
- Bonding and welding — PVC is joined with solvent cement, but PE and PP are not: these have to be welded or connected with compression fittings
Related terms
- PVC
- EPDM
- EPS
- Polyurethane
- Expansion joint
- Vapour control layer
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