Spunbonded Polypropylene (PP)
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Types and Durability
| Description
Spunbonded polypropylene |
Expected Lifespan
(Years) |
Adjustment Factors |
| Spunbonded polypropylene roof tile underlay. Low water vapour resistance/ high water vapour permeability, complying with the performance requirements of ASTM D 6757-02 (in excess of minimum quoted in BS 5250 for traditional sarking felts of 50 MNs/g) | 35+ | Test certificate from approved local testing authority : +5 years |
| Spunbonded polypropylene based, modified bitumen coated roof tile underlay. Medium water vapour resistance and permeability , complying with the performance requirements of ASTM D 6757-02 (similar to traditional sarking felts of 50 MNs/g) | 35+ | |
| Spunbonded polypropylene based, modified bitumen coated roof tile underlay with low to medium vapour resistance and medium to high vapour permeability | 35 | |
| Bitumen based reinforced sarking felt not manufactured to BS 747 Type 1F, or equivalent. | < 10 | None |
Assumption: Spunbonded polyproplylne underlays are generally intended for use over trusses/ rafters.
All underlays should be fixed with large head felt nails of copper, aluminium alloy or galvanized steel and fixed in accordance with BS 5534 Part 1.
Insulating underlays should not cause obstruction in the batten and tile space
Note: Some spunbonded polypropylene underlays may give rise to noise nuisance in areas of high wind uplift, due to the sheets flapping. Manufacturer’s guidance should avoid such problems through design and/ or fixing detailing.
Some underlays may incorporate a layer of aluminium foil intended to increase the insulating effect of the underlay.