Felt vs Breathable Membrane — Roofing
Compare traditional bituminous roofing felt with modern breathable roof membranes for UK pitched roofs, covering BS 5534 requirements and condensation risk.
Side-by-Side Comparison
| Feature | Traditional Felt (Type 1F) | Breathable Membrane |
|---|---|---|
| Material cost | £0.40-0.80/m² | £0.80-1.50/m² |
| Ventilation needed | Yes — eaves + high level | No (in most cold roofs) |
| Vapour resistance | High (HR class) | Low (LR class — vapour open) |
| Condensation risk | Higher if ventilation inadequate | Lower — moisture escapes |
| Lifespan | 20-30 years | 30-50 years |
| UV resistance | Poor — days | Good — up to 3 months |
| Total cost incl. ventilation | Higher (ventilation products) | Often lower overall |
| BS 5534 classification | HR underlay | LR underlay |
When Traditional Felt Is Appropriate
- Matching existing underlay on partial re-roofs for consistency
- Heritage or conservation area requirements
- Budget repairs where ventilation is already adequate
- Specific manufacturer systems requiring HR underlay
When to Choose Breathable Membrane
- All new-build pitched roofs (standard practice)
- Full re-roofs on existing buildings
- Loft conversions where ventilation space is limited
- Properties with condensation problems in the loft
- Cost saving by eliminating ventilation products
Related Calculators
Use the Felt and Batten Calculator for material quantities, or the Roof Ventilation Calculator for ventilation sizing.
How We Calculate This
Frequently Asked Questions
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Last updated: April 2026
All calculations are estimates. Verify with your supplier.