Bitumen 1F Felt and Breathable Membranes



1F Felt Environmental issues:

  • Bitumen 1F felt becomes sticky enough at 80°C-90°C (temperatures achieved in roofs in strong direct sunlight) for bitumen to be transferred onto bats.
  • Bitumen is made from crude oil, and produces fumes at high temperatures that can give off polycyclic aromatic hydrocarbons (PAH), which have been shown to be human carcinogens
  • Heating properties with an uninsulated 1F felt roof can release up to 10 tonnes of CO2 per year. Replacing 1F felt with a breathable membrane and additional insulation between the rafters can improve thermal performance by up to 87% and reduce CO2 emissions by 57%

1F Felt Construction issues: 

  • Bitumen 1F Felt is not breathable, and to prevent condensation requires a 50mm ventilated airgap beneath it, reducing the space available for insulation – or even preventing it from being used
  • Building regulation requires that the insulation performance of the element should be improved in retro-fitting work. Retro-fitting work where 1F bitumen roofing felt is used to replace a pre-existing breather membrane could contravene building regulations.
  • A roll of Bitumen 1F felt weighs 25kgs, making it necessary to use lifting equipment to get it on to a roof
  • Bitumen 1F Felt degrades over time as the bitumen dries out under heat

Breathable membranes and bats:

Standard breathable membranes are not safe for bats. The nonwoven continuous fibres used in the construction of these products (the fibres are half the width of a human hair) can be broken by bats claws and over time, these continuous fibres can be teased away from the membrane causing a fluffing of the product`s surface, which can cause entanglement. 



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