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U-Values & Condensation in thatch

Thatch Roof Rafters

U-Values & Condensation in thatch
Modern living under thatch has changed in the last 10 to 15 years, with the introduction of modern central heating, double/secondary glazing, power showers and more home owners wanting fully vaulted ceilings. In addition, the requirements and associated recommendations from Building Control and insurance companies see the requirement for fire barriers and increased levels of insulation to be installed within the roof structure.

All these areas can have an effect on the performance of thatched buildings, therefore all components of the roof structure need to be built into U-Value calculations/reports.

U-Values are expressed in units of watts per degree of temperature difference W/m²K. Overall U-Values will vary according to actual thickness and density of the thatch. For example:

  • 300mm thickness of Water Reed – 0.29 W/m²K
  • 300mm thickness of Long Straw – 0.23 W/m²K

For comparison, the standard in Part L of the Building Regulations (2010) for replacement roof insulation at rafter level is 0.18 W/m²K.

A suitable insulation product to help achieve a U-Value of 0.18 would be Thatchbatts® as they are non-combustible, high density slabs which also offer additional protection in terms of fire resistance.

Vapour Control
It is widely accepted in the construction industry that in addition to sufficient levels of insulation, vapour control layers are required to control vapour and reduce the risk of condensation. A correctly fitted vapour check will also play an important part in the way the building continues to perform in the long term.

Bespoke U-Value & Condensation Risk Analysis reports can be generated for thatched roofs and will take into account the design and construction, type of materials used and location within the country.

See the Thatching Advisory Services website for further information and product details.

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