Collaboration agrees calculation to measure U-valve allowances for insulation

A simplfied formula has been established to help specifiers to meet Part L (2006) energy efficiency requirements in rain screen construction.

The BRE (Building Research Establishment) and Rockwool collaboration has agreed a calculation to measure U-valve allowances for insulation to include thermal bridging.

The new figures are hoped to help specifiers to meet the regulations, making it significantly easier, more efficient and less expensive.

Tony Richards, technical sales manager of Rockwool, said: “Our new default calculation saves valuable time, money and hassle in an era of stringent industry regulation.”

Previous guides have presumed a default calculation for thermal bridging of rain screen insulation, if the designer had not made the recommended 3D thermal calculations.

The default value currently tends to result in uneconomic thickness of insulation, due to few designers and specifiers performing the complex calculations.

They recommend that an addition of 0.1W/m2K is allowed to the wall value in predicted bridging.

The point fixing must incorporate a 5mm thick thermal break pad and the calculation does not apply to metal rail systems.

Richards said: “In practice, this would mean adding approximately 40mm of Rockwool to a standard 100mm thick insulation slab.”

He added: “We offer a U-value calculation service and always recommend that all calculations are verified by the actual cladding manufacturer, using 3D thermal modelling software.”