U-value simulator: Getting the right insulation combination

U-value simulator

A revamped U-value tool from Actis will help specifiers choose correct insulation quickly and easily

A revamped tool aimed at helping specifiers choose the right combination of insulation materials for the desired U-value has an added feature to help those involved in roof refurb projects.

One of the new features of the upgraded Actis Hybrid online U-value simulator is an option for 400mm centres for roof refurb projects in addition to the default 600mm setting.

Another added functionality was inspired by the rising popularity of reflective breather membranes in timber frame wall applications.

Actis technical director Thomas Wiedmer, explained: “The rafters in most older roofs have 400mm centres rather than the 600mm centres found in new builds. This meant the original simulator made calculations difficult for builders carrying out refurbishment projects.”

The simulator shows how to achieve a U-value of 0.18 using 105mm Hybris and insulating breather membrane H Control Hybrid based on 400mm centres. The desired thermal efficiency can be achieved without the need to remove the roof tiles – something which would be required if the builder were to install a reflective insulating breather membrane such as Boost RHybrid Roof.

The simulator will offer a different solution for a builder working on a new build pitched roof with its wider, 600mm, rafter centres.

‘Ensuring thermal continuity and airtightness’

“In these cases, the target U-value, as long as it is below the limiting U-value, can vary,” said Wiedmer.

“It depends on the overall energy efficiency specification of the building (the SAP specification); that is, the overall U-value mix and the building technology used.

“Hybris plus H Control Hybrid or, alternatively, Hybris and Boost R Hybrid Roof are popular options here. Both can deliver a very good target U-value of 0.13. The benefits of using H Control Hybrid include its ability to counteract thermal bridging because it is flexible and can be squeezed into gaps and wrapped around corners to ensure that there is thermal continuity and airtightness.”

With reflective breather membranes now the norm in the timber frame market, the creators have added an option for users to choose from a standard breather membrane, a reflective membrane or Actis Boost R Hybrid in the timber frame wall section of the simulator.

An example for a timber frame wall would see an installer wanting to achieve a U-value of 0.16 use 105mm Hybris with H Control Hybrid and a generic reflective breather membrane. Those happy with a U-value of 0.22 might decide on 125mm Hybris with a generic reflective breather membrane.


Actis Insulation

Tel: 01249 462888


Simulator users can choose 400mm centres for roof refurb projects. This shows a 0.18 U-value using 105mm Hybris and H Control Hybrid.


 Please note: this is a commercial profile.


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