Constructing an energy efficient building: TFEE

Constructing an energy efficient building: TFEE

Meeting the target fabric energy efficiency (TFEE) is crucial when aiming to construct energy-efficient buildings. It's one of the key factors to consider when it comes to SAP calculations for new builds and you only have one chance to get it right.


The limit assigned to floors by the regulations is 0.25 W/m2K as an absolute maximum. Achieving less than this with floors is fairly simple, especially when using a quality PIR insulation board. However, good values are also possible when it comes to screed and concrete, making floors a good area to make up for areas that are lacking.


Roofs are required to have a UValue of no more than 0.20 W/m2K, but like with floors, it's relatively simple to attain a figure lower than this. Using PIR boards of around 100mm slotted in between rafters and mineral wool on plane roofs are very effective ways of lowering this number below the required level.


For the best results when fitting windows, choose those with an argon filling that are also triple glazed. Double glazing often falls short of the required value of 1.4 W/m2K.


External walls should have a U-Value of around 0.18 W/m2K, which is very difficult to achieve, especially when aiming for a 300mm structure involving bricks, cavity and block. The cavity size can be reduced to 125mm, or this value can be made up in other areas, so don't worry if your walls are an area that fall slightly short.

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