U-values, cause a surprising amount of stress.
Usually, someone has asked for a U-value, and there’s a lack of clarity about what it is.
A crucial element of SAP and SBEM calculations, U-values quantify the heat transfer through floors, walls and roofs and openings.
- The amount of heat transfer depends on the thickness and thermal conductivity of each building material in a cross-section of the thermal envelope.
- Part L contains limiting backstop U-value thresholds for all floors, walls, roofs, windows and doors. Low U-values are essential for all domestic projects to meet the Target Fabric Energy Efficiency (TFEE) threshold outlined under Part L1A 2013 as well as the mandatory averaged U-values in Wales now and expected in Part L 2020.
“Usually we can estimate heat loss in a 2D plane without a complex thermal model,” says Brandon Wipperfurth, senior sustainability and energy consultant at Darren Evans.
“The only time we do 3D U-values is for rainscreen cladding systems, or other bespoke walls usually involving abnormal repeating metal punctures through the insulation lines.
“Normal U-values are usually done as part of a SAP calculation, and are included in our service,” he adds.