Use this free online U-value calculator for walls, roofs and floors.

To estimate heat loss and check your build-ups against current UK Building Regulations Part L.

The tool is designed for architects, self-builders, energy consultants and contractors working on new homes, extensions and retrofits.

How to Use the Thomas Studio U-Value Calculator for Walls, Roofs and Floors

The Thomas Studio U-Value Calculator is split into three sections: Wall, Roof and Floor.

For each element:

• Use the drop-down menus to select the material layers, working from the external (cold) face through to the internal (warm) face.
• Enter the thickness of each layer in millimetres.

We’ve included two preset composite frame layers:

• 140 mm PIR insulated timber frame (47 × 140 studs @ 600 mm centres)
• 225 mm decoupled timber frame with full-fill blown Warmcel insulation

These options already allow for the mix of timber and insulation within the stud zone. If you use them, simply enter the appropriate thickness (e.g. 140 or 225 mm) and do not add separate timber or insulation layers for the same zone.

For externally ventilated constructions:

• If you are using a rainscreen cladding system, tick the rainscreen option to apply an improved external surface resistance (Rse) for the sheltered cavity.
• For ventilated warm roofs (tiles/slates or zinc/metal over a ventilated void above PIR), select the appropriate roof ventilation option. Do not include the ventilated void or outer roof covering as separate layers – start your build-up at the outer face of the insulation (or deck if the insulation is between rafters).

Once all layers are added, click “Calculate U-value”. The resulting U-value and total R-value are shown in the element panel and summarised at the bottom of the page, where they are compared against current Building Regulations target / limiting U-values so you can see whether your design meets, exceeds, or falls short of the standards.

For floors:

• Ground-bearing floors (slabs or beam-and-block bearing on the ground) require the floor area (m²) and exposed perimeter (m) so the calculator can apply the ISO 13370 ground-coupled method.
• Suspended floors and beam-and-block over a ventilated void should be modelled using the suspended floor option only – in this case you do not enter area or perimeter.

When you are happy with your results, enter your contact and project details, confirm you agree to data use in line with our Privacy Policy, and then download your U-Value report as a PDF.

We hope you find the Thomas Studio U-Value Calculator a useful tool in designing high-performance, energy-efficient buildings.