WTA U-Value & Condensation Risk Calculator v1.7

Construction Details

Element Orientation:

Exposure:

Add Material Layer: (add from inside to outside)

Material λ (W/mK) t (mm) μ R (m²K/W) Action

Heterogeneous Layer (Studs/Frame with Insulation) Enable for timber frame or steel frame walls with studs running through insulation (BS EN ISO 6946:2017 Clause 8)

⚠ Important:

Enable this ONLY when adding the insulation layer (not plasterboard, sheathing, or cladding)
The insulation thickness must be ≤ the stud depth
Example: 140mm mineral wool with 140mm deep studs
The studs run through the full depth of the insulation layer

Stud/Frame Configuration

Frame Type:

Stud Width (mm): Width perpendicular to wall (affects thermal bridging proportion)

Stud Depth (mm): Depth parallel to wall (must be ≥ insulation thickness)

Stud Spacing (mm centres):

Stud Material λ (W/mK): Timber softwood: 0.13 | Steel: 50 | Timber hardwood: 0.18

Stud Proportion (fraction of area): Automatically calculated: Stud Width / Spacing

How it works:

The layer will be calculated using the upper/lower limit method (BS EN ISO 6946:2017). The material selected above is the insulation between studs. The studs create a thermal bridge, reducing overall performance.

Construction Layers (Inside to Outside)

Material	λ (W/mK)	t (mm)	R (m²K/W)	μ	Reorder	Action
Internal Surface	-	-	0.13	-	-	-
External Surface	-	-	0.04	-	-	-

Environmental Conditions

Internal Temperature (°C):

External Temperature (°C):

Internal Relative Humidity (%):

External Relative Humidity (%):

Required Insulation Calculator

Target U-Value (W/m²K):

Layer to Vary:

Thermal Bridging Corrections (BR 443:2019)

Add thermal bridging corrections to calculate effective U-value (U_eff = U + ΔU)

Enable Thermal Bridging Corrections

Results

Total Thermal Resistance (R_total): 0.00 m²K/W

U-Value (Fabric Only): 0.00 W/m²K

Building Regulations Compliance: -

Mould Risk Assessment (BS 5250:2021)

Surface Temperature Factor (f_Rsi): -

Internal Surface Temperature: -

Condensation Risk Analysis (Glaser Method - BS EN ISO 13788:2012)

Vapour Pressure Profile at Interfaces

Interface	T (°C)	P_sat (Pa)	P_v (Pa)	Risk

WTA U-Value & Condensation Calculator v1.7