UK cavity walls · DriTherm 32 / 34 / 37
Knauf U-value calculator
Compare DriTherm slab thicknesses, add your wall layers and save the calculation.
The plaster and masonry values are editable examples, not verified specifications for your wall. Replace them with your project values.
Surface resistances and corrections
Defaults use horizontal heat flow and an exposed outside surface. Wall ties and air-gap corrections are not calculated automatically.
Wall U-value
Total R: — m²K/W
| Layer | Calculated R | Declared R |
|---|
DriTherm 32 / 100 mm: source note
Thermal table: R 3.10; EPD footnote: 3.15. The discrepancy is unresolved. This calculation uses 0.100 / 0.032 = 3.125 m²K/W. Knauf datasheet, page 2.
Plane-layer calculation. Not a compliance certificate. Method and limits.
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Data options
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DriTherm product data
At 100 mm, calculated insulation-layer resistance is 3.125 for DriTherm 32, 2.941 for 34 and 2.703 m²K/W for 37. These are layer values, not whole-wall U-values.
All 16 nominal thickness rows below come from the Knauf August 2025 datasheet, page 2, checked 30 August 2026. No unlisted thickness interpolation, live availability or current-price claim.
| Product | mm | λ W/mK | Declared R | Calculated R | Product code |
|---|---|---|---|---|---|
| DriTherm 32 | 75 | 0.032 | 2.30 | 2.344 | 715827 |
| DriTherm 32 | 85 | 0.032 | 2.65 | 2.656 | 715830 |
| DriTherm 32 | 100 | 0.032 | 3.10* | 3.125 | 715829 |
| DriTherm 32 | 125 | 0.032 | 3.90 | 3.906 | 715828 |
| DriTherm 32 | 150 | 0.032 | 4.65 | 4.688 | 580216 |
| DriTherm 34 | 75 | 0.034 | 2.20 | 2.206 | 715833 |
| DriTherm 34 | 100 | 0.034 | 2.90 | 2.941 | 715832 |
| DriTherm 34 | 125 | 0.034 | 3.65 | 3.676 | 715836 |
| DriTherm 34 | 150 | 0.034 | 4.40 | 4.412 | 715834 |
| DriTherm 37 | 50 | 0.037 | 1.35 | 1.351 | 316650 |
| DriTherm 37 | 65 | 0.037 | 1.75 | 1.757 | 316652 |
| DriTherm 37 | 75 | 0.037 | 2.00 | 2.027 | 316654 |
| DriTherm 37 | 85 | 0.037 | 2.25 | 2.297 | 316656 |
| DriTherm 37 | 100 | 0.037 | 2.70 | 2.703 | 715831 |
| DriTherm 37 | 125 | 0.037 | 3.35 | 3.378 | 316660 |
| DriTherm 37 | 150 | 0.037 | 4.05 | 4.054 | 715835 |
R units: m²K/W. *DriTherm 32 at 100 mm: thermal table 3.10 versus EPD footnote 3.15. The source conflict remains unresolved; calculated R is 3.125. No GWP values are included.
From insulation resistance to wall U-value
Learn to separate a manufacturer's declared layer resistance from the calculated resistance of a complete wall. The tool uses the same plane-layer core as the main U-value calculator.
R_total = Rsi + sum(R_layer) + Rse
U = 1 / R_total + additional correction
Worked example: 100 mm DriTherm 32
The illustrative wall starts with plaster 12.5 mm / 0.25 W/mK, inner leaf 100 mm / 0.20 W/mK, DriTherm 32 at 100 mm / 0.032 W/mK, and outer leaf 102.5 mm / 0.77 W/mK. Only the DriTherm property is taken from the named product source. Other layers are example assumptions, not generic masonry specifications.
Adding Rsi 0.13 and Rse 0.04 gives total R 3.978 m²K/W and U 0.251 W/m²K, with zero additional correction. Calculations retain unrounded intermediate values.
Default surface values are documented in UK government moisture-modelling research, page 12. Plane-conduction arithmetic is checked against the open-source ht conduction reference.
This page does not calculate wall-tie, air-gap or junction corrections, ground-coupled floors, condensation, fire behaviour or installation suitability. Enter a separately established correction where applicable. It does not certify ISO 6946 compliance or Building Regulations approval. Glass mineral wool cavity slabs are not interchangeable with industrial pipe insulation.
Questions about Knauf U-values
What is the difference between DriTherm 32, 34 and 37?
The selected UK datasheet gives conductivity of 0.032, 0.034 and 0.037 W/mK respectively. At the same thickness, the lower conductivity gives greater layer resistance. This is not a comparison of fire, moisture, acoustic or installation performance.
Is this the official Knauf U-value calculator?
No. This is an independent Inzonex calculator using attributed Knauf product data. Knauf does not endorse this page. The selected products are glass mineral wool slabs for full-fill external masonry cavity walls.
Why are there three resistance values for DriTherm 32 at 100 mm?
The August 2025 datasheet thermal table lists R 3.10 m2K/W, while its EPD footnote lists 3.15. Thickness divided by conductivity gives 3.125. The source discrepancy is unresolved; this tool retains both published values and calculates from thickness and conductivity.
Can I use the result for Building Regulations approval?
This page does not establish compliance. It calculates plane-layer resistance from entered values. Wall ties, air gaps, junctions, workmanship, condensation and fire requirements need project-specific assessment. A correction can be entered if established separately.
How can I save and compare walls?
Save up to four walls in this browser, or copy a project link that retains the inputs and comparisons. Excel contains numeric inputs and calculation formulas; PDF provides a readable report. Source CSV and JSON are available separately.
Cite or reuse the table
Inzonex (2026). DriTherm 32/34/37: 16 UK thickness and thermal-property rows, version knauf-dritherm-2026-08-30.1. Transcribed from Knauf Insulation's August 2025 datasheet, page 2; calculations by Inzonex.
Original selection and calculations may be reused with attribution to Inzonex. Manufacturer facts must retain Knauf source attribution. No rights are granted over the upstream PDF, images, logos, trademarks or program code.
No manufacturer endorsement. These are manufacturer-published properties and original calculations, not first-party laboratory measurements.
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