Wall U-value Comparison in Ireland — Five Systems, the Numbers

Wall U-value comparison for Irish self-builds (W/m²K, lower is better). Blockwork with external insulation: 0.15–0.22. ICF: 0.13–0.20. Timber frame: 0.13–0.18. SIPs: 0.10–0.15. CLT: 0.13–0.18. Part L 2022 backstop is 0.18 W/m²K. BER A1 typically needs 0.13–0.16. Passive House needs 0.10–0.15. Lower U-value = better insulation. Most systems can hit any target with enough insulation; the trade-off is wall thickness and cost. A 200 mm SIP with 150 mm EPS core achieves 0.10; a 300 mm block wall with 100 mm external insulation achieves 0.15. The wall thickness affects the footprint of the house and the cost of the foundation.

TL;DR

• Wall U-values (W/m²K): block 0.15–0.22, ICF 0.13–0.20, timber frame 0.13–0.18, SIPs 0.10–0.15, CLT 0.13–0.18.

• Part L 2022 backstop is 0.18 W/m²K. BER A1 typically needs 0.13–0.16. Passive House needs 0.10–0.15.

• Lower U-value = better insulation. Most systems can hit any target with enough insulation; the trade-off is wall thickness and cost.

When this matters most

You're at wall-system choice stage and need to compare U-values.

When this doesn't apply

You've already specified the wall system.

Frequently asked questions

What is the Part L 2022 wall U-value?

0.18 W/m²K is the backstop. BER A1 typically needs 0.13–0.16. Passive House needs 0.10–0.15.

Which wall system has the lowest U-value?

SIPs, at 0.10 W/m²K with a 200 mm panel. Timber frame and ICF reach 0.13–0.18. Blockwork with external insulation reaches 0.15–0.22.

What is U-value?

A measure of how much heat passes through a material. Lower is better. U-value in W/m²K means watts per square metre per degree Kelvin of temperature difference.

Sources

Building Regulations 2023, TGD-L. https://www.gov.ie/