External Insulation in Ireland — The EWI Decision for Blockwork, BER, and Thermal Bridging
On this page
External insulation (EWI): 50–150 mm on the outside of the wall. Eliminates thermal bridges. Adds 5–15% to wall cost.
External insulation (EWI) is insulation on the outside of the wall, typically fixed with adhesive and mechanical fixings, then rendered or clad. 50–150 mm. Most Irish self-builds on blockwork use 50–100 mm of EWI as part of the wall build-up. 100 mm hits 0.13 W/m²K. EWI eliminates thermal bridges at the floor and roof junctions (the points where the wall meets the floor or roof, which can be 30–50% of the wall's heat loss if uninsulated). Adds 5–15% to the wall cost. Saves 10–20% on heating demand. Eliminates cold bridges that can cause condensation and mould. The render or cladding is fixed to the EWI; the EWI is fixed to the wall. Standard build-up: 100 mm block inner leaf, 50 mm cavity, 100 mm block outer leaf, 100 mm EWI, render finish.
TL;DR
External insulation (EWI): 50–150 mm of insulation on the outside of the wall. Eliminates thermal bridges at the floor and roof junctions.
Most Irish self-builds on blockwork use 50–100 mm of EWI as part of the wall build-up. 100 mm hits 0.13 W/m²K.
Adds 5–15% to the wall cost. Saves 10–20% on heating demand. Eliminates cold bridges that can cause condensation and mould.
When this matters most
You're specifying the wall build-up.
When this doesn't apply
Walls are built and insulated.
Frequently asked questions
How much does external insulation cost in Ireland?
€80–€140/m² installed (EWI plus render). For a 150 m² house with ~200 m² of wall: €16,000–€28,000. Adds 5–15% to the wall cost but eliminates thermal bridges.
What is the U-value of external insulation?
Depends on the thickness. 50 mm of EPS on a block wall achieves 0.30 W/m²K (poor). 100 mm of PIR achieves 0.13 W/m²K (BER A1). 150 mm of EPS achieves 0.15 W/m²K.
What is a thermal bridge?
A point in the building envelope where heat passes through more easily than the surrounding area. Common at floor-wall junctions, roof-wall junctions, and around windows. Uninsulated thermal bridges can be 30–50% of the wall's heat loss.
Sources
Building Regulations 2023, TGD-L. https://www.gov.ie/
Frequently asked questions
How much does external insulation cost in Ireland?
€80–€140/m² installed (EWI plus render). For a 150 m² house with ~200 m² of wall: €16,000–€28,000. Adds 5–15% to the wall cost but eliminates thermal bridges.
What is the U-value of external insulation?
Depends on the thickness. 50 mm of EPS on a block wall achieves 0.30 W/m²K (poor). 100 mm of PIR achieves 0.13 W/m²K (BER A1). 150 mm of EPS achieves 0.15 W/m²K.
What is a thermal bridge?
A point in the building envelope where heat passes through more easily than the surrounding area. Common at floor-wall junctions, roof-wall junctions, and around windows. Uninsulated thermal bridges can be 30–50% of the wall's heat loss.
When this matters most
You're specifying the wall build-up.
When this doesn't apply
Walls are built and insulated.
Where to go next
Next decision
The next step in your build sequence.