Measuring your walls for external insulation
Measure each outside wall's length and its height to the eaves, multiply, and add the triangle of each gable (half the width times the height from the eaves to the ridge). That's the gross wall. Take away the windows and doors for the net wall. Party walls with next door don't count.
A tape, a notebook and ten minutes: your wall area, gross and net.
Free, no obligation. One registered contractor prices it, not five.
- 91 m²outside wall on a typical semi-D
- 128 m²on a typical detached house
- ½ × w × hfor each gable triangle
- Netless windows and doors
Step by step
- List the outside walls. Front, back, gables, extensions and porches. Leave out walls shared with next door.
- Length × height for each, to the eaves. Count the bricks or courses if you can't reach: a brick course is about 75 mm.
- Add the gables: half the width × the height from the eaves to the ridge.
- Take off the openings: width × height of each window and door. That's your net wall.
- Compare: the typical outside wall for your type is in the table below.
Typical outside wall by type
| House | A quarter are under | Median | A quarter are over |
|---|---|---|---|
| Detached | 96 m² | 128 m² | 169 m² |
| Semi-detached | 80 m² | 91 m² | 104 m² |
| End of terrace | 76 m² | 85 m² | 100 m² |
| Mid-terrace | 39 m² | 48 m² | 65 m² |
| Apartment | 29 m² | 43 m² | 58 m² |
Net outside wall on the BER register, homes built before 2011.
Your grant against your walls
Four quick taps. You see your grant, your wall, what a job that size typically costs and what's left. Your number is only asked for at the end, if you want a price.
An average semi-detached house: about 91 m² of outside wall, a typical job of about €23,200, the €6,000 grant, so about €17,200 left to pay.
How this is worked out
The grant is SEAI's fixed amount for your house type. The wall area is the median outside wall on the BER register for homes of your type built before 2011, or the smaller or larger quarter if you picked those. The typical job is what grant-funded external insulation typically costs for your house type, scaled to that wall. Your contractor prices your house after a look: it's a guide to plan with, never a quote. SEAI decides every grant.
Questions people ask
How do I work out my wall area for external insulation?
Measure each outside wall's length and its height to the eaves, multiply, and add the triangle of each gable (half the width times the height from the eaves to the ridge). That's the gross wall. Take away the windows and doors for the net wall. Party walls with next door don't count.
Do windows count in the wall area?
Take them off for the net wall. Contractors still price the reveals and sills around each one.
What's a typical wall area for a semi-D?
About 91 m² of net outside wall; a quarter are under 80 m² and a quarter over 104 m².
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Your grant against your walls
Four taps to your grant, your wall and what's left. Then, if you want, one SEAI-registered external insulation contractor who covers your county rings with a price.