Mayo · checked 29 October 2026
Cavity wall insulation in Mayo
The grant is national. The walls in Mayo aren't. What SEAI's BER register and Census 2022 say about homes in Castlebar, Ballina and Westport, and what it means for filling the cavity.
Figures checked against seai.ie on 29 October 2026.
cavitywallinsulation.ie is not SEAI or a government body and does not award grants.
Call for a price
- €1,800 detached, €850 mid-terrace, €700 apartment
- About €285 left to pay on a semi-D
- One SEAI-registered contractor rings you
On Mayo's BER certificates for homes built before 2011, 6% record an empty cavity wall, the job this grant pays for, and 40% a cavity that's only part insulated, against 4.5% and 28% across Ireland. The median detached house here has 111 m² of outside wall on its BER, against 128 m² nationally.
The grant itself is the same in every county: €700 to €1,800 by home type, or €900 to €2,300 at the higher rate (seai.ie, checked 29 October 2026). We pass your request to one SEAI-registered contractor who covers Mayo.
What stands out about Mayo homes
SEAI pays the same grant in every county. The walls aren't the same. Against the national figures, these are the things that stand out in Mayo, from Castlebar, Ballina and Westport to the rest of the county:
- 6% of Mayo's pre-2011 BERs record an empty cavity wall, against 4.5% nationally, the 3rd highest of the 26 counties. That's a cavity wall with no insulation in it, U-value 1.0 or worse: the job this grant was made for.
- Walls here are smaller than average. The median Mayo detached house has 111 m² of outside wall on its BER, against 128 m² nationally. The grant is fixed, so it covers more of a smaller job.
- Detached houses are 70% of Mayo homes, against 41% nationally (Census 2022). They get the top cavity grant, €1,800, and have the most outside wall to fill.
- 40% of Mayo's pre-2011 BERs record a cavity that's only part insulated, against 28% nationally, the 3rd highest of the 26 counties. That's usually boards fitted when the house was built. SEAI's standards allow the gap behind rigid boards to be filled if at least 40 mm is clear everywhere, but not a top-up over mineral wool (SEAI technical standards).
Mayo and Ireland compared
| Mayo | Ireland | Rank of 26 | |
|---|---|---|---|
| Households, Census 2022 | 51,996 | 1,836,728 | |
| Built before 2011, inside the grant | 91% | 90% | |
| Built 2011 or later | 6% | 8% | 14th |
| Detached houses | 70% | 41% | 3rd |
| BERs for homes built before 2011 | 21,451 | 751,700 | |
| Empty cavity wall | 6% | 4.5% | 3rd |
| Cavity, part insulated | 40% | 28% | 3rd |
| Hollow block | 0.4% | 4.2% | 23rd |
| Rated E, F or G | 29% | 25% | 5th |
| BERs for grant claims per 1,000 pre-2011 homes, 2026 | 44.5 | 42.1 | 15th |
| Heating degree days a year | 2,028 | 2,079 | 13th |
Households and year built: CSO Census 2022 (table F2007A), councils in the county added together. BER figures: SEAI BER Research Tool, the full public file downloaded 29 October 2026: 751,700 certificates for existing homes built before 2011, leaving out the BERs done for grant claims. Degree days near Castlebar: our sum from Met Éireann's 1991–2020 grid. Ranks are ours, 1st being the highest.
Next door, the share of pre-2011 BERs with an empty cavity wall: Sligo 3.5%, Roscommon 5%, Galway 5.4%. All 26 counties side by side.
The walls on Mayo BERs
The grant only pays where a cavity can be filled. SEAI's register holds 21,451 BER certificates for Mayo homes built before 2011, leaving out the ones done for grant claims. Their main wall:
| Main wall | Mayo | Ireland | For the grant |
|---|---|---|---|
| Empty cavity | 6% | 4.5% | The job this grant pays for |
| Cavity, part insulated | 40% | 28% | A survey decides: the 40 mm rule |
| Filled cavity | 23% | 16% | Done. Second measure is internal or external |
| Hollow block | 0.4% | 4.2% | Can't be pumped |
| Solid stone, brick or concrete | 14% | 14% | No cavity: internal or external |
| Timber frame | 3% | 6% | Can't be cavity insulated |
| Other or not recorded | 14% | 27% |
Empty cavity: a 300 or 425 mm cavity wall with a U-value of 1.0 or more. Source: SEAI's BER register, as above. Our count.
13% of the Mayo cavity walls on those certificates have no insulation at all, against 14% nationally. Hollow block, solid and timber frame walls, 17% of Mayo's certificates against 24% nationally, can't take a cavity fill: SEAI's standards say cavity hollow block walls are not suitable and timber frame homes cannot be cavity insulated (SEAI technical standards). For those the grant routes are internal or external insulation, and our sister site covers external wall insulation in Mayo.
The size of the job is the wall. Of Mayo houses built before 2011, the commonest type is the detached house (Census 2022). On BERs the median detached house has 111 m² of outside wall, against 128 m² nationally, so the fixed grant covers more of the job. SEAI publishes its median costs nationally, not by county.
| Home type | Outside wall, Mayo | Ireland |
|---|---|---|
| Detached house | 111 m² | 128 m² |
| Semi-D | 94 m² | 91 m² |
| End of terrace | 86 m² | 85 m² |
| Mid-terrace | 51 m² | 48 m² |
| Apartment | 49 m² | 43 m² |
Median wall area recorded on BER certificates for Mayo homes built before 2011: SEAI's BER register, as above. Our medians.
The only way to know your own wall is a survey: a small drilled hole and a borescope on each elevation, which SEAI's standards require before any fill (SEAI technical standards). Is my house suitable? has the checks you can do yourself first.
Heating, weather and grant claims in Mayo
The grant doesn't depend on the fuel, but the fuel decides what an empty cavity costs you each winter, and what the installer has to check. 61% of Mayo households heat mainly with oil (CSO Census 2022). An oil boiler needs its combustion air supply and flue kept clear, and the flue tested after pumping, as SEAI's standards require (SEAI technical standards).
| Main central heating | Mayo | Ireland |
|---|---|---|
| Oil | 61% | 39% |
| Natural gas | 3% | 33% |
| Electricity | 8% | 12% |
| Coal, peat or wood | 22% | 9% |
Share of all households, including those that didn't state a fuel: CSO Census 2022, table SAP2022T6T5CTY.
Castlebar has about 2,028 heating degree days a year on Met Éireann's 1991–2020 averages, against 2,079 for Ireland (our sum, base 15.5°C). The heat a wall loses rises in step with that number. 29% of Mayo's pre-2011 BERs are rated E, F or G, against 25% nationally (SEAI's BER register).
Every SEAI home grant needs a BER after the work, so the BERs done for grant claims track finished grant jobs of every kind, walls included. In Mayo there were 1,614 in 2024, 2,034 in 2025 and 2,118 in 2026 up to 29 October: 44.5 per 1,000 homes built before 2011, against 42.1 nationally (SEAI's BER register).
The cavity wall grant by home type
The grant is the same in Mayo as in every other county: a fixed amount by home type, whatever the contractor charges. Homeowners on a qualifying welfare payment, and homes in an active HAP tenancy or RAS arrangement, get the higher rate.
| Home type | Standard grant | Higher rate: welfare, HAP, RAS |
|---|---|---|
| Detached house | €1,800 | €2,300 |
| Semi-D or end of terrace | €1,300 | €1,700 |
| Mid-terrace | €850 | €1,100 |
| Apartment | €700 | €900 |
Source: seai.ie wall insulation page, checked 29 October 2026.
What's left after the grant, on SEAI's national median costs for January to June 2026. SEAI publishes no Mayo median, and we don't invent one:
| Home type | Median installed cost | SEAI grant | Typical cost after grant |
|---|---|---|---|
| Detached house | €2,350 | €1,800 | €550 |
| Semi-D or end of terrace | €1,585 | €1,300 | €285 |
| Mid-terrace | €1,250 | €850 | €400 |
| Apartment | €1,036 | €700 | €336 |
Costs: SEAI median costs, January to June 2026, from SEAI's median costs PDF (a sample of 23,412 completed upgrades; the cost each contractor submitted to SEAI at grant payment; VAT status not stated on the PDF), read 29 October 2026. Grants: seai.ie wall insulation page, checked 29 October 2026. One Irish cost guide gives €7.50 to €13 per m² including VAT (ShamFix, 31 July 2026).
- A home built and occupied before 31 December 2010, with an MPRN
- All external walls fully insulated: partial insulation isn't eligible
- An SEAI-registered contractor, and SEAI's grant offer before work starts
- An installer approved by NSAI for the system used
Two national registers, both searchable: SEAI's register of contractors, which the grant requires, and NSAI's register of cavity wall insulation installers, which SEAI's standards require for the system used. The rules in full: cavity wall insulation grant, cost, the job step by step and which wall grant fits.
FAQ
Mayo questions
Is the cavity wall grant different in Mayo?
No. SEAI pays the same fixed amounts in every county: €1,300 for a semi-D and €1,800 for a detached house, with higher rates for qualifying welfare recipients and HAP or RAS homes. What differs is the walls: 6% of Mayo's pre-2011 BERs record an empty cavity, against 4.5% nationally.
How many Mayo homes have an empty cavity wall?
6% of BER certificates for Mayo homes built before 2011 record an empty cavity with no insulation, the 3rd highest share of the 26 counties. Another 40% record a cavity that's part insulated, which a borescope survey checks against the 40 mm rule.
Can every Mayo house with block walls be pumped?
No. 0.4% of Mayo's pre-2011 BERs record hollow block and 3% timber frame, and SEAI's standards rule out a cavity fill in both. A survey with a small drilled hole and a borescope tells you which wall you have.
How many Mayo homes are too new for the grant?
Census 2022 counted 3,325 Mayo households in homes built in 2011 or later, 6% of the total. SEAI's wall grants are only for homes built and occupied before 31 December 2010.
Who will ring me in Mayo?
One SEAI-registered contractor who covers Mayo. They survey the walls, check the cavity with a borescope and give you a written price with VAT. Nothing is booked until you say yes, and SEAI approves the grant before any work starts.
Your grant
Your cavity wall grant in 3 taps
Tap your home type, when it was built and any earlier wall grant. Your SEAI grant shows as you go. Then leave your number and one SEAI-registered contractor who covers your area rings you with a price.
Where these numbers come from (9 public sources, checked 29 October 2026)
- SEAI wall insulation grant page
- SEAI Domestic Technical Standards and Specifications, v4.0
- CSO Census 2022, households by type and year built
- SEAI BER Research Tool (public BER file)
- Met Éireann 1991–2020 averages
- CSO Census 2022, central heating by county
- SEAI median costs of individual upgrades, Jan–Jun 2026
- SEAI's register of contractors
- NSAI's register of cavity wall insulation installers
Sources (1)
Prices and facts on this page were checked against these published pages. We are not connected to these businesses.
- ShamFix: shamfix.ie