Upgrade · Fabric · the walls · BER file 26 Sep 2026 · checked 8 Sep 2026
Internal wall insulation: 22% of homes sold or let have solid stone or brick walls
Internal wall insulation is insulated board fixed to the inside of every outside wall, then plastered and painted. 22% of homes sold or let whose wall type is known have solid stone or brick walls, the kind usually lined from inside (SEAI BER file, 26 Sep 2026). Insulating the walls moves the typical home's rating 46.7 points, more than windows or the attic. SEAI's typical price for a semi-detached house is €9,843 and the grant pays €3,500.
A cut-stone cottage in Geashill, Co. Offaly. Solid walls like these are usually insulated from the inside, so the front stays as it is.
Semi-detached cottage in Geashill, County Offaly · A.-K. D. · CC0 1.0 (public domain dedication)
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22%
Of homes sold or let with a known wall type have solid stone or brick walls
168,097 certificates with the wall type · BER file 26 Sep 2026
BER assessment46.7
Points on the BER scale it adds, for the typical home it applies to
kWh/m²/yr · research lane, BER file 26 Sep 2026
Our model63%
Older A- and B-rated houses with insulated walls. Rated C to E: 25%
Walls U ≤ 0.37 · built before 2011 · BER file 26 Sep 2026
BER assessment36%
Of SEAI's typical semi-D price paid by the grant
€3,500 of €9,843 · SEAI H1 2026
Published figureUpdated · grants checked · BER file · prices SEAI H1 2026 · How we know · Corrections
Where this sits · the heat chain
Most heat leaves through the walls, roof, floor and windows. Fix these first and the heating has less to replace.
- Fabricwalls, roof, floor, windows
- Airdraughts and ventilation
- Heatheat pump or boiler, radiators, controls
- Usebills, comfort, the BER
- The idea behind itFollow the heat
- You are hereInternal wall insulation
- Next questionHow much does SEAI pay towards internal wall insulation?
A third of the heat a semi-detached house built 1971–80 loses goes through its walls
Where a typical semi-detached house built 1971–80 loses its heat. This job acts on the walls, pin 3. BER assessment
A third of the heat a semi-detached house built 1971–80 loses goes through its walls
Walls 32%, windows 18%, air 17%, floor 11%, roof 10%, junctions 10%, doors 2%.
A section through a semi-detached house built 1971–80, front to back. Each arrow's width is that element's share of the heat the house loses for every degree it is warmer inside than out, from the insulation values and areas on 4,498 BER certificates for homes sold or let, assessed 2022–26. The median wall lets through 1.10 watts per square metre per degree, the roof 0.40 and the windows 2.80; the median heat loss indicator is 3.15, over the heat pump line of 2.3. Air (draughts, vents and open chimneys) isn't measured on a BER: it is what's left once the six measured elements are subtracted, so it carries the most uncertainty. The numbered pins show where each of the jobs acts, in the order they're usually done.
EstimateAir is estimated as the remainder (heat loss indicator × floor area, less walls, roof, floor, windows, doors and thermal bridging). Shares are rounded to sum to 100.
Sources: SEAI BER Research Tool, 8 Sep 2026 · Certificates for a sale or private letting assessed 2022–26 with a heat loss indicator: semi-detached house built 1971–80, 4,498 certificates
The numbers
| Element | Share of heat loss | Median |
|---|---|---|
| Walls | 32.0% | 1.10 W per m² per degree, 89 m² |
| Windows | 17.6% | 2.80 W per m² per degree, 21 m² |
| Air (estimated) | 16.8% | the remainder |
| Floor | 10.7% | 0.64 W per m² per degree, 60 m² |
| Roof | 10.5% | 0.40 W per m² per degree, 61 m² |
| Junctions | 10.2% | cold bridges at joins |
| Doors | 2.2% | 2.95 W per m² per degree, 2 m² |
On its own, internal wall insulation moves a rating 46.7 points; a heat pump, 93
What one job on its own does to the typical home's rating, where the job applies. One letter on the new scale is 50 points. Our model
Internal wall insulation: 46.7 points on its own, where it applies
Where the job applies, the median gain is 93 kilowatt-hours per square metre a year for a heat pump, 60.7 for solar panels, 46.7 for wall insulation and 10.4 for new windows. One letter on the new scale is 50.
Each bar is the median improvement to a home's BER from that one job on its own, among homes sold or let where the job applies, worked out on each certificate's own figures. A heat pump moves the rating nearly two letters in the D to F range; attic insulation, draught-stripping and blocking chimneys barely move the rating on their own. The bracket shows one letter's width (50, for D, E and F). The bars are not additive.
EstimateOur model: the research lane's one-job recalculation on each certificate's own figures (BER file of 26 Sep 2026, not the site's 8 Sep file). It matches SEAI’s published heat loss to a median ratio of 1.00 and uses the electricity factor in force on each certificate’s date.
Sources: fixmyber research lane, research/ber/s4_thresholds.py, 26 Sep 2026
The numbers
| Job | Median gain, kWh per m² a year |
|---|---|
| Heat pump | 93 |
| Solar panels | 60.7 |
| Wall insulation | 46.7 |
| New windows | 10.4 |
| Attic insulation | 6.1 |
| Blocking chimneys | 2.4 |
| Draught-stripping | 0.4 |
Older A- and B-rated houses are 2 times as likely to have insulated walls
What older houses rated A or B have, against those rated C to E. BER assessment
63% of older A- and B-rated houses have insulated walls; 25% of those rated C to E
The biggest gap is insulated walls: 63% against 25%.
- Insulated walls. Rated A or B: 63%. Rated C to E: 25%.
- Solar panels. Rated A or B: 47%. Rated C to E: 10%.
- An insulated floor. Rated A or B: 74%. Rated C to E: 40%.
- Attic at the grant standard. Rated A or B: 33%. Rated C to E: 19%.
- High-performance windows. Rated A or B: 26%. Rated C to E: 3.8%.
- A heat pump. Rated A or B: 21%. Rated C to E: 0.2%.
- Solar water heating. Rated A or B: 7.8%. Rated C to E: 2.2%.
- Mechanical ventilation. Rated A or B: 7.2%. Rated C to E: 0.9%.
Each pair of bars is the share of houses built before 2011 that have the upgrade, among those rated A or B (dark) and those rated C to E (grey), from every certificate issued 2019-2026. Insulated walls: 62.8% against 25.4%. It shows what the better-rated houses have, not proof of what got them there: newer houses are more often A or B and were built with some of these.
Sources: SEAI BER Research Tool, every existing-home certificate 2019–26 for houses built before 2011 (440,689 certificates), 26 Sep 2026 · Insulated walls: Walls U ≤ 0.37 · Solar panels: Solar PV · An insulated floor: Floor U ≤ 0.45 · Attic at the grant standard: Roof U ≤ 0.16 · High-performance windows: Windows U ≤ 1.6 · A heat pump: Heat pump · Solar water heating: Solar water · Mechanical ventilation: Mechanical ventilation
The numbers
| Upgrade | Rated A or B | Rated C to E |
|---|---|---|
| Insulated walls | 62.8% | 25.4% |
| Solar panels | 46.9% | 9.7% |
| An insulated floor | 73.6% | 39.9% |
| Attic at the grant standard | 33.3% | 19.3% |
| High-performance windows | 26.1% | 3.8% |
| A heat pump | 20.9% | 0.2% |
| Solar water heating | 7.8% | 2.2% |
| Mechanical ventilation | 7.2% | 0.9% |
What internal wall insulation is, and what it's like to live through
Internal wall insulation is insulated board fixed to the inside of every outside wall, then plastered and painted. The house looks the same from the road and warms up faster inside.
What it is
The plaster comes off the outside walls, insulated boards go on, and a vapour control layer, plasterboard, a skim and paint go over them. Skirtings, sockets and radiators come off first and go back on last. It is done one room at a time, so you can usually stay in the house — but the room being worked on is out of use, and SEAI describe the work as disruptive and dusty.
It's the answer for a wall with no cavity to fill, and for a house where wrapping the outside is out of the question: a protected structure, a terrace where your wall isn't yours to change, or a front elevation nobody wants rendered over.
The gain is fast heat. A dry-lined room warms in minutes, because you are only heating the air and the boards, not the whole mass of stone or block behind them.
Compared with wrapping the house outside
| Internal (dry lining) | External (the wrap) | |
|---|---|---|
| Typical cost, semi | €9,843 | €23,219 |
| Grant, semi | €3,500 | see the external page |
| The look of the house | unchanged outside | new render, new colour |
| Room size | a little smaller in every room | unchanged |
| Living through it | rooms cleared one at a time, dust | you stay put; scaffolding outside |
| How the room feels | heats quickly, cools quickly | slow and steady, holds heat for hours |
| Planning permission | never needed | sometimes — ask the council |
| Chimney breasts and party walls | awkward corners, easy to leave a gap | not an issue |
Grant €1,500 to €4,500 by house type, €3,500 semi-detached. SEAI median cost €9,843 (semi), against €23,219 external. U target for grant-aided dry lining 0.27 W/m²K. Whole-surface solution required — every external wall. Planning permission is not required for internal insulation. Amounts verified 2026-10-03.
Where the saving comes from
A solid wall loses heat straight through it, and the thicker and denser the wall the more heat it holds on the way. Insulation on the inside face puts a barrier between the room and that mass. Heat from the radiator now stays in the air and in the surfaces you touch, instead of soaking into the block and away.
The trade-off is that the wall behind is colder than it used to be. That's why the vapour layer matters, and why the fiddly corners — where a chimney breast, an internal wall or a floor meets an outside wall — are where a bad job goes wrong. Warm damp air reaching a cold surface makes mould. A good contractor insulates the returns at those junctions for exactly that reason.
Modelled wall heat loss for that group of homes: U 0.60 → 0.37 W/m²K. Of the 212 kinds of home we publish a number for, 98 have dry lining in the cheapest grant-eligible route to a B; external wall insulation appears in 0 of them. That is a cost ranking inside the model, not advice about any one wall. detached|1970-1989|D|oil: cost p50 €36,848, grant €22,300, you pay p25–p75 €7,300–€21,700, saving €1,797/yr, payback 4.7–12.4 yrs, n=23,707, confidence 0.9
Questions people ask
- How much room do I lose?
- SEAI put it as a small amount of space in each room, and that's fair — it is the thickness of the board plus the plasterboard over it. You notice it at window reveals and in a small bathroom more than in a sitting room. Deep window boards and a slightly narrower hall are the visible cost of the job.
- What has to come off the walls?
- Skirting boards, sockets and switches, radiators, and anything screwed to an outside wall — shelves, a wall-hung television, kitchen units. SEAI describe the work as disruptive and dusty and say the rooms have to be cleared. Curtain poles and pictures go back on afterwards, but not in the same holes.
- Is it worth doing if I'm redecorating anyway?
- That's the best time to do it. The plaster is coming off and the room is being painted either way, so the extra work is the boards and the second skim. SEAI make the same point. If the room is fine and you'd be wrecking it for no other reason, wrapping the house outside may suit you better.
How we know
- Ratings: From SEAI's BER Research Tool (files of 8 Sep 2026 and 26 Sep 2026): certificates for homes sold or let, and every certificate for houses built before 2011. A BER is a standard calculation, not a meter reading.
- One job at a time: Our model reworks each certificate with one job done, on the BER file of 26 Sep 2026. Its heat loss matches SEAI's own figure to a median ratio of 1.00. A group figure, not an assessment of your house.
- Grants and prices: SEAI's grant pages, read on the dates shown, and SEAI's median costs of individual upgrades for 2025. A median is a middle price, not a quote.
Sources
seai.ie · insulation · seai.ie · wall insulation · seai.ie · Median costs of individual energy upgrades
Found a mistake? Every fix is dated on Corrections. Method in full: How we know.
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Updated · grants checked · BER file · prices SEAI H1 2026 · How we know · Corrections