Cavity wall insulation is the cheapest and fastest insulation upgrade there is, usually one day and often under €1,000 to you after the grant. The catch is that a large share of Irish houses do not have a fillable cavity at all, and a smaller share have one that should be left alone.
| Upgrade | Apartment | Mid-terrace | Semi-D / end | Detached |
|---|---|---|---|---|
| Cavity wall insulation | €700 | €850 | €1,300 | €1,800 |
| Cavity wall, qualifying welfare payment | €900 | €1,100 | €1,700 | €2,300 |
SEAI amounts current at August 2026. Cavity rates were increased on 3 February 2026 and the welfare rate was added on 2 March 2026.
€700 for an apartment, €850 mid-terrace, €1,300 semi-detached or end of terrace, €1,800 detached. If you are on a qualifying welfare payment the amounts rise to €900, €1,100, €1,700 and €2,300.
These went up in February 2026 to reflect what the work actually costs now, so if you priced this in 2023 and parked it, price it again.
On most semi-detached houses the grant covers a very large share of the job. That is unusual among the SEAI grants and it is the main reason cavity fill is normally the first thing to do, not the last.
This is where most Irish homeowners get stopped, and almost nobody says it out loud. A great many Irish houses built from the 1950s through the 1970s are hollow concrete block, not cavity block. Hollow block walls look like they have a void because they do, but it is inside the block, not between two leaves. Bonded bead systems are not approved for masonry cavity block construction, so those walls cannot be pumped. Neither can timber frame or steel frame.
Older houses, roughly pre 1940, are usually solid stone or solid brick with no cavity at all. Houses built from the late 1970s onward are usually genuine cavity construction, and houses from the late 1990s onward may already have partial fill insulation boards in the cavity, which rules out bead fill.
There is only one way to know for certain, and it is quick. A borescope survey. The installer drills a small hole, puts a camera in and looks. Any competent contractor will do this before quoting and it takes minutes. If somebody quotes you for cavity fill without ever looking inside the wall, that tells you what you need to know about them.
The cavity also has to be at least 50mm wide across the whole wall for most approved systems, and clear of debris. If your house turns out not to suit, internal dry lining and external wall insulation are the two routes left.
Certified installers work to a pre-installation survey with a defined list of conditions that make a wall unsuitable. It is worth knowing that list, because the person telling you your wall is fine is usually the person selling you the fill.
A wall is classed as unsuitable if the inner leaf shows, or has shown, evidence of water penetration that has not been corrected. The outer leaf must be free of cracks, defective mortar, damaged render and spalled brick. Gutters and downpipes must be working. Sills and copings must actually throw water clear of the wall, because water sitting on top of insulation can bridge across and bring damp inside.
Exposure matters too. In severe exposure areas, meaning a driving rain index of 5 square metres per second per year or more, approved systems are limited to rendered walls or impervious cladding. Unrendered fair faced brickwork in an exposed coastal or western location is not a candidate. Cavities more than 12 metres above the lowest ground level are also excluded.
None of this means cavity fill is risky in general. It means the survey is the safety step, and a contractor who skips it is the risk.
Here is the mechanism, because it is not what most people assume. Filling the cavity makes the inner wall surface warmer, and warm surfaces attract less condensation, not more. On that count the house gets better.
The problems come from two places. Water crossing the cavity, which is what the suitability survey exists to prevent, and ventilation. A house that was leaky and draughty was also being ventilated by accident. Insulate it, and if you have blocked up wall vents or you have no extract fans working in the kitchen and bathroom, the moisture your household produces every day has nowhere to go, and it will show up on the coldest surface left, usually a window reveal or a north facing corner.
SEAI's own technical standards require contractors to make sure the works do not compromise the existing ventilation in the home. Hold them to it. Do not let anyone seal your wall vents, and if you have a bathroom fan that does not work, fix it in the same month. That is the difference between a warmer house and a mouldy one, and it costs very little.
Cavity fill is priced by wall area and typically comes in well under the cost of any other wall measure, often in the low thousands for a full house and sometimes less. On a typical semi-detached house the €1,300 grant covers a substantial part of that.
Ask for the price in writing before you mention the grant, then ask what changes. This is the measure where the gap between the quoted price and the grant is smallest, so a quote that jumps when SEAI is mentioned is very visible.
You should also ask what happens if the survey finds the wall unsuitable. A reasonable contractor will not charge you for a survey that ends in no work. Get that agreed up front.
Your home must have been built and occupied before 31 December 2010 and have an MPRN. The work must be done by an SEAI registered contractor and you must have grant approval before anything starts. You need a post-works BER before SEAI pays out.
The second wall rule now works in your favour. If you take the cavity grant now, you can still apply later for either internal or external wall insulation as a second wall measure. If you take external first, you get nothing after it. So cavity first, external later, is the sequence that keeps the most options open.
Owner occupiers, first-time buyers, companies, registered charities, holiday homes, approved housing bodies and landlords of tenanted properties can all apply for insulation grants. If you are on a low income or certain welfare payments, check the Warmer Homes Scheme first, because it may cover the work in full rather than partly.
Bonded polystyrene bead is the most common choice in Ireland now. The beads are blown in with an adhesive so they bond into a mass rather than settling, which was the failure mode of loose fills years ago. Blown mineral wool is the other option and is water repellent rather than water resistant.
For most homeowners the material matters less than two other things. That the system holds a current NSAI Agrément certificate, and that the installer is certified for that specific system. Ask for the Agrément number and check it.
Ask also how many drill holes and how they will be made good. Bead fill leaves a grid of small filled holes across the wall. On rendered walls they disappear. On fair faced brick they can be visible for a while.
Walls are the single largest heat loss surface in most houses, bigger than the roof and much bigger than the windows. Filling an empty cavity is the highest return per euro of anything on the SEAI list.
You will feel it as an absence of draught and cold radiating off the walls before you see it on a bill, and the room that was always cold will usually stop being the room that is always cold.
It will not on its own take a house to a B rating. Pair it with attic insulation, which is the other cheap win, and you have done the two measures that make a heat pump viable later.
Tell us your county and we will introduce SEAI registered cavity wall installers who cover your area.
€700 for an apartment, €850 mid-terrace, €1,300 semi-detached or end of terrace and €1,800 detached. On a qualifying welfare payment it is €900, €1,100, €1,700 and €2,300.
A borescope survey. The installer drills a small hole and looks inside with a camera. The cavity needs to be at least 50mm wide across the whole wall and clear of debris. Hollow concrete block, timber frame, steel frame and solid stone or brick walls cannot be pumped.
No. Approved bead systems are not certified for masonry cavity block construction, which covers a lot of Irish houses from the 1950s to the 1970s. Internal dry lining or external wall insulation are the options for those homes, and both carry larger grants.
Not in a suitable wall. It makes the inner surface warmer, which reduces condensation. Problems come from filling a wall that already lets water across, which the pre-installation survey exists to catch, or from insulating a house and then blocking its ventilation. Keep your wall vents open and your extract fans working.
On a typical semi-detached house the grant covers a large share of the job and homeowners often pay a few hundred euro. Get the price in writing before you mention the grant, and agree in advance that you are not charged if the survey finds the wall unsuitable.
Yes. If you previously received a cavity wall insulation grant you can apply for either an internal or an external wall insulation grant as a second wall measure. This changed on 2 March 2026.
Usually one day for a standard house, sometimes less. There is no disruption inside and you do not need to move out or clear rooms.
Checked against the official pages on 27 August 2026. Grant terms change, so confirm current amounts with SEAI or your installer before you commit.