Pumped cavity wall insulation

What "pumped" means

A cavity wall is two parallel leaves of masonry with a gap between them. SEAI's standards call it twin-leaf construction, and they say the insulation must fill the full depth of the cavity, with the gap that is left never less than 40 mm (SEAI Domestic Technical Standards and Specifications, v4.0, July 2026, clause 6.1, read 29 October 2026). The pump is a machine in the installer's van that blows the insulation through a hose into each drilled hole. For bead systems a binder is sprayed on as the beads go in, so they set into one block inside the wall. Bonded bead insulation explains the material. This page is about the job.

The alternative to pumping is to open the wall or insulate on a face of it: internal dry lining or external insulation. Both cost several times more. For a cavity wall with a clear cavity, pumping is the method SEAI's grant funds first. Which wall grant fits your walls? has the three side by side.

Who is allowed to pump a cavity wall

For the SEAI grant the installer must be on SEAI's register of contractors. SEAI's standards also require the installer to be an Agrément-approved installer for the exact system they use, with an approved installer number, listed on NSAI's register, and at least one person on the team must carry an installer identity card issued by the certificate holder (SEAI Domestic Technical Standards and Specifications, v4.0, July 2026, clause 6.1, read 29 October 2026). NSAI's scheme adds that approved installers are audited before registration and about once a year after it, and that NSAI removes installers who don't comply from its web register (NSAI Agrément CWI installer scheme, D-IAB-003 revision 5, read 29 October 2026).

You can check both lists yourself before anyone drills a hole: SEAI's registered contractor search and NSAI's register of cavity wall insulation installers.

The pumped job, step by step

1. Survey, with a borescope.SEAI's standards require a pre-installation survey by a trained surveyor, with a borescope inspection on at least two test holes per elevation, and a written report for the homeowner. The survey checks cavity width, debris, wall ties, any existing insulation and the cause of any damp. Each test hole is sealed with colour-matched weatherproof sealant.
2. Exposure and defects.The walls' exposure to wind-driven rain is assessed, because it limits which fill can be used. Visible defects that could let water in go on the survey report, and the homeowner fixes them before any work starts.
3. Services, vents and flues.Vents, ducts and flues are sleeved through both leaves. PVC-sheathed electric cables are put in conduit, and the ESB Networks cable must not touch the insulation. If the cavity is open at the top it is capped first. Brushes go in at party walls so bead can't travel into the neighbour's cavity.
4. Drilling and filling.A pattern of holes is drilled through the outer leaf, following the system's Agrément certificate. The insulation is pumped in at every hole. A second borescope survey, on all the drill holes, is done during the install to confirm the hole pattern matches the certificate and the cavity is filling.
5. Checks after filling.Ventilation openings are checked for blockage. Flues are tested before and after, for example with a smoke test. Any bead blown into the attic is removed and the leak sealed. The meter box is checked for bead.
6. Paperwork.The installer keeps the survey sheets, borescope results, combustion appliance checks and bead-to-adhesive test results for SEAI to inspect. The homeowner gets the Agrément certificate and the warranty, and under NSAI's scheme an installer's declaration.

Steps from SEAI Domestic Technical Standards and Specifications, v4.0, July 2026, clause 6.1, read 29 October 2026, and NSAI Agrément CWI installer scheme, D-IAB-003 revision 5, read 29 October 2026.

What the installer's declaration must say

NSAI's scheme requires the installer to give you a declaration on completion, stating the work was done to the scheme using an NSAI-certified product. It must include at least (NSAI scheme, clause 4.2 q):

• The Agrément certificate system name and number
• The wall area insulated, in m²
• The declared installed insulation thickness
• The volume of insulation used, in m³
• The declared thermal resistance values
• The place and date of installation

Keep it with the SEAI paperwork. If a problem shows up later, it is the document that says what went into the wall and how much.

Walls that can't be pumped

SEAI's standards say cavity hollow block walls are not suitable for cavity wall insulation, and timber frame homes cannot be cavity insulated (SEAI technical standards). A cavity already part-filled with mineral wool is not recommended for a top-up, though a residual cavity behind rigid boards can be filled if at least 40 mm remains everywhere. A borescope settles it. Is my house suitable? goes through the checks.

Cold weather and the binder

Low temperatures can affect the adhesive that bonds the beads, so SEAI's standards tell installers to follow the manufacturer's instructions before working in cold weather (SEAI technical standards). A flow-rate test checks the bead-to-adhesive ratio, so the beads are neither over-bonded nor under-bonded and don't leak. Ask the installer how they handle a cold morning.

Cost and time

• €7.50 to €13 per m² including VAT (ShamFix, 31 July 2026), for pumped bonded bead with materials and labour.
• €1,585 median for a semi-D and €2,350 for a detached house: 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.
• About €285 for a semi-D after the €1,300 SEAI grant.
• Usually one day for a house, according to one Dublin installer (Osber, page updated 31 August 2026).

The full breakdown by house type is on cavity wall insulation cost.

Questions for the installer, from SEAI's own guide

• Is the cavity suitable for fully filling with insulation? How has this been, or will this be, assessed?
• What system is recommended for my cavity wall?
• Will the system result in any dampness or condensation on the walls, or interfere with ventilation? How will this be avoided?
• How big is the cavity?
• What guarantee or warranty is available for the system?

From SEAI's homeowner's guide to wall insulation.

Questions people ask