Depths

How thick should attic insulation be?

Thick enough to reach a U-value of 0.16 W/m²K. For mineral or glass wool, SEAI says that typically takes 300 mm; for PIR rigid board, about 150 mm. It goes in two layers: one between the joists, one across them.

Most attics topped up years ago have 100 to 200 mm. That's below the standard the grant pays for.

Get a free quote Check my grant

Free, no obligation. One SEAI-registered contractor prices it, not five.

€2,000SEAI attic grant for a detached house
€2,500at the higher rate
€300 to €600typically left to pay on a semi-D
300 mmof wool: what SEAI's standard takes

The numbers

Depth and U-value

0 mm: SEAI's own example records a bare attic at a U-value of 2.3.
300 mm of wool, or about 150 mm of PIR: 0.16, SEAI's standard.
The median pre-2011 Irish house: 0.27 on its BER, well short of 0.16.

Lower U-value means less heat lost. Going from 2.3 to 0.16 is the big gain; going from 0.27 to 0.16 is a smaller one, but it's what the grant pays for.

200 mm

Is 200 mm enough?

Not for the grant. 200 mm rolls are sold widely in Ireland, but SEAI's standard asks for the U-value 300 mm of wool typically reaches. If you have 200 mm, a top-up across the joists can bring it up. The contractor measures what's there.

Laying it

The way SEAI wants it laid

The first layer between the joists, no more than 25 mm above or below their tops.
The second layer across the joists, tucked into the eaves without blocking them.
Not squashed: compressed wool loses much of its effect.
The same depth everywhere, where practicable.
Storage areas raised on new joists, or done in a thinner high-performance board, with 50 mm of air under the boards.

Blown or rolls

Blown-in wool, rolls or boards

SEAI names mineral wool and glass wool as the most common, and EPS, XPS, PIR and phenolic boards as the foam options. Any of them can be used if it's suitable for Irish conditions, CE-marked or Agrément-certified, and reaches 0.16. Blown wool suits low or awkward attics; rolls suit open ones; boards suit storage areas where height is short. Spray foam is a different matter: read this first.

Best way

The best way to insulate an attic

For most Irish attics: wool to 300 mm in two layers, the eaves kept open, the hatch insulated and sealed, the tank and pipes lagged, and a raised walkway. That's what SEAI's standard asks for, and it's what the grant pays for.

Grant check

Your attic grant and what's left to pay

Two taps: your home, and which rate fits you. The answer is SEAI's fixed grant and its own median cost for the job.

Your home

Which fits you?

Homeowner or landlordThe standard rateOn a qualifying welfare paymentOr a landlord with a HAP or RAS tenantFirst-time buyerBought a second-hand home since 1 January 2025

Your SEAI attic insulation grant

€1,500

SEAI median cost, Jan to Jun 2026: €2,101
Left to pay at the median: €601

SEAI's fixed grant for a semi-d or end of terrace at the standard rate is €1,500. SEAI's median cost for attic insulation on a semi-d or end of terrace from January to June 2026 was €2,101. €2,101 less €1,500 leaves about €601. Our sum; your quote can be higher or lower.

Send this for a real price

How this is worked out

The grant is SEAI's fixed amount for that home type and rate, as Citizens Information lists it. The median cost is SEAI's own figure from grant-funded attic jobs completed between January and June 2026; the PDF doesn't say whether VAT is in. Left to pay is the median less the grant, our sum. The home must have been built and lived in before 2011, the contractor must be on SEAI's register, and SEAI must approve the grant before work starts. It's an estimate, never a quote.

FAQ

Questions people ask

How many mm of insulation do I need in my attic?

About 300 mm of mineral or glass wool, or about 150 mm of PIR board, to reach SEAI's U-value of 0.16.

Is 200 mm loft insulation enough in Ireland?

Not to the standard SEAI's grant pays for. A top-up across the joists usually brings it up to 300 mm.

Can I top up existing attic insulation with the grant?

The grant is for reaching the standard, whatever's there now. The contractor surveys it and records the depth before and after.

Should I insulate the attic floor or the roof?

For an attic used only for storage, the floor (ceiling level) is simpler and cheaper. For a room in the roof, the roof itself.

Keep reading