External wall insulation: EPS vs mineral wool vs PIR costs
What external wall insulation costs in the UK with EPS, mineral wool, phenolic or PIR boards, how thickness changes the price, and the 0% VAT deadline.
Insulating 150 m² of solid wall from outside with 140 mm EPS boards, our mid-range benchmark, typically costs £26,000 with 0% VAT. Non-combustible mineral wool at the same thickness is about £30,500. Phenolic and PIR boards cost more per square metre but reach the same performance with a thinner board. Installing insulation is charged at 0% VAT until 31 March 2027, and our figures use that rate.
Every board on the same house
The table prices the same two-storey house with 150 m² of wall, the same scaffolding, trims, render and labour, changing only the insulation board at our mid-range thickness.
| Material | Typical | Usual range | Lifespan |
|---|---|---|---|
| EPS polystyrene | £26,000 | £20,300 – £33,800 | 30-50 years |
| PIR | £26,000 | £20,300 – £33,900 | 30-50 years |
| Mineral / rock wool (non-combustible) | £30,500 | £23,800 – £39,600 | 40-60 years |
| Phenolic (thinner for the same performance) | £31,300 | £24,400 – £40,700 | 30-50 years |
The difference between two rows is roughly what the change of board costs you. Change the wall area and see every line in our External wall insulation.
The boards
EPS (expanded polystyrene)
EPS (£26,000) is the most widely used board for external wall insulation. It is light, easy to cut and fix, and the cheapest for a given thickness. It lasts 30-50 years behind a sound render. The drawbacks: it is combustible, and it is not vapour-open, so detailing around the edges matters.
Mineral wool (rock wool)
Mineral wool boards (£30,500) are non-combustible and vapour-open, which suits older solid walls that need to breathe, and they dampen sound better than EPS. They are heavier and denser, so they need more fixings and more care to install, which is why they cost more. Expect 40-60 years. Where fire performance matters, for example on taller buildings or close to a boundary, rules can restrict combustible insulation; your installer or building control will tell you what applies.
Phenolic
Phenolic boards (£31,300) insulate much better per millimetre: 120 mm of phenolic performs like about 140-160 mm of EPS. That makes them useful where thickness is tight - at window reveals, next to a boundary or under deep eaves. They cost more per square metre and last 30-50 years.
PIR
PIR boards (£26,000) are also thinner for the same performance, and often used on specific details rather than whole walls. Like phenolic, they are combustible and must be part of a tested system.
Whichever board you choose, it should be part of a complete, tested system from one manufacturer - board, adhesive, fixings, mesh and render - installed by a firm approved for that system.
How thickness changes the price
Thicker boards insulate better, but cost more and project further from the wall. With EPS, the whole job costs about:
| Thickness | Typical price, 150 m² with EPS |
|---|---|
| 100 mm | £23,400 |
| 140 mm | £26,000 |
| 180 mm | £28,600 |
| 200 mm | £29,900 |
Most of the cost is scaffolding, labour and render, which do not change with thickness, so going thicker is usually cheap relative to the whole job. The limits are practical: window sills, roof overhangs and downpipes all have to be extended or moved further as the board gets thicker, and those items are not in our estimate.
What the price includes
- Scaffolding for about two months, put up and taken down
- Insulation boards bonded and fixed to the walls with a reinforced base coat
- Starter profile with a drip at the base of the wall
- Mesh corner beads on corners and window reveals
- Sealing under the eaves
- A silicone-based render finish: primer plus two coats
Not included: new window sills, extending roof overhangs, moving downpipes, gutters, lights or satellite dishes, repairs to damp or damaged walls, and design and permits.
We build the estimate from the area, the hours an installer and labourers need at local labour rates, plus materials, and check the totals against market prices and real quotes.
0% VAT and other help
Installing energy-saving materials, including insulation, is charged at 0% VAT until 31 March 2027, and our figures already use that rate. A job that finishes after the deadline may not get it, so allow for the time an external wall project takes to design and schedule.
The Warm Homes Plan, published in January 2026, commits £15bn to 2030, including grants for low-income households and low- or zero-interest loans that are being phased in. External wall insulation can also need planning permission in some cases, especially in conservation areas, because it changes how the house looks. Check with your council before you commit.
Which to choose
- Lowest cost on a typical house: EPS at 100-140 mm.
- Older solid walls, fire and noise concerns: mineral wool.
- Where thickness is limited: phenolic or PIR on the tight areas.
Check your quote
Ask for quotes that name the system, board type and thickness, and list scaffolding, trims, render and making good separately. Then compare the total with typical prices where you live using our "Is my quote fair?" tool: Is my quote fair?.