Solid and internal wall insulation

Internal wall insulation

Internal wall insulation (IWI) insulates the inside face of external walls using insulated plasterboard, an insulated stud wall or breathable wood fibre boards with lime plaster. It's used where the outside appearance must stay the same or when you're renovating room by room.

Keeps the outside of the house exactly as it is
Can be done one room at a time during a renovation
Insulated plasterboard, stud wall or breathable systems
Loses roughly 50–100mm per insulated wall
Needs careful detailing at floor joists, reveals and corners
Sockets, radiators, skirting and coving are moved and refitted

Get a guide price See prices

A bedroom wall being lined with insulated plasterboard around a window, with dust sheets and a stepladder

Free survey for internal wall insulation

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What are the options for internal insulation?

Insulated plasterboard — PIR or phenolic foam bonded to plasterboard, fixed to the wall and skimmed. Thinnest option.
Insulated stud wall — a timber or metal frame filled with insulation, with a vapour control layer and plasterboard. Takes more space but runs services easily.
Wood fibre and lime — breathable boards finished in lime plaster, for older walls that need to manage moisture.

Typical build-up

Typical build-up: 37.5–72.5mm insulated plasterboard, or 50–100mm stud wall
Space lost: ≈50–100mm per wall
Typical U-value: ≈0.30–0.45 W/m²K on solid brick
Duration: 3–5 days per room
Approvals: Building Regulations in England and Wales

What are the risks with internal insulation?

Insulating inside makes the masonry colder, so moisture risk rises. Weak points are where floor joists bear into the wall, window reveals and corners. A condensation risk check for the build-up, a continuous vapour control layer where specified, and returning insulation into reveals deal with most of it.

Do I need Building Regulations approval?

Yes, in England and Wales once you insulate or replaster more than half of a wall's area (or more than a quarter of the building's whole envelope), it's treated as renovating a thermal element. The wall should reach about 0.30 W/m²K where practical, and building control needs to be involved.

Internal wall insulation prices

Internal wall insulation guide prices
Item	Guide price	Notes
Insulated plasterboard, supplied and skimmed	£75–£110 per m²0% VAT
Insulated stud wall	£90–£130 per m²0% VAT
Typical bedroom, one external wall	£1,795–£2,9950% VAT	Including making good

Guide prices are confirmed by a fixed written quote after a free survey. 0% VAT: installing insulation in a home is zero-rated until 31 March 2027, so these figures are the total; 5% applies from 1 April 2027.

How it works

Tell us about the property
Use the quote tool or form, or call free on 0800 088 6248.
Free survey
We measure the walls, check condition and confirm planning and building control.
Fixed written quote
The system, details, access, exclusions and VAT, in writing. Anything hidden is priced and agreed before extra work.
Installation and handover
Work planned around the weather, then inspected and documented.