SWIP IWI is a BBA-certified internal wall insulation system designed for the solid-wall homes that can't take cavity fill. Stay Warm Insulation installs it as a manufacturer-approved installer. If you've been searching for “SWIP insulation” and want to know what it is, how it performs and what it costs, this guide explains it in plain terms.
What is SWIP insulation?
SWIP IWI is a complete internal wall insulation (IWI) system from the specialist system manufacturer SWIP. Rather than a single board, it is a tested kit of parts certified to work together:
- SWIP EcoStuds — thermally engineered composite studs (rigid insulation bonded to OSB), fixed to the existing wall. Because the stud itself is an insulator, there is no cold bridge at every stud line — the weakness of traditional timber- or metal-framed IWI.
- SWIP EcoBatt slabs — water-repellent glass mineral wool, friction-fitted between the studs with no gaps. Euroclass A1 fire rated (the best possible) and made largely from recycled glass.
- Vapour control membrane — an airtight layer on the warm side of the insulation, taped and sealed at every edge (more on this below).
- Plasterboard finish, sealed at the perimeter, skimmed and ready to decorate — with insulated reveal boards for window and door openings so the insulation stays continuous around them.
The system is BBA certified and carries a 25-year system guarantee. We install it with our own PAS2030-19 certified, TrustMark-registered team — so the system designer stands behind the components, and one accountable installer stands behind the workmanship.
How the system works
Standard 65mm or 95mm EcoStuds are fixed to the wall at 600mm centres, EcoBatt slabs fill the bays completely, the vapour membrane goes over the insulation, and plasterboard finishes the wall. The system sits tight to the existing wall — no air gap behind it for warm room air to circulate in — which matters because uncontrolled air movement behind an IWI system is a major hidden cause of heat loss and condensation in battened systems.
Where space is tight — window reveals, around stairs, narrow lobbies — thin insulated reveal boards keep those surfaces insulated too, preventing the cold spots that would otherwise attract condensation and mould.
Thermal performance
A typical uninsulated 9-inch solid brick wall has a U-value of roughly 2.0 W/m²K — among the worst-performing walls in British housing. With SWIP:
| System | U-value achieved |
|---|---|
| SWIP 65mm system | 0.43 W/m²K |
| SWIP 95mm system | 0.30 W/m²K |
| Doubled-up 65mm studs | 0.24 W/m²K |
The 95mm system takes that 2.0 wall to 0.30 — an improvement of over 80% in heat loss through the wall. And because the EcoStuds insulate rather than bridge, the system is around 13% more thermally efficient than a timber-stud build-up of the same thickness — or put another way, it achieves the same performance with less lost room space.
Moisture and condensation — the part that matters most
The biggest risk with any internal wall insulation is moisture: insulate the room side of a solid wall badly and you can trap condensation inside the construction. The SWIP system addresses this with a vapour control layer on the warm side of the insulation, sealed airtight with system tapes. Two membranes are available, chosen for the property: the standard closed membrane, or the Intello intelligent membrane for more exposed locations — a climate-responsive layer that closes against moisture in winter and opens to let the structure dry out in summer.
Condensation-risk analysis to BS 5250 shows no interstitial condensation forming in a wall insulated with the correctly installed system. Two honest caveats we apply on every job: any existing damp must be diagnosed and fixed before insulating — IWI must never be used to hide a damp wall — and background ventilation has to be maintained, which we check as part of the survey. See our guide on condensation, damp and mould after insulation for the full picture.
SWIP for period and solid-wall homes
The system is designed for existing solid-wall and uninsulated cavity homes — typically Victorian, Edwardian and other pre-1920s houses. Because it is fitted from the inside, the outside of the building is untouched, which makes it the practical route for conservation areas, protected frontages and anywhere the brickwork should stay visible. It can be installed room by room to suit phased budgets, and installation isn't weather-dependent. To check what kind of wall you have, see cavity wall vs solid wall.
Practical limits worth knowing: building regulations cap the system's use at 11 metres above ground level (a fire-safety rule that affects taller buildings, not houses); log burners and flues need 200mm clearance; and radiators are re-fixed through to the studs, never to plasterboard alone. All of this is handled in the survey and installation as standard. If you're weighing internal against external insulation, our EWI vs IWI comparison sets the two side by side.
What SWIP insulation costs
SWIP is priced like other quality-assured internal wall insulation. As a guide:
| Scope | Typical cost |
|---|---|
| Per square metre | £100–£140 / m² |
| A single room | £1,800–£4,000 |
| A full 3-bed house | £8,000–£15,000 |
These are indicative ranges, not a quote. The real cost depends on how many external walls you're treating, the system thickness, the condition of the walls, and the finishing details. Stay Warm provides a fixed, written price after a free survey, with no obligation — so you know exactly what you'll pay before any work begins.
Ready to find out what SWIP would cost for your home? Get a free quote and we'll arrange a free survey at a time that suits you.
SWIP insulation FAQs
What is SWIP insulation?
SWIP IWI is a BBA-certified internal wall insulation system made by the system manufacturer SWIP. It insulates solid walls from the inside using thermally engineered composite studs (insulation bonded to OSB), water-repellent glass mineral wool slabs fitted between them, an airtight vapour control membrane, and a plasterboard finish. Stay Warm Insulation installs the system as a manufacturer-approved installer, and it carries a 25-year system guarantee.
How much does SWIP insulation cost?
As internal wall insulation, SWIP typically works out at roughly £100–£140 per m² installed, depending on the room, the condition of the walls and the level of finish. A single room often falls between £1,800 and £4,000, while insulating a full three-bedroom house generally ranges from about £8,000 to £15,000. Every home is different, so the only accurate figure is a fixed quote following a free survey.
Is SWIP suitable for period homes?
Yes — the system is designed for existing solid-wall (and uninsulated cavity) homes, which includes most Victorian, Edwardian and pre-1920s properties. Because it is fitted internally, the outside of the building is untouched, so it suits conservation areas and protected frontages. Any damp must be fixed before installation — no internal insulation should ever be used to cover a damp wall — and the vapour membrane is chosen to suit the property’s exposure.
How is SWIP different from standard internal wall insulation?
The stud. Traditional IWI framing uses timber or metal studs, and every stud is a thermal bridge — a cold strip running through the insulation. SWIP EcoStuds are made of insulation bonded to OSB, so the stud itself insulates. That removes the bridging, makes the system around 13% more thermally efficient than a timber-stud build-up of the same thickness, and lets it achieve its rated U-values with less depth. It is also a complete tested system — studs, slabs, membrane, tapes and sealant are certified to work together, rather than mixed parts.
Does SWIP help with noise?
As a side benefit, yes. The mineral wool core absorbs sound energy and the new plasterboard lining adds mass, so an airborne noise improvement of up to 5dB through the treated wall is typical — a clearly noticeable reduction.