Internal cork insulation · IWI
Internal cork insulation that fixes cold walls — without losing the room.
A 3–6 mm sprayed cork system applied to the inside of cold, damp or mould-prone walls. Raises surface temperature above the dew point, stays vapour-permeable, and keeps your skirtings, sockets and floor area intact.
Why internal cork
When you can't go external — but cold walls are ruining the room.
Listed façades, conservation areas, mid-terrace party walls, ground-floor flats with shared elevations: there are plenty of UK properties where external wall insulation simply isn't an option. The cold-wall problem stays — and shows up as condensation runs, peeling paint, and black mould blooms on north-facing bedrooms and behind furniture.
Internal cork insulation solves it from the inside. Two sprayed coats, only millimetres thick, bonded directly to the existing plaster. The wall surface temperature rises, the dew point retreats into the wall fabric rather than your room air, and the condensation cycle stops. Decoration goes straight on top.
Where we use it
Cold bedrooms, kitchen extensions, behind wardrobes.
Single-room interventions: a north-facing bedroom that's always 2°C colder than the rest of the house, a kitchen extension with a freezing party wall, a return wall behind a wardrobe that's grown black mould since the new windows went in.
Whole-property IWI: pre-1920s solid-wall homes where external work is constrained by Article 4 directives, conservation status, or a neighbour who won't co-sign the elevation. Cork lets us upgrade the thermal performance from inside without ripping the rooms apart.
What you get
Warm walls, no mould, almost no room loss.
Lifts wall surface temperature
Raises internal surface temperature above the dew point — condensation can't form.
Stops black mould at source
Removes the cold-surface cause rather than masking with anti-mould paint.
Class 1 vapour-permeable
Existing moisture in the wall can dry out — no trapped damp behind the coating.
Only 3–6 mm thick
Skirtings, sockets, architraves and radiators stay in place. No lost floor area.
Paint or wallpaper-ready
Finish with breathable mineral or silicate paint, or leave as a textured cork finish.
Non-toxic, low-VOC
Safe for occupied homes, nurseries and bedrooms. No off-gassing.
Internal cork insulation FAQs
The practical questions homeowners ask.
- What is internal cork insulation?
- Internal cork insulation is a sprayed cork coating applied to the inside face of cold or damp walls. At 3–6 mm thick it raises the wall surface temperature above the dew point, eliminates cold-bridge condensation, and adds a thermal layer without losing significant room space like insulated plasterboard does.
- When should I choose internal over external cork insulation?
- Internal cork is the right call when external work isn't possible — listed façades, conservation areas where the external appearance must be preserved, mid-terrace flats with shared elevations, or where only one room (typically a north-facing bedroom or extension) has the cold-wall problem.
- Will internal cork insulation reduce room size?
- Barely. Sprayed internal cork is only 3–6 mm thick — versus the 50–100 mm lost to insulated plasterboard or stud-and-batten IWI systems. Skirtings, sockets, architraves and radiators usually stay in place.
- Does internal cork insulation stop condensation and black mould?
- Yes. Mould grows where warm, moist room air meets a cold surface and condenses. Cork lifts the surface temperature so condensation can't form, while staying vapour-permeable so existing moisture can dry out. We routinely use it to fix chronic black-mould patches on north-facing walls and behind wardrobes.
- Can internal cork insulation be painted or wallpapered over?
- Yes. It can be left as a textured finish or skimmed, then decorated with breathable paint or wallpaper. We recommend mineral or silicate paints to preserve the breathability of the system.
- How long does an internal cork installation take?
- Most single rooms are completed in 1–2 days, including masking, surface prep, two coats of cork and finish. Whole-house IWI typically takes 5–10 days depending on size and access.