Insulated Plasterboard: UK Guide

What is insulated plasterboard?

Insulated plasterboard (also called thermal laminate or insulated dry lining) is a composite panel combining standard plasterboard with an insulation layer. The insulation is factory-bonded to the back of the board, creating a single product that provides both the wall finish and thermal performance.

Most UK products use PIR (polyisocyanurate) foam insulation because it offers high thermal performance in a thin layer. EPS (expanded polystyrene) is cheaper but thicker for the same U-value. The plasterboard face is usually 12.5mm thick, with insulation ranging from 20mm to 90mm depending on the required performance.

Common brands include Kingspan Kooltherm K118, Celotex PL4000, and Recticel Eurowall. All are manufactured to similar standards and performance levels.

When to use insulated plasterboard

Internal wall insulation (IWI) in retrofit

Solid-walled houses (brick, stone, concrete) built before 1920 often lack cavity walls. External insulation is expensive and changes the appearance. Internal insulation using insulated plasterboard is faster and cheaper. You lose some room width (50-100mm) but gain significant thermal improvement and reduced heating bills.

New builds and extensions

Building Regulations Part L requires minimum U-values for walls (typically 0.18-0.28 W/m²K depending on build type). Insulated plasterboard on internal faces of masonry walls helps meet these targets. Also used on party walls to provide thermal separation between dwellings.

Cold rooms or unheated spaces

Bedrooms above garages, rooms backing onto unheated stairwells, or walls adjoining unheated extensions benefit from insulated board. Stops cold bridging and condensation problems.

When separate insulation is better

Very thick insulation requirements (150mm+) are easier to achieve with separate boards. Irregular walls needing battening and levelling work better with separate insulation cut to fit. DIY projects on a budget: separate materials are cheaper.

Insulation types: PIR vs EPS

PIR (polyisocyanurate) foam

High-performance foam with thermal conductivity (lambda) around 0.022-0.023 W/mK. Thin layers provide good U-values. Foil facings on both sides improve performance and provide a vapour barrier. More expensive than EPS. Most common type in UK insulated plasterboard.

EPS (expanded polystyrene) foam

Lower-performance foam with lambda around 0.030-0.038 W/mK. Requires thicker layers for the same U-value as PIR. Cheaper. Breathable (no vapour barrier). Used where thickness is not a constraint and cost is critical.

Phenolic foam

Very high performance (lambda 0.018-0.020 W/mK) but expensive and less common. Used in space-constrained applications like narrow hallways or where every millimetre of room width matters.

Thickness options and U-values

Insulated plasterboard is sold by total thickness (board plus insulation). Performance is expressed as U-value (lower is better). Typical options for PIR-backed boards:

U-values assume installation on a solid masonry wall with plaster dabs or battens. Actual values depend on the existing wall construction, fixings, and detailing.

Installation methods

Dot and dab (adhesive dabs)

Most common method. Apply blobs of plasterboard adhesive to the wall in a grid pattern (typically 300mm spacing). Press the insulated board onto the dabs, check for level and plumb. Fast, no framework needed. Suitable for reasonably flat walls (variation less than 10mm).

Mechanical fixing to battens

Fix timber or metal battens to the wall, then screw the insulated board to the battens. Used when walls are very uneven, when dot and dab is not suitable, or where higher loadings are expected (heavy wall units, grab rails). More labour but stronger fixing.

Continuous adhesive

Spread adhesive across the whole back of the board rather than dabs. Eliminates air gaps behind the board, improving thermal performance slightly and reducing air infiltration. More adhesive required, slower to apply. Used in very high-performance builds.

Building Regulations Part L compliance

Part L (Conservation of fuel and power) sets minimum U-values for walls in new builds and extensions. As of 2023 edition:

• New dwellings: Maximum 0.18 W/m²K for external walls
• Extensions: Maximum 0.28 W/m²K (or match existing if better)
• Renovations over 25% of surface area: Upgrade to 0.30 W/m²K or better

A solid brick wall (uninsulated) has a U-value around 2.0 W/m²K. Adding 70mm PIR-backed plasterboard brings it down to 0.18-0.20 W/m²K, meeting new-build standards. For extensions, 40-50mm insulation suffices (U-value 0.25-0.28 W/m²K).

Check manufacturer datasheets for certified U-values. Building Control will require calculations or third-party certification (BBA, BRE) for sign-off.

Vapour control and condensation risk

Insulating internally moves the dew point closer to the inner face of the masonry wall. This increases condensation risk inside the wall if warm moist air penetrates the insulation. PIR-backed boards have foil facings that act as a vapour barrier, reducing this risk.

Best practice

• Tape all joints: Use foil tape over board joints to maintain vapour barrier continuity.
• Seal penetrations: Electrical boxes, pipes, and cables must be sealed with acoustic putty or expanding foam.
• Ensure adequate ventilation: Insulated rooms produce the same moisture but have less wall to absorb it. Use trickle vents or mechanical ventilation.
• Avoid EPS on cold walls: EPS is breathable. On very cold solid walls, use PIR with foil facing or add a separate vapour control layer.

For complex cases (basement walls, very exposed locations), consult a building physicist or use hygrothermal modelling software (WUFI) to check condensation risk.

Cost comparison

Insulated plasterboard costs more than separate insulation plus standard board, but saves labour.

Insulated board (all-in-one)

• 52.5mm (40mm PIR): £18-24 per 1200x2400mm sheet
• 72.5mm (60mm PIR): £22-28 per sheet
• 102.5mm (90mm PIR): £28-36 per sheet

Separate materials

• 50mm PIR board: £12-16 per 1200x2400mm sheet
• 12.5mm plasterboard: £6-8 per sheet
• Total: £18-24 (similar to insulated board)

Material cost is similar. Insulated board is faster to install (one product, one fix). Separate materials offer more flexibility if walls are uneven or you need non-standard thicknesses. For whole-house IWI projects, labour savings make insulated board worthwhile. For small areas or DIY, separate materials are easier.

Related guides

• Plasterboard: Complete Guide
• Plasterboard Sizes UK
• Soundproof Plasterboard Explained
• Plasterboard Jointing Techniques