Insulated Plasterboard

What Is Insulated Plasterboard?

Insulated plasterboard combines a gypsum plasterboard facing with a bonded layer of thermal insulation, allowing walls to be insulated and drylined in a single installation. Also known as thermal plasterboard, it is commonly fitted to the internal face of external walls in extensions, loft conversions, garages and refurbishment projects. Boards are available with PIR, EPS or phenolic insulation cores, offering different levels of thermal resistance, overall thickness and cost. When installed as part of a correctly designed wall system, insulated plasterboard can reduce heat loss while creating a smooth internal surface ready for jointing, skimming and decoration.

What Is the Best Insulated Plasterboard for Solid Walls?

There is no single best insulated plasterboard for solid walls. The correct choice depends on the existing wall construction, its condition, the available internal space and the thermal performance required for the complete wall.

Before selecting an internal wall insulation plasterboard, check:

• Whether the wall is dry, stable and free from defective finishes
• The required U-value for the completed wall construction
• How much internal floor space can be lost
• Whether a vapour control layer or condensation assessment is required
• Which fixing method is approved for the board and substrate

PIR and phenolic boards are particularly useful when strong thermal performance is required without an excessively thick internal build-up. EPS can be a practical, lower-cost option where a more basic improvement is sufficient.

PIR Plasterboard vs EPS Insulated Plasterboard

PIR and EPS boards perform the same basic two-in-one function, but their insulation cores have different thermal properties.

• PIR plasterboard: PIR plasterbaords have a declared thermal conductivity of 0.022 W/mK. The lower conductivity means they can provide greater thermal resistance from a comparatively slim insulation layer.
• EPS insulated plasterboard: EPS plasterbaords have a declared thermal conductivity of 0.038 W/mK. They are lightweight and cost-effective, making it suitable for projects requiring a basic thermal upgrade.

PIR insulated plasterboard is generally the stronger choice where room space is restricted or a higher R-value is needed. EPS may be more appropriate where price, low board thickness and ease of handling are the main priorities. Compare the declared performance rather than choosing by insulated plasterboard prices alone.

Choosing the Right Board Thickness

Total board thickness includes both the insulation core and the plasterboard facing. A thicker board will normally provide greater thermal resistance within the same product system, but insulation material and declared R-value must also be considered.

• 37.5mm insulated plasterboard: A space-conscious PIR option consisting of 25mm insulation and 12.5mm plasterboard.
• 52.5mm insulated plasterboard: A useful middle option when more insulation is required without moving to the thickest board. Customers comparing 52.5mm PIR insulated plasterboard should confirm the exact overall thickness, insulation build-up and R-value.
• 62.5mm insulated plasterboard: A stronger thermal upgrade for projects where the additional internal depth is acceptable. This 62.5mm PIR insulated plasterboard combines 50mm PIR with 12.5mm plasterboard and has a declared R-value of 2.30m²K/W.

Each current insulated plasterboard sheet measures 2400mm × 1200mm and covers 2.88m². Divide the net wall area by 2.88 to estimate the number of boards, then allow extra material for cuts, openings, damaged edges and the installation layout.

Insulated Plasterboard vs Foil Backed Plasterboard

Insulated plasterboard and foil backed plasterboard are designed for different purposes.

Insulated boards contain a bonded PIR, EPS or phenolic insulation layer that increases the thermal resistance of the wall. Foil backed plasterboard is normally a standard gypsum board with a metallised backing designed primarily to provide integrated vapour control. It should not be treated as an equivalent substitute where a calculated thermal-insulation upgrade is required.

Some PIR laminated boards also incorporate an integral vapour control layer within their facing. To create a continuous layer, the joints and relevant junctions must be sealed and taped in accordance with the specified system. Neither product should be used to conceal an active damp problem, and standard insulated boards are not automatically suitable for wet rooms or areas exposed to continuous humidity.

Fixing and Finishing Insulated Plasterboard

The installation method must match the selected board, wall substrate and manufacturer’s instructions. Certain PIR systems are suitable for proprietary adhesive-dab fixing followed by secondary thermally broken mechanical restraint. EPS products may require a different fixing pattern, so instructions for one board should not be applied automatically to another.

Before fixing, remove loose finishes and make sure the wall is dry and sufficiently level. Use suitable Plasterboard Adhesive where adhesive installation is permitted, together with the specified Plasterboard Fixings. Boards should be tightly butted to reduce gaps and unwanted heat movement. Tapered edges can then be taped and jointed or prepared for a plaster skim. Where the board provides vapour control, seal the joints and perimeter details as required to maintain continuity.

Before you buy insulated plasterboard, compare the board type, thickness, thermal resistance and live prices shown above. MGN Builders Merchants supplies PIR insulated plasterboard across London, Essex and surrounding areas, subject to stock and postcode availability. Enter your delivery postcode or contact the team for help selecting the correct quantity and specification for your project.