Older properties often lose heat much faster than homes built to current standards. Insulated plasterboard is widely used during retrofit projects because it combines a PIR insulation core with a plasterboard finish, allowing the wall to be insulated and finished in a single installation.
Before you place an order, check these four points:
- Choose a board thickness that meets your target U-value.
- Make sure the fixing method suits the wall substrate.
- Select the right edge type for the finish you want.
- Check whether the wall build-up needs additional vapour control.
Missing any of these checks can mean the finished wall falls short of its thermal target or creates extra work once the boards arrive on site. Taking the time to confirm each point before ordering makes it much easier to choose insulated plasterboard that’s right for the wall type, substrate and finish on your project.
Confirm the Board Thickness for Your Target U-Value
The existing wall construction determines where you start. Solid brick, blockwork and timber frame walls all perform differently, so the PIR insulation thickness needed to reach the U-value required under Part L of the Building Regulations will vary.
How Wall Construction Affects Board Thickness
For many solid wall retrofit projects, a 25mm PIR-backed board improves thermal performance but may not be enough to meet Part L on its own. A 40mm board is often chosen where a greater reduction in heat loss is required, while thicker options such as 52.5mm are commonly specified for walls with particularly poor thermal performance.
Celotex, Kingspan and Gyproc Thermaline all produce insulated plasterboard across this thickness range. Fortunately, Online Insulation makes it easy to get insulated plasterboard that’s matched to your wall construction and target U-value.
Check the U-Value Before Ordering
Before ordering, carry out a U-value calculation using the existing wall construction and the proposed PIR thickness. This confirms whether the selected board meets the required level of thermal performance.
Match the Fixing Method to the Substrate
Insulated plasterboard is generally installed using either dot-and-dab adhesive or mechanical fixings. The right method depends on the condition of the wall, the weight of the board and any airtightness requirements.
- Dot-and-dab: Adhesive dabs are applied directly to the wall. This method is commonly used on flat, sound substrates in UK retrofit projects.
- Mechanical fixing: Screws or plugs secure the board through to the substrate. This is often the better choice for uneven walls or where a firmer fixing is required.
Some insulated plasterboard products are suitable for both methods, while others are approved for only one. Fire performance or loading requirements may also affect the fixing method that can be used.
The condition of the wall matters just as much. Loose material, damp patches and uneven areas should be dealt with before installation, as they can reduce the strength of the fixing regardless of the board selected.
Comparing the technical data sheet with the condition of the substrate before ordering reduces the chance of choosing a board that isn’t suitable for the installation method.
Check the Edge Type Against the Intended Finish
Insulated plasterboard is supplied with either tapered or square edges. The edge profile affects the finishing stage rather than the thermal performance of the board.
- Tapered edge: Creates a recessed joint for tape-and-jointing or skim finishing and is the usual choice where a smooth painted finish is required.
- Square edge: Has no recess and is generally used where boards meet frames, reveals or adjoining surfaces. It is not intended for tape-and-jointing.
Choosing the correct edge type before placing the order avoids delays, extra materials and unnecessary changes during installation.
Plan the Vapour Control Strategy Before Ordering
PIR-backed insulated plasterboard includes a foil facing on the insulation side that slows the movement of moisture through the wall construction. In some wall build-ups, this provides enough vapour resistance. In others, a separate vapour control layer is still needed.
Solid wall retrofit projects need particular attention. When insulated plasterboard is fitted to the inside face of a solid brick or block wall, the position of the vapour control layer should be considered during the design stage. Depending on the wall construction, an additional vapour control layer may still be required even when PIR-backed boards are used.
Checking this before materials are ordered reduces the risk of condensation forming behind the insulation and helps the finished wall comply with current Building Regulations.
Complete These Checks Before You Order
Before ordering insulated plasterboard for a retrofit wall upgrade, confirm these four points:
- The board thickness meets the target U-value.
- The fixing method is suitable for the substrate.
- The edge type matches the planned finish.
- The vapour control strategy is appropriate for the wall construction.
Working through these checks before ordering keeps the installation on schedule and gives you confidence that the finished wall will perform as intended.
Once you have confirmed the wall type, completed the U-value calculation and checked the technical data sheet for your chosen board, you can place the order knowing the specification matches the project.
