What is Celotex PL4025?

The PL4025 is a thermal laminate plasterboard from Celotex comprising a rigid PIR (polyisocyanurate) insulation layer bonded to a 12.5 mm tapered-edge plasterboard. The total thickness is 37.5 mm (typically 25 mm PIR + 12.5 mm plasterboard).
It comes in standard sheet size 2400 mm × 1200 mm. 
Thermal conductivity is 0.022 W/m·K, offering high performance insulation.

Key Specifications & Features

Here’s a breakdown of the most important specs and what they mean:

• Dimensions: 2400 mm (L) × 1200 mm (W), thickness 37.5 mm overall.

• Core material: Rigid PIR insulation, with low-GWP (global warming potential) and zero ozone-depletion potential (ODP).

• Thermal conductivity (λ): 0.022 W/m·K — indicates very efficient insulation.

• R-Value: For PL4025 (25 mm insulation + 12.5mm board) an R-value of about 1.20 m²K/W is cited for internal masonry wall application.

• Fire / reaction to fire: The boards achieve Euroclass B-s1,d0 (under EN 13501-1) in typical listings.

• Certifications: BBA Certificate 16/5357 (Plasterboard Thermal Laminate) for correct installation in the specified use.

• Environmental credentials: Zero ODP, low GWP, and rated “A+” in the BRE Green Guide for the product range.

• Applications: Suitable for internal insulation of masonry walls, timber frame linings, pitched roofs (between/under rafters), flat roofs (under joists).

• 2-in-1 solution: Because the insulation is bonded to plasterboard, you get insulation and dry-lining in one step—saving installation time.

Why Choose PL4025? Benefits

Here are the main advantages:

1. Space-saving high performance: Because the PIR is high performance (λ=0.022 W/m·K), you can achieve required U-values with less thickness compared to older or lower-grade insulation.

2. Faster installation: By combining plasterboard and insulation, you reduce handling, separate board/insulation work and waste.

3. Improved energy efficiency: Less heat loss means lower heating bills, better comfort, and helps building compliance for retrofit or new build.

4. Quality finish: The plasterboard has tapered edges, giving a smoother join finish for decorating or tiling.

5. Versatility: Can be used in various building elements (walls, roofs, timber frame, solid walls) making it flexible for many projects.

6. Sustainable credentials: With zero ODP and low GWP, it aligns with modern sustainability requirements.

Typical Installation Scenarios & Tips

Here are some practical advice and scenarios for using PL4025 effectively.

Internal masonry wall upgrade

You might fix the board direct onto existing masonry via dot-and-dab adhesive or mechanical fixings. The product can improve U-value significantly and give a dry-lined finish ready for decoration. Ensure you follow the manufacturer’s datasheet and any BBA certificate conditions.
Tip: Seal all joints, very carefully manage the flooring-wall interface and ensure adequate vapour control if required.

Timber-frame or stud wall lining

For timber frame walls, PL4025 can be fixed to studs, providing both insulation and internal lining in one. The rigidity of boards helps with handling and finish.
Tip: Ensure fixings go to manufacturer specification; avoid bridging insulation gaps which reduce performance.

Roof/loft conversion

In sloped ceilings or loft conversions, PL4025 can be used between/under rafters or joists. The thinner 37.5mm profile is useful when headroom is limited.
Tip: In roof zones, always check fire regulations (especially if it’s compartment floor/ceiling) and condensation risk. Good ventilation and vapour control often remain important.

Finish & decoration

Once fixed, the plasterboard side provides a standard finish ready to tape, skim, and decorate. Tapered edge helps for a cleaner finish.
Tip: For tiling, ensure boards are firmly fixed, joints treated, and surface adequately primed for tile adhesive.

What to Look Out For / Limitations

No product is perfect for every scenario. Here are some caveats and things to check:

• Thickness constraint: At 37.5 mm thickness overall, if you’re trying to achieve very low U-values (e.g., Passivhaus) you may still need additional insulation elsewhere or thicker boards.

• Fire regulations in tall buildings: Some PIR insulation products are restricted in external wall use of buildings over certain heights (e.g., 18 m in England). PL4025 listings note “you need to satisfy yourself that use of the product meets all relevant national Building Regulations and relevant restrictions.”

• Installation quality matters: The board’s performance depends on proper fitting—tight joints, proper fixings, sealing edges, avoiding thermal bridging. Poor installation may erode performance.

• Moisture / vapour control: In some situations (especially roofs or cold bridging scenarios), vapour control or additional detailing may be required to avoid condensation risk.

• Storage & handling: PIR boards need to be stored flat, dry, and protected from sunlight and moisture.

• Cost vs basics: While PL4025 offers high performance, it may cost more than.basic insulation + plasterboard separately. But the time savings and performance gains often justify it.

Summary & Final Thoughts

The Celotex PL4025 is a strong choice for internal insulation/dry-lining when you want a high performance, time-efficient solution. Its combined insulation + plasterboard format, excellent thermal performance (λ 0.022 W/m·K), and versatility make it suitable for both retrofit and new build.

If you’re working on a project where head-room is limited, or you need to upgrade wall/roof insulation while minimizing thickness, PL4025 should be high on your list. Just make sure you follow manufacturer installation guidelines, check building regulations (especially fire/height) and consider whether the thickness meets your target U-value or if you’ll need additional measures.