How to Install PIR Insulation Boards on External Wall?

In recent years, PIR insulation boards have become a popular choice for insulating external walls due to their high thermal efficiency, lightweight properties, and excellent moisture resistance. With growing concerns about energy costs and environmental impact, homeowners and contractors are increasingly turning to PIR insulation boards to improve building energy performance.

This article provides a step-by-step guide on how to install PIR insulation boards on external walls, discusses whether these boards can be used outside, and offers essential tips for ensuring an effective insulation installation. Whether you're a homeowner looking to improve your property's energy efficiency or a contractor seeking the best insulation solution, this guide will provide valuable insights.

Can PIR Insulation Be Used Outside?

Yes, PIR insulation boards can be used outside, and they are commonly used in external wall insulation (EWI) systems. PIR insulation boards are made from polyisocyanurate (PIR) foam, which offers superior thermal resistance compared to traditional insulation materials like fiberglass or mineral wool. However, when installing these boards externally, it's essential to consider the following:

1. Weather Resistance

While PIR insulation boards have excellent thermal properties, they need adequate protection from direct exposure to the elements. Typically, these boards are covered with a render system, cladding, or weatherproof membrane to prevent degradation from UV rays, moisture, and mechanical damage.

2. Fire Safety Compliance

Building regulations often require insulation materials to meet specific fire resistance standards. Some PIR insulation boards come with fire-retardant facings, but it's crucial to ensure compliance with local building codes before installation.

3. Compatibility with External Wall Systems

PIR insulation boards are compatible with various external wall systems, including:

• Solid masonry walls

• Timber frame constructions

• Steel frame buildings

• Brick and block cavity walls (as part of an external insulation system)

4. Moisture Management

To prevent condensation buildup, PIR insulation boards should be installed with a breathable membrane or vapour control layer, depending on the building structure. Proper detailing at joints and edges will help maintain insulation performance.

How to Install PIR Insulation Boards on External Wall?

Installing PIR insulation boards on an external wall requires careful planning, the right materials, and proper execution. Below is a step-by-step guide to ensure a successful installation.

Materials and Tools Needed:

Before starting the installation, gather the following materials and tools:

Materials:

• PIR insulation boards (choose the right thickness for your project)

• External wall adhesive or mechanical fixings

• Breathable membrane or vapour control layer (if required)

• External render system or cladding

• Insulation board joint tape

• Sealant for edges and gaps

Tools:

• Measuring tape

• Utility knife or insulation saw

• Spirit level

• Trowel (for applying adhesive)

• Drill (for mechanical fixings)

• Safety goggles and gloves

Step 1: Prepare the External Wall Surface

Before installing PIR insulation boards, the external wall surface must be clean, dry, and structurally sound. Follow these steps:

1. Remove any debris, dust, or loose materials from the wall surface.

2. Repair cracks or damaged areas to ensure a stable substrate.

3. Check for damp issues—if present, resolve them before proceeding.

Step 2: Determine the Insulation Thickness

The thickness of PIR insulation boards depends on your required thermal performance. Here's a comparison of thickness vs. thermal resistance:

Board Thickness (mm)	Thermal Resistance (R-Value) (m²K/W)
25mm	1.13
50mm	2.25
75mm	3.38
100mm	4.50

The recommended thickness varies based on climate conditions and building regulations.

Step 3: Measure and Cut PIR Insulation Boards

1. Measure the wall dimensions and mark the cutting lines on the PIR insulation boards.

2. Use a utility knife or insulation saw to cut the boards accurately.

3. Ensure boards fit tightly together to minimize thermal bridging.

Step 4: Fixing PIR Insulation Boards to the External Wall

There are two primary methods for fixing PIR insulation boards to an external wall:

Method 1: Adhesive Fixing

1. Apply external wall insulation adhesive to the back of each board using a notched trowel.

2. Press the board firmly onto the wall and ensure even contact.

3. Use a spirit level to check for alignment.

4. Allow the adhesive to set before proceeding to the next step.

Method 2: Mechanical Fixings

1. Drill holes through the PIR insulation boards and into the wall.

2. Insert insulation fixings (such as insulation anchors or washers) into the pre-drilled holes.

3. Secure the boards using screws or special insulation plugs.

For enhanced stability, a combination of adhesive and mechanical fixings is recommended.

Step 5: Sealing Joints and Gaps

To prevent thermal bridging and air leakage:

1. Apply insulation board joint tape at all seams.

2. Use sealant around board edges and at junctions with windows and doors.

Step 6: Apply a Protective Finish

Once the PIR insulation boards are securely installed, apply a protective finish:

Option 1: Render System

• Apply a basecoat render with embedded reinforcement mesh.

• Once dry, apply a topcoat render for a weather-resistant finish.

Option 2: Cladding

• Install cladding materials (e.g., timber, brick slips, PVC, metal).

• Ensure proper ventilation behind the cladding to prevent moisture buildup.

Step 7: Final Inspection and Maintenance

1. Check for any gaps or misaligned boards.

2. Ensure all fixings are secure.

3. Regularly inspect the insulation system for signs of wear or damage.

Conclusion

Installing PIR insulation boards on an external wall is an effective way to enhance a building's energy efficiency, reduce heat loss, and improve comfort levels. These boards provide excellent thermal insulation, moisture resistance, and ease of installation. However, proper planning, correct installation techniques, and protective finishes are crucial to ensure long-term performance.

By following the step-by-step installation guide, homeowners and contractors can maximize the benefits of PIR insulation boards, resulting in lower energy bills and a more sustainable living environment.

FAQs

1. What is the best thickness for PIR insulation boards for external walls?

The ideal thickness depends on the desired thermal resistance. Generally, 50mm to 100mm PIR insulation boards are used for external wall insulation.

2. Can PIR insulation boards be left exposed outside?

No, PIR insulation boards must be covered with a protective layer such as a render system or cladding to prevent UV and moisture damage.

3. Do I need a vapour control layer with PIR insulation boards?

It depends on the wall type. In high-humidity areas, a vapour control layer may be necessary to prevent condensation.

4. How long do PIR insulation boards last?

When properly installed and protected, PIR insulation boards can last over 25 to 50 years, maintaining their insulation performance.

5. Are PIR insulation boards better than EPS or XPS insulation?

Yes, PIR insulation boards have a higher thermal resistance (R-value) per mm compared to EPS (Expanded Polystyrene) and XPS (Extruded Polystyrene), making them a more space-efficient insulation solution.