Floor Insulation Boards

What are Floor Insulation Boards?

Floor insulation boards are insulation panels used to combat heat loss through a building’s floor. Whether in direct contact with the ground or placed above suspended timber floors, these rigid panels help to seal off energy-draining gaps.

Ideal for use in both new builds and retrofitting projects, they offer versatile solutions for different floor types, including solid concrete and suspended timber floors.

Types of Floor Insulation Boards

Several types of rigid insulation boards are commonly used for floors. Each has unique thermal, structural, and moisture-resistance characteristics.

PIR (Polyisocyanurate) Boards

Products: Celotex GA4000, XR4000; Unilin Xtratherm Thin-R

• Composition: Closed-cell PIR foam core with foil facings on both sides, usually low-emissivity aluminium.
• Thermal Conductivity: Approx. 0.022-0.026 W/mK.
  
  

Performance Characteristics:

• Traps insulating gases in its closed-cell structure, offering low thermal conductivity.
• Foil facings reflect radiant heat and act as a vapour control layer.

Common Applications:

• Solid concrete floors (above or below slab)
• Suspended timber floors
• Underfloor heating systems
  
  

Available Thicknesses: 20mm to 200mm

Phenolic Foam Boards

Products: Kingspan Kooltherm K103

• Composition: Fine closed-cell phenolic foam with foil composite facings.
• Thermal Conductivity: Among the lowest available, approx. 0.018-0.020 W/mK.
  
  

Performance Characteristics:

• Superior thermal resistance allows thinner build-ups.
• Excellent fire performance compared to other foam insulants.

Common Applications:

• High-performance builds with space constraints.
• Solid and suspended floors, including underfloor heating.

Available Thicknesses: 25mm to 150mm

EPS (Expanded Polystyrene) Boards

Products: EPS70, EPS100, EPS150

• Composition: Moulded polystyrene beads expanded (EPS) and fused into rigid boards.
• Thermal Conductivity: Approx. 0.036-0.038 W/mK.

Performance Characteristics:

• Lightweight and cost-effective.
• Insulates via trapped still air within closed cells.
• Available in various compressive strengths (70-150 kPa at 10% deformation).

Common Applications:

• Ground-bearing concrete slabs (above or below slab)
• Suspended timber floors
  
  

Available Thicknesses: 25mm to 150mm

XPS (Extruded Polystyrene) Boards

Products: Kingspan GreenGuard XPS

• Composition: Extruded, closed-cell foam with uniform density.
• Thermal Conductivity: Approx. 0.033-0.036 W/mK.
  
  

Performance Characteristics:

• Highly moisture-resistant and dimensionally stable.
• High compressive strength - ideal for heavy floor loads.

Common Applications:

• Inverted flat roofs
• Cold storage facilities
• Ground-bearing concrete floors with high moisture exposure
  
  

Available Thicknesses: 30mm to 120mm

Flooring Applications That Benefit From Floor Insulation Boards

• Underfloor Heating Systems: Floor insulation boards are commonly used in conjunction with underfloor heating systems. They minimise heat loss and help to distribute the heat evenly across the floor surface.
• Floating Floors: When installing floating floors, such as laminate or engineered wood, insulation boards can be placed beneath to provide thermal insulation and reduce noise transmission between floors.
• Concrete Floor Insulation: In concrete flooring, insulation boards placed beneath the concrete slab enhance both energy efficiency and structural stability. This method is particularly effective in commercial and industrial settings.
• Suspended Floors: Insulation boards can be used between floor joists in suspended floors. This helps maintain a consistent indoor temperature and prevents heat loss through the floor.
• Loft Conversions: For converting attics or lofts into liveable spaces, floor insulation boards are vital. 

Choosing the Right Floor Insulation Board

Selecting the appropriate board depends on multiple factors:

• Target U-Value: Must meet or exceed building regulation requirements.
• Floor Type: Some boards are better suited to solid concrete slabs; others work well in suspended timber floors.
• Compressive Strength: Heavily trafficked floors or those supporting heavy loads require high-strength insulation.
• Moisture Exposure: Areas with damp risk (e.g., ground floors, basements) may require XPS or moisture-resistant PIR.
• Build-Up Depth: Where space is limited, boards with higher thermal performance per mm - like phenolic or PIR - may be preferable.

Laying Floor Insulation Boards

Please note when laying insulation you may need other building materials such as a damp-proof membrane.

• Prepare the floorboards - Clear any debris and dust away. You might have to use a layer of plywood to ensure the floor level is flat.
• Prime solid floor - You need to prime a concrete floor before you lay insulation boards. Thermal primers can help to further reduce the loss of heat from your home. If you are laying insulation under timber floors, you do not have to worry about primer. You can also lay a damp proof membrane below or above the floor.
• Cut the boards - You can cut floor insulation boards with a standard utility knife. We recommend marking your measurements on the board before cutting to avoid mistakes.
• Place the boards - You should stagger insulation boards to reduce drafts. If you are laying solid floor insulation, use an adhesive to secure them in place. For a suspended timber floor, we recommend screwing the boards into place at 300mm intervals across the floor space. It's important not to block air bricks.
• Seal the joints - You need to make sure that the seams between the joints are sealed. Lots of people use waterproof tape to seal the joints. Some people go the extra mile and use acrylic sealant before the tape.

Always consult a professional.