150mm Insulation Board

A 150mm insulation board is typically specified as part of the structural build-up. This is not a finishing layer or a quick thermal upgrade. It is a depth chosen at the design stage to control a building’s thermal behaviour.

What is a 150mm thick insulation board?

A 150mm thick insulation board is a rigid, full-depth insulation panel engineered to fit within a defined structural build-up. Boards this deep are planned in from the start because they influence roof depths, floor levels, and wall build-ups.

Both thickness and material influence the board’s performance. The depth increases the thermal resistance by extending the heat flow path, which is what insulation is meant to do.

Unlike flexible insulation, the 150mm thick insulation board is less prone to sagging or being compressed when correctly installed and supported. It holds its form, which means the insulation layer stays consistent across the whole surface. That consistency helps reduce cold bridging and uneven heat loss problems often associated with gaps, compression, or poor detailing.

These boards are commonly supplied in standard formats such as 2400 x 1200 x 150mm insulation boards and are easy to set out across joists, rafters, or wall zones with minimal cutting.

What is 150mm insulation board used for?

A 150mm insulation thickness board is used where thinner materials would not meet U-value targets without layering.

• Cladding – used behind external cladding systems to control heat loss through the main structure while keeping the outer finish ventilated.
• Flat roofs – Often installed above the deck in warm roof systems. A 150mm roof insulation board keeps the structure warm, reducing condensation risk when correctly detailed with a vapour control layer.
• Pitched roofs – Chosen when rafters allow deeper insulation without complex layering. Installers often use 150mm to help achieve compliance while keeping the build-up straightforward.
• Floors – Used where ground heat loss is a concern, especially on new slabs. It reduces downward heat loss into the ground.
• Heavy-duty floors – Specified on sites expecting higher point loads. At this depth, performance and compressive strength work together when the appropriate compressive strength grade is specified.
• Framing walls – Installed between studs in timber or steel frames to create a deep insulation zone.
• Internal masonry walls – Used where internal space can accommodate deeper build-ups and high thermal resistance is needed without external alterations.

What types of 150mm insulation board are there?

PIR Insulation (Polyisocyanurate)

PIR is often a common choice at this thickness. PIR insulation board 150mm performs well across roofs, walls, and floors while remaining easy to handle and fix.

PIR is valued for its predictable behaviour. It cuts cleanly, fits neatly between structural elements, and works across a range of applications without specialist detailing.

EPS Insulation (Expanded Polystyrene)

EPS is ideal when you need depth without adding unnecessary cost. The material uses trapped air to slow down heat transfer, making it a practical choice where space is available. EPS is typically the most cost-effective option for use in floors and walls when the correct grade is selected and moisture exposure is controlled.

Installers like EPS because it’s light and easy to cut and handle. It’s often specified where large areas need insulating without pushing material costs too high.

XPS Insulation (Extruded Polystyrene)

XPS closed-cell structure resists water uptake far better than most boards.

The board maintains good thermal performance even when conditions are less than ideal, making it a go-to for ground floors and perimeter details.

XPS 150mm is commonly used below slabs and in areas where damp conditions would compromise other materials.

Phenolic Insulation

Phenolic foam is commonly used where high thermal performance is needed in a limited space.
It delivers strong insulation values for its thickness. A 150mm depth helps maximise performance without pushing build-ups beyond acceptable limits.

Phenolic boards are more brittle than PIR; they should be handled carefully during cutting and installation.

Benefits of 150mm insulation board

Here are the benefits of installing a 150mm thick insulation board:

• Strong resistance to heat loss without stacking multiple layers
• Helps buildings meet strict energy standards more easily
• Reduces cold spots by creating a continuous insulation layer
• Suitable for roofs, walls, and floors with planned depth
• Long service life when correctly installed
• Minimal installation errors. Using a single 150mm layer instead of stacking multiple layers reduces detailing errors and installation time.