40mm Insulation Board K15

The 40mm insulation board is a rigid insulation board used to reduce heat loss through elements of the building fabric. It is usually specified where space is limited, but additional thermal resistance is required.

40mm insulation boards deliver a notable improvement in warmth without altering the main structure of the wall, floor, or roof.

What is 40mm insulation thickness board?

The 40mm thick insulation board is manufactured to a thickness of 40mm, which is enough to reduce heat flow meaningfully. Insulation works by slowing heat transfer by trapping still air or limiting thermal conduction.

A 40mm insulation board thickness provides greater thermal resistance than thinner lining boards. But it is not intended to replace full-depth insulation systems required for regulatory compliance.

What is 40mm thick insulation board used for?

A thick 40mm insulation board is typically used where control of build-up depth is critical:

Internal wall linings where internal space loss must be minimised.
Stud walls to improve comfort and reduce cold surface temperatures.
Floors where height build-up must be kept tight, and the board is rated for the expected loads.
Junctions, reveals, and service zones to reduce localised thermal bridging.

It is rarely used on its own in roofs, floors, or external walls. Instead, it usually supports thicker insulation elsewhere in the build-up.

Types of insulation 40mm thick board

Different materials are available at this thickness, including:

EPS Insulation (expanded polystyrene)

EPS is a lightweight foam made by fusing expanded beads. Between these beads is trapped air, which slows heat transfer. EPS is easy to handle and cut, and at 40mm, it is often used in walls or backing layers where structural loads are low, and the EPS grade is suitable. It can also be used in floors where an appropriate EPS grade is specified.

XPS insulation (extruded polystyrene)

XPS is strong under load and highly resistant to moisture. It is mainly fitted on floors and in areas exposed to damp conditions.

Phenolic Insulation foam

Phenolic boards deliver very high thermal performance for their depth. At 40mm, they can achieve comparable U-values to thicker layers of lower-performance materials. They are installed where space is severely limited, and performance targets are demanding.

PIR Insulation (polyisocyanurate)

PIR insulating boards are manufactured with a rigid polyisocyanurate foam core faced with aluminium foil. They are commonly specified in walls, floors, and roofs, as they offer solid thermal resistance in a manageable panel format.

Kingspan Optim-R VIP (vacuum insulated panel)

VIPs contain a sealed core with most of the air removed. This gives extremely low heat transfer for the thickness. A 40mm VIP offers very high performance but must be supplied in the exact dimensions required and handled carefully, as cutting or puncturing the panel irreversibly degrades its thermal performance.

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