120mm Insulation Board

A 120mm insulation board is a thick layer of rigid insulation used where low heat loss is required and sufficient installation depth is available. At 120mm thickness, the insulation forms a significant part of the building’s thermal envelope, helping structures meet modern energy efficiency standards.

What is 120mm thick insulation board?

120mm thick insulation board has an insulation depth of approximately 120mm from face to face. The board is rigid, meaning it keeps its shape and fits tightly between or against building elements.

Many 120mm insulation boards use a closed-cell structure, where gas trapped within sealed cells slows heat transfer.

A 120mm insulation thickness board is usually preferred when designers want to achieve low U-values. It also comes in handy for upgrading older buildings susceptible to high heat leakage. It is commonly specified for refurbishment projects, extensions, and high-spec new builds with demanding energy performance targets.

What is 120mm insulation thickness board used for?

An insulation 120mm thickness board is used in areas with high heat loss or where building regulations push performance higher. These can be:

• Flat roofs, especially warm roof systems using a 120mm flat roof insulation board 
• Pitched roofs, between and over rafters
• Floors, including solid or suspended floor subject to regular load
• Internal masonry walls, where space allows for deep lining
• Framing walls, timber or metal stud
• Cladding systems, as part of an external wall build-up

120mm insulation board significantly contribute to improved thermal comfort and heat reduction when correctly installed. However, to maintain performance, you must detail it carefully around junctions, fixings, and edges.

Types of 120mm insulation board

120mm insulation boards are available in these common types:

PIR insulation (Polyisocyanurate)

120mm PIR insulation board offers strong thermal performance for its thickness. It balances cost, performance, and availability, which is why it suits most general building work – whether walls, roofs, or floors.

Phenolic insulation Foam Board

Phenolic boards offer very high thermal performance for the same depth and slightly better insulation than PIR at 120mm. They are often preferred where performance targets are strict – for example, internal wall linings on refurb projects.

XPS insulation (Extruded Polystyrene)

XPS panels do not insulate as well as PIR or phenolic at the same thickness. However, XPS offers superior moisture resistance and compressive strength. It is often used below ground or in floors where compressive strength matters more than maximum thermal value.

Benefits of insulation 120mm board

Installing 120mm insulation boards:

• Provides a significant reduction in heat loss.
• Helps meet demanding U-value targets.
• Improves thermal comfort and temperature stability.
• Reduces heating demand over the life of the building.
• Suits walls, roofs, and floors when space allows.