110mm Insulation

110mm insulation is used in wall, roof, or floor build-ups to provide good thermal resistance. This thickness is a practical choice for modern builds because it offers strong insulation while still fitting into many common construction cavities or layered build-ups.

What is 110mm thick insulation?

110mm thick insulation is simply insulation that measures nominally 110 mm from face to face. In practice, it is most commonly supplied as rigid panels with high‑performance foam cores.

The boards are typically faced with foil or other facings that help with vapour control when correctly detailed as part of the wall/roof build-up.

What is 110mm insulation thickness used for?

110mm insulation is thick enough to meet or help meet Part L Building Regulation targets in walls and roofs, but not so bulky that you lose significant internal space.

Here’s where it is used:

• Roof insulation – Used on pitched and flat roofing systems. Between rafters or above ceilings to keep heat from escaping through the top of a house.
• Wall insulation – To provide a continuous insulating layer in timber frames or solid walls.
• Floor insulation – Under a ground floor or beams to minimise heat loss into the ground or unheated spaces.

110mm boards can be cut and handled on site using standard tools.

All types of 110mm insulation

The most common 110mm insulation materials in the UK construction industry are PIR and phenolic foam. Foil-faced PIR and phenolic boards are usually installed on the warm side to aid vapour control where required by design.

The λ-value for PIR boards at this thickness is typically around 0.022 W/m·K, while phenolic foam can be slightly better (~0.020 W/m·K).

PIR insulation boards

These rigid foam boards are widely used on many jobs. They have a closed‑cell structure that traps tiny pockets of gas, making them excellent at restricting heat flow.

Made from polyisocyanurate foam with a foil or similar facing, PIR boards offer exceptional thermal performance (approximately λ = 0.022 W/m·K for a board of this thickness). They also have good compressive strength and are therefore suitable for typical floor and roof loads when properly supported.

PIR boards are widely stocked and used for floors, roofs, and walls.

Phenolic insulation boards

These are another type of rigid foam in which the core is made of phenolic resin. What sets them apart is their high insulation value per thickness, thanks to a fine closed‑cell structure.

Phenolic foam typically provides better insulation per millimetre than PIR, so a thick 110mm insulation board can deliver strong thermal resistance while staying relatively slim.

They are particularly useful when you want to push to very low heat loss (low U‑values) in a space where you cannot afford extra bulk.

Phenolic boards are also lightweight and resist moisture ingress, but must still be protected.

Other materials

You may also find other rigid foams like XPS insulation (extruded polystyrene) cut to around 110mm for specialist uses (e.g., high moisture or load conditions), but this is less common in general insulation boards for walls or roofs.

Fibrous insulation, such as rock wool or glass wool, is usually supplied in slightly variable thicknesses.