15mm loft insulation is designed to enhance thermal control in tight spaces. It is a precision layer that plays an essential supporting role in floors, roof details, and wall build-ups connected to loft spaces.
15mm thick loft insulation refers to a rigid insulation board with a fixed depth of 15mm. In the UK, this thickness is most commonly manufactured from PIR (polyisocyanurate) foam.
15mm PIR has an R-value of roughly 0.68m²K/W, which is nowhere near enough to meet typical Part L elemental U-values requirements on its own, but it works well as:
15mm PIR boards are used in wall, roof, and floor insulation, especially where headroom or detailing limits thickness.
However, 15mm on its own will not achieve the current Part L U-value targets for these structures. Its R-value (roughly 0.68m²K/W) is far below the resistance required to achieve typical new-build elemental targets.
Instead, 15mm insulation is used as a supplementary layer on:
On loft conversion jobs, space is gold. A 15mm board can:
In pitched roofs, 15mm thick loft insulation may be used:
Being rigid and foil-faced, it also helps with airtightness when foil joints are taped properly, edges sealed, and service penetrations properly detailed.
In knee walls or dormer structures, 15mm PIR:
At Insulation Wholesale, we stock PIR loft insulation 15mm thick. Its main features include:
This is the standard specification for this thickness.
You can buy 15mm loft insulation online from Insulation Wholesale. We stock UK-manufactured PIR loft insulation boards in 15mm. We offer pallet deals, low wholesale pricing, and delivery to your site. Fast quotation turnaround is available.
Yes. PIR boards at 15mm are easy to cut.
Use:
Score deeply on both sides and cut through the core for a clean edge. Seal joints with foil tape to ensure airtightness. Always measure carefully so there are no gaps.
The 15mm rigid PIR insulation board is easy to install. Fixing methods vary by installation location:
Under rafters or ceilings
On floors
On walls
Most 15mm loft insulation in the UK is PIR (polyisocyanurate). It’s a rigid foam formed through a chemical reaction between polyols and isocyanates.
It contains:
Mineral wool is not produced at 15mm because it would offer very little resistance at that depth.
For rigid loft boards, 15mm is typically the thinnest commonly stocked PIR thickness in the UK, with options available up to 200mm. Below that, you may find multifoil reflective layers and specialist thermal laminates.
But in standard board form, 15mm thick loft insulation is usually the starting point for rigid PIR insulation.
15mm Unilin Thin-R PIR insulation is a foil faced, high-performance insulation solution that offers exceptional thermal efficiency and durability. This polyisocyanurate insulation board, formerly known as Xtratherm, is ideal for a range of applications, such as floors, pitched roofs, and walls.