30mm loft insulation is a thin, rigid or semi-rigid layer used to enhance thermal control in tight spaces.
It is not the depth you would choose to insulate an entire cold loft on its own, but it plays an important supporting role in many roof and floor build-ups.
It serves as a precision layer designed to improve performance, reduce cold bridging, and add controlled thermal resistance where thicker products will not fit.
What is 30mm thick loft insulation?
Thick 30mm loft insulation refers to boards or slabs manufactured to a uniform nominal thickness of 30mm. This usually means either rigid PIR boards (polyisocyanurate foam) or high-density rock mineral wool slabs.
PIR boards are:
Closed-cell in structure, with foil facings on both sides
Rigid, with good compressive resistance for internal building applications
Lightweight
They are used when you need thermal performance from minimal depth.
30mm rock mineral wool (stone wool) offers:
Non-combustible fire resistance
Good acoustic absorption in your living space
Vapour permeability
Flexibility that allows a close friction fit between timber or metal framing
A 30mm mineral wool loft insulation solution is often chosen for fire and sound reasons rather than for maximum thermal efficiency.
What is thick 30mm loft insulation used for?
A 30mm thick loft insulation board or slab is rarely used across the whole loft floor in a cold roof. Instead, it is suitable for use in targeted areas where build-up depth is restricted or detailing needs tightening.
In typical site applications, it is commonly used in the following areas:
1. Floor applications
30mm PIR can be laid over structural decking or between battens as part of a layered floor build-up in loft conversions.
Typical example:
100mm between joists
30mm over joists to reduce thermal bridging
18mm chipboard above
The continuous insulation layer above the joists improves thermal continuity and comfort underfoot. It also helps reduce cold stripes caused by timber joists interrupting insulation.
30mm enhances the system, but does not replace deeper insulation where Building Regulations require lower U-values.
2. Framing walls
In dormer cheeks or stud partitions within a loft conversion, 30mm boards may be used:
Between studs where cavity depth is limited
As an internal overboard layer
To reduce thermal bridging through timber studs
Mineral wool versions fit tightly between studs and improve sound separation. PIR boards give stronger thermal performance when space is tight.
3. Internal masonry walls
Where loft spaces meet gable or party walls, a 30mm layer can be fixed internally to reduce heat loss and cold bridging at junctions.
PIR boards are mechanically fixed or adhesively bonded, with joints taped. Mineral wool slabs are friction-fitted within a battened lining system.
This application is common in retrofit loft upgrades where full cavity insulation is not feasible.
4. Pitched roof build-ups
Within a pitched roof, 30mm loft insulation is often used:
As an internal under-rafter layer
Between rafters where depth is limited
As part of a layered build-up that allows services to be routed without penetrating the primary insulation layer
For example:
100mm between rafters
30mm across rafters internally
Plasterboard beneath
The cross-layer reduces thermal bridging from timber rafters and improves overall U-value consistency.
Some multifoil products, such as SuperFOIL insulation 30mm thick loft variants, are also used in pitched roof systems where reflective layers are specified, though performance depends heavily on correct air gaps and installation details.
Types of 30mm loft insulation
We stock two main types:
PIR insulation boards 30mm
2400mm x 1200mm x 30mm PIR insulation board is best for:
Maximum thermal resistance per millimetre
Low-depth build-ups
Over-boarding
Key features:
Lambda around 0.022 W/mK
High compressive strength
Foil-faced
Light and easy to handle
This is usually the go-to option when someone specifies 30mm loft insulation thickness for thermal efficiency reasons.
Rock mineral wool slabs 30mm
Best for:
Fire protection
Acoustic improvement
Breathable constructions
Key features:
Non-combustible (Euroclass A1)
Flexible fit
Vapour permeable
Heavier than PIR
If the priority is fire rating or sound insulation, mineral wool is often a better choice than rigid foam.
At Insulation Wholesale, you can purchase 30mm Loft Insulation at low wholesale prices with fast delivery for most of items within 2-5 days. Competitive rates guaranteed.
FAQ
Where to buy 30mm loft insulation?
You can purchase your 30mm loft insulation online from Insulation Wholesale. We stock PIR and mineral wool options in UK stock, ready for fast delivery to your site. Our prices are competitive, with trade discounts, pallet deals, and a fast quote service available.
How to cut 30mm loft insulation?
PIR boards: Place the board on a stable surface, then score with a sharp utility knife against a straight edge. Then snap over a firm edge. To get cleaner edges, use a fine-tooth saw.
Mineral wool slabs: Use a long insulation knife or serrated blade. Cut a little oversized (5–10mm) so the slab friction-fits between studs.
Wear appropriate PPE, including gloves, eye protection, and a dust mask.
Where to fix 30mm loft insulation?
It depends on the build-up:
Between rafters – Improves thermal resistance within a pitched roof while keeping the roof height unchanged. Used where rafter depth allows partial fill.
Across rafters – Reduces cold bridging through timber rafters and improves overall U-value consistency. Often used in loft conversions.
Between floor joists – Slows heat loss through the loft floor in a cold roof setup. When used alongside deeper insulation.
Over structural decking – Adds a continuous thermal layer and reduces cold bridging through joists below. Common in loft conversion floor upgrades.
Within stud frames – Improves thermal and acoustic performance in dormer cheeks and internal partitions.
Against gable or party walls – Reduces cold bridging and the risk of surface condensation on exposed masonry.
Check condensation risk in line with BS5250. When adding internal insulation layers, the vapour control layer positioning matters.
How much does 30mm loft insulation cost per square metre?
Indicative UK price ranges (excluding VAT):
30mm PIR costs roughly £10–£18 per m²
30mm mineral wool slab goes for roughly £6–£12 per m²
Prices vary by brand, board size, and order volume. Bulk buying usually lowers the per-square-metre rate.
We supply 30mm loft insulation in bulk, and provide fast nationwide delivery from UK stock. For larger quantities of insulation products, request a fast quote, and we will provide accurate project pricing.
30mm Recticel Eurothane GP is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Recticel is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
£18.31£21.97Ex VATInc VAT£6.36£7.63Per M2Add to cart
30mm Ecotherm Eco-Versal is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Ecotherm Eco-Versal is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
£18.99£22.79Ex VATInc VAT£6.59£7.91Per M2Add to cart
30mm IKO Enertherm ALU PIR (polyisocyanurate) insulation is a top-quality insulation board featuring a rigid PIR foam core and reflective aluminium foil facings. It delivers outstanding thermal performance and moisture resistance, making it suitable for various installations and an ideal choice for different energy-efficient projects.
All three models 30mm Kingspan Therma PIR Insulation Board:
30mm Thermapitch TP10
30mm Thermafloor TF70
30mm Thermawall TW55
share the same high-performance PIR core and low-emissivity foil facings, offering excellent thermal efficiency and easy installation. Although labeled differently, these boards share identical technical specifications.
£269.23£323.08Ex VATInc VAT£9.35£11.22Per M2Add to cart
30mm Mannok PIR Insulation Board is an excellent choice for anyone looking for a high-performance insulation solution that provides superior thermal efficiency. It is ideal for use in any construction project, such as commercial and residential, in wall applications as well as roofing and flooring applications.
30mm Rockwool RWA45 has been developed for thermal, acoustic and fire performance in a range of construction types. It is suitable for applications on partition walls, ceilings, floors and roofs.
30mm 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.
