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100mm Celotex GA4100 PIR Insulation Board 2400mm x 1200mm (8′ x 4′) 2.88m2
100mm Celotex GA4100 is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Celotex is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.
£40.17£48.20 Ex VATInc VAT£13.95£16.74 Per M2 Add to cart -
100mm Ecotherm Eco-Versal Rigid PIR Insulation Board 2400mm x 1200mm (8′ x 4′) 2.88m2
100mm 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.
£40.34£48.41 Ex VATInc VAT£14.01£16.81 Per M2 Add to cart -
100mm Isover Spacesaver Insulation Loft Roll 14.13m2
100mm Isover Spacesaver Insulation Loft Roll is an efficient and easy-to-install solution for insulating loft spaces, designed to enhance energy efficiency and home comfort.
£32.79£39.35 Ex VATInc VAT£2.32£2.78 Per m2 Add to cart -
100mm Knauf Insulation Loft Roll 44 Combi-Cut 13.89m2 Roll
Knauf Insulation Loft Roll 44 is a non-combustible glass mineral wool roll supplied in a Combi-Cut format. It is designed for use in cold lofts. Manufactured using Knauf Insulation’s unique bio-based binder, ECOSE® Technology.
£29.89£35.87 Ex VATInc VAT£2.15£2.58 Per m2 Add to cart -
100mm ODE Insulation Loft Roll 10.83m2
100mm ODE Insulation Loft Roll is a highly effective thermal loft solution for improving home energy efficiency. Made from eco-friendly materials, it offers a simple and effective way to improve comfort while lowering energy costs.
£22.84£27.41 Ex VATInc VAT£2.11£2.53 Per m2 Add to cart -
100mm Recticel Eurothane GP PIR Insulation Board 2400mm x 1200mm (8′ x 4′) 2.88m2
100mm 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.
£37.85£45.42 Ex VATInc VAT£13.14£15.77 Per M2 Add to cart -
100mm Rockwool Flexi Slab Acoustic Insulation 1200mm x 600mm 4.32m2 Pack
100mm Rockwool Flexi has been designed as a multi-use, dual-purpose acoustic and thermal mineral wool insulation with a unique flexible edge along one side. It is suitable for use all over the home, in pitched roof rafters, framed external walls, internal partitions, intermediate floors, separating walls and floors, and timber suspended ground floors.
£42.91£51.49 Ex VATInc VAT£9.93£11.92 Per m2 Add to cart -
100mm Rockwool RWA45 Acoustic Insulation Slab 1200 x 600mm 2.88m2 Pack
100mm 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.
£23.41£28.09 Ex VATInc VAT£8.13£9.76 Per m2 Add to cart -
100mm Superglass 44 Multi Loft Roll Insulation 12.12m2 Roll
Multi-Roll 44 is a lightweight, non-combustible glass mineral wool roll, designed to provide thermal insulation in lofts. This roll is typically used for insulating loft spaces and cold roofs but can also be used in a multitude of different applications.
£27.35£32.82 Ex VATInc VAT£2.26£2.71 Per m2 Add to cart
100mm Loft Insulation
100mm of loft insulation is a commonly used thickness in many loft insulation build-ups. It is substantial enough to help reduce heat loss and can be installed without requiring major structural redesign in many UK homes.
What is loft insulation 100mm?
Loft insulation 100mm is manufactured to a nominal thickness of 100mm. It comes in boards, slabs, and rolls and is suitable for roof-space applications.
100mm insulation depth provides a measurable level of thermal resistance, but the exact resistance depends entirely on the material, such as Isover or Knauf insulation.
- PIR rigid boards have low thermal conductivity, commonly around 0.022 W/mK
- Glass mineral wool rolls or slabs typically have a thermal conductivity of around 0.040 – 0.044 W/mK, depending on product grade, such as a 100mm Knauf loft roll.
- Rock mineral wool slabs often have around 0.034–0.037 W/mK
What is 100mm thick loft insulation used for?
Between loft joists (cold lofts)
100mm glass or rock wool is commonly installed between timber ceiling joists. This acts as the base layer in many cases. Additional insulation is then laid crosswise above to help achieve current Building Regulations guidance (Approved Document L).
100mm mineral wool on its own will not normally achieve the commonly targeted U-values of around 0.16 W/m²K for existing loft upgrades, but it forms a strong first layer.
Loft floor upgrades
Where lofts are used only for storage, 100mm PIR between joists can help maintain thermal performance while supporting the use of raised boarding above. Because PIR offers higher thermal resistance per millimetre, it’s often selected for use where height is restricted.
Pitched roof insulation (warm roof construction)
In rafter-level builds, 100mm PIR is commonly fixed either between or across rafters. In many cases, it forms part of a layered system, combined with an additional continuous layer to reduce thermal bridging.
Loft framing walls and internal masonry walls
In loft conversions, knee walls or dwarf walls often need insulation to enhance energy efficiency. 100mm boards or mineral wool slabs are used within timber framing to maintain continuity of the thermal envelope. Vapour control and airtightness detailing become critical here to prevent interstitial condensation.
Types of 100mm loft insulation
We stock three main categories of 100mm loft insulation:
PIR insulation
These are high-performing, foil-faced boards.
- Low thermal conductivity – around 0.022 W/mK
- They are ideal for tight spaces and areas with demanding target U-values
- They require accurate cutting and a tight fit
Glass wool insulation (rolls or slabs)
Both slabs and loft insulation rolls 100mm are light and flexible.
- They friction-fit easily between joists, making installation straightforward.
- Provide effective acoustic absorption
- Lower cost per m²
- Needs greater thickness than PIR to achieve similar thermal insulation results
Rock mineral wool (slabs)
- Typically classified as Euroclass A1 reaction to fire (non-combustible)
- Often chosen where fire separation or sound reduction is important
Consider the product’s performance per millimetre, fire rating, acoustic insulation needs, and budget when choosing between materials.
Benefits of 100mm loft insulation thickness
- Noticeable thermal performance improvement compared with thinner insulation layers
- Fits standard joist and rafter depths without major structural change
- Works as a dependable base layer in multi-layer systems
- Balances cost and performance effectively
- Mineral wool versions improve sound absorption
- Rock mineral wool provides high fire resistance
100mm thick insulation loft roll 44 can significantly reduce heat loss through the roof when correctly installed.
Why choose our thick 100mm loft insulation?
At Insulation Wholesale, we keep supplies simple and efficient by:
- Hold strong UK stock levels of popular items, such as the 100mm Knauf loft roll.
- Offer competitive pricing and clear bulk rates
- Provide pallet deals for larger projects
- Deliver directly to your site or home
- Provide fast quotes for trade accounts
- Support both DIY customers and contractors
- Keep our 100mm loft insulation prices transparent and trade-friendly
Our team understands U-values, detailing, and compliance, and is always ready to provide guidance when needed.
FAQ
Where to buy 100mm loft insulation online?
You can buy 100mm thick loft insulation online from Insulation Wholesale. We offer PIR boards, glass wool rolls, and rock mineral wool slabs in loft Insulation 100mm options, ready for dispatch. With bulk discounts, fast nationwide delivery, and knowledgeable support, we make it straightforward to order the right material for your job.
How good is 100mm loft insulation?
It is effective when used correctly. The answer depends not only on thickness, but also on material and build-up.
- 100mm mineral wool provides roughly 2.27 m²K/W at 0.044 W/mK. On its own, this is typically insufficient to meet modern upgrade targets for the loft insulation roll. But as part of a layered build-up, it performs well.
- 100mm PIR at 0.022 W/mK achieves around 4.5 m²K/W, giving significantly stronger thermal resistance per layer.
How to cut loft 100mm insulation?
Mineral wool insulation roll: Use a long insulation knife or serrated blade, and cut against a straight edge to get clean lines.
PIR boards: Score with a sharp knife, and then snap over a straight edge. A fine-tooth saw gives better control when making multiple cuts.
DIY guide for installing 100mm loft insulation
- Check joist depth and condition.
- Lay mineral wool between joists without compressing it.
- If using PIR, cut precisely to friction-fit between timber members.
- Keep ventilation paths clear at eaves in cold roofs.
- Install cross-layer insulation if required to meet U-value targets.
- Do not cover recessed light fittings unless rated for insulation contact.
Follow Approved Document L and manufacturer instructions for the specific application.
What is the R-value of 100mm mineral wool loft insulation?
R-value is based on the product’s thermal conductivity. It is calculated as thickness (in metres) divided by thermal conductivity (λ)
Here’s how R-values stack based on different lambda values:
- 0.044 W/mK delivers R ≈ 2.27 m²K/W
- 0.037 W/mK delivers R ≈ 2.70 m²K/W
- 0.034 W/mK delivers R ≈ 2.94 m²K/W
We supply 100mm loft insulation at competitive prices and offer fast nationwide delivery direct to your site or project location. Ready to insulate your home? Contact us today.
