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50mm Celotex GA4050 PIR Insulation Board 2400mm x 1200mm (8′ x 4′) 2.88m2
50mm Celotex GA4050 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.
£23.40£28.08 Ex VATInc VAT£8.13£9.76 Per M2 Add to cart
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50mm Loft Insulation GA4000
50mm loft insulation is a practical working depth used when space is limited or when you are layering materials to reach a calculated U-value. It helps you adjust thermal performance without excessively raising floor levels or rafter depth.
What is 50mm thick loft insulation?
50mm thick loft insulation is a thermal layer measuring 50mm in depth, supplied either as rigid boards (typically PIR) or as flexible mineral wool slabs or rolls.
Materials like PIR insulation board trap gas within closed cells. The trapped gas within the material is a poor thermal conductor, which means heat transfer is slowed significantly.
Mineral wool performs differently. It traps still air between fibres, and because air is a poor heat conductor, the fibres disrupt heat flow (typically 0.035–0.040 W/mK).
Because of those conductivity values, 50mm insulation loft boards made from PIR provide more resistance per millimetre than mineral wool.
But a single layer of 50mm loft insulation solution will not meet the typical Part L new-build cold loft roof target of around 0.16 W/m²K on its own. It is usually combined with other layers to reach compliance.
Insulation 50mm loft thickness is specified where height is controlled, or where you are improving rather than rebuilding.
What is 50mm loft insulation used for?
Thin 50mm loft insulation is commonly installed on:
Floor applications
Floor build-up matters a lot in loft conversions. You may lay 50mm PIR between or over joists to add thermal performance without increasing floor height. It is often paired with acoustic insulation and a structural deck for enhanced energy efficiency.
A 50mm loft insulation roll is not suitable as a structural floor layer, but mineral wool at this depth can reduce sound transfer between floors when installed between joists.
Roof (cold loft ceiling level)
You may be topping up an older property with, say, 100mm already in place. Adding loft insulation 50mm thick perpendicular to the first layer reduces thermal bridging across joists. It improves performance but still falls short of full 270mm guidance unless additional insulation layers are added.
Pitched roof
Between rafters, 50mm PIR is common where rafter depth is shallow. It is normally combined with additional insulation under the rafters. Ventilation gaps above insulation must be maintained in cold roof designs to prevent condensation risk.
- Ventilation requirements control should be designed in line with document Part C and BS 5250.
- Warm roof constructions do not require ventilation above insulation, subject to condensation risk assessment.
- Cold-pitched roofs do require maintained airflow.
Walls and framing walls
In timber frame partitions within a loft conversion, 50mm mineral wool slabs help with sound and some thermal control. PIR at 50mm can also line internal studwork to limit heat loss from conditioned rooms into cold voids.
Internal masonry walls
On solid brick gable walls inside a loft space, 50mm PIR boards fixed mechanically or with adhesive can significantly reduce heat loss. A vapour control layer may be required depending on the build-up to manage interstitial condensation.
Types of 50mm loft insulation
At Insulation Wholesale, we stock two main categories:
PIR Insulation (rigid boards)
These are rigid 50mm loft insulation boards.
- Usually foil-faced
- Thermal conductivity around 0.022 W/mK
- High compressive strength
- Suitable for floors, pitched roofs, and internal wall lining
PIR boards provide strong thermal resistance at low thickness. They must be tightly fitted to avoid gaps, as air leakage reduces performance.
Mineral wool insulation (rolls or slabs)
These are often specified where fire resistance and sound absorption matter more than maximum thermal value per millimetre, especially in roof insulation.
- Thermal conductivity typically 0.035–0.040 W/mK
- Non-combustible (Euroclass A1 reaction to fire)
- Good acoustic absorption
- Flexible and easy to friction-fit, glass mineral wool rolls are ideal for various applications.
A loft insulation roll 50mm thick, such as glass mineral wool, is easier to fit around irregular shapes.
At Insulation Wholesale, you can purchase 50mm Loft Insulation at low wholesale prices with fast delivery for most of items within 2-5 days. Competitive rates guaranteed.
FAQ
Where to purchase 50mm loft insulation in the UK?
You can buy 50mm loft thickness insulation online from Insulation Wholesale. We stock PIR boards and mineral wool options in 50mm loft insulation thickness, ready for fast nationwide delivery. Most products are UK stock, meaning less waiting and fewer delays. Our team works with trade and self-build customers every day, so we understand site deadlines and staged deliveries.
How to cut 50mm loft insulation?
PIR boards:
- Mark clearly with a straight edge.
- Score deeply with a sharp knife.
- Snap over a firm edge.
- Trim foil facing cleanly.
For precise work (like between rafters), a fine-tooth saw can help. Remember to wear gloves and eye protection.
Mineral wool rolls or slabs:
- Lay insulation on a flat board.
- Use a long insulation knife for cutting wool insulation.
- Compress slightly while cutting for a straight edge.
How to install 50mm loft insulation?
Installation depends on build-up:
- Cold loft ceiling level: Lay mineral wool between joists first. Add cross-layering if topping up. Do not block eaves ventilation to maintain energy efficiency.
- Between rafters (pitched roof): Cut boards 2–3mm wider than the gap for a friction fit. Maintain required ventilation above unless building a warm roof design.
- Floor build-up: Install boards tightly together. Tape joints if required to ensure the effectiveness of insulation products. Lay structural decking above without compressing insulation.
Check Building Regulations for required U-values, and manage condensation risk using appropriate vapour control layers.
How effective is 50mm Insulation loft?
It depends on the material and context.
- 50mm PIR: Strong thermal resistance for its depth. Good where space is tight.
- 50mm mineral wool: Moderate thermal performance but excellent fire and acoustic performance.
On its own, thin 50mm loft insulation will not meet full cold-roof targets. As part of a layered system, it plays a valuable role in controlling heat flow and improving comfort.
Need loft insulation 50mm thick for your next job? We supply a comprehensive range of loft insulation boards and slabs at low wholesale pricing with fast nationwide delivery.
