Isover CWS 32 Cavity Wall Slab
Price range: £33.50 through £37.00
Isover CWS 32 cavity wall slab with 0.032 W/mK thermal conductivity, Euroclass A1 fire rating and BBA approval for full or partial fill masonry cavities.
Isover CWS 32 Cavity Wall Slab
Isover CWS 32 is a high-performance glass mineral wool slab designed for thermal insulation in external masonry cavity walls. Suitable for both full-fill and partial-fill applications, it delivers a declared thermal conductivity of 0.032 W/mK and achieves Euroclass A1 non-combustible classification.
Manufactured with a water-repellent binder, the slabs are strong, resilient and flexible. At 455mm wide, they are designed to align with standard wall tie spacing for efficient installation. When fully filling the cavity, retaining discs are not required.
Performance
- Thermal conductivity (λD): 0.032 W/mK
- Euroclass: A1 (EN 13501-1)
- Standard: BS EN 13162
- Designation code: MW-EN 13162-T4-WS
- UKCA marked
- CE marked
- BBA Approved: Certificate 18/5560 (full & partial fill)
Environmental Credentials
- Manufactured from up to 84% recycled glass
- Produced using 100% renewable electricity
- Manufactured under ISO 14001 Environmental Management System
- Manufactured under ISO 9001 Quality Management System
- EUCEB certified (conforming with Note Q of Regulation EC 1272/2008)
Applications
- Full-fill masonry cavity walls
- Partial-fill masonry cavity walls
- Residential and commercial new build
Cavity Width & Thickness Selection
Isover CWS 32 is available in 100mm, 125mm and 150mm thicknesses to suit different cavity wall constructions and U-value requirements.
- 100mm cavity wall insulation – commonly used in 100mm full-fill masonry cavities.
- 125mm cavity wall insulation – suitable for wider cavities or improved thermal targets.
- 150mm cavity wall insulation – used where enhanced fabric performance is required in new build construction.
The correct thickness depends on cavity width, wall build-up and target U-value under Approved Document L.
Dimensions
- Length: 1200mm
- Width: 455mm
Building Regulations & Compliance
When correctly specified and installed, Isover CWS 32 can contribute to compliance with:
- Approved Document L – Conservation of Fuel and Power
- Approved Document B – Fire Safety
- Approved Document C – Resistance to Moisture
Use of the product must satisfy all relevant national Building Regulations and height restrictions. Compliance depends on the complete wall construction and project-specific detailing.
Handling & Safety
Glass mineral wool may cause temporary mechanical skin irritation during handling. Cutting may generate dust. Appropriate PPE should be worn in accordance with COSHH and Workplace Exposure Limits (WEL 5mg/m³ 8-hour TWA).
The product is not classified as hazardous under UK REACH. Refer to the Isover Safe Use Instruction Sheet for full guidance.
Installation Overview
Installation Principles
- Install slabs tightly between wall ties with no gaps.
- Stagger vertical joints between courses.
- Ensure slabs remain flush to the inner leaf.
- Prevent mortar droppings bridging the cavity.
- Follow BBA Certificate 18/5560 installation conditions.
Installation must comply with current Building Regulations, including Approved Documents L, B and C, and manufacturer technical guidance.
| Weight | N/A |
|---|---|
| Length | 1200mm |
| Width | 455mm |
| Thermal Conductivity | 0.032 W/Mk |
| Fire Rating | Euroclass A1 |
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What is Isover CWS 32 cavity wall insulation?
Isover CWS 32 is a glass mineral wool slab designed for use in masonry cavity walls. It provides excellent thermal performance while also offering sound insulation and fire resistance, making it a popular choice for new build homes and extensions.
What thermal performance does it provide?
Isover CWS 32 has a thermal conductivity (λ value) of 0.032 W/mK, which means it’s highly efficient at reducing heat loss through cavity walls and can help lower energy bills when installed correctly.
Is it suitable for all types of cavity walls?
Yes, it’s designed for full-fill masonry cavity walls in both new build and extension projects. However, the cavity must be at least 75mm wide, and walls should be constructed to prevent water penetration in line with building regulations.
What does the “32” in Isover CWS 32 mean?
The “32” refers to the product’s thermal conductivity value of 0.032 W/mK. The lower the number, the better the insulation performance – so CWS 32 offers excellent thermal efficiency compared to standard cavity wall insulation products.
Does Isover CWS 32 meet the latest Part L Building Regulations?
Yes, Isover CWS 32 is specifically designed to help builders and designers achieve compliance with the latest Part L (Conservation of Fuel and Power) requirements. Its low thermal conductivity of 0.032 W/mK enables cavity walls to achieve the U-values set out in current regulations, supporting more energy-efficient buildings.
Isover manufacture glass mineral wool insulation used within walls, floors and roof structures. These insulation products are designed to improve thermal efficiency and acoustic performance within buildings.
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