Rockwool Soffit Slab

Similarly to other crucial aspects of a buildings structure, fire protection (to reduce the spread of fire) and insulation (to reduce heat loss) are essential, concrete soffits are no exception.
The Rockwool Soffit Slab is a mineral wool fire resistant insulation for concrete soffits, not only does the soffit slab offer thermal and fir protection benefits it also provides important acoustic benefits. 

Rockwool High Impact Soffit slab achieves a thermal conductivity of 0.034/mK as well as offering up to 4 hours of fire resistance. The Soffit slab comes in thicknesses from 130 to 160mm.

*Always Refer Back To The Manufactures Specification Document 

Download Specification

ROCKWOOL Soffit Slab is manufactured using high performing, non-combustible stone wool insulation. Available with a plain, foil or tissue facing which can provide up to 4 hours fire protection to the underside of concrete soffits.

Hi-Impact Soffit Slab

With a 6mm rigid fibre cement board facing, this combination of two noncombustible products provides increased impact resistance and durability. Available in various thicknesses, the off-white facing can be easily decorated to match design and colour schemes.


Suitable for use with concrete soffits where a thermal, fire or acoustic performance is required.


Fire performance

Soffit Slabs have been tested to BS EN 1363-1 to offer fire protection to reinforced concrete soffits. When applied to the soffit using the recommended fixings and pattern, 130 and 140mm thick products, with and without facings, provide 3 hours fire insulation and integrity to a minimum 90mm thick floor slab. 150 and 160mm thicknesses provide 4 hours to a minimum 150mm thick slab.

Thermal performance

ROCKWOOL® Soffit Slab has a thermal conductivity (k value) of 0.034 W/mK.
Thermal resistance of un-faced Soffit Slab:

• 130mm Soffit Slab: 3.82 m²K/W
• 145mm Soffit Slab: 4.26 m²K/W
• 160mm Soffit Slab: 4.70 m²K/W

A typical construction comprising of a 150mm concrete floor slab underlined with 130mm thick Soffit Slab would achieve a U-value of 0.25W/m2 K. A U-value of 0.20 W/m2 K can be achieved using 160mm thick Soffit Slab.


ROCKWOOL® Soffit Slabs are chemically inert and compatible with most materials with which they are likely to come into contact in normal building applications.


ROCKWOOL® Soffit Slabs offer no sustenance to vermin and do not encourage the growth of fungi, moulds or bacteria.


When fixing a tile or modular system, it is advisable to start with a focus reference slab in the centre of the soffit with subsequent slabs being fixed working towards each edge. The use of string lines or laser alignment equipment will assist in ensuring alignment and squareness of the installation.

Mechanical fixings

Soffit Slabs should be fixed direct to the concrete soffit using Ejot DDS fixings with the Ejot DDT70 washer or similar. Recommended number and pattern of fixings for each slab size are shown in figures 1 and 2 below. Care should be taken not to over-tighten fixings to prevent damage to slab surface. For further information on fixing type and suitability, please refer to the fixing manufacturer.

Specification clauses

The insulation/fire protection of the concrete soffit is to be ROCKWOOL® Soffit Slab alu-faced / High impact / white tissue / black tissue / un-faced1 ……… thick2, as manufactured by ROCKWOOL® Limited, Pencoed, Bridgend CF35 6NY and installed in accordance with the manufacturer’s recommendations.


This product should only be utilised for applications as outlined in the relevant ROCKWOOL product datasheet and in accordance with the relevant ROCKWOOL Fire Resistance Testing. Additionally the product must be installed in accordance with the current ROCKWOOL guidelines. For further information please visit or contact our Technical Solutions Team on 01656 868490

Supporting information

For further information relating to any aspect of the FirePro range, please refer to the applicable ROCKWOOL standard details at or contact the ROCKWOOL technical solution team on 01656 868490 or

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