When is slab insulation required?

Mineral wool slab insulation is installed to: Improve warmth in rooms above an unheated void or basement. Cut draughts rising through gaps in older floors. Reduce sound transfer between storeys. Boost heat retention in suspended timber floors. Comply with regulatory standards for insulation. Mineral wool is chosen here because it fills the cavity well, handles moisture safely, and adds acoustic improvement. Rigid boards cannot match these qualities in a timber floor setup.

How thick should slab insulation be?

Wool slab insulation is primarily used with suspended timber floors, not under concrete slabs. Thickness should be between 50mm and 150mm. It all depends on the thermal target and the depth of the joists. Upgrades and new builds working to achieve greater heat retention usually need 100–150mm.

How to cut slab insulation?

Insulation knives are ideal, but a fine-tooth handsaw or serrated bread knife is fine to use. Place the insulation on a flat surface. This ensures a neat and even cut. Mark the cutting line. Cut through the slab, keeping the edge straight. Remember to wear a long-sleeved garment, gloves, and a mask to shield the skin from loose fibres.

How to install slab insulation?

To install mineral wool slabs: Take note of the distance from stud to stud or joist to joist. Carefully cut the insulation so it is slightly wider than this distance by 10–15mm. This allows the slab to grip the sides firmly. Insert the wool slab gently into position so it friction-fits without any fixings. Cut and use smaller bits of the insulation to fill all gaps. Focus on the areas around pipes and corners. This will limit heat loss or sound leaks. Cover with flooring or plasterboard. Some applications may have extra steps or special requirements. So check the user manual to confirm what the process needs.

What is slab insulation?

Slab insulation is a name commonly used when referring to mineral wool insulants. These are semi-rigid sheets made from either rock wool or glass wool. What stands out about slab insulation is that it holds its shape pretty well and fits neatly between studs or joists. It is also breathable, fire-safe, and moisture-resistant, providing acoustic and fire protection in addition to general thermal insulation.

Where and how can insulation slabs be used?

Mineral wool slabs are used in a wide range of building projects because they are firm enough to hold their shape and flexible enough to fill awkward spaces. Here’s how they are used in the most common applications: Stud Walls Mineral wool slabs are a natural fit for stud partitions. Their semi-rigid structure lets them grip the sides of the studs, so they stay put without fixings. When installed in a compact, gap-free manner, they reduce noise between rooms and help retain warmth in the building. Because they are noncombustible, they also add an extra layer of fire protection inside the wall build-up. Suspended Flooring In suspended timber floors, mineral wool slabs sit between the joists. They push slightly against the sides to create a tight fit, stopping draughts that may rise from the void below. This helps rooms feel warmer and reduces sound movement between levels. The material also handles moisture safely – an important detail in older floors that need to breathe. Masonry Cavity Walls Mineral wool is used in cavity walls, but not the everyday slabs used for partitions. Instead, builders choose cavity-specific mineral wool boards designed to: resist water tracking across the fibres keep their shape over time fit neatly in brick-and-block cavities These boards slide into the cavity as the wall is built, creating a continuous layer of insulation from course to course. Rainscreen Facades Rainscreen systems use façade-grade mineral wool boards. These are firmer and denser than typical slabs and stay stable behind cladding while allowing moisture to escape through the ventilated cavity. Their noncombustible rating also supports fire-safe façade design. Installers fix these boards directly to the substrate before the ventilated cladding goes on. Soffits For soffits – like car park ceilings and exposed concrete decks – builders use high-density mineral wool boards made for overhead work. These boards often come with a protective facing so they can be left visible. They are fixed directly to the concrete slab, giving the exposed underside a neat finish while improving the thermal performance of the floor above.

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75mm Superglass Superwall 36 Cavity Wall Slab 5.46m2 Pack

75mm Superglass Superwall 36 is non-combustible and water repellent glass mineral wool insulation cavity wall batt. The flexible batt is supplied at 455mm wide to allow easy installation between standard vertical wall tie spacings and minimum on-site cutting and waste.

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90mm Rockwool Flexi Slab Acoustic Insulation 1200mm x 600mm 86.40m2 Pallet

90mm 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.

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85mm URSA 32 Cavity Wall Insulation Slab 3.69m2 Pack

85mm URSA Cavity Batt is a lightweight, semi-rigid glass mineral wool slab treated with silicon-based water repellent. It is suitable for use in both fully and partially filled masonry cavity walls up to 25m high.

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