Rockwool RWA45 75mm

ROCKWOOL RWA45 75mm Technical Specifications

ROCKWOOL RWA45 75mm Acoustic Mineral Wool is a semi-rigid stone wool insulation slab used for acoustic, thermal and fire insulation in walls, floors, ceilings, partitions and roof constructions. With a nominal density of 45kg/m³, RWA45 is a practical general-purpose insulation slab for building cavities and acoustic systems.

Product Specification

Suitable Applications

ROCKWOOL RWA45 75mm can be used in a wide range of acoustic, thermal and fire insulation applications. It is commonly installed within:

• Stud walls and partition walls
• Party wall soundproofing systems
• Floor joist cavities
• Ceiling voids and suspended ceiling systems
• Drylining and acoustic wall systems
• Service voids and boxed-in areas
• Roof and loft insulation applications
• Home offices, studios, media rooms and commercial spaces

Acoustic Use

ROCKWOOL RWA45 is used to help absorb sound within wall, floor and ceiling cavities. Its stone wool fibre structure helps reduce sound movement inside the void and can improve the overall performance of a complete acoustic build-up.

RWA45 is mainly used to help with airborne noise, such as voices, TV noise, music and general room-to-room sound transfer. In floor and ceiling systems, it can also support the wider acoustic build-up by reducing resonance within the cavity.

Common System Uses

• Between timber studs in wall soundproofing systems
• Between floor joists as part of a floor soundproofing build-up
• Above suspended ceilings or within ceiling voids
• Behind acoustic plasterboard systems
• Combined with Tecsound acoustic membranes
• Combined with resilient bars or furring channel systems
• Used with acoustic sealant to reduce weak points around edges and junctions

RWA45 vs RW3 and RW5

The main difference between RWA45, RW3 and RW5 is density. ROCKWOOL RWA45 is typically 45kg/m³, RW3 is typically 60kg/m³, and RW5 is typically 100kg/m³.

RWA45 is a strong general-purpose option for acoustic, thermal and fire insulation. RW3 and RW5 are denser options and may be preferred where the acoustic specification calls for a higher-density mineral wool slab.

Important Performance Note

ROCKWOOL RWA45 is an acoustic insulation slab, not a complete soundproofing system on its own. It performs best when used inside a full wall, floor or ceiling build-up with suitable acoustic boards, membranes, isolation products and properly sealed joints.

The final soundproofing result will depend on the existing structure, cavity depth, installation quality, surrounding materials and how well gaps and flanking paths are controlled.

Handling Advice

ROCKWOOL RWA45 slabs can be cut to fit between studs, joists and other framing. For best results, cut the slabs neatly so they fit snugly within the cavity without being heavily compressed. Over-compressing mineral wool can reduce its effectiveness within the acoustic build-up.

If you are unsure whether RWA45 75mm is the correct thickness or density for your project, please contact our team before ordering. We can help advise on the most suitable insulation and soundproofing system for your room, noise issue and available cavity depth.

How to Install ROCKWOOL RWA45 75mm Acoustic Mineral Wool

ROCKWOOL RWA45 75mm Acoustic Mineral Wool is designed to be fitted into wall, floor and ceiling cavities as part of an acoustic, thermal and fire insulation system. With a density of 45kg/m³, RWA45 is a practical general-purpose mineral wool slab for residential, commercial and trade installations.

The 75mm thickness is a useful middle option for medium-depth cavities. It provides more depth than 50mm insulation while being easier to fit into many spaces than a full 100mm slab. For the best result, the slabs should be cut neatly and fitted snugly without being heavily compressed.

What You’ll Need

• ROCKWOOL RWA45 75mm Acoustic Mineral Wool slabs
• Measuring tape
• Insulation saw or sharp serrated knife
• Straight edge or board for cutting
• Gloves
• Long-sleeved clothing
• Dust mask
• Safety glasses
• Waste bag for offcuts
• Acoustic sealant, if sealing around the system

Before You Start

Check the available cavity depth before fitting the slabs. ROCKWOOL RWA45 75mm is suitable for cavities that can accept a 75mm slab without excessive compression.

If the cavity is shallower than 75mm, avoid forcing the slab into place. Over-compression can reduce the consistency of the insulation layer and may make the installation less effective.

Step 1: Prepare the Area

Before installing the insulation, make sure the cavity or frame is ready. The installation area should be:

• Clean — remove dust, loose debris and leftover materials.
• Dry — avoid installing insulation into damp cavities.
• Clear — check for cables, pipework, fixings and other obstructions.
• Stable — make sure studs, joists, battens or framing are secure before fitting.

Take care around electrical cables, pipework and other services. Do not cut, crush or damage existing services when fitting the slabs.

Step 2: Measure the Cavity

1. Measure the width and height of the cavity between studs, joists or framing.
2. Check the cavity depth to confirm that 75mm RWA45 is suitable.
3. Mark the required slab size before cutting.

For a secure friction fit, cut the slab slightly oversized by a few millimetres. This helps the insulation stay in position and reduces gaps around the edges.

Step 3: Cut the RWA45 Slabs

1. Place the slab on a stable cutting surface.
2. Use a straight edge or board as a cutting guide.
3. Cut the slab using an insulation saw or sharp serrated knife.
4. Trim carefully around pipes, cables and awkward shapes where needed.

Clean, accurate cutting helps the slab fit properly and keeps the cavity evenly filled. Try to avoid leaving gaps around the edges, services or framing.

Step 4: Fit the Slabs into the Cavity

1. Place the cut slab into the cavity.
2. Push it gently into position.
3. Make sure it fits snugly between the studs, joists or framing.
4. Check that the slab fills the space evenly without being crushed.

The slab should sit securely in place, but it should not be heavily compressed. A neat friction fit is usually best for acoustic and thermal performance.

Step 5: Fill Gaps and Awkward Areas

Use offcuts to fill small gaps around edges, joists, studs, pipes and irregular spaces. The aim is to keep the cavity evenly filled with no obvious voids.

Sound and heat can travel through weak points, so careful fitting around awkward areas can help improve the overall result.

Step 6: Add the Next Layer

Once the RWA45 is fitted, the next part of the system can be installed. Depending on the project, this may include:

• Acoustic plasterboard
• Standard plasterboard
• TECSOUND acoustic membrane
• Resilient bars
• Furring channels
• Floating floor layers
• Service void linings
• Acoustic sealant around edges and joints

ROCKWOOL RWA45 performs best as part of a complete build-up. The insulation absorbs sound within the cavity, while boards, membranes and isolation products help add mass, reduce vibration transfer and improve the finished system.

Installing RWA45 75mm in Walls

For stud walls, partition walls and party wall upgrades, fit the RWA45 between the vertical studs. Cut each slab to fit snugly, then install the chosen plasterboard or acoustic lining system over the frame.

For improved wall soundproofing, RWA45 can be combined with acoustic plasterboard, Tecsound membrane, resilient bars or furring channels depending on the wall construction.

Installing RWA45 75mm in Floors

For timber floor systems, fit RWA45 between the floor joists. The slabs should sit securely within the void without dropping, sagging or leaving large gaps.

RWA45 can help reduce sound movement through the floor cavity, but impact noise from footsteps usually requires additional products such as acoustic underlay, resilient layers or a floating floor system.

Installing RWA45 75mm in Ceilings

For ceiling systems, fit RWA45 between ceiling joists or within the ceiling void. Work carefully overhead and cut the slabs to manageable sizes where needed.

For improved ceiling soundproofing, RWA45 is often used with resilient bars, furring channels, acoustic plasterboard, Tecsound membrane and acoustic sealant.

Installing RWA45 75mm in Service Voids

RWA45 75mm can also be used in suitable service voids and boxed-in areas where acoustic and thermal insulation are required. Cut neatly around pipework, cables and other services, keeping the insulation continuous without crushing the slab.

Where the main issue is pipe noise, RWA45 may form part of the wider system, but pipe-specific products such as acoustic pipe wrap may also be needed.

Installation Tips

• Wear PPE — use gloves, long sleeves, eye protection and a dust mask when cutting and fitting mineral wool.
• Cut slightly oversized — this helps the slabs friction-fit into the cavity.
• Avoid over-compression — heavily compressed insulation may reduce consistency and performance.
• Fill the full cavity — avoid gaps around edges, joists, studs, pipes and cables.
• Use offcuts carefully — small pieces can fill awkward spaces and reduce waste.
• Choose the right thickness — 75mm RWA45 is best for cavities that can accept this depth without crushing the slab.
• Use within a full system — combine with suitable boards, membranes and sealants for better soundproofing performance.

Important Soundproofing Note

ROCKWOOL RWA45 is an acoustic insulation slab, not a complete soundproofing system by itself. It helps absorb sound inside the cavity, but the final soundproofing result depends on the complete wall, floor or ceiling build-up.

For best results, combine RWA45 with suitable acoustic boards, membranes, isolation products and acoustic sealant. If you are unsure whether RWA45 75mm is the right thickness or density for your project, please contact our team before fitting. We can help advise on the most suitable system based on your room, cavity depth and noise issue.