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General ROCKWOOL Insulation FAQs

General Questions

What is ROCKWOOL insulation and how is it made?

ROCKWOOL insulation is a stone-based insulation. It is sourced from abundant lava deposits of volcanic rocks which are melted in a cupola furnace like a controlled man-made volcano. As the re-melted lava comes out of the furnace, it is spun, given water repellency treatment and bound together in a wool-like fleece.

ROCKWOOL insulation is a mineral wool, which is inorganic and ideal for thermal insulation, fire protection, acoustic control and environmental purposes. During the manufacturing process, ROCKWOOL insulation is cut, shaped and combined into many different products for a wide variety of applications including buildings, systems, services, marine and offshore.

What is the difference between stone wool and other types of insulation?

ROCKWOOL stone wool is made from volcanic rock and achieves an European Reaction to Fire Classification of A1 - non combustible. Stone wool is also a durable choice; its properties and benefits don’t reduce or change over time and the product will effectively perform for the lifetime of the building.

If ROCKWOOL insulation is made of stone, will it be heavier than other types of insulation?

Although ROCKWOOL stone wool insulation is made of rock, the natural material has been converted to a wool substance which is not difficult to handle. You might need someone to help manoeuvre the packaged product up into the loft space, but one person can easily handle our roll and loose lay products alone.

Will ROCKWOOL insulation attract rodents or mould?

ROCKWOOL insulation is a naturally inert, rot proof material that does not encourage or support the growth of funghi, moulds or bacteria. ROCKWOOL insulation does not offer sustenance to insects or vermin.

Is ROCKWOOL a glass wool insulation?

No, ROCKWOOL insulation is a stone mineral wool manufactured from volcanic rock. Learn more about ROCKWOOL here.

Why is ROCKWOOL is itchy?

ROCKWOOL insulation being manufactured from rock fibres is classified as a mechanical irritant.  As with any DIY/Construction job, the correct PPE should be worn to protect yourself i.e. gloves, long sleeve clothing, trousers, etc.  If you do get ROCKWOOL on your skin, it is recommended to rinse with cold water.  

I’m worried about the fibres from ROCKWOOL products. Will these harm me if I breathe them in?

Once installed, ROCKWOOL products will not emit fibres or particles if the ROCKWOOL products are not further disturbed.  Measurements taken within insulated buildings have shown that the levels of airborne mineral wool fibres are so low that they are not usually detectable.  ROCKWOOL stone wool insulation fibres are bio-soluble which means they are harmlessly cleared by the body should they be inhaled or ingested. 

What is the difference between stone wool and other types of home insulation?

ROCKWOOL® stone wool is made from volcanic rock and achieves an European Reaction to Fire Classification of A1 - non combustible.  It is an inorganic insulation product which falls into the category of mineral wool insulation along with glass wool.  Other foam type insulations in the market place are classified as thermoset such as PIR/PUR/Phenolic or thermoplastic such as EPS/XPS. Stone wool is versatile and as well as thermal properties, has inherent fire and acoustic benefits no matter what product you are specifying.  Stone wool is a durable choice; its properties and benefits don’t reduce or change over time and the product will effectively perform for the lifetime of the building.

Product Performance FAQs

Product Performance

Do you have BBA certification for your products?

Yes, we have several products which have been certified by the BBA and these include:

Do you have a guarantee for your products?

No, we do not issue guarantees for individual products available for sale through distribution.  We are able to supply a standard durability statement for ROCKWOOL insulation, however, any guarantees issued will be the responsibility of the builder/contractor.  ROCKWOOL products are covered by the usual legal protection offered by the Sale of Goods Act, (so far it applies in dealings between businesses), and in accordance with ROCKWOOL's standard terms and conditions of business. 

Do ROCKWOOL have certificates demonstrating that there is a certified EMS (e.g. ISO 14001 certificates) for the product manufacture and also for any quarried or mined mineral over 20% of input?

Yes - ROCKWOOL have ISO 14001 certification. As a stone wool insulation manufacturer we also need to provide evidence that any mined or quarried material making up 20% or more of our process input should also have a certified environmental management system to show responsible sourcing.  The certificates can be found in the Certificate Library within the 'Product Documentation' section of the website. 

The ROCKWOOL Sustainability brochure contains further information on environmental credentials and recycling.


What acoustic qualities does ROCKWOOL insulation have?

ROCKWOOL insulation is used by specialists in many demanding acoustic applications. ROCKWOOL stone wool insulation works in two distinct ways to reduce noise, either by impeding the transmission of sound through an element of the structure or by absorption of sound at the surface.

What dB rating can I achieve with ROCKWOOL insulation?

The dB rating (acoustic performance) of any ROCKWOOL product is determined by the total construction. The acoustic performance of a construction will be dependent upon the sound path, the mass and absorbative qualities of the products used within the construction. ROCKWOOL products have been tested in a number of standard constructions - to find out more, speak to our technical solutions team.

How do I reduce noise from next door?

We have a range of tested solutions for walls, floors and flanking sound transmission to meet or exceed the current acoustic requirements for Approved Document Part E.

Discover more about our popular Sound Insulation Slab here.

I am insulating a music room. What products do you recommend?

We would suggest lining the walls with a tissue faced slab such as RW3 or RW4. The insulation product would then need to be protected from damage. Typically, this would be achieved by installing a perforated sheet.

How do I reduce noise from next door?

That depends on what kind of wall or partition needs insulating acoustically. Acoustic improvement can be complicated, but there are several ROCKWOOL products and systems which can help reduce interference sounds though structures.  Impact, reflective and penetrating sounds transmit in different ways and behave differently in varying frequency ranges. The principle on which ROCKWOOL acts successfully as an acoustic insulant is by diffusing and absorbing the sound waves. 

For walls and partitions ROCKWOOL semi-rigid slabs (RW Slab range), FLEXI or Thermal and Sound Slabs will provide effective reductions in decibel levels (dB) These can be fixed against walls, or in timber frames separated from the main structures to avoid the possibility of sound bridging.  See the Soundpro Brochure for details.


Is ROCKWOOL insulation Class O?

Yes, ROCKWOOL insulation actually achieves a higher European rating and is classified as Euroclass A1 non-combustible in accordance with BS EN 13501-1 – Reaction to Fire Classification.  Class O products under the British Standards would be expected to achieve the equivalent of a Euroclass B – combustible.  Unlike the Euroclasses, Class O does not measure how a product will behave when involved in a fire, i.e. does the product contribute to the fire to allow the fire to develop further.

What fire rating do ROCKWOOL products have?

Insulation materials do not hold fire ratings on their own, they are always tested as part of a system or application as a whole.


My insulation has been left out in the rain and has got wet. Can I still use it?

Yes, the insulation is open cell meaning that it will allow air movement through it.  The product will therefore dry out and can be used as long as it has not been damaged.  In line with good building practice we do not recommend that the product is installed whilst wet as it will take longer for the product and structure to dry out.


How long will ROCKWOOL insulation last before I need to replace it?

Tests from old construction sites show that our products have retained their insulation characteristics and properties for more than 55 years


What environmental impacts/benefits are there from using ROCKWOOL insulation?

The natural basic rock material for making ROCKWOOL stone wool insulation is an abundant resource. Great care is taken during both the manufacturing process and distribution of finished insulation products to minimise any environmental impact. The ROCKWOOL operations team monitors the production processes carefully to ensure any emissions are within specified limits. It is ROCKWOOL Group policy to adhere to environmental standards better than national or local requirements. Please visit the Sustainabilty section of the website or the Sustainabilty brochure for more in-depth information.

Can I achieve a BREEAM insulation credit when specifying a Green Guide ‘C’ rated material?

The Mat 04 (BREEAM 2011) or Mat 06 (BREEAM 2008) credit for insulation is split into two credits; one for the embodied impact of the insulation and the other for responsible sourcing.

The embodied impact credit is calculated from the volume weighted thermal resistances for each of insulation products in the building. Each insulation product in the building is calculated as follows:

  • (Area of insulation (m2) X thickness (m)) x Thermal Conductivity (W/mK) OR
  • Total volume of insulation used (m3) / Thermal Conductivity (W/mK)

Once this has been applied, along with the Green Guide rating points for each of the insulation materials used, you will have values for the total area weighted thermal resistance and the Green Guide rating correction. These are then divided and if the resulting number is higher than or equal to 2, the credit can be achieved. Therefore it is still possible to specify a product that has a C rating as when this is thrown into the mix with the rest of the insulation products, many of which may score A or A+, the area weighting may still allow for the credit to be achieved. Therefore it should not be assumed that because you have specified a ‘C’ rated product in the Green Guide that the credit cannot be achieved. ‘C’ rated products may offer features that allow you to  obtain other credits such as HEA 05 (BREEAM 2011) or HEA 13 (BREEAM 2008) Acoustic performance whilst potentially still allowing the mentioned insulation credit to still be awarded. Some A+ or A rated products may not allow this.

ROCKWOOL Products Comparison FAQs

Product Comparison

Can I use my Sound Insulation slab for a thermal application or do I need to buy the Thermal slab?

Yes, ROCKWOOL insulation has natural inherent properties for thermal, fire and sound which is present in all products. Therefore, if you are using a sound insulation slab, you will automatically get a thermal and fire benefit.  The only exception is for masonry cavity walls which must use the specific performance tested product which is ROCKWOOL cavity for full fill applications.

Can I use Sound Slab in a thermal application?

Yes, ROCKWOOL products all provide a thermal and acoustic performance.

What is the difference between Sound Slab, Flexi and RWA45?

The products vary in density, thermal performance, approved thickness and physical characteristics. FLEXI® as an example, is purposefully manufactured with flexible edge technology to ensure a good fit within framed applications.

Installation FAQs

General Questions

Can I double layer ROCKWOOL products?

Yes, ROCKWOOL products can be double layered.  We recommend staggering the joints in accordance with good building practice to minimise the potential for thermal bridging through joints.

How do I cut ROCKWOOL?

ROCKWOOL insulation can easily be cut with a long bladed knife or insulation saw available from DIY/Builders Merchant outlets. Please ensure the correct PPE is worn when using or cutting insulation.

Do I need to wear any protective clothing to fit ROCKWOOL insulation in my loft?

It is always recommended that the appropriate personal protection equipment is worn when carrying out DIY jobs.  Therefore, it is recommended that you wear long sleeves, gloves and a mask to ensure your comfort.  

Can I use ROCKWOOL insulation with electrical wires and cables?

Yes. To prevent possible overheating, electrical cables, transformers and the housings to light-fittings which protrude into the loft space should not be fully covered by insulation.  If electrical cables have sufficient slack in them, they should also be raised above the insulation. Transformers should be lifted clear of the insulation.  If cables cannot be raised above the insulation, a ‘derating’ of 50% should be assumed.  It is important to ensure that the current-carrying capacity of any cables to be covered is sufficient for the application – this is particularly important for heavy-duty cables serving high power items such as showers, cookers, dense arrays of lights, etc.

Sections of cable 500mm or less in length, which are covered by insulation, will not normally need to be re-routed or de-rated.  Guidance on requirements can also be found in the I.E.E. Wiring Regulations (BS 7671).

Roofs and Lofts

How can the gaps between the head of a block work wall and a tiled or slated pitched roof be sealed to prevent fire spread to the adjacent property?

There are two paths which require sealing to maintain the fire compartmentation at this junction – between the masonry wall and the underside of the roofing felt and within the timber batten void, between the felt and the tiles/slates. 300mm wide strips of 30mm thick ROCKWOOL® RWA45 can be used in both instances. Provided the masonry wall width is at least 250mm and the insulation is inserted under at least 10% compression, the 60-minute requirement of Building Regulations will be met.

Can the ROCKWOOL Roll be cut into 300mm widths?

Yes, the ROCKWOOL Roll can be cut to whatever width you require.  The ROCKWOOL Roll is supplied in 1200mm widths with cutting guides on the packaging for 600mm or 400mm centres for ease of use as these are the most common widths.  However, if your joists are narrower, all you need to do is measure from the end of the roll and cut to the desired width.  Leave the packaging on whilst cutting as this makes it easier to handle and put into place.  All you then need to do is cut the packaging, roll out and remove the plastic.  

Floors and Ceilings

Can ROCKWOOL insulation be used below the DPC?

All modern buildings incorporate a damp proof course (DPC), which prevents moisture from the ground being drawn up by capillary action.  The current Approved Document C2 (2013 edition) – Resistance to moisture and BS 8215:1991 states a damp proof course should be installed at least 150mm above perimeter ground level.  The requirement of 150mm above ground level is to reduce the incidence of ‘splashback’ from rain and to ensure a minimum amount of elevation above standing water that may occur in periods of heavy rain, etc.  This is ‘Good Practice’ guidance for most buildings built approximately within the last 30 years.  ROCKWOOL insulation products will not absorb water by capillary action and can be used in situations where it bridges the DPC in walls.  We do not recommend that the insulation product is submerged in water.

Can ROCKWOOL be installed underneath site concrete or screed?

Yes, ROCKFLOOR® is the ideal product for this. The desired thickness of ROCKFLOOR® can be laid on a dry, firm surface, and flooring applied immediately over it to create a warm free-floating floor, which has thermal, acoustic, and fire protective properties. ROCKFLOOR® will accommodate all traditional flooring coverings. ROCKFLOOR® can also be laid on a ground floor over a dpc membrane with a concrete screed poured directly over it, providing an insulated platform. The thickness of the screed will vary depending on the intended load.

Can I use your products below DPC?

Yes but only in specific cases. Open Cell insulation like ours should not be allowed to sit in standing water; if this is the case then a closed cell material will be needed.

When installing recessed lighting within a ceiling are there any precautions required if there is already insulation between the joists?

It is recommended that when installing down lighters within a ceiling you should install acoustic/fire covers to maintain an air void/flow around them. This prevents the light from over-heating which could cause the light's to fail more frequently. These are available from DIY merchants.

Fire Protection and Fire Stopping

Do you have approved installers for fire stopping/protection products?

We do not have ROCKWOOL experienced installers, however, we do recommend that you use a third party accredited contractor who will be experienced in this area.  A list of accredited contractors can be found on the ASFP or FIRAS websites.

What fixings and fixing pattern do I need to use for Duoslab/Soffit Slab?

We have suggested fixing types and patterns on our data sheets but they are suggestions only, if you chose to use any other fixing or pattern then the fixing supplier must confirm type, size, material, suitability and pattern.

Application FAQs


I have a masonry cavity wall. Will blowing insulation within the cavity reduce the noise from next door?

Using ROCKWOOL Cavity or ROCKWOOL ENERGYSAVER® to fully fill a separating blockwork cavity wall can help to reduce flanking sound within the cavity space. This is an effective treatment for addressing speech, television and general living noise, and will typically boost performance by around 3 - 8 dB.

Which type of cavity wall insulation is best?

There are basically three choices.

If you are building new property, ROCKWOOL Cavity Wall Batts will provide maximum energy savings. These fully fill the cavity, yet their special water repellency prevents water transmission across the cavity. If 'low energy' design is involved, wide cavity structures can use double thicknesses of ROCKWOOL Cavity Wall Batts to create improved U- values.

The second choice is ROCKWOOL High Performance Partial Fill Cavity Slab. This is a system which allows a cavity to be maintained by clip fixing the special dual-density slabs against the inner leaf. This specially engineered product offers enhanced performance due to the consistent close fit achieved against the uneven surface of the inner leaf masonry.

The third alternative is for both new-build and existing property (subject to survey). ROCKWOOL ENERGYSAVER® Cavity Wall Insulation is a blown wool system operated by Approved ROCKWOOL Installers subject to BBA inspection. Holes are drilled at pattern intervals in the outer (or inner) leaf of the cavity wall and granulated ROCKWOOL is blown into the cavity space to fill to a pre-determined density. The holes are then made good with matching mortar. This system achieves effective improvement of U-values especially for existing poorly insulated houses. Domestic installation carries a 25 year CIGA guarantee. 

Is my house suitable for cavity wall insulation?

Approved CIGA installers will carry out an inspection to assess the suitability of the property to have blown insulation installed. Further information regarding approved installers and what to expect can be found on the CIGA website.

How can I prevent fire entering a cavity wall around window and door openings and subsequently spreading throughout the building envelope?

ROCKWOOL® fire rated cavity closers, ROCKCLOSE® and SP Firestop OSCB are designed to provide a tight, fire resistant seal in a masonry cavity around window or door openings.  ROCKCLOSE®is a first-fix built-in product which will achieve 30 minutes fire resistance and also meet the Part L requirement for minimising cold bridging. 

Which ROCKWOOL external wall systems can be used to insulate facades, and improve older housing?

RAINSCREEN DUO Slab is a specially designed dual density insulation product for direct fixing to facades where a rainscreen cladding system has been selected. The outer higher density surface is robust and designed to allow for exposure to weather conditions while cladding systems are erected. Meanwhile, the inner surface makes consistent close contact with the old exterior of the building, providing a significant improvement in thermal performance.  Cladding options available can be found on the Rockpanel website.

Floors and Ceilings

Does ROCKWOOL have 1 hour fire rated timber floor construction?

Yes - ROCKWOOL FLEXI 100mm has been tested to provide the 1 hour fire resistance to timber joisted floor constructions. Chicken wire galvanised steel mesh, nominal 25mm mesh size x 0.7mm thick, is fitted over the joists so that it is in contact with the top and sides of each joist and in contact with the upper face of the ceiling. ROCKWOOL FLEXI, 100mm thick, is fitted between the joists so that it is in contact with the mesh trays and therefore nominally flush with the bottom of the joists.


To see the full build-up, please refer to the ROCKWOOL FLEXI Datasheet.

How do I reduce noise from downstairs?

Acoustic improvement can be complicated, but there are several ROCKWOOL products and systems which can help reduce interference sounds though structures. Impact, reflective and penetrating sounds transmit in different ways and behave differently in varying frequency ranges. The principle on which ROCKWOOL acts successfully as an acoustic insulant is by diffusing and absorbing the sound waves. For floors, Acoustic ROCKFLOOR® is an insulation board for acoustic performance in a variety of buildings. 

Roofs and Lofts

Should loft insulation be fitted between the joists or be placed over the joists?

The most effective way to insulate your loft is to have a layer of insulation that sits snugly in the spaces between the joists (either a roll product or loose lay) followed by a top layer crossways across the joists. The total depth of the insulation should be at least 270 – 300 mm for the best results and to meet current building regulations.

Can ROCKWOOL products be used for the pitched rafters of a roof?

Yes - ROCKWOOL FLEXI® can be used between the rafters. The flexible edge of the product allows for a tight fit between rafters therefore minimising cold bridges. Alternatively, a warm pitched roof system is available which utilises ROCKWOOL FLEXI® between the rafters and an overlay board of HARDROCK over the top of the rafters. Solutions can be found in the ROCKWOOL Part L brochure.

I want to top up my loft insulation but what is already there isn't stone wool. Do I need to remove this or can I just lay a ROCKWOOL product on the top?

You can simply top up any existing insulation with ROCKWOOL. Our loose lay product means you can fill any gaps around the edges easily before laying a roll of insulation over the top.

Do I need to maintain the ventilation at the eaves of the roof or can I fit the roll insulation into this void?

With better insulation, the loft will be colder and therefore more prone to condensation if not adequately ventilated. It is therefore important to maintain the air flow through the loft space normally via the eaves. This air flow can be maintained by installing eaves ventilators.

How can the gaps between the head of a block work wall and a tiled or slated pitched roof be sealed to prevent fire spread to the adjacent property?

There are two paths which require sealing to maintain the fire compartmentation at this junction – between the masonry wall and the underside of the roofing felt and within the timber batten void, between the felt and the tiles/slates. 300mm wide strips of 30mm thick ROCKWOOL® RWA45 can be used in both instances. Provided the masonry wall width is at least 250mm and the insulation is inserted under at least 10% compression, the 60-minute requirement of Building Regulations will be met.

How can a common loft area be split up to achieve the 60-minute compartmentation requirement between dwellings?

Two layers of ROCKWOOL® Fire Barriers (50mm with staggered vertical joints) suspended from the soffit will satisfy this requirement. The Barriers should be installed in accordance with the product data sheet using the proprietary fixings, and also sealed to the head of the compartment wall to maintain the integrity of the entire system.

Can I still use the loft area for storage after I’ve fitted ROCKWOOL insulation?

You can still use loft space for storage by installing loft stilts available from DIY outlets.  These are very simple to use and create a raised platform above the insulation layer that can then be used for storage.

Do I need to clear the loft entirely before undertaking home loft insulation?

If you are already using your loft space for storage, you might not want to move everything down into your home whilst you fit insulation. A tried and tested technique is to move the loft contents to one side and then fit the insulation and add loft stilt storage platforms on the other side. Then you simply move the contents on to the storage layer and complete the insulation on the remaining loft space. 


Can ROCKWOOL help reduce noise transmitted through pipes and air conditioning systems, or from plant and machinery?

Yes, there are several products which can help. ROCKWOOL's proven combination of high acoustic porosity, acoustic frictional resistance and light weight makes it ideal for use in a wide range of demanding situations. Products to look for include Techwrap and TechtubeDuctwrap and ductslab and pre-formed pipe sections such as H&V sections.

Fire Protection and Fire Stopping

Can I use any ROCKWOOL product to provide fire protection or fire stopping?

ROCKWOOL insulation is classified as A1 non-combustible however, products need to be tested for the specific application they are proposed to be used for and must be tested to perform for the fire resistance period required.  Therefore, the correct and tested product must be specified for fire applications.

What product do I use for protection from fire for structural steel beams and columns?

BEAMCLAD fire protection boards can provide up to 4 hours fire protection to steel beams and columns. 

If appearance is important, the Beamclad board system can be installed to provide boxed or profiled protection for 2,3, or 4 sided, exposed steel conditions. Available with tissue, foil or plain facing it can be glued or pin-fixed into position to provide a neat finish which, if required, can be decorated.  Any finishes should not detract from the tested performance of the product. 

Beamclad boards are easy to cut to required shapes on site, allowing service penetrations to be neatly accommodated. 

ROCKWOOL Insulation Density FAQs


What density is ROCKWOOL insulation?

There is no single answer to this. ROCKWOOL products are destined for a wide variety of applications needing different densities, each of which is designed into the product at the manufacturing stage. The most familiar ROCKWOOL product will be ROCKWOOL Roll, a light density 22 kilogram per cubic metre (kg/m³) material used typically for loft insulation. At the other end of the density range is a system for cladding buildings using a high density panel - Rockpanel - of compressed ROCKWOOL insulation at over 1000 kg/m3.  The versatile range of ROCKWOOL products includes rolls, slabs, boards, dual density systems, mats, pipes, fabricated and loose wools, all of which are provided in a range of densities and thicknesses suitable for their best application.

Can I specify an insulation product by density?

Specification of ROCKWOOL insulation products should be carried out by their application area.  It is important to ensure that the product is tested and certified for its purpose to ensure it performs as required.  This is particularly important for Fire protection/stopping applications. 

Do you have a product with a minimum density of 10kg/m3?

The minimum density product we manufacture is the ROCKWOOL Roll with a nominal density of 22kg/m3 which meets the 10kg/m3 minimum requirement.

Looking for support? The ROCKWOOL Trade Application Guide is here.

Packed full of product information, building regulation compliance criteria and installation advice, the must-have manual tells you everything you need to know about our non-combustible stone wool insulation.

Trade Application Guide

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