Introduction to Solid Wall Insulation (SWI) - Knauf Insulation


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About Knauf Insulation

The Knauf group was established in Germany in 1932 and today remains one of the world's leading building materials producers with over 100 manufacturing locations. Knauf insulation has over 30 manufacturing sites worldwide producing glass and rock mineral wool extruded polystyrene and extruded polyethylene insulation. In the UK the four manufacturing plants can be found at Saint Helens and cwmbran where they produce glass mineral wool. Hartlepool where they produce polyfoam extruded polystyrene and extruded polyethylene and Queensferry where rock silk rock mineral wool is produced these four plants ensure that canal be insulation remains today the uk's principle insulation producer roll your mouse over the locations to learn more about them.


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Technical Support

At Knauf insulation we recognise that possessing a thorough knowledge of insulation products is essential to enable us to reduce energy consumption. Our technical advisory centre TAC continues to provide personal high level Technical Support including U-value calculations condensation analysis and assistance with CAD drawings and NBS clauses.


Support is also available on our website there's also a selection of:

  • Sector guides,
  • Product data sheets,
  • COSHH data.
  • The new industry leading Knauf insulation solutions for buildings.


Ecose Technology

Knauf insulation Ecose technology is a revolutionary new formaldehyde free binder technology based on rapidly renewable materials instead of Petro-based chemicals it reduces embodied energy and delivers superior environmental sustainability. Ecose technology was developed for glass and rock mineral wool insulation but offers the same potential benefits to other products where resin substitution would be an advantage. Products made with Ecose technology on more sustainable as they have the added benefit of using a binder that is up to 70% less energy intensive and traditional binders.


Ecose technology uses rapidly renewable bio based materials to replace traditional chemicals the manufacturing emissions are also reduced and since there is no formaldehyde or fennel used with, it contributes to improving the indoor air quality of buildings. The distinctive new look to Knauf insulation mineral wool products is all thanks to Ecose technology and creates the next generation of insulation products. This binding process leads to a natural shade of earthy brown free from die or colourants. This breakthrough is a result of five years of intensive research and development as part of our commitment to being at the forefront of sustainability.


With Ecose technology rapidly renewable bio based materials replaced the traditional chemicals to create more advanced and sustainable products. In addition Ecose technology could help to reduce our carbon footprint in a world where we all need to trade a little more lightly.



This module explains how the choice of insulation affects exterior wall design and thermal and fire performance. after completing it you will: 

  • Understand the principles of solid wall insulation systems.
  • Understand what regulations affect these systems.
  • Be aware of the different types of insulation and their performance characteristics.
  • Understand the fire performance of insulation products or materials.


Programme Structure

This module contains 3 main sections the first section gives a general overview of solid wall insulation systems their benefits and applications the second and third section looks at internal and external wall systems respectively and outlines the standards and regulations that apply to these systems as well as looking at the systems in more detail in regards to construction and performance criteria.


Why Insulation?

The UK's housing stock is estimated at approximately 24.5 million dwellings, approximately 36% of these dwellings consist of non cavity wall construction, solid brick, solid stone, pre-1944 timber frame and non traditional construction i.e. concrete.


As much as 45% of the heat can escape through uninsulated solid walls insulating solid walls brings many benefits, it not only prevents heat loss in the winter, it also reduces heat gain in the summer, lower fuel bills which also means less fuel debt and fuel poverty, increased value of property, reduced maintenance, less risk of ill health, minimises energy consumption and CO2 emissions associated with the dwelling, compliance with building regulations.


Choosing a System

Solid wall insulation systems can be installed on the inside or the outside of the wall construction either option will reduce heat loss and increase comfort in your home the choice of which system to use can be dictated by:

  • Physical suitability of the building and location, for example, can the exterior facade be extended thus changing the building line and footprint?
  • Design and aesthetic considerations such as whether the facade of the building can be changed or whether internal space is a suitable for internal insulation.
  • Budget constraints. Some systems can be substantially cheaper than others however the trade off can be the level of insulation that can be achieved.


Internal Wall Insulation Advantages and Disadvantages

Using internal wall insulation systems has both advantages and disadvantages.



  • They provide a quick thermal response enabling room comfort levels to be achieved more quickly than with an external wall insulation system.
  • This is particularly beneficial in intermittently heated buildings such as dwellings.
  • The installation of an internal insulation system isolates the thermal mass of the external walls from the internal environment which improves the response time of the heating system.
  • Comfortable room temperatures are quickly achieved and the time periods when the heating system is in operation are reduced.



  • Where internal walls and intermediate floors butt up against external walls, there is a risk of creating cold bridges which could reduce the efficiency of the installed system and lead to surface condensation and mould growth.
  • In order to prevent this occurring these areas should be insulated.
  • Thermal mass benefits of exterior wall are lost.
  • Usable internal space is reduced.


Studwork, Rigid Thermal Boards and Flexible Thermal Linings

There are three main types of internal insulation systems.



A combination of metal or timber studwork insulation filled within the cavity and insulated or standard plasterboard. This is ideally done when renovating an existing room or a complete dwelling.


Rigid thermal board -

thermal laminates are a composite of plasterboard and thermal insulation, the insulation backing can be specified in a variety of thicknesses. insulation in excess of 60MM will typically be required to achieve best practice performance up to 100mm of insulation can be included thermal boards are fixed to treated timber battens which are in turn fixed to the wall surface.


Flexible thermal linings 

Flexible thermal linings are used in solid wall homes, mansard roofs and dormer ceilings the lining is 10 millimeters thick and made from a natural product (latex) in an open and closed cellular construction and has a durable glass fibre face that can be decorated with emulsion, wallpaper or even tiled. These products are used to assist in preventing surface condensation and mould growth and provide less thermal performance than installing 12.5mm plasterboard on plaster dads.


Thermally Engineered Studwork

Stud work systems gives some of the best thermal values of all the internal insulation solutions a typical 225mm 9 inches thick an insulated masonry external wall with a dense plaster to the internal walls will achieve a U-value of approximately 2.10 Watts per metre squared Kelvin. The same wall using 75MM thermally engineered stud work will achieve a U value of at least 0.35 Watts per metre squared Kelvin an improvement in thermal performance of almost 80%. If a typical 3 bedroom semi detached house was upgraded in this manner it would reduce the carbon emissions associated with the house by approximately 2.4 tonnes per year. If traditional studwork systems are not suitably designed thermal bridging can occur as the lower thermal resistance of the timber and metal stud creates a thermal bridge from the exterior wall to the inside surface.


To get around the problems associated with thermal bridging and traditional studwork solutions Thermally engineered composite studs can be used because of the materials used in their construction these composite studs provide a high level of thermal resistance comparable to the actual thermal insulation installed between them.


Standards - Building Regulations

Parts B, C and L of the building regulations are most relevant to internal insulation systems. Section B2 of the building regulations deals with internal fire spread within linings. Materials are required to resist the spread of fire, the rate of which is dependent on building type, room size, room location and occupancy. Various tables within the document give further guidance details on the types of materials and construction materials used for walls are covered by several standards. Notably for national classifications for standard is BS476, fire tests on building materials and structures. European classifications are described in BS EN 13501-1: 2002 fire classification of construction products and building elements.


System Details


Thermal Performance of Studwork

With the ever greater need for higher insulation values within buildings especially in existing stock, studwork systems would seem to be a logical choice in most cases. A typical construction for an insulated stud work system might consist of:

  • A solid masonry wall with existing interior wall surface,
  • thermally engineered studs consisting of extruded polystyrene bonded to oriented strand boards OSB.
  • High performance water repellent glass mineral wool
  • 12.5mm vapour check plasterboard


The advantages are:

  • A highly cost effective and efficient solution.
  • Quick and easy to install.
  • The insulation and component parts contain a very high recycled content.
  • Highly sustainable insulation products manufactured from abundant raw material sources.
  • It further improves acoustic performance of studwork systems.
  • System components are unaffected by moisture.


Insulated studs can typically have an insulation thermal conductivity value of 0.030 Watts per meter Kelvin and an oriented strand board value of 0.130 Watts per meter Kelvin.


The OSB components should be manufactured with materials obtained from FSC certificated forests, the acoustic performance of a solid masonry external wall can be significantly improved by the installation of an insulated studwork system. A typical improvement of up to 5 decibels can be expected.


External Wall Insulation EWI


Benefits of EWI Systems

There are many benefits in using external wall insulation systems:

  • They are insulated externally thus keeping the walls warm and preventing condensation forming,
  • They allow some types of buildings substructure to act as a heat store increasing thermal efficiency,
  • They can prevent thermal bridging,
  • They can accommodate a huge variety of decorative external envelopes for both traditional and contemporary building styles,
  • They provide a stabilized structural fabric that prevents movement due to thermal shock,
  • They contribute towards sound reduction,
  • They are lightweight when compared with brick and masonry.


New Build

For new build applications external wall insulation systems give the designer and builder several advantages. Current building regulations thermal performance requirements can be met using a variety of insulation products including rock mineral wool and extruded polystyrene and also accommodate future changes. There's a wide range of construction options and design flexibility and it allows fast construction times making it cost effective. But external wall insulation also has advantages for refurbishment applications such as upgrades to run down housing stock, extending building life through waterproofing and thermal upgrades of properties. Remodeling old or redundant buildings for new uses and because of the inherent flexibility of the systems it has a relatively small impact on the building inhabitants and the interior spaces.


Render Systems

Broadly speaking external wall insulation systems usually consist of an insulation layer fixed to the exterior of the structure with a render finish applied directly on top typically the render consists of a reinforced base coat with a decorative finish top coat.


Render on Insulation

Render on insulation creates a building with high thermal mass which is ideal for properties in continuous occupation the render finish is both decorative and waterproof.


Building Regulations that May Apply to External Wall Insulation Systems

Where external cladding systems are concerned it's necessary to consider several sections of the building regulations. All the following approved documents will be relevant to some extent for the purposes of this CPD module we will be looking at the thermal and fire performance of insulation. 


Fire Spread

In some circumstances fire can spread through cavities within external cladding systems, these cavities can be part of the system design such as rain screen cladding or can be formed by the delamination or differential movement caused by the fire itself. As flames enter these cavities and in some cases consume the insulation within them they can become elongated and spread within the system. Unchecked fire can spread rapidly through buildings reaching other floors via window openings, this process can have devastating effects on high rise buildings. Garnock Court in Irvine, Scotland suffered such a fate in 1999 and prompted a parliamentary inquiry.


Building Regulations

Approved document B fire safety gives guidance for external thermal insulation, it states the external envelope of a building should not provide a medium for fire spread if it is likely to be a risk to health and safety. The use of combustible materials in the cladding system and extensive cavities may present such a risk


Appendix A of the document gives detailed information on performance of materials products and structures.


Approved document B requires buildings over 18 metres to have class zero national class or class BS3D2 or better European class ratings.


BRE Report BR 135

Approved document B makes reference to the BRE report BR135 fire performance of external insulation for walls of multi Storey buildings.


The report describes full scale test data on cladding systems from BS8414-1:2002 and BS8414-2:2005 the report divides insulating materials typically used in external cladding systems into three groups:


Non-combustible materials and materials of limited combustibility

Generally rock and glass mineral wool products which have formed into slabs.



Products such as polyurethane foam PUR, polyisocyanurate foam PIR and phenolic foam are typically provided as boards. These products are often faced with materials such as glass fibre or aluminium foil.



Expanded polystyrene EPS and extruded polystyrene XPS can be supplied in both a fire retardant and non-fire retardant form. Again this material is generally supplied as boards the relative fire performance of the three insulation groups is summarised in BR135.


Rock mineral wool clearly has many advantages over thermosets and thermoplastics; it can resist fire for longer and at far higher temperatures. It does not combust and therefore won't add to the fire load. And it won't produce dangerous and potentially lethal smoke.


Using mineral wool could make a significant difference to the buildings integrity during a fire, the safe evacuation of its occupants and the effectiveness of the emergency services and means of access into the building.


Fire Barriers

There are a number of cavity barriers on the market that employ the use of intumescent strips or coatings in order to seal cavities typically fire barriers are mineral fibre slab mfs or mineral fibre lamella MFL which are manufactured from rock mineral wool the same material used to insulate the building.


The key design elements for fire barriers are:

  • The fire barrier should form a continuous band through the insulation layer at each floor level.
  • Any abutting of material should ensure that no cavity exists for fire to track or pass through.
  • The non combustible material should be bonded and tied back to the wall to ensure that no fire path can be created.
  • Cavity barriers are made from rock mineral wool. A building insulated with rock mineral wool does not require fire barriers.


System Details


Render on Insulation

A typical construction consists of:

  • An existing or new solid masonry wall, with external insulation of a rock mineral wool slab.
  • An adhesive bonds the insulation to the building substrate or friction fit mechanical fixings are used to fix the insulation to the substrate or a combination of the two.
  • Reinforcing mesh
  • Two coats of render are typical and applied in accordance with manufacturers instructions.
  • A rock mineral wool lamellar is used for adhesive fixing this is a high compressive strength product which is made by cutting into strips and turned through 90 degrees so that the mineral wool strands lie at right angles to the insulation surface.


The advantages are:

  • Compression resistant insulation slabs offering a high level of support to render.
  • Joints between the slabs knit together preventing thermal bridging.
  • The non combustible insulation requires no cavity barriers making installation quick and simple.
  • Moisture repellent insulation.
  • Mineral wool slab is a Zero ODP (ozone depletion potential) and Zero GWP (global warming potential) insulation product.


Refer to system designers recommendations for further specification of components and installation details. The rigidity of rock mineral wool slabs makes them easy to handle and less prone to site damage than less robust options. The compression resistance of the rock mineral wool slabs behind the render system provides excellent support and helps to prevent impact damage, thereby prolonging the service life of the insulated facade. Dense rock mineral wool slabs have a thermal conductivity value of approximately 0.037 Watts per meter Kelvin. They are non combustible and classified as euroclass A1 to BS EN ISO 13501-1. Because the insulation is non combustible cavity fire barriers are not required.



So, in summary we've seen:

  • The principles of solid wall insulation systems.
  • The part that the approved documents play in both guidance for fire safety and thermal performance.
  • The importance of BR135 specifically to external wall insulation systems.
  • The different properties of various insulation types in both thermal and fire resistance performance.
  • How fire can spread within an external rendered insulation system and what can happen if specification of suitable materials and good building practice are not observed.
  • The benefits of using rock mineral wool for its insulation properties and superior fire resistance when compared to alternative solutions.
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