Cellular Glass - Insulating the Whole Building - FOAMGLAS®


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This presentation will look at the characteristics of a unique structural material called cellular glass.



Today we will consider its use as an insulation for buildings. In 1937 Pittsburgh Corning Corporation built their first Cellular Glass manufacturing facility in Pittsburgh USA. Subsequently production plants were constructed in Europe the newest being opened in 2008 at Klasterec in the Czech Republic.

Looking toward the future the construction of new production facilities is planned to service the worlds expanding economies. Today we will see how cellular glass insulation is manufactured. We will find out about its green credentials and sustainability.


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We will look at:

  • How does water vapour moisture and condensation affect buildings.
  • How does cellular glass perform under different environmental and structural conditions?
  • We will apply the unique material properties of cellular glass to a building looking at how we can reduce the risks associated with thermal bridging structural material and thermal performance failures.


Manufacturing Process

What ingredients go into making cellular glass local recycling companies supply scrap automobile glass and waste from the window industry. We had sand which is an abundant local resource.


Certified green electricity from Norwegian and Swiss hydro power plants supply power to the cellular glass factory at Tessenderlo in Belgium. This introduction of green energy is just one part of our commitment to reducing the amount of embodied energy required in the manufacturing process. Further information on our energy strategy may be found within the environmental product declaration.


Here we see the production process firstly at stage one, the raw materials are weighed ground up mixed and loaded into a hopper. Which empties raw materials into the electrical furnace. The furnace at stage two produces molten glass which had stage three is pulled off and rapidly cooled on a conveyor belt. During stage 4, a mix of the cool glass graded recycled glass and minerals are loaded into large rotating corundum cylinders. A fine glass powder is produced, and it is poured into stainless steel moulding trays. At stage five these trays passed through a cellulating oven and a natural oxidising reaction takes place which causes the molten glass powder in the trays to expand creating the glass lamps with their hermetically sealed glass cell structure.


During stage six the slabs are taken from the mould and placed into an annealing furnace, where they are slowly cooled to remove temperature stresses.


At stage 7 the production batch undergoes various quality checks before the slabs are cut and trimmed to size. Any off cuts returned to stage 4 loaded into the rotating cylinders to make more powder mix. Finally, at stage eight the cellular glass materials are packaged and dispatched.


Here we have a short film showing us the complete process from the raw materials to finish product.


Cellular Glass - Material Properties

Here we have two microscope images of cellular glass. The hermetically sealed glass walled cells are clearly visible, they will not allow the transmission of liquid gas or vapour through the material.


The insulating performance of any material is significantly lowered when it absorbs even a small amount of moisture. With its truly closed cell structure the insulating capabilities of cellular glass remain permanent for the lifetime of the building. For the building market arrange of cellular glass slab and board insulation products are available in a wide variety of uniform or tapered thickness. Adjustments during the manufacturing process alter the density of the cellular glass.


This in turn changes the thermal conductivity. Lower density materials have a lower thermal conductivity value, and are used for sophist walls and facades. Where a higher compressive strength is required you would specify a higher density cellular glass material.


Ecology and Sustainability - EPD

Cellular glass insulation is manufactured from minimum 60% locally sourced recycled glass, including scrap car windscreens and off cuts from the window industry. Raw materials are mineral based for example sand, which is an abundant natural resource. The hermetically sealed glass cell structure is naturally produced. It is free from ecologically harmful blowing agents and flame retardants. Mutagenesis or carcinogenic chemicals are not used during production. Cellular glass is an inert non-toxic material, at the end of the buildings life cellular glass can be safely used for landscaping incorporated into hardcore or be used to manufacture thermal blocks and screeds.


The European organisation nature plus examines the origin of all recycled and raw materials used by a manufacturer. Nature plus also considers the environmental impact of both the manufacturing process and the work at the construction site.


The Association of Sustainable Building Products represents nature plus here in the UK, they review existing and forthcoming environmental policies, lobby government for a new approach to all construction works, and promote the use of recycled and sustainable building materials. Selecting truly sustainable products is now part of the design process. Cellular glass insulation meets with the highest standards and features within many specification guides, including the Green Guide to specification.


The cellular grass manufacturing facilities conform to strict environmental complaints and are registered for ISO 14,001 accreditation.


Full details are within the EPD the environmental product declaration and independently produced report which is used for assessing the green credentials of all materials.


A global warming potential of less than five is considered very good, cellular glass insulation has a global warming potential of less than one and an ozone depleting potential of zero.


Building Physics (what is it?)

Building physics analyses the effects of the physical phenomena in buildings it's an applied science where physics describes the attitude of materials under different circumstances. Design specifications will vary depending upon the purpose and location of the building. The cinema in a warm lowland climate is very different to a swimming pool in the high mountains, each building has its own internal and external conditions. This directly affects our choice of insulation and how that insulation will perform under the local environmental conditions. Internally the swimming pool is a warm damp environment, the cinema will have air conditioning.


Building Physics - Water Vapour

When water is warmed it evaporates and becomes water vapour. It is held within the air where it's invisible, the amount of water present in the air is termed as relative humidity. When the air is cooled it comes to a critical temperature where the water vapour can no longer be held within the air and condensates back to a liquid, this critical temperature is called the dew point temperature. When the dew point is on the surface of a material, we get surface condensation, when the dew point is within a material or structure, we get interstitial condensation. If we know how the building is constructed this dew point temperature can be calculated. The dew point calculation is not part of the U value SAP or SPM calculations.


Building Physics - The Direction of Vapour Drive

Here in the United Kingdom it's generally accepted that the internal temperature of the building is higher than the external temperature. This temperature difference hot internal to cold external creates pressure, which forces the warm moist air out through the building fabric to the exterior. This pressure is commonly referred to as vapor drive. To control the movement of vapor manufacturers of mineral wall and plastic foam based insulation materials, recommend a fully sealed vapour control layer is installed on the warm side, beneath the insulation. Vapour control layers can effectively reduce the amount of water vapour passing into the insulation layer. This helps to reduce the risk of the dew point occurring the production of water vapour and interstitial condensation. Water inside any material will reduce its thermal performance. Vapour control layers should always be installed correctly with sufficient joint overlaps and joint tapes.


Building Physics - Moisture - Condensation Risk

Vapour control layers are usually a sheet material with tape joints and are usually loose laid stapled or nailed in place. Here we will replicate a real life situation where we have a hole or tear in the vapour control layer.


This short film demonstrates how the insulation materials will react to water vapour.


We have four glass beakers each filled with boiling water. This replicates the water vapour drive in a building. Samples of insulation materials are placed over the top of each of the glass beakers; cellular glass, plastic foam, perlite and mineral wool. Finally, we place a beaker over each sample to capture any water vapour. As the warm moist air rises it will try to find its way through the insulation, due to the sealed glass wall cell structure of cellular glass no water vapour is able to pass through it, ensuring the insulation remains dry and unaffected by moisture.


Note that the warm moisture passes through plastic material and collected the beaker above, where it is cooled to below its dew point temperature and free flowing water condensation occurs.


The blown cell structure of the plastic foam sample was unable to prevent the passage of water vapour. Moisture within these materials reduces their thermal performance.


This is repeated with the samples of perlite and mineral wool. Moisture within these materials reduces their thermal performance that early dependent upon a completely sealed vapour control layer.


There are many different types and sealant methods for the vapour control layer. It is a fundamental part of the building, without a reliable vapour control layer the dew point will occur inside the structure, producing interstitial condensation, which in turn will reduce the thermal performance of the insulation.


Once the thermal performance is lowered the dew point will happen quicker and the volume of interstitial condensation will increase.


Building Physics - Vapour Resistance of Materials

Water vapour is invisible held within the air, it can pass through materials. The ability of a material to slow the movement of this vapour is termed as its vapour resistance, and has the unit mu. Air has a vapour resistance of 1 mu. Warm air with water vapour is passing from the kitchen through the roof structure, the vapour control layer, the insulation and the waterproofing membrane. Shown here in green we see similar glass has a mu value many times higher than the other installations. To retain their thermal performance these other installations rely upon a vapour control layer. Vapour control layers come in many designs and are typically a combination of polythene and aluminium. Joint adhesive completes a cellular glass system, which has an extremely high vapour resistance of up to 70,000.


Building Physics - The Direction of Vapour Drive

The United Kingdom has four Seasons the external climatic conditions change depending on the time of year. However, it is not always warmer on the inside than the outside. When we use air conditioning systems the external temperature is usually higher than the internal temperature. The warm side of the insulation is actually to the outside of the building. Therefore, the vapour drive is not always from inside to out. So which side of the insulation should the vapour control layer be installed above or below? When we consider our changing climate, this question becomes increasingly important.


In areas of the world which experienced high external temperatures combined with the humid climate, the vapour control layer is placed on the outside of the insulation layer. Cellular glass is a closed cell material with its adhesive seal joints we have a vapour barrier for the full thickness of the insulation. Completely protecting the building from vapour drive irrespective of the internal and external climatic conditions, it prevents the passage of water vapour in any direction.


As we have seen water vapour when cooled to below its dew point temperature turns back to a liquid and causes surface condensation.


Poorly fitted vapour control layers and poor design detailing leads to the serious problem of interstitial condensation, leading to moisture forming within the actual building structure.


Water vapour has passed through a hole in the polythene membrane and condensation has taken place, creating the ideal conditions for mould to grow. Moisture behind the plaster has caused its bond to fail and come away from the brickwork structure behind. Moisture within the floor has caused the floor covering to expand and warp. Condensation in the walls and ceiling has caused staining and mould growth. In all three cases interstitial condensation has caused a build-up of moisture within the fabric of the building, hidden from view and undetected until there is a failure to the internal finishes or worse still the structure of the building.


Building Physics - Fire - Combustibility & Fumes

In the laboratory fire tests are carried out on insulation materials. In this short film clip we have constructed tunnels of insulation materials to replicate the corridors in public buildings. We're looking for flash over potential and fumes.


Here we see a sample of cellular glass insulation. The insulation material does not burn, give off toxic fumes or contribute to fire and as a result achieved an A1 euro class classification. When we carry out the same test using a plastic foam in this case polyisocyanurate insulation, immediately the foam begins to burn and give off toxic fumes including high levels of hydrogen cyanide. It continues to burn once the fire source has been removed. This product achieves a D rating in the euro class classification. The same test is repeated using phenolic foam, whilst there is some improvement the material still gives off toxic fumes and continues to support combustion once the flame source has been removed. As a result, it achieves a C rating in the euro class classification. It is important to remember it is the toxic fumes and smoke not the flames that prevent your escape from a burning building.


Building Physics - Compressive Strength

Designers face special challenges when designing insulation systems for load bearing areas. Building regulations demand continuity of the insulation around the building envelope, so these critical load bearing areas require a robust long term solution to reduce the risk of thermal bridging, and damage from heavy loads. Upon floors the movement in the soft insulation is counteracted by using a layer of protective screed. On roofs the membrane simply stretch as the insulation materials below compresses. Cellular glass has an extremely high compressive strength and does not deflect, bend or move under load it significantly reduces the risk of fatal screeds and leaking roof membranes. In most cases Cellular glass can withstand the compressive loads without the need for a protective screed.

Plastic foams offer a load bearing capability of 175 kilo newtons per square metre, and extruded polystyrene and maximum of 700K newtons per square metre. But they compress by at least 10% well before these figures are actually achieved. A 150mm thickness of extruded polystyrene will compress by a minimum of 15 millimetres before it can support the actual load sitting upon it.


Building Physics - Co-efficient of Thermal Expansion

The coefficient of thermal expansion describes how the size of the material changes with an increase or decrease in temperature. An insulating material which is not dimensionally stable can reduce insulation efficiency in two ways.

  • Problem 1, plastic insulation boards are glued and mechanically fixed to a structure, as the temperature changes the plastic foam expands and shrinks. This continual expansion and contraction create stresses and eventual failure to the glue joints, tape joints, mechanical fixings, vapour control layers, and waterproofing membranes.
  • Problem 2, contraction during the winter months causes the insulation joints to open up creating cold spots. For energy efficient buildings insulation with tight closed joints at all times of the year is particularly important. Cellular glass insulation has a similar thermal expansion coefficient to concrete and steel. Cellular glass is adhesive bonded onto the structure. The thermal movement problems associated with plastic foam are completely eliminated.


The Properties of Cellular Glass Insulation

We have seen various laboratory tests and reviewed the environmental product declaration. Cellular glass insulation is unaffected by water or moisture, does not allow for the passage of gas or water vapour, is non-combustible. It will not burn will not contribute to fire, or give off toxic fumes. Cellular glass is dimensionally stable expanding and contracting at the same rate as concrete and steel. Vermin and insects can't use cellular glass for nesting or food. Cellular glass has very high compressive strength supporting significant loads without any movement or deformation. It's easily cut and shaped using simple hand tools. Cellular glass is friendly to the environment, it has a global warming potential of one and an ozone depletion potential of 0, it is a minimum 60% scrap glass it can be recycled, and most importantly its thermal performance is permanent for the lifetime of the building.


Design Solutions - Compact Roof - Warm Roof

We are now going to look in detail at a number of design solutions each using cellular glass insulation to reduce the design risks. First roofing applications featuring the warm compact roof system for concrete metal and timber structures. Cellular glasses suit all types of waterproofing system for traditional hot asphalt to hot or cold applied membrane systems and metal roofing systems. To ensure that workmanship is to a high standard we encourage the use of contractors who are members of the National Federation of roofing contractors. Here we have a training which demonstrates the installation of cellular glass insulation using cold applied bitumen based adhesive.


First, we prime the concrete deck using a roller or brush. The cold applied adhesive is poured onto the substrate. Using a notched spreader an even layer of adhesive is applied over the area. Edges are dipped into the adhesive and slabs are laid into position. The adhesive provides a single vapour air and watertight joint across the entire roof area. In this instance the cellular glasses supplied with a factory coating of bitumen ready to accept a torch on membrane. Here a two layer bitumen membrane system provides the primary roof covering. As membranes are torched onto the insulation layer, a flood of bitumen moves forward and seals all the joints. A wide range of data sheets with design and installation advice for all types of flat roofing are available for download.


Custom Design - Tapered Insulation

Where we have a flat structure the cellular glass insulation can be supplied with a sloped top surface, to ensure water runs off to the drains. Typically for new build projects architectural details and drawings are used as the starting point for the proposed design. A detailed site survey may also be required, a design drawing is produced showing the tapered insulation layout the critical heights and dimensions.


At door thresholds water outlets and parapets, the maximum and minimum heights are taken into account. We considered the slope the direction of drainage and the location of gutters and drains. All this is done whilst ensuring the overall average thickness of the tapered insulation system meets the required thermal performance. During manufacture each piece of cellular glass insulation is individually machine tapered and is given a unique part number, which matches up with its position on the layout drawing.


Case Studies

Why is a structural insulation material required? Below this concrete podium roof slab is the Shard visitor centre. The roof slab extends from within London Bridge station around to the entrance for the Shard tower. 8000 people per day walkover this roof slab with an access route for maintenance and emergency vehicle it was necessary to install an insulation with proven structural strength. The circular column support at the front of the Shard can be seen on both photos and upon the tapered insulation draw. The drainage system is hidden from view at paving level a discreet slot drain is all that can be seen. The larger box drain runs in channels within the cellular glass insulation layer. The tapered cellular glass is installed as a built up system, using the tapered insulation drawing as a guide it is bonded onto the concrete structure. All the joints are adhesive sealed to ensure a high performance vapour barrier. A membrane is laid over the insulation followed by motor bedding brains and finally the paving.


The Shard tower needs a lot of window cleaning. Tapered Cellular glass is again used up on the floor of the services platform high up on level 75 where compressive strength dimensional stability and insured long term performance are mandatory.


Design Solutions - Compact Roof (Standing Seam)

With wide range of finishes such as copper zinc aluminium and stainless steel, metal standing seem roofs are very popular. By combining the structural strength of cellular glass with a unique thermally isolated fixing plate we can reduce both thermal bridging and the risk of interstitial condensation. The cellular glass can be installed on flat, pitched or curved structures such as timber concrete and metal. The system prevents moisture vapour from the interior reaching the metal roof, so it is particularly popular for buildings such as swimming pools and spas.


Top left we see the build-up of a standing roof with cellular glass insulation adhesive bonded onto a metal deck structure.


The fixing plate is inserted into the cellular glass. A waterproof membrane is then bonded over the whole roof giving a fully walkable and waterproof surface. The plant is under the membrane and becomes the fixing point for the metal roof brackets, which in turn secure the metal standing seem roof sheets. When using a traditional design, the soft insulation is laid over the vapour control layer. The metal roof brackets are positioned on the vapour control layer. Screws passed through the vapour barrier and fix the bracket to the parent structure, creating thousands of punctures each of which must be correctly sealed. Each bracket becomes a thermal bridge and the screw ends are visible on the underside of the deck structure. The cellular class provides a support for the standing seam roof sheets, a thermal break, a vapour barrier and the insulation. Using the metal plate method there is no thermal path between the metal standing seam proof and the parent structure. The cellular glass vapour barrier has no fixing holes through it and there are no ugly screw fixings to be seen protruding on the underside of the roof deck. With cellular glass the underside of the roof deck can be finished soffit, no visible fixings, no homes through the vapour barrier. For design and construction of this unique standing seam roof system assistance can be provided by contractors who are members of the Federation of traditional metal roofing contractors.


Design Solutions - Facade

After construction is completed many facades are almost inaccessible, so the insulation and vapour control layer should be robust and reliable. The unique properties of cellular glass reduced the risk of condensation and provide a non-combustible insulation layer, which remains thermally efficient for the lifetime of the building. Cellular glass is suitable for all facade materials including cement panel, glass fibre, stone render, green planting, and metal.


High value facade materials such as stone and metal have an extremely long life span. The insulation and vapour control system must be of equal quality and proven reliability. You don't want to remove the facade because the materials behind have failed.


Training School - Installing Cellular Glass Onto Wall

Here we are at a contract a training school. The senior training instructor will show us how to install cellular glass onto a vertical surface. We start by preparing a diluted primer coat to seal the surface. The primer is applied over the whole wall. We thoroughly mix the adhesive and cement powder. A notched spreader is used to coat the surface and edges with adhesive. The Cellular glass insulation slab is pushed firmly onto the wall ensuring the joints are tightly closed and filled with adhesive.


Design Solutions - Facade - Fixing Methods

Thermal bridging from facade fixing systems can be as high as 80%. Using the unique properties of cellular glass means we can reduce the thermal bridging to as little as 4%. Traditional facade insulation systems require vapour control layers or breather membranes and special jointing tapes. When using the cellular glass method all of these are unnecessary. As we recently saw for vertical surfaces the cellular glass insulation is bonded back to the substrate using adhesives. For facades are purpose designed pre-punched serrated metal plate is pushed into the insulation layer, and a thermally isolated fixing is inserted and secured through to the parent structure. The structural characteristics of the cellular glass combined with this unique plate method significantly reduces thermal bridging, and the plate provides the fixing point for a wide range of facade fixings and cladding support. A full range of data sheets with design and installation advice are available for download.


Case Study - Aardman Animations

On the 10th of October 2005 the roof of the Aardman animations building near Temple Meads in Bristol collapsed, after fire tore through the Victorian building. The history of many films including Wallace and Gromit was lost. Safety and reliability were paramount for the replacement building. The Aardman designed team selected the cellular glass system for the ventilated timber façade. With minimal cold bridging the euro class A1 rating protection from water vapour and a thermal performance which remains permanent for the lifetime of the building, the cellular glass system fulfilled all the design requirements. It provides the most reliable and risk free insulation system.


Interiors - Wall, Floor, Soffit

Extremes of temperature and humidity are commonplace and as we know invisible water vapour is around us at all times. With the correct detailed design, a reduction in thermal bridging and a reliable insulation system the interior finishes remain functional and do not suffer from unnecessary water vapour and condensation problems. Cellular glass is ideal for all interiors, for floors which will take heavy loads, for all types of internal finishes including tiles renders plasters and cladding panels, many of which are simply glued onto the cellular glass without the need for studwork or fixings. For many public buildings fire safety is high on the agenda and Cellular glass provides that fire safety both inside and outside the building.


Interior Refurbishment and Preventing Water Damage

For refurbishment work the old surfaces are cleaned and stabilised. Cellular glass is simply adhesive bonded onto the structure, supporting stud work is usually not required. Services are recessed into the structure or surface of the cellular glass. Plasterboard plaster and tiles are applied directly into the surface of the cellular glass. Internal space is maximised, there are no hidden air pockets or voids for moisture to accumulate or mould to grow.


Refurbishing a property after flooding runs to thousands of pounds but are the replacement internal materials any better than the originals. Cellular glass has the unique property of being hermetically sealed and non-hygroscopic it doesn't soak up water. Cellular glass can't hold back the flood, but it can protect the interior finishes. As cellular glass insulated asphalt floor is non-absorbent send it across with waterproof wall finishes will also help to reduce the water damage.


Building Physics - Eliminatng Thermal Bridging

Here we see cellular glasses being laid as a perimeter insulation to prevent thermal bridging beneath brickwork or block work. The cellular glass blocks are incorporated into the structure, laid into a soft mortar bed. The first layer of bricks or blocks on top of the insulation layer distribute the load uniformly over their full surface. Marked in red here on the sectional details are just a few uses for the cellular glass block.


Design Solutions - Below Ground - Foundations

Cellular glass neither creeps nor settles under load. It is unaffected by groundwater and hydrostatic pressure and with simple detailing ensures the insulation system is continuous joined at all wall floor and foundation junctions. Externally belowground Cellular glass is fitted alongside all popular waterproofing systems. It's installed above or below raft foundations and ground slabs with strip footings. And to the external or internal side of the retaining walls. Internally belowground cellular glass can be bonded directly to the internal walls and floors or installed in conjunction with the cavity membrane system, which directs vertical and horizontal moisture to a drain systems. A full range of data sheets with design and installation advice are available for download.


Technical Support

Our team provide a full range of technical services including thermal performance and dew point calculations and data sheets for applications materials and installation instructions, for contractors also provide installation training. Within the RIBA website you can download a full range of cellular glass data sheets, including NBS specifications and installation instructions. We trust you found the presentation interesting and informative, and now to test your knowledge we have a series of multiple choice questions.

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