Engineering glass extensions for stability and safety

Glass extensions are currently one of the most popular ways to add extra living space to a property. These all-glass structures are a fantastic choice for those looking to flood their home with natural light and make the most of the views from their home. For a spacious indoor-outdoor area that can be used for a variety of functions, a glass extension is hard to beat.

But, while they look amazing and can enhance your lifestyle, are glass extensions safe?

It’s natural to have concerns about the stability and safety of a structure that is largely made of glass. You may wonder how it will fare in extreme weather or how strong the glass is.

Every bespoke glazed extension is absolutely unique in size and design to fulfil the vision and requirements of the homeowner. Each one will therefore have a completely unique set of factors combining to test its stability and safety. This includes its environment and the weather; the topography of the site, such as any slope towards or away from the main property; and the structural integrity of the building it will be attached to.

No matter what shape and size it is, a glass extension needs to be designed, engineered and installed to mitigate these factors. Additional safety and stability can be created with safety glass, reinforced aluminium, extra-strong fixings and suitable foundations. Much of this will require detailed calculations by a qualified structural engineer to ensure it complies with the relevant building regulations and British standards.

If you're planning a glass extension for your home and are feeling daunted by the technicalities, don't worry! We manage all aspects of ensuring the safety and stability of your structure. Our highly experienced and technically competent team will carry out all the required steps and checks. If you are interested in the detail of what these are, read on.

Safety of glass extensions

To ensure that fully glazed extensions is safe, a number of things are considered. This includes the dimensions of the pane and the forces imposed on it by snow and wind. It also includes its position within the structure in relation to the people within it. This informs how thick the glass should be and the areas where safety glass should be used.

Safety glass

Safety glass is stronger and less likely to break than standard float (annealed) glass. It also breaks in a way that makes it safer than standard glass.

There are two types of safety glass: toughened glass (also known as tempered glass) and laminated glass. Each is manufactured in a different way and has distinct benefits and applications.

Toughened glass is up to five times stronger than annealed glass and when broken, it shatters into small cubes. This prevents injury from the jagged shards of glass that you get when standard glass breaks.

By law, toughened glass must be used in areas called ‘Critical Locations’ where breakage or impact with standard (annealed) glass could cause serious injury. In domestic buildings, critical locations as laid out in Section 5 of Approved Document K of the Building Regulations are:

• Glass doors in full or minimum 1500mm from floor level
• Glass adjacent to doors to the same height as a minimum and 300mm from the edge of the door
• Any glazing below 800mm from floor level

Laminated glass is made from two panes of glass stuck together with a strong-binding resin called PVB (polyvinyl butyral) or similar, as there are so many different laminates available. The double layer of glass combined with the resin not only creates extra strength but when it breaks, the glass is held in place by the PVB layer. For this reason, laminated glass is used in glazed roofs and skylights on the inside pane to stop broken glass falling on to people below.

Toughened glass is stronger than laminated glass and usually has the highest A/1 safety rating, whereas laminated is classed as B/2. But because they break in different ways, for some applications laminated glass may be more suitable, such as the glass roofs mentioned above.

Safety glass carries a kitemark with a European standard number of BS EN 14449 for laminated glass and BS EN 12150 for toughened glass. A good building regulations officer would check compliance of safety glass by looking for these or applicable CE marks.

Stability of glass extensions

The stability of an all-glass structure is affected by factors such as its size, height and shape, the forces imposed on it by the weather, how it interacts with the main property, and the terrain and inclines of its location.

Detailed calculations are needed to enable the correct manufacture of all elements of the glass extension so it provides the stability required. These should be carried out by a structural engineer, based on a site survey and the drawings that the designer, working with the customer, has produced. This ensures that the structure envisaged by the customer can be successfully implemented as intended and will not put people at risk by being unsafe or unstable.

These calculations then allow the site to be prepared properly with the correct foundations and the installation carried out correctly, for example with the appropriate fixings.

Snow load

Various types of weather can impose different forces on a glass extension. As part of the calculations required to ensure the stability and strength of a glass structure, the snow load needs to be calculated. This is covered by British and European Standard BS EN 1991-1-3.

The downward force on a glass roof from snow and ice is worked out based on weather data for average snowfall in the location of the property. The average snow load in the UK is 600N/m², or around 60kg/m².

Again, a qualified structural engineer will be able to make the snow load calculations.

Wind loading

Covered by British Standards 6399, wind load refers to forces on a structure from the wind. It takes into account both the positive and negative forces (pressure and suction) on each part of the extension.

A structural engineer will do lots of calculations to determine the effect of the wind on a glass extension’s stability. All these calculations need to take into account the forces imposed on all areas of the structure, from the roof down to the feet, and even into the foundations. The angle of each pane of glass can also affect the impact of the wind on it. There are usually certain areas of the glass extension, sometimes even just the smallest strip of glazing, which are subject to particular force from the wind.

The calculations inform the placement of additional reinforcement on the structure. For example, it will determine the strength of the wall plate (where the extension connects to the building), the eaves beam and the length of the structural inserts within the legs or post (the vertical columns that hold up the eaves beam).

In addition, the calculations also tell you which areas will require stronger or additional fixings during installation. This applies to all fixings including wall plate fixings, feet fixings and leg fixings into spigots.

Dead and live loads

The dead and live load is about the impact of the load that the new structure introduces to the existing property.

Again calculated by a structural engineer, it includes checking that the beams above any of the property’s existing openings is substantial enough for the new imposed loads from the glass extension.

Foundations

The foundations are hugely important in ensuring the stability of the glass extension, so it’s essential that they are calculated correctly and designed by a qualified structural engineer. At the same time, other elements that may affect the foundations will be checked, including existing services such as drains, ducts, pipes and cables.

Steel

The frame of glass extensions is usually made from aluminium for robustness and durability. However, steel inserts are used where additional strength is needed for stability, such as in areas of the structure subject to higher wind or snow loads, or features such as internal or external awnings.

Thermal expansion and contraction

Changes in air temperature and the effect of direct heat from the sun can make the materials in a glass extension expand and contract.

Tolerances are included to take into account differences in expansion and contraction of the extension. Different technologies and materials can then be used to allow for movement as and where necessary, which prevents damage to the structure and materials.

Engineering Solarlux glass extensions for stability and safety

There are many factors that give Solarlux glass extensions stability and safety. Key to this are the high-quality materials and the precision engineering that ensures the product will withstand the forces imposed on it. Every element of the structure is rigorously tested to exceed British Standards or relevant equivalents.

As a UK partner for Solarlux and a specialist glazing company in our own right, our Yorkshire design and installation team ensure compliance with all relevant building regulations regarding the stability and safety of our glass extensions.

Stability

We feel it’s important for our Yorkshire team to work with an independent structural engineer, employed by our customer, on our own calculations. This allows us to get to the detail of the design, which ensures we can double check that the right calculations have been made for the glass extension to be stable and safe, prior to Solarlux's own checks.

The structural engineer also carries out the foundation design, working alongside the project builder. They check all the existing services such as drains, ducts, pipes and cables that will get in the way of the foundation design.

Throughout the journey from design to installation, each Solarlux glass extension is reviewed and calculated by Solarlux's in-house static engineer working at its manufacturing headquarters in Germany to ensure it is thoroughly stable and safe.

Our team visit the site prior to installation to check that everything including the foundations has been done correctly.

We do all this this because we believe in doing the job right. We know the devil is in the detail. Our team come from a background in construction and therefore look at the project as a whole and how our part fits in to it all. We are among just a handful of Solarlux partners with the skills and experience to install glass extensions, so we recognise what's needed to ensure the stability and safety of these structures.

We scrutinise every detail, liaising throughout with the Solarlux technician and static engineer in Germany, before the final drawings go into manufacture. We balance this with what we know the customer wants to achieve for their preferred aesthetics and functionality.

Safety glass

Solarlux glass extensions use safety glass throughout, which goes way beyond what's required by building regulations. We do not use standard float glass at all, even on small panes that are exempt under building regulations.

In a Solarlux glass roof, the outside panes are toughened and the inside laminated. This means that the outside pane, which is more likely to suffer an impact, is the strongest. But if the glass does break, then it is stopped from crashing down by the laminated pane.

As a company, we do not think the building regulations are clear enough in stipulating that the inside pane of all glass roofs should be laminated. We have asked the GGF (Glass and Glazing Federation) to lobby the Government about making the building regulations clearer on this.

Snow load

A 65kg/m² snow loading is typically applied to all Solarlux glass extensions in the UK. Average snow loads for most parts of the country are around 60kg/m² - so Solarlux's standard is based on a worst case scenario and covers all bases. In actual fact, the lowest snow load that Solarlux allows for its glass extensions is 65kg/m², and they can go as high as 350kg/m² - which is very handy for their customers in places such as the Alps!

Wind loading

Our structural engineer calculates the wind load on the proposed glass extension at both zero degrees (straight on) and at 90 degrees, and provides a highly detailed drawing. The entire structure is assessed, including any new wall or walls that the customer is creating as part of the glass extension design.

In addition, we always ask the structural engineer to design all the fixings, including the critical fixings and any gluelam fixings, that we are going to need. We always go way overboard, even down to the size of the screws, to ensure the stability and safety of every extension we install.

Steel

Galvanised steel is used by Solarlux to reinforce the aluminium frames where needed. It can be placed in the feet going down to the foundations from the aluminium legs of the glass extension. Two layers of bitumen paint are applied to the feet where they touch the foundations so it protects them from any potential damp from the concrete.

Steel is also used in the eaves beam and the rafters where required to maintain the thermal break. This strengthens the structure for wind and snow loading, as well as to support things like internal or external awnings.

Thermal expansion and contraction

Thermal expansion and contraction is taken into account as part of the Solarlux product design and by Germany's static engineer when they do their calculations. Depending on the tolerance required, we use different technologies and materials to allow for movement and create the weather, air and thermal seals between the new extension and the existing or new building structures.

Are glass extensions safe from a security point of view? For information, read our article about how secure bi-folding and sliding doors are.