Dominic Meakins of Demon Designs explores the different factors to be aware of when specifying glass or appointing a glass contractor for your self-build, in particular when it comes to getting glass balustrades right
Stunning, unique features can be achieved by the use of glass within your building. But when it comes to considering glass for your self-build project, where do you start if you don’t have an architect or engineer on board?
You could pick a glazing company from the internet and hope for the best, however we would strongly recommend first doing some background research. To find a suitable glazing contractor, ask for recommendations and look at their portfolio of completed projects. Seek references, don’t just rely on online reviews, and – this is vital – check that they have suitable insurances. When you’ve made your choice, ensure that all information you are given (and may rely on in a dispute) is confirmed in writing. Back up all assurances given to you in electronic format to a secure location, or as hard copies.
Next, consider the specification of the glass, which will depend greatly on the intended use of the building (with most self-builders it would be domestic use), and where the glass is within the building. Does the glass protect occupants from a fall? Should the glass ever get broken, how do you ensure it will break safely and not risk injuring the occupants, or passers-by?
A fall is defined in Document K of the Building Regulations as any change in levels greater than 600 mm in domestic dwellings (380 mm in commercial). So the glass specification would be the same for a patio raised 1 metre off the ground as for a first floor balcony.
There are two main types of glass used in balustrades, toughened glass and toughened laminated glass. Toughened glass is around four times stronger the regular float glass and is very strong in most conditions, but is fragile on its edges and corners. If it fails it breaks into very small cubes, making it less likely to cause injury from cuts. It also means there is no protection left if it fails.
Toughened glass panels on their own can be used as infill panels within framed or posted systems, and will always require a handrail fixed to the walls or adjacent glass panels, to provide support and fall protection if the panel breaks. Toughened laminated glass is where two (or more) sheets of toughened glass are bonded together using a clear interlayer. They hold the glass together if one or more panels break, providing some protection. There are three different materials used for the interlayers PVB, EVA and SGP, and each has a particular use and benefit.
PVB (PolyVinyl Butyral) is the most common, and has been around for decades. It is used in car windshields. PVB holds the panels of glass together and, when used in a balustrade, is very successful when one panel of glass breaks. If both panels of glass break, it becomes very flexible, but still holds together in a big sheet. EVA (Ethylene-Vinyl Acetate) is relatively new compared to PVB. The major advantage of EVA over PVB is it has better water resistance, so is recommended for external balustrades (PVB can be used outside, but the edges require sealing to prevent water creeping into the interlayer).
SGP (Sentry Glass Plus) is an ‘ionoplast’ interlayer; SGP being a brand name by DuPont although there are other ionoplasts entering the market from all the major manufacturers. Ionoplasts are the ultimate interlayer. Developed in the USA for storm resistance, they are capable of withstanding large forces when laminated in glass. Ionoplasts are very stable but also rigid. This means they provide structural support even when both panels of glass are broken. In addition, due to the added strength, they can be designed to reduce the thickness of the glass, making the installation lighter.
Where glass is concerned, size always matters. The bigger the panels you wish to create, the stronger and thicker the glass (and supporting framework) needs to be, and don’t forget that on a restricted site, the glass will have to be transported safely to the area in which it is to be installed. If the panels are so large as to require a crane, the hire costs can be significant.
Glass companies that specialise in the installation of architectural glass usually offer free general advice on the safe use of glass and how it needs to be supported, so seek advice early. Don’t just build an opening and hope it will be suitable for the glazing later. Additional support may be required to meet local wind loads and meet the Building Regulations. It will be expensive to install such support retrospectively.
As an example, one of the most common errors is constructing a balcony from timber then deciding to install a frameless glass balustrade. This usually requires load-bearing steelwork within the timber balcony structure.
Remember, even if you do not need planning permission, you will still need to comply with Building Regulations.
When it comes to balustrades, size and performance are the driving factors. Small spans can be accomplished using simple glass clamping brackets, however if you are looking for large spans, especially using frameless glass, the glass thickness will increase, requiring additional structural supports. If you are looking for an ‘all glass’ look, then the glass will end up acting as a structural element in the building. At the extreme you may become limited by the manufacturing sizes available, the physical weight of the glass and the budget.
As a rule of thumb, glass weighs 2.5 kg per square metre, per millimetre of thickness. Therefore 1 m2 of 10 mm thick glass will weigh 25 kg. When considering a structural glass balustrade panel, 1.1 m high x 4 m wide, using 21.5 mm thick toughened and laminated glass, the weight of the glass alone would be over 230 kg, and would need special lifting equipment or a crane to install it.
The glazing contractor may be able to provide engineering calculations. but be prepared to employ your own structural engineer to check the supporting structures are suitable.
To conclude, the key is to seek advice early. There are a number of small architectural and structural glass companies who specialise in this area who have the experience with the problems and challenges facing the self-builder.
Dominic Meakins is managing director of Demon Designs