Glass balustrades, in particular, frameless glass balustrades, are a popular use of structural glazing to provide a protection against level changes in an architectural design. The advantage of using glass for such a barrier means that it is completely transparent and clear, minimising disruption on views from within the building and also minimising the impact the existence of the barrier has on the building design.
When specifying a glass balustrade on a project there are various elements that need to be considered to ensure that you are specifying a balustrade that is both strong and safe. Thankfully IQ has been designing structural glass balustrades for many years and understand the requirements from such a design. Below are some of the key areas of Building Regulations and the relevant building standards that govern the use and design of structural glass balustrades.
If you have any questions about the specification of a structural glass balustrade for your project just get in touch with the team at IQ who will be happy to offer specific and tailored project advice.
Where is a Balustrade Required?
A glass balustrade is the use of frameless glass as a protective barrier. In most cases, a glass balustrade would be used to protect against a change in floor level or drop.
Balustrades in private residential buildings (dwellings) require a balustrade when the difference in floor level is greater than 600mm.
In all building types other than a dwelling a balustrade is needed;
- on staircases with more than two risers
- where the floor level change is more than 380mm
The above is the required location for a balustrade but of course, you can integrate glass balustrades anywhere you wish in a design. They could also be useful to provide direction or guidance for people moving through a building or structure.
Popular applications for a structural glass balustrade would be a:
- mezzanine floor
- external balcony
- rooftop space
- terraced areas
You can see some more examples of glass balustrades broken down by use on our Pinterest Board: Glass Balustrades.
Height Requirements for Glass Balustrades
The dictated height of the glazed balustrade needed will be determined by the building’s use and is detailed in Building Regulations Part K (Diagram 3.1). These are given in the height of the balustrade above Finished Floor Level (FFL).
In a private residential building a balustrade is needed:
|At opening windows (expect roof windows in loft extensions, See Building Regulations Part B1)||800mm|
|Internal Balustrades (stairs, landings, ramps, edges of internal floors etc.)||900mm|
|External Balustrades (balconies, edges of roofs, external stairs etc)||1100mm|
Commercial, assembly and retail spaces have different height requirements for their balustrades. The purpose of these height requirements is to ensure that the balustrade offers adequate protection from level changes considering the likely traffic and use of the space.
Design Criteria for Glass Balustrades?
There are various sections of regulations and codes of practice that dictate the strength and design requirements for a frameless glass balustrade. The main requirements for a balustrade are to provide a protective barrier that is able to resist the likely forces applied to it with minimal deflection and without the possibility of it being penetrated.
When designing a structural glass balustrade we need to keep in mind the below:
Line Load = a horizontal force at the top of the balustrade. Intended to mimic the force of a person leaning on the top of the balustrade. It is measured in kN/m and loading requirements are given be EN 1991-1-1.
Uniformly Distributed Load (UDL) = a horizontal force applied uniformly to the midsection of the balustrade. This is applied across the entire face of the balustrade. It is given in kN/m2 and is governed by EN 1991-1-4.
Concentrated Load = a horizontal load designed to take into account any sudden or accidental pressures applied to the balustrade face. This is designed to give an accurate indication of the balustrade under sudden human impact. Loading requirements are given in EN 1991-1-1 and measured in kN.
Another requirement of glass balustrade design is that, should the area be accessible or frequented by children, a sphere of 100mm should not be able to pass through the gaps between each structural glass panel of the guarding.
Load Requirements of Glass Balustrades?
The required loading strength of a glass balustrade will depend on the use of the building and its intended traffic. The below table is collected from both Building Regulations Part B and BS.EN.1991-1, part 1 and part 4.
|Building Occupancy Class (according to Building Regulations Part B)||Line Load, applied 1100mm above FFL||UDL, applied to entire glass face below line load height||Concentrated Load, applied to any part of the glass panel below line load height|
|1||0.36 kN/m||0.5 kN/m2||0.25 kN|
|2||0.74 kN/m||1.0 kN/m2||0.5 kN|
|3||1.5 kN/m||1.5 kN/m2||1.5 kN|
|4||3.0 kN/m||1.5 kN/m2||1.5 kN|
These requirements are a safety regulation that means should someone fall against the balustrade or a large force applied to it, it will not break, and thus the public are not endangered.
Glass Specifications for Frameless Balustrades?
The standard structural glass specification from IQ for frameless glass balustrades adheres to all residential regulations and load requirements (Building Occupancy Classes 1 and 2). For public buildings and projects where a higher load requirement exists (Building Occupancy Classes 3 and 4) IQ can provide a structural glass specification and base fixing that can withstand a significant horizontal load of up to 3 kN/m with the use of high strength interlayers.
The strengthening interlayers used by the IQ design team are a specialist architectural glazing interlayer designed to increase the strength of a toughened laminated glass structure significantly. Their strength is such that even if the thick toughened glass panels within a structural glass balustrade were to be broken, the ionoplast interlayer between the panes maintains the structural integrity of the glass balustrade until a replacement can be installed.
As long as IQ is fully aware of the location and purpose of the balustrade we can engineer our glass specification and base fixings to ensure that a safe and efficient guarding is installed whilst achieving the design you want.
Deflection in Balustrades
It is understood that any balustrade structure will have a certain amount of deflection. The accepted deflection for all balustrading is calculated as L/65 (where L is the distance between the fixing and the top edge of the balustrade) or 25mm.
In order to minimise any head deflection (which some users find unsettling) IQ use an increased (or over specified) glass panel as standard. This reduces the amount of movement that is felt at the head of the balustrade and in our experience creates a more comfortable experience for the user. This is not normal practice for all architectural glaziers to make sure to check with your supplier whether they consider this in their glass balustrade design.
Do Glass Balustrades need a continuous handrail?
It is a common question from architects in the process of specifying a glass balustrade.
The simple answer is no, you do not always need a continuous handrail even if the glass is completely frameless.
Handrails are not necessary according to BS6180:2011 Section 8.5.2:
"a handrail should always be used unless a laminated toughened glass construction is used that would remain in situ if a panel fails."
So if you use a glass specification that will remain in situ should the glass panel fails then you do not need a continuous handrail.
At IQ we use a toughened laminated glass construction as standard for all frameless glass balustrades. In addition, you have the option of including an extra strengthening interlayer within the glass makeup. This ionoplast interlayer is strong in itself and will remain standing even if both glass panels fail. The use of a strengthening interlayer within the balustrade then negates the need for a continuous handrail to your frameless balustrade.
We include this strengthening interlayer as standard for all external glass balustrades. If you also want this balustrade to internal glazing please let us know.
Design Options for Glass Balustrades
A Frameless Glass Balustrade
In a frameless glass balustrade, the glass is designed to withstand all loadings applied including line loading, UDL and concentrated. Generally, the glass would be one fixed at the base either via the design of a clamping or bolting method or with the use of structural bonding of the glass to the building structure.
The glass specification will always need to be a pane of toughened and laminated glass with an adequate interlayer. The exact glass specification and interlayer will be determined by the type of project (and therefore the line load requirements) and the height of the balustrade.
A frameless glass balustrade is often the preferred design of using glass as a balustrade. These structural glass safety barriers are clear and frameless, posing minimum distribution to both sightlines and building aesthetics.
A Barrier with Glass Infill Panel
This type of glass balustrade is characterised by a main outer frame that surrounds both the edges of each glass pane and the top. The glass in these constructions does not provide any strength or support to the mainframe.
The main frame must be designed to withstand the required Line Load for the balustrade. The infill glazed panel must carry the UDL and concentrated loads required for the project.
In these constructions, the glass specification used is much lower due to the presence of a surrounding frame. The negative side effect is that the glass is not frameless and will not provide a seamless, unobstructed finish.
Strengthening Interlayers for Architectural Glazing
Structural Glass Balustrades from IQ Glass
Eurocode EN 1991-1-1 Part 1-1 General Actions - Densities, self-weight and imposed loads
Eurocode EN 1991-1-4 Part 1-4 General Actions – Wind actions
BS 6180: 2011 Barriers in and about buildings – Code of Practice
EN 12600 Glass in building – Pendulum test – Impact test method and classification for flat glass
BS 6262-4: Glazing for building – Part 4: Safety Related to Human Impact – Code of Safety
BS 6262-6: Glazing for building – Part 6: Code of practice for special applications
Building Regulations Approved Document K
Building Regulations Approved Document B1