Yesterday BSI, delivered a webinar on balcony standard BS8579:2020 – A Guide to the design of balconies and terraces, in conjunction with Resibuild as a media partner. Balconies and terraces are becoming increasingly popular as a way of offering high rise building occupants outside space; however, until now there’s been a lack of consensus in the UK on their optimum design.
With key speakers from around the industry, this webinar tackled the key elements of this new standard; and here we outline the principal takeaways from this valuable event...
Mark Taylor, Technical Director at Allies Morrison Architects delivered the opening presentation, seeking to clarify the vague guidance from various standards and regulations into a single document. He started by defining what a balcony is! Various parties have different names for what they refer to balconies. With this standard, the BSI has sought to draw a line in the sand as to what was and wasn't an open or an enclosed balcony - as this governs where the weather and thermal lines should be.
KEY TAKEAWAYS: GENERAL BS8579
The enclosure starts with safety differences but also need to add solar control etc because of their enclosed nature.
If adding the thermal line on the outside of the terrace then the enclosed balcony would become an internal room and no longer fall under the remit of BS8579
The standard relies heavily on BS991 and BS 9999
New terminology definitions
Controlled drainage: Drainage from a balcony that prevents water ingress to the interior and staining of the external of a building and nuisance to persons under or around the balcony or damage of the landscaping below.
Edge Drainage: Drainage of a water-collecting surface via the edge of a balcony.
Juliet Guarding's: The new name for Juliet balconies, as they don't fall under the remit of balconies - because they can't be stood on, thus the new reclassification
Other words which have been added include 'principle water collecting surface', 'Ingress level', and 'weather screen'
Mark is responsible for technical design and quality at Allies and Morrison. He is Chair of BSI panel for BS8579 and a member of BIBA Regulations and Standards Committee. He sits as a board member of the Society of Façade Engineering.
STRUCTURAL CONSIDERATIONS
Founder of Sapphire Balconies, Andrew Parsons examined the structural considerations of balconies and how they are connected to buildings referencing DFMA (Design for Manufacture and Assembly) and offsite quality controls.
KEY TAKEAWAYS: STRUCTURAL CONSIDERATIONS:
Balcony sizes are often defined by the geographic documents like the London Housing Design Guide, meaning the balconies are generally between 3 and 9sqm in the city
Corner balconies are particularly susceptible to wind loadings.
Inset balconies are now being changed from positive drainage
Fin walls becoming more common because of the ban on laminate glass
Balconies are more commonly being mounted to walls with tie rods etc often because of MMC wall systems etc.
In the past, many balconies were unappealingly ‘bouncy’ The new standard considered the L/360 (Twice the Eurocode)
There is a 5Hz natural frequency minimum vertical frequency.
The 5mm max deflection has been added which is more important and easier to manage as you can apply a 2Kn load
CLT (Cross laminated timber) not so common in the UK but more common in countries like Canada.
BS8579 has taken loadings from BS6180, Eurocodes and BS 16612 and 1090
BS8579 requires a 2kN/m load to be designed into balconies.
Slab should be considered in the deflection of a balcony in addition to the balcony anchor and the balcony Cassette.
Safety:
Safe install of balconies: working at heights should be avoided and so should working underneath of balconies
Safe balcony maintenance is also a requirement of those designing balconies
Consideration of end of life should also be a consideration both for safety and environmental
Soffits are encouraged for hot drinks etc and also the prevention of fire spread in various ways.
Max loads: BS8579 recommends a sign (like a lift) to demonstrate what is safe use for a resident.
Kicker plates are recommended and part of the BS8579 guidance covers how to work out heights of the balcony balustrading.
Balcony testing: this should cover both wind testing and also Structural tests
The service life of a balcony is defined in more detail above 2.4m and is an obligation for those designing balconies.
Wind uplift should be considered when selecting decking and other surfaces including paving.
Slip resistance is a new area covered in BS8579 and the standard also stipulates the rubber to be used.
Slot and hole diameters are defined in BS8579
Note: Sapphire have created a BS8579 explainer whitepaper which can be found here.
INCLUSION DESIGN
Jane Simpson an Inclusion and Access Specialist discussed the accessibility of balconies. Jane noted that although most accessibility regulations are similar they do differ in different areas of the UK and that meeting AD M requirements does not automatically mean you have met the requirements of the Disability Act. Accessibility of balconies
KEY TAKEAWAYS: ACCESS
Certain grants also define what inclusivity may be needed for example ‘Sports England’ requires wider doorways
BS8579 does require an accessible threshold and there are various companies developing sloped and watertight/airtight thresholds
BS8579 requires a minimum of a 1500x1500 turning circle. Although it’s worth noting most electric wheelchairs do require a wider turning circle.
AD M requires clear edges and leading side considerations.
BS8579 asks for 300mm either side of sliding doors for accessibility.
Surfaces should not allow slots of 8mm holes and 90 degrees to be
Balcony views shouldn't be obscured for wheelchair users.
FIRE
Fire standards for balconies are included in BS9991 and Part B of the building regulations; however several high profile fires, including the Bolton Cube and Barking Riverside happened during the drafting of BS8579 and were therefore considered. Levitt Bernstein’s Technical Design Director, Tony Hall delivered a presentation clarifying how the requirements apply to balconies.
The first question is why can't 7(2) be followed for fire guidance on terraces and balconies? Why did BS8579 need to comment? This is not clear in regulation 7 as it doesn't clearly define between balconies and terraces as it just refers to attachments being mandatory. Are terraces attachments? Not really!
KEY TAKEAWAYS : FIRE
Four key aspects of fire in BS8579
Not be composed of materials or designed such that they provide a medium for undue fire spread over the external envelope of the building.
Not propagate fire downwards (e.g. Not produce falling brands or flaming/molten droplets or debris capable of initiating fire below)
Be designed to minimise the risk of becoming detached from the face of the building and present a hazard to persons below (e.g. Firefighters and public)
Be designed to minimise the risk of prejudicing the stability of the building when undergoing large deformations resulting from fire exposure.
Fire performance requires items to be of a minimum A2-s1, on buildings above 11m above the lowest ground level.
One of the key requirements is stopping drips from dropping by adding non-combustible soffits.
Balcony sizes are often defined by the geographic documents like the London Housing Design Guide, meaning the balconies are generally between 3 and 9sqm in the city
Laminate glass:
Often used because of daylight and views etc.
Laminate glass is included as an exemption by 96/603/EC however it includes a 1% requirement which isn't achieved by normal laminates
BS8579 does mention that where not possible to achieve all aspects of life safety and performance using materials of at least class A1
It does, however, in BS8579 reference the national standards
DRAINAGE
BS8579 requires that balconies and terraces have some form of controlled drainage. John Purser a Drainage Outlet Consultant looked at two options:
o Edge drainage
o Pipe drainage
KEY TAKEAWAYS: DRAINAGE
Draining away from doors is a very important part to consider
Small balconies are not usually a problem
Most balconies benefit from the shelter of balconies above and from their balustrades (dependent on the type of guarding)
The catchment area is defined for drainage calculations
Drainage should consider cumulative flow if outlets drain on to balconies below.
Concrete and pipe drained balconies should always have a warning pipe so if outlets get blocked it is visible
WIND EFFECTS
Daniel Hackett of RWDI consultant engineers identified the four key areas where wind affects balconies
a. Height above ground
b. Exposure to the prevailing wind direction
c. Especially in the case of exposed corners or acute angels
d. The effect of channelling or funnelling because of nearby buildings which can create various changes and accelerations.
and discussed the design considerations:
The building structure and cladding elements are covered to a point in Eurocodes but BS8579 adds this from a point of balconies
There is a net positive and net negative pressure on balustrades
Up to buildings of 50m the guidance of BS8579 defines wind guidance to be split by balconies near the roof or corners (requiring 1.8 Cp, net) and those midface balconies (requiring 1.5 Cp,net).
Microclimate requirements. Higher wind speed limits the types of activities and comfort of people. Particularly important is the proximity to corners of a building. BS8579 covers some potentially beneficial designs:
a. Increase height of guarding to 1.5m or more
b. Adding side screens (fins)
c. Or dividers on larger balconies.
The knock-on effects of adding dividers etc or increasing height is the need to consider wind load increases, this may be required by local policy too.
Wind microclimate may also cause objects/furniture to move. Consider including tie-down points for furnishings etc. on balconies.
THERMAL, ACOUSTIC AND SECURITY CONSIDERATIONS
Balcony thermal, acoustic, and security considerations of balconies were addressed by Mark Taylor in the final summary presentation of the webinar.
KEY TAKEAWAYS: THERMAL, ACOUSTIC AND SECURITY CONSIDERATIONS
The inclusion of balconies or terraces does mean penetrations.
Consideration is required to assess 1D heat flow (terraces, adjacent wall and soffits) 2D (Junctions and interfaces) and 3D heat flow (Brackets) there is guidance as to these in the standard
Acoustics. Balconies can mitigate or accentuate by reflecting sound or by reducing sound pressure by guarding being solid.
The standard does offer guidance if there are particular sound considerations.
BSI Q&A answered by the panel
Q: How should privacy and overlooking neighbours be addressed
A: Consider privacy expectation. Balconies tend to be more private than terraces but like guarding there isn't much consideration in BS8579 other than dividers and consider inclusivity so that permanently seated users can also see out from a balcony
Q: What is the standard guidance on structural requirements
A; there is only a commentary that the effects should consider deformation to minimise the risk of a balcony becoming detached 9991 and 9999 are referred to for this aspect of guidance
Q: What pedestal and decking fire requirements are there?
A: flooring should be Class A2 - some components can be excluded, if recessed with a firewall beside the balcony, this needs considering but otherwise no other wall
Q: What is the guidance of using toughened vs laminate glass
A: the right place for this is BS6180 rather than BS8579. the BS6180 is under review and so one vs the other isn't covered in this. In terms of post, breakage containment is noted to consider post breakage but doesn't give answers as to how.
Q: Can laminate glass be used
A: With so much uncertainty it was felt some guidance was needed. The standard is a guide to design not a code of practice. There are various benefits to it and the standard feels there is a role for glass and that laminate glass is a safety function. Designers need to consider the post breakage and laminate benefits this. Laminate glass is being heavily researched at the moment and there are further standards to come out, particularly for how to test balconies for fire spread. The standard tries to remain neutral but recommends that it is based on a risk assessment.
Before the standard was launched we had Andrew speak at the Shard. to access this recording click here
or to access a 3-way interview of Allies Morrison and Sapphire about the standard you can view the recording here
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