BS8579 EXPLAINED - Notes from the BSI panel webinar

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.


  • 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.


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.


  • 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.


  1. Safe install of balconies: working at heights should be avoided and so should working underneath of balconies

  2. Safe balcony maintenance is also a requirement of those designing balconies

  3. 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.


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


  • Certain grants also define what inclusivity may be needed for example ‘Sports England’ requires wider doorways

  • BS8579 does require an accessib