If you’re asking the question:
‘Do we stick with the traditional method of constructing balconies on site?’
‘Do we move to Bolt-on-Balconies?’
(lets call them BoBs for short)
The following may leave you with another question:
‘Why wouldn’t we?’
With the significant rise in material prices, labour, energy and transport costs, as well as all the guidance within…
- Environmental, Social, and Governance (ESG)
- Modern Methods of Construction (MMC)
- Design for Manufacture & Assembly (DfMA)
- Platform Design Programme
…there is a noticeable shift to off-site design, manufacture and site installation of BoBs within the residential construction market.
Concrete balconies, constructed ‘traditionally’, involve constructing a concrete slab that can be cantilevered and subsequently waterproofed, then fitted with fascia, balustrade and decking.
BoBs are largely manufactured off-site, delivered to site complete, craned into position and ‘bolted’ to the frame via stub brackets, which are in turn attached to connections within the concrete or directly to the steel frame.
UK Government’s 2025 Construction strategy includes the Design for Manufacture and Assembly (DfMA) approach, one that aims to build 50% faster, at 33% lower cost and decreasing carbon emissions by 50%. The illustration to the right highlights the key areas of focus within the approach
Manufactures / Assembly
Installation / Construction
In line with DfMA, BOBs are designed to be manufactured off-site and delivered (largely speaking fully complete) to site. Therefore, the design element focusses on the challenge to provide a BOB that is cheaper, quicker to manufacture and install, whilst in accordance with BS and insurers technical guidance.
Consideration within effective design of the Levolux Sereniti BOB has focussed upon:
Minimising the quantity of material, number of parts and weight
Maximising the use of cost effective and sustainable materials
Decreasing the time taken to assemble the BOB
The solution to these design challenges has been provided through a balanced and considered use of steel, aluminium (both sheet and extrusion) as well as an innovative approach to providing a design considering all areas of the off-site manufacture process.
MANUFACTURE / ASSEMBLY
Levolux BoBs are fully assembled off-site. Manufacturing the balconies in a factory-controlled environment provides numerous benefits that are also included within the DfMA approach:
1. Health & Safety – Factory controlled environments consider the H&S protocols of the manufacture process as well as the well-being of personnel providing assembly.
2. Labour & Skills – the component assembly process is simplified by affective design enabling the use of trained labour managed within the factory environment.
3. Quality Control – more effectively managed in factory-controlled environments as opposed to site with multi trades.
4. Time/Program – Factory conditions provide greater efficiency through controlled environments and the lack of uncontrollable natural factors such as weather.
Concrete balconies require a thermal break across the full extent of the balcony edge connecting to the concrete frame (figure A). BoBs are connected to the fabric of the building via a stub bracket which in turn is bolted to steel connections within the slab/building frame (figure B). This type of connection into the building frame is limited to local steel connectors only and thermal breaks are provided for each, therefore the extent is far less and the risk of cold bridging is greatly reduced.
Most types of concrete balconies require to be ‘tanked’ or waterproofed as well as drained. This requires additional site trades and subcontract arrangements as well as time and cost against requirements for bolt-on-balconies.
It also invariably increases the thickness of the concrete slab/floor finish vs the bolt-on alternative requirements.
Concrete balconies require scaffold for the complete duration of the pour, waterproofing and construction. However, the bolt-on equivalent requires no scaffold for the balcony installation and thus it can be struck far earlier in the program compared with concrete, thus reducing cost.
Installation of the balconies can start prior to the scaffold being struck in full by incorporating the use of cantilever lifting beams. This ‘top down’ approach can provide reduction in program and subsequently cost. Consideration must be given in terms of H&S and working beneath a suspended load.
When all the factors mentioned are considered and the comparisons are made, one vital ‘other’ benefit that many clients have confirmed across numerous projects is cost, judging by the growth in the market over the last few years, the Bolt-on Balcony approach is more commercially effective.
Hence the point made right at the start of this comparison, ‘Why wouldn’t you use the Bolt-on Balcony approach as opposed to any other?’ It simply offers benefits across the majority of key considerations.