How to Connect Balconies to Unitised Facade Builds

Following the recent publication of its white paper on unitised facade builds, Sapphire Balconies examines this growing trend and the technical considerations to bear in mind when designing this type of external building envelope with balconies.

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An increase in offsite manufacturing is revolutionising the way buildings are constructed and aluminium unitised facades, consisting of prefabricated and offsite-assembled units, play a key role in this revolution. Commenting on this trend, Nick Haughton, Balcony Expert at Sapphire, says: “Used for technically challenging projects, fast-track schemes, new builds and refurbishment, these units can be transported directly from the factory to site for fast installation on pre-prepared fixings.”

Aluminium is used to form the frame for each panel which can be one or two storeys high and typically the width of a single glazing bay. Opening vents, glazing and infill panels are built into the panel which is sealed offsite prior to delivery. They offer a range of design variations within the facade structure, including different panel sizes, colours and materials, and these can be incorporated into the balcony design to complement and enhance the building’s architectural aesthetic.

Key advantages

There are a number of advantages to a unitised system over traditional methods, and these can be further optimised when combined with an offsite-manufactured balcony system, such as Sapphire’s Glide-On balconies – an innovative solution which is delivered preassembled and factory-finished to a high-quality standard with minimal onsite finishing.

The three key benefits of this approach are:

1. Safety
Less work is completed on site compared to the ‘kit-of-parts’ approach. With balconies and panels manufactured offsite, the onsite safety risks are significantly reduced, especially the risks associated with working at height as unitised facades can be installed without scaffolding.

2. Quality
Assembling panels and balconies offsite in controlled environments allows for more rigorous quality checks and controls. A better quality of structural and aesthetic operations can also be completed in the factory setting.

3. Time spent onsite/preliminary costs
Since fabrication is done offsite, the time spent on the construction site is much reduced, resulting in further efficiency. And fewer trades are required onsite, reducing coordination of trades and programme delays.

There is also an additional benefit of using a lightweight balcony, like Sapphire’s Glide-On system, with aluminium unitised facades as it means fewer anchors to the building structure are required and; therefore, less waterproofing and fireproofing are needed at junctions.

Innovations

As unitised facades have become more common in today’s construction environment, new innovations have enabled simple and effective connection between balconies and this type of facade. These methods offer clear advantages over traditional techniques and, since the COVID-19 pandemic, have proven their worth, especially from an efficiency and sustainability perspective.

When fixing balconies to an aluminium unitised facade, Sapphire uses a bespoke anchor consisting of a cast-in floor bracket, an inner stub, an outer stub and connection fixings. Typically, connection begins by casting balcony brackets into the slab, stubs are then assembled to the facade unit and the units installed. The top and bottom plates are then installed, and the balcony guided into place on the facade. Balcony arms can then be secured to the stubs, and the arms bolted together.

According to Nick Haughton, there are many benefits to using this connection method. He comments: “Because the whole panel is manufactured offsite, thermal breaks are incorporated within the panel, so in most applications, there is no need for a thermal break at the slab edge.” Also, any external waterproofing can be completed prior to panel installation, saving programme time. Furthermore, no outside access from the balcony below is required to seal around the hole, and internal insulation can be fitted before installing the panel, which is better for both access and control.

Flexibility

A residential development at Tottenham Hale in London involving 164 V-shaped balconies using Sapphire’s Glide-On Cassettes and a unitised facade demonstrates the importance of flexibility when it comes to balcony connections. Nick Haughton explains: “When you are working with a completely offsite-manufactured panel, including the balcony bracket, that bracket has to have the flexibility to ensure precise connection between the unitised facade and balcony without putting too much pressure on the panel. At Tottenham Hale, the bracket was purpose-designed to take up to 20mm +/- in all directions.”

Key design considerations

A high-quality balcony system, backed by an experienced team, is essential to maximise the benefits of unitised facade builds. From Sapphire’s experience, working in partnership with the facade supplier at an early stage of the project can reduce confusion and interface difficulties further down the line. Key considerations when designing this type of build with balconies include:

•  Standardisation and repeatability are important in the design floor to floor. Bespoke detailing and many panel and balcony types increase cost as they reduce the savings that can be made offsite. Standardisation can impact supply-chain procurement and speed of construction.

•  Physical capacity of aluminium unitised panels can lead to complications, and so early engagement between the unitised facade and balcony providers is important to minimise difficult interfaces.

•  Deflection of floor slabs must be compatible with system requirements.

•  U-values. Insulation is usually possible only with the spandrel/non-glazed areas, so unless a secondary method is applied internally, the performance can be limited.

•  Programme. As balcony and panel install ascends the building at the same pace, the building’s interior can be finished as the exterior is completed on lower floors, enabling faster completion.

Challenging resistance

As architects and contractors continue to meet demand for shorter programming times, the use of aluminium unitised facades and offsite -manufactured balconies can reduce onsite work significantly. This enables faster installations and means homes can be opened for sale much sooner than traditional builds. However, despite these advantages, some building designers and contractors remain resistant to change, says Nick Haughton. To help overcome this challenge, Sapphire has researched and written an informative white paper on this subject. “The aim is to provide readers with a clear overview of aluminium unitised panels,” he explains, “as well as an understanding of why they have become popular, together with expert advice on how they can incorporate balconies.”

To obtain a free copy of Sapphire’s white paper, ‘How to Connect Balconies to Unitised Facade Builds’, please visit Sapphire White Papers.

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