Stub interfaces

Whilst Glide-On technology has made the installation of a balcony quicker than ever, making sure the anchors, arms and stub interfaces are correct can take careful consideration. The area between the doors and the concrete slab is very small with a lot of intricate design work and taking firestopping, water and weatherproofing into account is crucial. However, with minimal build-up, your anchor and firestop solution can still fit in the slab space available, and Sapphire has the solutions to make this stress-free.


Protecting the penetrations on a façade from potential fire risk is incredibly important and one way to do so is through firestops. A firestop is a form of passive fire protection that is used to seal penetrations, openings, and joints between different compartments, maintaining the continuity of a cavity barrier.

One type of firestop is Sapphire’s StubGuard, a mineral-fibre firestop, snugly covering the stub of a balcony’s arm anchor. The StubGuard has become a common choice amongst developers considering the need for extensive firestop testing, bolstering fire engineering judgements in this area. The StubGuard can be customised in depth increments of 50mm, making it a straightforward choice for custom balcony designs and is simple to install, providing a robust solution for minimising heat loss and increasing fire protection in this critical area.

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Weatherproofing balcony stubs

Weatherproofing a stub interface is crucial for not only colder or extremely wet climates but also as a preventative measure against flooding, freeze and thaw. For example, considering drainage at the design stage is vital. Should your balcony be fitted with positive, controlled edge draining or with rear-pipe draining? Each can be beneficial from either efficiency or cost perspectives, but consideration should be taken.

Solving condensation, freeze and thaw issues in balconies is a further problem-solving task in balcony design. If a balcony stub interface is not designed well where it penetrates a facade, thermal bridging can occur and compromise the thermal performance of the apartment itself. Solving this bridging issue could be as simple as making sure the interface between the building and balcony is minimised by using fewer anchors.

The best position for balcony anchors

A further important aspect of the installation to consider is the optimal positioning or spacing of a balcony’s arm anchors. Spacing the arms out can be greatly beneficial and by being flexible with the spacing of our anchors, we can ensure that the stub will work in optimal locations relevant to the structure.

Furthermore, by allowing our anchors to be positioned optimally, it decreases the need for excess penetration which could lead to thermal bridging or unwanted fire-stopping challenges.

Taking stub interfaces into account is a hugely important consideration in balcony connection and helps assist with keeping a Golden Thread of fire safety alive. Sapphire’s Passport app gives continuous balcony traceability and can assist with maintaining a Golden Thread of information around fire safety whilst being simple to install. Weatherproofing a stub interface is another key consideration as it can remove the threat of thermal bridging, condensation, freeze and thaw.

Each of these considerations should be taken at an early stage and once done, the design of your balconies could be improved considerably.

To put what you’ve learned to use, design a balcony of your own using COACH:

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Tailor the balcony to your exact project requirements. Options include drainage, balustrades to soffits and many more

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