Water and external systems · Decks & Paving
Bracket Supported Balcony System
This entry sets out how an externally supported balcony converts a single structural crossing into many separate fixings, and what that exchange costs in sealing, drainage, movement and corrosion terms.
Educational reference entry. How this system behaves depends on climate, jurisdiction, loading, substrate, the adjacent systems it meets, how the building is used, the manufacturer's instructions and qualified professional design.
Overview
What bracket supported balcony is
In a bracket-supported balcony the platform does not come out of the building. It is hung on the wall, propped against it, or stood beside it on its own columns. The structural work happens outside the line of the wall, which removes the continuous element passing through the insulated line and replaces it with a set of discrete connections.
That substitution is the whole design. Each connection has to find something structural behind the finish to fix into, has to pass through whatever controls water and air at that point, and has to stay protected against corrosion in a position nobody will look at again. One difficult junction becomes many smaller ones, repeated along an elevation. The arrangement also permits an open platform, which a solid projection does not, leaving the frame and the fixings visible from below.
The nearest sibling is the cantilevered balcony connection system, and the two are told apart by looking underneath. If brackets, hangers or posts are holding the platform up, the load has been taken outside the envelope and this entry applies. If the platform simply continues from the floor with nothing beneath it, the load crosses the envelope as one member and the cantilever entry applies instead.
Terminology
Common names and aliases
These names describe the same assembly. The encyclopedia keeps one entry per system so that a trade term or a regional name never becomes a second, thinner page.
- bolt-on balcony
- hung balcony
- externally supported balcony
- retrofit balcony system
- post and bracket balcony
Purpose
What this system is intended to do
The job the assembly exists to perform, conceptually. An intention is not a guarantee that any particular build achieves it.
- Support an external platform without passing a continuous structural element through the wall.
- Return balcony loads into identified structure through a defined and designed set of fixings.
- Allow a drained, open platform whose underside can be seen and reached from outside.
- Permit a balcony where a projection of the floor structure cannot be formed at all.
- Accommodate movement between the balcony and the building it is attached to.
Composition
The roles this system is made of
What each part does in the assembly and what it depends on — never a product, a thickness, a fixing or a determination that anything is adequate for the role.
Order is not meaningful in this system. These roles interact as parts of one whole rather than stacking up in a sequence, so the list below is not a build-up and nothing should be read into the order it appears in.
- Primary supportBrackets, hangers or columns
The external support arrangement carrying the platform. Whether load goes back into the wall, up to structure above or down to the ground changes what has to be verified behind the finish, and it changes what happens where the support meets the ground.
- AttachmentFixings into the supporting structure
The connections transferring load into the frame, floor edge or wall behind. What they are fixed into matters more than what they are made of, because a fixing landing in cladding, insulation or an outer leaf is not a support at all.
- Jointing and sealingClosure at each penetration
Every fixing passes through whatever controls water and air on that wall. Each pass has to be closed, and each is a place where water can be led inward along the fixing itself, which is why penetrations are counted and located rather than left to the installer.
- Drainage planeDrained platform surface
An open or falling platform surface keeps standing water off the frame and away from the wall behind. Where water leaves the platform, and what it lands on below, is part of the design rather than a consequence discovered afterwards.
- SubstratePlatform frame and surface support
The frame spanning between the supports that carries the walking surface. Its depth, its material and its connection to the brackets determine both what the platform can carry and how it is assembled above the supports.
- ProtectionCorrosion protection and inspection access
Coatings, metal choice and detailing that keep the support arrangement serviceable in a wet and exposed position. Because the supports are outside, they can be seen; whether they are actually looked at depends on access being arranged in advance.
- Edge and terminationJunction with the wall build-up behind
The gap or contact between platform and wall, and the way cladding, render or brickwork is closed around the supports. It decides whether water running down the wall is shed clear of the balcony or delivered onto its frame.
Interaction
How the parts work together
The reason this is a system rather than a list of parts: what depends on what, and what stops working when one part is changed.
The number and position of penetrations is the design variable everything else follows from. Each bracket has to land on structure, and structure sits where the frame is, not where the elevation would prefer the balcony to be. Moving a bracket to suit the elevation takes the fixing off structure; keeping it on structure moves the platform. Settling that tension before the wall is finished is the difference between sealed penetrations and improvised ones.
Sealing and drainage at each fixing are the same problem, not separate ones. A closed penetration relies on water not standing against it, so the platform has to shed water away from the wall and the wall has to shed water clear of the fixings. Where the frame sits close against the elevation, water running down the wall reaches the fixings first and stays there, loading the closure continuously instead of occasionally.
The balcony and the building move independently. The platform is exposed on every face while the building is not, so the connection has to accept relative movement without working the closures or the fixings loose. Holding the two rigidly together at several points along a run removes that freedom, and the movement then appears wherever the assembly is weakest, usually at a closure and sometimes at a fixing.
Corrosion is the slow version of the same interaction. Fixings sit inside the wall build-up where they cannot be seen, at a point wetted by whatever gets past the closure, and often in contact with a different metal in the bracket. What protects them is decided at design stage, and the only later evidence that the decision was wrong is movement or staining appearing at the platform.
Materials
Material families commonly met in each role
Commonly encountered, not recommended. Whether a material suits a given project depends on the whole assembly, the exposure, the manufacturer's documentation and qualified professional review.
Primary support
Balcony support arrangements are commonly encountered in these metal families. How each behaves in an exposed external position, and in contact with the other metals in the assembly, is a design matter informed by the manufacturer's information.
Attachment
Fixings into the supporting structure commonly come from these families. What a fixing can carry depends on the structure it lands in as much as on the fixing itself, which is why the anchor is designed rather than chosen from a range.
Protection
Protective treatments for external steelwork are commonly encountered in these categories. Whether a treatment remains effective at cut edges, drilled holes and contact faces is set out by the coating manufacturer and confirmed by the designer.
Jointing and sealing
Closing a fixing penetration commonly involves materials from these families, usually acting together rather than singly. Adhesion to the specific substrates, and durability in a continuously wetted position, are manufacturer statements rather than properties of a category.
Finish surface
Platform surfaces on externally supported balconies are commonly encountered in these families. Open surfaces change what falls through to whatever is below and closed surfaces change what has to be drained, so the decision is not only about appearance.
Junctions
Where this system meets others
Interfaces are where most assemblies actually fail, so they are set out explicitly rather than left inside the prose. What resolves a junction is a detail designed for the specific building — not a rule of thumb.
Each fixing as an envelope penetration
Every bracket fixing is a penetration of the layers controlling water and air on that wall, and the general treatment of such penetrations belongs with the envelope penetration sealing system. What is specific here is that they are repeated, structurally loaded and permanently wetted.
Read about Penetration Sealing →Supports through a rainscreen
Where the wall is a ventilated rainscreen, the bracket has to reach past the cladding and the cavity to structure behind, and the cladding has to be closed around it without stopping the cavity working. Support and facade are set out together or not at all.
Read about Rainscreen Facade →Fixing into a cavity wall
An outer masonry leaf is not the structure. Fixing a balcony to it, or through it without knowing what lies behind, is a common failure of assumption on existing buildings, and what can actually be fixed into needs establishing before anything is designed.
Read about Twin-Leaf Cavity Wall →Guarding on an externally supported platform
Guarding is often part of the same fabricated assembly as the platform frame, which removes fixings through the walking surface but concentrates load into the brackets. The two then form a single structural item and cannot be altered independently.
Read about Guarding System →Where columns reach the ground
A balcony carried on posts delivers its load to the ground, and the bearing that receives it is a ground question rather than a balcony one. Conditions at the base of an existing wall are frequently different from those anyone assumed.
Read about Pad Foundation →The wall's drainage plane behind
Water running down the wall reaches the balcony fixings on its way. Whether the wall's drainage plane sheds that water clear of the supports, or onto them, is settled by the wall detailing rather than by the balcony.
Read about Water Control Layer →
Considerations
Topics worth discussing
Which topics genuinely apply to this system and what to raise about them. Measured values, classes and ratings come from a qualified professional's design for the specific building, not from a reference page.
- Interfaces
- Nearly all the design content sits at the fixings and at the wall behind them. What each fixing lands in has to be established rather than assumed, and on an existing building that usually means opening up and inspecting first.
- Moisture
- The fixings are wetted by water running down the wall as well as by water leaving the platform. Keeping both away from the penetrations does more than any single product applied at the penetration itself.
- Durability
- Metal in an exposed position, in contact with other metals and sometimes with treated timber, is where the long-term condition of this system is decided. Breaks in a protective coating at cut edges and drilled holes are the usual starting point.
- Movement
- The balcony and the building expand, contract and settle differently. Whether the connection is meant to hold them rigidly together or to allow relative movement is a decision that has to be made explicitly rather than left to the detail.
- Maintenance and access
- Being outside the wall, the supports can be inspected, but only if someone can reach them. Access at height, and who is responsible for arranging it, belongs in the handover rather than being discovered long afterwards.
- Buildability
- Adding a balcony to a finished or occupied building means working through completed layers. The sequence, the temporary opening up and the making good all act on the layers that control water and air across that elevation.
Design
Questions the design has to answer
The decisions this assembly turns on. They are questions rather than answers, because the answer depends on the building.
- What structure will the brackets actually land in, and how has that been confirmed?
- How many penetrations of the wall does the support arrangement create, and where are they?
- Does the wall shed water clear of the fixings, or straight down onto them?
- Is the platform open or closed, and where does water leaving it end up?
- Is the guarding part of the same fabricated assembly as the platform frame?
- How will the supports be reached for inspection once the building is occupied?
- Is relative movement between balcony and building being allowed for, and at which connection?
Boundaries
Commonly misunderstood points
Distinctions that are easy to blur, and the places where a familiar term means something narrower than it sounds.
- An externally supported balcony is often described as avoiding a thermal bridge entirely, when the fixings still cross the insulated line.
- The outer leaf of a wall is frequently mistaken for structure, particularly on existing buildings where nothing has been opened up.
- Closing a penetration is treated as the answer, when keeping water away from it is what allows that closure to last.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- What have you established about the structure behind the wall at each proposed fixing position?
- How is each penetration through the water and air control layers being closed?
- What corrosion protection is proposed, and what happens at cut and drilled surfaces?
- Is the connection intended to be rigid, or to accommodate movement between balcony and building?
- Where does water leaving the platform go, and what is directly below it?
- How will the supports and their fixings be inspected once the balcony is in use?
What this page does not do
- Fixing a balcony into existing construction is a structural matter requiring investigation and design by a qualified engineer.
- No statement here indicates that any fixing arrangement is adequate for a given wall, structure or loading.
- Balconies added to existing buildings can raise questions with the relevant authority that lie outside the scope of this entry.
- Working at height for installation and later inspection carries safety requirements determined by others.
Related systems
How this system relates to others
Every link states what the relationship actually is, rather than leaving a bare list of related pages to be read as a suggestion.
Alternatives
Different systems answering the same need. Listing them together is not a comparison and does not suggest one is better — which, if either, suits a project is a design decision.
Meets these systems
Systems this one physically meets. The junction is usually where the design problem lives, so these are worth reading together.
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this assembly involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this system comes up.
Inspiration
Related Ideas Library pages
Design directions where this system commonly appears.
Decks, Paving and Hard Landscape Systems
External surfaces people stand on, plus the substructure, edge, support and guarding that make one usable, each decided by the layer beneath and the route its water takes.
Browse all decks & paving entries →