Water and external systems · Decks & Paving
Balustrade and Guarding System
This entry reads guarding as an unbroken chain from infill to anchorage to the structure behind, and explains why its base fixings are structural connections and penetrations of a water-shedding layer at the same time.
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 guarding system is
Guarding is the assembly standing at an edge where there is a drop. Its parts are easy to name, being an infill, something holding that infill up, usually something to hold at the top, and fixings at the bottom. It is also easy to misjudge, because the part deciding whether it works is the part nobody looks at.
Read it as a chain. A force applied at the top of the infill travels into the frame, down the posts, into the base anchorage and out into whatever the anchorage is fixed to. The chain is only as good as its weakest link, and the weakest link is normally the last one, which is the substrate behind the fixing. Changing an infill panel, moving a post or fixing into a different material alters the chain, so none of those is a cosmetic decision.
The nearest sibling here is the bracket-supported balcony system, and the distinction is what the entity actually is. A balcony is a platform; guarding is the edge assembly at a change of level, and the same assembly appears at decks, balconies, roof terraces, stairs and mezzanine edges. It is published once and referenced from each of them rather than described separately in every place it occurs.
On external decks, balconies and terraces the chain has to pass through a layer that is shedding water, so every base fixing is doing a structural job and a weathering job at once, and these pull against each other. A Juliet balcony, where guarding stands at an opening with no platform to walk onto, is a narrow case of the same assembly.
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.
- balustrade
- edge protection guarding
- handrail and infill system
- barrier and infill assembly
- guard rail system
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.
- Form a physical barrier at an edge where there is a change of level.
- Transfer forces applied at that barrier back into a structure able to receive them.
- Provide something to hold where the edge runs alongside a route people walk.
- Close the gap between barrier and surface in a manner consistent with how the space is used.
- Do all of that without becoming the route by which water enters the construction below.
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.
- ProtectionInfill or barrier element
The panel, bars, mesh or solid element filling between the supports. It is what people lean on and what objects strike, and how it behaves under those actions is a property of the element, its fixings and its supports acting together.
- Primary supportPosts, frame or structural uprights
The members holding the infill and gathering load from it. Their positions are set by the structure below rather than by appearance, and moving them once the supporting construction is complete is rarely the small change it looks like.
- Finish surfaceTop rail and handrail
The upper member, which may be a structural part of the assembly, a graspable handrail, or both at once. Where it is structural, interrupting or removing it changes how the whole assembly behaves and not simply how it looks.
- AttachmentBase anchorage
The fixings and baseplates connecting the assembly to the construction below. This is where the chain either completes or stops, and it is normally covered by a plate, a finish or a surface build-up as soon as it has been made.
- SubstrateThe construction behind the anchorage
The slab, frame, joist, trimmer or masonry actually receiving the load. Guarding fixed to a finish, a coping, an outer leaf or a surface build-up has been fixed to something that was never designed to take it.
- Jointing and sealingClosure and water shedding at the fixings
Where the base anchorage passes through a layer shedding water, the closure at that point has to survive a joint being loaded and moved. Closing a moving structural fixing is a different problem from closing a static penetration.
- Edge and terminationEnds, returns and junctions with adjoining guarding
Where a run stops, turns, meets a wall or meets a different guarding type, the chain has to complete at that point too. Ends and returns are where posts are most heavily loaded and where the anchorage detail most often changes.
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 assembly behaves as a load path, and the load path is continuous only if every connection in it is. Infill fixed into a frame, fixed to posts, fixed to a baseplate bolted into structure, behaves in a way that can be understood. The same assembly with the baseplate landing on a screed, a topping or a coping stone does not, however sound the visible parts appear.
Post position and structure position have to agree, and the agreement has to be reached before the surface below is finished. Once a deck, terrace or slab is complete, the available post positions are limited to whatever lies underneath, and the usual response of shifting a post or adding a plate changes both the loads on the remaining posts and the relationship of the fixings to the layers below.
On any external edge the anchorage is also a hole in a layer that is shedding water, and the two requirements work against each other. A rigid fixing concentrates movement at the closure around it, while a fixing allowed to move slightly protects that closure but softens the chain. Neither is resolved by sealant alone, which is why guarding over a water-resisting layer is designed in from the start rather than added later.
Substituting one infill for another is a change to the whole assembly. A different panel changes the weight the posts carry, the way force is delivered into them, and the gaps left between elements, and those gaps interact with how the space is used. That last point is a safety question belonging with the people responsible for it rather than a matter of material preference.
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
Posts and frames are commonly encountered in these families. Section, connection detail and corrosion behaviour differ within every one of them, and what a given assembly can carry is established by testing and design rather than by the material name.
Protection
Infill elements are commonly encountered in these families. How an infill behaves when struck or leaned on, and what happens if it fails, are properties of the tested assembly and belong with the designer and the manufacturer's documentation.
Attachment
Base anchorages are commonly encountered in these metal families. The capacity of an anchorage depends on what it is fixed into as much as on the fixing itself, so anchor design sits with the engineer and with the anchor manufacturer's data.
Finish surface
Handrails, top rails and their applied finishes are commonly encountered in these families. Grip when wet, surface warmth in sun and the way a coating wears at a hand-contact point are all things the designer weighs using product information.
Jointing and sealing
Closing around base fixings commonly involves these families. A closed structural fixing is a joint that moves under load, and whether a product tolerates that in a given position is stated in its documentation rather than assumed from the category.
Components
Building components that fill these roles
The discrete elements commonly occupying each role in this assembly. This is a different statement from the material families above: those name what a role is commonly made of, these name the positioned elements that occupy it. Commonly encountered, never recommended.
Edge and termination
Primary support
Protection
- Infill →Closes the zone between the posts, the rail and the base, and carries what is applied to it into the posts.
- Balustrade Post →The vertical member carrying the guarding and delivering its loads to the structure.
- Handrail →The graspable member the system's posts carry, and commonly the element horizontal load is applied to.
Boundary
Where this system ends and meets another
The edge of this system. Everything above is inside it; each junction below is a condition at its boundary, where an adjacent system or an adjacent building condition takes over. Junctions are where most assemblies actually fail, so they are set out explicitly rather than left inside the prose. What resolves one is a detail designed for the specific building — not a rule of thumb.
Guarding on a timber deck
On a framed deck the anchorage lands in joists, trimmers or posts forming part of the deck structure. Those members have to be present in the right places, which makes guarding a framing decision taken with the deck rather than after it is built.
Read about Timber Deck Framing →Guarding on a projecting balcony
On a cantilever the anchorage returns load into the projecting element and its fixings cross the balcony's water-shedding layer. Fixing down onto the top surface delivers the load to the projection in bending, while fixing to the outer edge delivers it to the slab edge, and which member ends up receiving it settles whether the anchorage can be reached again once the surface build-up is complete.
Read about Cantilevered Balcony →Guarding at a parapet
Where a parapet already exists, the guard may sit on it, behind it or through it. Anchoring into a coping or into the top of a parapet puts the fixing into the most weather-exposed and often the least structural part of that construction.
Read about Parapet System →Guarding on a roof terrace
On a roof terrace the guard has to be supported by structure lying below insulation and a water-resisting layer. Reaching it means either penetrating those layers or using a support arrangement designed to avoid doing so, and that is settled early.
Read about Trafficked Roof Deck →Guarding through loose-laid paving
Loose units cannot support a guard. Posts pass through the paving layer to structure below, so unit cutting, pedestal positions and the closure at each pass all have to be coordinated with how the paving is set out.
Read about Pedestal Terrace Paving →Guarding at an internal edge
Indoors the water-shedding requirement disappears and the chain becomes purely structural, but the substrate question does not change. The anchorage still has to reach the structure rather than the floor finish laid over it.
Read about Mezzanine Structure →Base fixings as envelope penetrations
External base fixings are penetrations as well as connections, so penetration closure practice applies at every post.
Read about Penetration Sealing →Gravity Retaining Wall
Where there is a fall from the top of the wall, guarding may be required and it applies horizontal force at the very place a gravity wall is least able to accept it. Fixing guarding into the top of a mass wall after it is built is a structural alteration.
Read about Gravity Retaining Wall →Cantilever Retaining Wall
Guarding applies horizontal force at the top of the stem, the point furthest from the base and therefore the most demanding place to apply it. Retrofitting posts into the top of an existing wall introduces both that force and penetrations into the cover protecting its reinforcement.
Read about Cantilever Retaining Wall →Reinforced Soil Wall
Posts set into the top of a layered structure both cut reinforcement locally and apply horizontal force to a face designed to carry very little. Guarding at such a wall is usually supported independently behind it, which is a decision taken during design.
Read about Reinforced Soil Wall →Bracket Supported Balcony
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 Bracket Supported Balcony →Trafficked Deck Membrane
Fixings through a bonded seamless surface breach the layer resisting water at a point that is also structurally loaded. Where a guard is being fitted, fixing positions belong in the surfacing design and not in a later trade's method.
Read about Trafficked Deck Membrane →Rigid Paving
Guarding at a level change is fixed back into structure, and its anchorages pass through both the surface and the bed. Each penetration is a discontinuity in the bond and a route for water into a construction that cannot drain, so the two systems are detailed together.
Read about Rigid Paving →Water-Retaining Structure
Where the surround stands above the water or above lower ground, guarding is anchored into the structure or the deck beside it. An anchorage near the top of a containing wall is a penetration in a sensitive zone, and where guarding is required at all is a jurisdictional question.
Read about Water-Retaining Structure →Fence and Gate
Marking a boundary and guarding a drop are different duties with different requirements, and a line that does both is being asked to satisfy the guarding requirement. Which requirement governs, and what it asks for, varies by jurisdiction and is not settled by the fence looking substantial.
Read about Fence and Gate →Stair Structure
Guarding at the open edge of a flight or a landing is a separate assembly, and everything about the infill, the posts, the rail and their anchorage belongs to it. What this system provides is the construction behind that anchorage, which is why where guarding will stand has to be known while the flight and landings are being designed rather than after they are built.
Read about Stair Structure →
Internal junctions
Junction conditions inside this system
Junctions between the components within this assembly, rather than at its boundary. An entry exists only where the condition between two elements governs how the assembly behaves — two parts touching is not on its own a junction worth naming.
Balustrade Post to Stair Landing
Where a guarding post is fixed into the edge of a landing, delivering everything the guarding resists into a small platform.
Structural transfer · Movement · Buildability
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.
- Durability
- Guarding is handled, leaned on, weathered and, outdoors, cleaned with whatever is nearest. Wear concentrates at the handrail and at the base of the posts, and at the base it matters structurally rather than only visually.
- Interfaces
- The assembly meets a surface, a structure and often a water-shedding layer at the same point. Coordination between the trades responsible for each of those is where most of the difficulty in this system lies.
- Moisture
- At an external base fixing, water reaches a structural connection and a penetration in the same place. Standing water at the foot of a post is a condition to design out rather than to seal against afterwards.
- Movement
- Long runs of metal guarding change dimension with temperature while the structure below does not follow. Where that difference is absorbed, and what happens at the anchorages when it is not, is a design decision made in advance.
- Maintenance and access
- Fixings are usually covered as soon as they are made. Whether they can be exposed, checked and tightened later is decided by the detail chosen at design stage rather than by whoever inspects the building afterwards.
- Documentation
- The infill, the fixings and the substrate they went into are what any later alteration depends on knowing. Without that record, changing a panel or relocating a post means investigating the assembly from scratch.
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 lies below each proposed post position, and was it there before the guard was designed?
- Is the top rail structural, or a handrail carried by the frame beneath it?
- Does the anchorage pass through a layer that is shedding water, and what closes that pass?
- Can the base fixings be reached and inspected once the surface around them is finished?
- Is this an external edge, an internal edge or a stair, and does one detail suit all of them?
- If the infill is changed later, does the rest of the assembly still behave as it was designed to?
Boundaries
Commonly misunderstood points
Distinctions that are easy to blur, and the places where a familiar term means something narrower than it sounds.
- Guarding is often chosen as an appearance item, when its behaviour is set by the anchorage and the structure behind it.
- A coping, a topping or a surface build-up is regularly treated as something a guard can simply be fixed to.
- Glass infill is assumed to be a single product, when the way a panel is supported changes what the assembly does entirely.
- Sealing around a base fixing is thought of as waterproofing, when it is a joint loaded and moved every time the guard is used.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Who is designing this guarding as a structural item, and what are they designing it against?
- What is each base fixing landing in, and has that been verified rather than assumed?
- How is the water-shedding layer closed where the anchorage passes through it?
- Does the proposed infill, and the gaps around it, suit the way this space will actually be used?
- What happens at the ends of the run, at returns and where the guard meets a wall?
- Is the assembly a tested arrangement, and does the installation match what was tested?
- How would this guarding be inspected once the surrounding finishes are complete?
What this page does not do
- Guarding is safety-critical. Whether it is required, how high it must stand and what it must resist are determinations for qualified professionals and the relevant authority.
- Nothing in this entry indicates that any material, fixing or arrangement is adequate for a particular edge.
- Existing guarding of unknown construction should be assessed by a competent person before anyone relies on it.
- Changing an infill, a post position or a fixing alters a safety-critical load path and is not a like-for-like substitution.
- Working at an unguarded edge during construction or inspection carries risks managed by others, not by this entry.
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.
Commonly built alongside
Systems routinely present in the same building without a junction recorded between them and this one. Where two systems do meet, the junction is set out above instead.
Applications
Building contexts this system is used in
The functional parts of a building this assembly is commonly met in. This is membership, not a ranking and not a recommendation: several systems answer any one context, and which of them suits a project is a design decision. A context appearing here does not mean the system is suitable, permitted or adequate for it.
- Deck & Terrace · External works
- External Works · External works
- Stair & Ramp · Structure
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 →