Building envelope · Facades & Cladding
Precast Concrete Facade Panel System
This entry moves the performance question in a precast facade away from the concrete and onto the joints and the fixings: how a panel is supported and restrained, how joints weather, and how factory precision is reconciled with a structure built on site.
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 precast facade panels is
Large units are cast in a controlled environment, delivered complete with their finish, and lifted into position against a structure that was built where it stands. Each unit is supported at a small number of points and restrained at others, and the visible facade is then the sum of those units and the lines between them. The faces are continuous while those lines are the discontinuities that move, age and are renewed, which is why the weathering question in this facade belongs to the joint.
The nearest sibling is the load-bearing precast panel system, and the test is what happens at a floor. A cladding panel is hung at discrete points, and there is a joint at every storey precisely so that the structure can move without the panel being asked to follow it. A load-bearing panel continues the load path: floors bear on it, and it is holding up what is above. Look for a movement joint at each level and for a bracket rather than a bearing, and the two are told apart from the outside.
The joint is therefore where the design choice is made, and there are broadly two philosophies. One relies on a sealed line, which is simple and depends on the seal remaining sound. The other uses a baffle and a drained chamber, so that water passing the outer line is collected and returned outside rather than continuing inward. Which is present determines what happens when the outer line eventually ages.
The last shared problem is tolerance. A factory product arrives accurate; a frame built on site arrives within a range. That difference has to be taken up somewhere, and if adjustment was not designed into the fixings it will be taken up in the joints instead, which is where it becomes visible from the street and where the weathering detail starts to vary panel by panel.
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.
- architectural precast cladding
- storey-height facade panels
- factory-cast facade units
- hung precast facade
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.
- Deliver large areas of finished facade as complete units, with the finish formed under controlled conditions rather than on site.
- Transfer panel self-weight and wind load back to the structure at chosen points while leaving the panel free of structural duty.
- Weather the building at designed joints, either sealed or baffled and drained, rather than through the panel faces.
- Absorb the difference between a precise factory unit and a structure built within site tolerances through adjustable fixings.
- Allow the structure to shorten, deflect and move without transferring that movement into a rigid cast unit.
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.
- Finish surfaceCast facade unit
The panel itself, carrying its finish, its reveals and often its openings as one piece. It presents a large uninterrupted face, which is why the working parts of the facade are the joints and fixings around it, and its rigidity is why it cannot follow structural movement.
- Primary supportStructure receiving the panels
The frame, slab edge or wall the fixings reach. Its accuracy governs how much adjustment is needed, and its own movement, from shortening, deflection and thermal change, is what the fixings and joints have to accommodate rather than resist.
- AttachmentSupport and restraint fixings
Two different duties usually carried by different components: a small number of points take the weight, while others hold the panel in plane without adding a second load path. Confusing the two is what turns building movement into cracking in a unit.
- Jointing and sealingJoint weathering: seal or baffle
The line between units, formed either as a sealed joint or as an outer baffle with a chamber behind it. This is where the facade meets the weather, and whether it has a second line of defence decides what an aged outer seal actually means.
- Drainage planeDrained joint chamber and outlets
In a two-stage joint, the space behind the baffle where water is collected and returned outside at intervals. The horizontal and vertical joints have to work together for that to happen, because water in a vertical joint has to be intercepted at a crossing.
- Thermal layerInsulation line and its continuity
Insulation placed behind the panel or cast within it. Every support and restraint fixing crosses that line, so thermal continuity is decided by the fixing layout rather than by the insulation, and the joint zone is where continuity is hardest to hold.
- Control layerBacking wall or spandrel closure
The construction behind the panel that carries the air and water control layers where the panel does not, particularly at floor edges and around openings. It is doing the continuity work that a facade of discrete units cannot do for itself.
- Edge and terminationTolerance, adjustment and movement provision
Slotted holes, shims, packers and the designed clearances that let a precise unit meet an imprecise structure. They are the difference between a facade that can be set out to a line and one where every deviation appears in the visible joints.
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.
Because the face is continuous and the joints are not, everything the facade does about water happens in the lines between units, and the choice of joint philosophy is therefore the design decision that matters most. A single sealed line puts all of the duty on one material at one plane; a baffled joint with a drained chamber accepts that the outer line will one day admit water and gives that water a route back out. The difference does not show on the day of completion, only much later.
Support and restraint have to stay separate. If a panel is held rigidly at more than one bearing point, the structure's own shortening and deflection are no longer accommodated: they are transmitted into a stiff cast unit, and the unit responds by cracking, usually at its weakest section around an opening. Slotted holes and sliding connections exist to keep those two duties apart, and they only work while their clearances remain free.
Every fixing crosses the insulation line and reaches back to the structure, so the fixing layout is simultaneously a structural, thermal and weathering decision. Reducing the number of penetrations concentrates load; spreading them creates more crossings. That trade is settled by the facade engineer, and where the joint zone falls it also has to be reconciled with the backing construction that carries continuity behind the panels.
Tolerance ties all of this together. The panel arrives at factory accuracy and the structure exists at site accuracy, and only the fixings can absorb the difference. If the adjustment runs out, the deviation moves into the joint, and the joint is also the weathering element, so a setting-out problem becomes a water problem. That is why a facade of this kind is largely decided before anything reaches the site.
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.
Finish surface
Cast unit families of these kinds are commonly encountered as facade panels. Which is encountered on a given building follows from the panel size, the finish and the structural design, all of which are established by the design team and the manufacturer.
Attachment
Fixing and bracket components of these families are commonly encountered supporting and restraining panels. Because these connections are structural and largely unreachable afterwards, their selection sits with the structural and facade engineers.
Jointing and sealing
Sealing components of these kinds are commonly encountered in facade joints. Which one is encountered depends on joint movement, on the concrete face and on staining behaviour, and those judgements belong with the designer and the documentation.
Thermal layer
Insulation families of this sort are commonly encountered behind or within panels. How the layer is held, and what happens where a fixing crosses it, are matters for the facade design rather than properties of the insulation itself.
Control layer
Sheet and tape families of these kinds are commonly encountered on the backing construction behind panels. Whether any can be installed and inspected before panels arrive is a programme question as much as a technical one.
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.
Slab edge and column faces
The frame provides the fixing points and also the movement the panels must tolerate, from shortening and from floor deflection. Cast-in fixings have to be positioned before the frame is poured, which puts a facade decision very early in the structural programme.
Read about Concrete Frame →Steel edge beams and connections
A steel frame moves differently and offers a different fixing opportunity, usually welded or bolted rather than cast in. It also deflects under load in ways that a rigid panel cannot follow, so the restraint arrangement is where that difference is settled.
Read about Steel Frame →Openings formed in the unit
Where an opening is cast into a panel, the frame meets a factory-formed reveal at factory tolerance, which is usually kinder than a site-built opening. The perimeter still has to weather and to connect to the control layers behind the panel.
Read about Window Opening Interface →Top panel and parapet
The uppermost units meet the roof edge, where facade joints, roof upstands and coping all converge. Water shed from the roof arrives at the top of the joint system, and the coping decides whether it enters the joint or is thrown clear.
Read about Parapet System →Fixings crossing the insulation
The support and restraint layout is fixed for structural reasons and then has to be reconciled with a continuous insulation line. Because the fixings are buried in the joint zone, the reconciliation happens on paper long before anything is lifted.
Read about Thermal Bridging Control →Continuity behind discrete units
A facade of separate panels cannot be continuous by itself, so continuity is carried by the backing wall and closures behind. Where those are absent at a floor edge, the joint between panels becomes the only line between inside and outside.
Read about Air Barrier System →
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.
- Movement
- Structural shortening, floor deflection and thermal change all arrive at a rigid unit through its fixings. Whether the fixings let that movement pass or resist it determines whether the panel stays intact, and the evidence appears as cracking at openings.
- Moisture
- The joints, not the faces, are where this facade is designed to meet water, so a moisture problem is looked for there first. That makes the joint design, and whether it has a second line behind the first, the whole of the moisture conversation.
- Thermal
- Continuity is interrupted at every support and restraint point, and the joint zone at each floor is where the insulation line is hardest to maintain. What the assembly achieves is calculated for the specific arrangement by a qualified professional.
- Durability
- Concrete faces weather according to how water runs across them, so drips, reveals and the pattern of run-off determine how an elevation looks as it ages. Streaking below a joint or a sill is a geometry outcome rather than a material fault.
- Buildability
- Fixing positions are decided before the structure is built and cannot be moved afterwards without difficulty. That front-loads the design and turns late changes to panel layout into a coordination problem rather than merely a fabrication one.
- Maintenance and access
- Joints are the maintained element in this facade, and they are reached from outside at height. Whether an access arrangement exists determines whether joint renewal is a planned operation or one that waits until water appears indoors.
- Documentation
- Panel marks, fixing types and joint details form a record without which no later intervention is straightforward. A facade of near-identical units is easy to misread on site, and the drawings are what distinguish one panel from its neighbour.
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.
- Whether the joints are sealed or baffled and drained is the decision that determines what happens when the outer line eventually ages.
- Which fixings support and which merely restrain, and whether the restraints can genuinely slide, decides how structural movement is absorbed.
- How much adjustment is built into the fixings, and what happens when it runs out, is worth understanding before the frame is set out.
- Where the insulation line runs behind the panels, and what carries continuity at each floor edge, has to be resolved with the structural design.
- How water shed from the roof arrives at the top of the joint system, and what throws it clear, is a coping decision made early.
- Where run-off will streak the faces as the building weathers is decided by reveals and drips, not by the concrete mix.
- What access will exist for later joint inspection and renewal on each elevation is a design question, not a facilities one.
Boundaries
Commonly misunderstood points
Distinctions that are easy to blur, and the places where a familiar term means something narrower than it sounds.
- The concrete is assumed to be doing the weathering, when the design locates that duty at the joints between units rather than on the faces.
- A cladding panel is confused with a load-bearing one, when the first is hung from the structure and the second is the structure.
- Restraint fixings are treated as extra support, when adding a second load path is what forces building movement into a rigid unit.
- Uneven joints are read as poor workmanship, when they usually show structural tolerance appearing where the adjustment ran out.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Are the joints designed as a single sealed line or as a baffled joint with a drained chamber behind it?
- Which fixings carry the weight of each panel, which only restrain it, and how is movement allowed to pass through them?
- How much adjustment is available at each fixing, and what is the plan if the structure is outside the assumed range?
- What carries the air and water control layers behind the panels, particularly at each floor edge?
- How will the joints be inspected and renewed later, and what access has been assumed for that work?
- What record will exist of panel positions, fixing types and joint details once the facade is complete?
What this page does not do
- A joint seal is not a permanent condition, and a facade relying on a single line has no second defence once that line ages.
- No part of this assembly resists water in isolation; the behaviour belongs to panels, joints, fixings and the backing construction acting together.
- Adding fixings to a hung panel to make it feel more secure can remove the freedom the design relied on to absorb structural movement.
- Fire and structural provisions at the floor edge behind these panels are determined separately by qualified professionals for the specific building.
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.
Commonly built alongside
Systems routinely present in the same building without necessarily touching this one.
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.
Facade and Cladding Systems
Outer skins carried on a wall that is already complete behind them, where the support, the joint and the cavity carry the durable knowledge rather than the finish.
Browse all facades & cladding entries →