Building envelope · External Wall Build-Ups
Masonry Infill Wall to Frame System
This entry treats the gap between the masonry and the frame as the organising idea of the wall, so that head details, restraint and panel support can each be read as either preserving the frame's independence from the wall or quietly removing it.
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 masonry infill wall is
In an infill wall the frame is the structure and the masonry is not. The wall carries its own weight down to whatever supports each panel, resists wind pressure and suction across its face and hands that load back into the frame, and does nothing else. Every feature of the assembly follows from that division: the wall is doing less work than a masonry wall looks like it is doing.
The frame moves. Concrete frames shrink and creep, steel frames deflect under the floors they carry, and both settle. Fired-clay masonry expands over time while concrete and calcium silicate masonry shrink. Two elements built in contact are therefore changing size in different directions, and the deliberate gaps between them are what allow that to happen without one loading the other.
The gap at the head is the feature that is most often lost. It is left open, with a compressible filler and a seal, so that the frame above can deflect without coming to bear on the panel below. Packed solid with mortar, grout or a rigid board — which is easily done, and invisible once the wall is finished — it turns a non-loadbearing panel into a prop under a beam that was never designed to be propped.
Because the wall occupies only the space between frame members, the frame itself is outside the wall for the purposes of every control layer. The air line, water line and thermal layer have to cross the columns, the beams and the floor edges as well as the masonry, and the facade carried on the panel face is interrupted at every one of them.
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.
- infill masonry wall
- blockwork infill wall
- frame and infill wall
- non-loadbearing infill panel
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.
- Fill the openings in a frame with a wall that encloses the building without carrying any part of it.
- Take wind load on the face of each panel and transfer it into the frame through restraint that does not also transfer vertical load.
- Keep the frame free to deflect, shrink and settle without bearing onto the masonry beneath it.
- Give each panel a defined support at which its own weight is taken, rather than stacking panels on one another up the building.
- Allow the masonry and the frame to change size in different directions without either restraining the other.
- Provide a background on which control layers and a facade can be carried across both the panel and the frame zone.
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 supportThe frame and its floor edges
The columns, beams and floor plates that carry the building and define the openings the wall fills. Their material governs how the panel can be tied to them, how much they will move once loaded, and whether the panel's weight is taken on the floor edge itself or on something fixed to it.
- SubstrateInfill masonry panel
The non-loadbearing leaf or leaves built within each opening. The panel spans between its restraints to resist wind, carries only its own weight to the support beneath it, and becomes the background that the control layers and the facade outboard of it are fixed to or bedded onto.
- Edge and terminationDeflection gap at the head
The space deliberately left between the top of the panel and the underside of the structure above, so that the frame can move without bearing on the wall. It is filled with something compressible and closed with a seal, and it is the single feature on which the panel's non-loadbearing status actually depends.
- AttachmentFlank restraint ties and channels
The ties, cast-in or fixed channels and sliding anchors at the columns that hold the panel in plane against wind while allowing the panel and the frame to move relative to one another. Restraint that is rigid in every direction is restraint that also transfers movement, which is the condition it exists to avoid.
- Primary supportPanel support at each level
The floor edge, nib or angle on which each panel's self-weight is taken. Where that support sits decides how tall a panel is, where the horizontal breaks in the wall fall, and whether the facade carried on the face has a joint at that level that it would not have had on a continuous wall.
- Jointing and sealingCompressible fillers and movement joints
The fillers, backings and seals closing the head gap, the flank gaps and the vertical movement joints within larger panels. They close the wall visually and against air and water while leaving the gap able to close and open, which is a different requirement from filling it.
- Control layerAir and water lines across the frame zone
The continuation of the barrier and drainage planes across the columns, beams and floor edges that the masonry does not occupy. The panel is the easy part of that line; the changeover onto structural members, and the crossing of every movement gap, is where continuity is won or lost.
- Thermal layerInsulation over the frame members
The insulation carried across the panel and across the frame, since a column or a floor edge left uninsulated is a conductive element running the full height or length of the building. Where the insulation sits relative to the frame also decides which side of the thermal line the frame itself is on.
- Finish surfaceFacade, cladding or render on the panel face
The outer layer carried on the assembled wall, which reads as continuous while the construction behind it is not. It has to be interrupted where the wall is interrupted, so the movement provision at the head and flanks has to appear in the facade as well as in the masonry.
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 head gap and the panel's non-loadbearing status are the same fact. Pack the gap solid — the commonest single thing done to these walls — and the frame begins to load a wall that was never designed to carry it, in a way that is invisible from either face and only becomes apparent when the masonry starts to distress.
Restraint and movement are in tension with each other at the flanks. The panel has to be held in plane against wind and simultaneously left free to move relative to the frame, so the restraint has to be stiff in one direction and permissive in another. Tie the panel rigidly to the columns and the differential movement between a clay leaf and a concrete or steel frame has nowhere to go.
Where the panel is supported decides the shape of the wall. Support every panel at its own floor and the wall becomes a stack of independent panels with a horizontal break at each level, which the facade has to acknowledge. Carry the masonry past the floor edge instead and the panel becomes taller, its support and restraint change, and the facade joint disappears along with the movement provision behind it.
The control layers cross two very different backgrounds in the same plane. The masonry is dimensionally forgiving and takes a bonded membrane or a render easily; the frame is precise, conductive and moving, and every changeover between them coincides with a gap. Continuity across the frame zone is therefore set by the details at the columns and floor edges rather than by anything happening in the middle of a panel.
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
These frame families are commonly encountered carrying buildings whose external walls are infilled in masonry. How much a given frame moves once loaded, and in which directions, is an engineering matter established for the particular structure.
Substrate
Infill panels are commonly built in these masonry families. Clay and concrete-based units change size over time in opposite directions, which is why the direction of long-term movement is a property of the unit family as well as of the frame it sits in.
Attachment
Restraint ties, channels and anchors at the flanks and head are commonly formed in these families. What a given restraint permits and what it resists is a property of the component and its installation rather than of the metal, and is confirmed from the manufacturer's documentation.
Jointing and sealing
Compressible fillers, backings and sealants from these families are commonly met closing head and flank gaps. Their function here is to close a gap that has to stay able to move, which is a different requirement from filling a gap that will stay still.
Thermal layer
These insulation families are commonly encountered carried across both the panel and the frame members. How the layer continues past a column or a floor edge is a detailing question rather than a property of the board.
Finish surface
Facades carried on infill panels are commonly met in these families among others. Whether a given finish can bridge the frame zone, and how it is interrupted where the wall is interrupted, is settled by the facade designer.
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.
Panels within a steel frame
A steel frame deflects under the floors it carries and its members are set out to fabrication tolerances that a masonry trade does not work to. Both facts land at the same junction: the head gap has to absorb the deflection and the flank restraint has to take up the difference between where the column is drawn and where it is.
Read about Steel Frame →Panels within a concrete frame
A cast frame shrinks and creeps for a long period after it is built, and it does so downwards onto whatever is beneath each floor. The panel built tight under a soffit early in that period is the panel most likely to end up carrying load it was not designed for.
Read about Concrete Frame →Openings formed within the panel
An opening in an infill panel sits within an element that is itself moving relative to the frame around it, so the window perimeter has to accommodate movement at the panel edges as well as at its own. Where the opening head is close to the panel head, the two movement provisions are competing for the same space.
Read about Window Opening Interface →The infill built as a cavity wall
Where the infill is built as twin leaves with a tied cavity, the cavity logic and the infill logic apply at once: the cavity has to be interrupted and drained at every floor-level support, and the ties across it have to coexist with the restraint arrangements at the flanks.
Read about Twin-Leaf Cavity Wall →Interruption of a cavity at each support
Every support angle, nib or floor edge crossing a cavity is an interruption, and water travelling down inside the wall arrives at it. Where trays are provided, their stop ends and drainage openings have to coincide with the support rather than with the drawing grid.
Read about Cavity Trays →Render carried across panel and frame
A render worked onto the panel face meets a structural member with a different background, a different suction and a different movement pattern at every panel edge. Carrying the coats straight across that change is what puts a crack on the line of the frame.
Read about Direct Render →The floor edge and the line it forms
The junction between the top of one panel, the edge of the floor and the bottom of the panel above collects the head gap, the panel support, the control-layer changeover and, where the floor is a line with a regulated fire-resisting duty, a sealing arrangement that sits outside this reference. These are commonly detailed by different parties for the same few inches of wall.
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
- The frame and the masonry change size in different directions and on different timescales, and the whole assembly exists to let them. What each panel has to accommodate at its head and flanks depends on the frame material, the loads it carries and the masonry chosen, and is established by the designer.
- Interfaces
- The wall is defined by its edges rather than by its middle. Almost everything that matters — support, restraint, movement provision, control-layer continuity, facade interruption — happens where the panel meets the frame, which is also where responsibility commonly changes hands.
- Buildability
- The head gap is built early and concealed soon after, and closing it is often the last operation on a panel that other trades are already working around. Whether it stays open once the wall is finished is a matter of sequence and supervision as much as of design.
- Thermal
- The frame members the wall does not occupy are conductive elements running through the envelope, and how the insulation crosses them decides whether they sit inside or outside the thermal line. What that means for a given building is assessed rather than assumed.
- Moisture
- The gaps that make the wall work are also routes through it, so the air and water lines have to cross every one of them. Water reaching a support angle or a floor edge inside the wall has to be given a way back out at that level.
- Documentation
- Once a facade is on, nobody can see whether the head gap is open, what the restraint at the columns actually permits, or where each panel is supported. Recording those decisions is what makes later alteration, and later diagnosis of cracking, possible.
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.
- Which element is carrying the building here, and what is the masonry being asked to carry besides itself?
- Where is each panel supported, and does the facade acknowledge that support line?
- How wide is the head gap being left, what closes it, and who is closing it?
- What do the flank restraints permit and what do they resist, in each direction?
- How do the air and water lines cross the columns, the beams and the floor edges?
- Does the insulation continue past the frame members, or does it stop at the edge of each panel?
- Are the movement gaps at head and flanks expressed in the facade, or is the facade running continuously across them?
- Who is responsible for the few inches at each floor edge where support, movement, control layers and any fire-resisting duty all meet?
Boundaries
Commonly misunderstood points
Distinctions that are easy to blur, and the places where a familiar term means something narrower than it sounds.
- An infill wall is not a loadbearing wall built inside a frame. It carries its own weight and wind load and nothing else, and the details that keep it that way are the point of the assembly.
- A masonry panel that reaches the soffit above is not automatically supporting it, and a panel packed tight to that soffit is not automatically safe either. What matters is whether the gap was left and whether it is still there.
- This entry is the coordinated wall condition, not the masonry unit or the panel as a component met by other systems. The panel appears inside several other systems; here the frame, the gaps, the restraint and the panel are read together as one wall.
- Filling the head gap does not make the wall stronger. It changes what the wall is, from something the frame stands past to something the frame stands on.
- A frame does not stop moving once the building is finished. Concrete continues to shrink and creep and floors continue to deflect under the loads they carry, which is why the gap is for the life of the building rather than for the construction period.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- What movement has been allowed for at the head of each panel, and what establishes that figure for this frame?
- How is each panel supported, and is any panel bearing on the one below it?
- What do the flank restraints permit, and how has that been reconciled with wind load on the panel?
- How do the air and water control lines cross the columns, beams and floor edges?
- How is the insulation continued past the frame members, and what has been assessed about the result?
- How is water that reaches a support angle or floor edge inside the wall returned to the outside?
- Where the floor edge carries a fire-resisting duty, who is specifying the sealing arrangement there?
- How will anyone confirm later that the head gaps are still open?
What this page does not do
- This entry describes how the assembly is organised. It is not a specification, a wall build-up for a particular building, or a substitute for design by a qualified professional.
- Whether a panel is loadbearing, how it is supported and what movement is provided for are structural determinations and are never inferred from a general reference.
- Fire-resisting sealing at floor edges and around openings is a regulated subject with its own tested arrangements, deliberately outside the scope of this entry.
- Filling, propping or cutting into an existing infill panel can change how the frame and the wall share load, and such work belongs with the building's structural engineer.
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.
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.
- External Wall · Envelope
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.
External Wall Build-Up Systems
Complete external walls read as a layer order: where in the thickness of the wall water is stopped, and in which direction the wall is allowed to dry afterwards.
Browse all external wall build-ups entries →