The short answer
The architect sets the look and the performance the wall must meet, often with a facade consultant. The specialist curtain walling contractor then takes on the detailed design, calculations and fabrication drawings for its chosen system. The key decisions, like system type, module and glass, need settling early because they drive cost and programme.
On this page
Curtain walling is usually designed in two halves. The design team decides what the wall must look like and how it must perform. A specialist contractor then designs exactly how its system will achieve that, and makes it. Understanding where the line falls between the two avoids gaps, duplication and arguments later.
The design team’s part
Architect
The architect sets the appearance: the grid, the proportion of glass to solid, frame sizes and colour, the glass tint and any fins, shading or feature elements. They also coordinate the wall with the structure, the roof, the floors and the rest of the facade.
Facade consultant
On larger or more complex projects, a facade consultant writes the performance specification and checks the specialist’s design. They advise on system choice, glass selection, thermal and solar performance, wind loads, testing, and the interfaces that cause most trouble.
Other consultants
- The structural engineer confirms the slab edges can take the bracket loads and sets the movement the wall must accept.
- The energy assessor sets the U-value and g-value the wall needs to pass the building’s energy calculation.
- The fire engineer says which parts of the wall need a fire rating and how fire is stopped at each floor.
The specialist’s part
When the curtain walling package is let, the specialist usually takes on detailed design for its system. That includes:
- fabrication drawings for every frame, panel and junction,
- structural calculations for brackets, mullions, transoms and glass,
- the whole wall U-value and any condensation risk analysis,
- glass specification to meet safety, thermal and acoustic requirements,
- proposals for testing, both in the laboratory and on site.
The architect or facade consultant reviews and comments on the design, and the specialist carries the responsibility for it, backed by professional indemnity insurance.
When the decisions get made
| Stage | Decisions |
|---|---|
| Concept | Glazed area, overall look, whether curtain walling suits the building |
| Spatial coordination | System type (stick, unitised or structural), grid module, slab edge zone, rough budget |
| Technical design | Performance specification, glass make-up, fire strategy for the facade, test requirements |
| Tender | Specialist chosen; they start detailed design and calculations |
| Manufacturing | Fabrication drawings approved, materials ordered, mock-up tested where required |
The most expensive mistakes come from leaving system choice and grid module too late. A unitised wall needs a long lead time, and changing the module after the slab edges are cast means redesign.
Decisions to settle early
System type
Stick, unitised or structural glazing each bring different costs, programmes and access needs. Published cost data from March 2025 put a typical stick system at about £450 to £525 per m² and unitised at about £1,400 to £1,600 per m². See the cost calculator.
Module
The width between mullions and the height between transoms set pane sizes. Larger panes look cleaner but are heavier, harder to handle, dearer and limited by what the glass factories can make. A regular module keeps costs down.
Glass
Thermal, solar and safety needs all affect the glass make-up. Where people could fall against or collide with glass, Approved Document K applies. Laminated and toughened glass, acoustic interlayers and fire-resisting glass each add weight and cost.
Performance
The specification should state wind load, air and water classes, thermal targets, acoustic needs and any security level, so every tenderer prices the same thing. CWCT publishes a specifier’s checklist as part of its standard.
Regulation
On higher-risk buildings, residential blocks of 18 m or seven storeys with two or more homes in England, building work is approved by the Building Safety Regulator through gateways. The facade design must be developed enough to pass these before work starts.
Design for maintenance
A good design plans how the wall will be cleaned, inspected and repaired. That includes access for window cleaning, a way to replace a broken pane at height, and a maintenance schedule for gaskets and seals. These questions are cheap to answer at design stage and expensive later.
Getting a specialist involved
Specialists can give early advice on system choice, module and budget before the package is tendered. If you would like to talk to a curtain walling specialist about a design, use the form below and we will look for one that covers the project.