Commercial curtain walling

Stick-built or unitised — the decision that sets your programme

Stick systems arrive as loose mullions, transoms and glass and are assembled in place. They are cheaper per square metre, tolerate an imperfect structural frame, and suit refurbishment and low-to-mid rise work. The trade-off is time on site and a longer exposure to weather.

Unitised systems arrive as finished storey-height cassettes, glazed and sealed in a factory, and are craned into place. Factory conditions give a tighter seal and far better repeatability, and a floor can be closed in a day. They cost more, need a longer lead time before anything reaches site, and they demand a frame surveyed to tight tolerance because there is no scope to adjust on the day.

Thermal performance and Part L

The number that matters to building control is the whole-facade U-value, not the glass figure on the unit label. A 1.0 W/m²K sealed unit set into an aluminium frame with a weak thermal break will still hand you a facade figure closer to 1.8 once the frame is included.

Polyamide thermal breaks, warm-edge spacers and a considered frame-to-glass ratio are what move that number. On refurbishment we model the facade before ordering so the figure you submit is the figure you achieve.

Movement, tolerance and why frames fail early

A curtain wall has to absorb building movement, thermal expansion and wind deflection without transferring any of it into the glass. Deflection is normally limited to span over 200 for the glass edge. Where that is ignored, the failures show up within a couple of winters as bowed transoms, failed gaskets and water at the head of the opening lights.

Setting blocks, expansion joints at every floor level and a properly detailed movement allowance at the perimeter are not optional extras.