Shading, Canopies and Everything Else Hung Off a Facade

The shading record sets out four consequences arriving at one point. A single connection transfers a cantilever load, interrupts the insulation, perforates the water and air control layers, and passes through a cladding element designed only to carry itself. It then states why they cannot be separated: sealing the hole better does not help if the arm is fixed to the wrong thing, and reaching the right structural element does not help if the seal cannot follow the movement between facade and frame.

The load is also not what it looks like. A cantilevered element multiplies its own weight into leverage at the fixing, and wind on a bank of louvres both pushes and lifts rather than simply pressing, so the reversal is often the case the connection has to be designed around.

Where the facade is a drained screen, the arm crosses cladding, a drained cavity, insulation and a control layer in one run. Two requirements follow: the cavity has to stay drained around the penetration, and the cladding must not become the thing carrying the element.

The rainscreen record approaches the same junction from its own side, noting that fins, canopies and brackets fixed after the cladding is complete are new penetrations through a finished screen, and asking whether they reach a backing element chosen to receive them or simply land on cladding designed only to carry itself. That is a question to ask before installation rather than after.

A rendered external insulation build-up is a thin coat carried on a compressible board. The shading record states the consequence: each arm has to cross the reinforced render and the insulation to reach a backing element chosen to receive it, because a thin finish on compressible board cannot take a prying, cantilevered load at the point of fixing.

The facade record lists the same problem as one of its own design questions, noting that every pipe, bracket, meter and light currently on the wall has to be re-fixed through the added depth, and that each needs backing that can carry it, a sleeve or profile that keeps the insulation edge covered, and a seal that tolerates the movement of what passes through.

Curtain walling often carries shading directly on its mullions, which turns a facade frame into a support for a cantilever. The record asks two things of that: whether the frame was designed for the load, and how the fixing crosses the isolating component within the section, since the thermal break sits inside the load path.

The curtain walling record adds its own caution from the other direction: fixing anything to a mullion after completion loads a member designed for wind and may cross the isolating component within its section. Both records point the decision at the facade engineer rather than at the installer.

Where the wall is framed in cold-formed steel, the record describes elements passing through the wall — balcony arms, canopy supports and plant fixings — as designed penetrations of both the thermal layer and the weather layer, not fixings made after the wall is built.

The reason is the frame. Each bracket punctures the weather layer, crosses the thermal layer in metal and delivers a concentrated load into a thin section, and the number and arrangement follow from the element and its wind loading. A late addition is therefore a change to the wall rather than an addition to it.

Where an element has to cross the insulation line and carry load, the interruption cannot simply be filled with insulation because the filling would have to carry the load. The structural thermal break record describes the answer as placing a body of lower-conductivity material within the joint and passing through it only what has to transfer load, with capacity, stiffness, movement and tolerance determined by the responsible engineer.

The junction record for a cantilever member names the two ways it goes wrong and where each one shows. Where the break is left out, the projection becomes a continuous cold line into the floor at the position the structure is most concentrated. Where the break is treated as insulation rather than as a loaded component, it can compress under a load that never comes off it, so the projection drops at its tip and the fall on its surface reverses.

Every attachment is a designed opening through the water and air control layers, made from outside and expected to remain sealed while the element moves. A metal element in full sun moves against a facade that moves on its own terms and a structure that moves on a third, so the connection has to allow that without loosening and the seal has to remain closed while it happens.

The record states the corollary as a caution: a rigid seal at a moving joint is a defect waiting to appear. It also notes that the number of penetrations is set by the shading layout drawn much earlier, which is why the layout is a control-layer decision as well as a daylight one.

Elements hung off a facade sit in the most exposed position on the building, collect what falls on them, and need cleaning and inspection from the outside face at height. An adjustable system adds actuators, sensors, wiring and controls in that position, so the record treats the access strategy as part of deciding whether to have one at all.

They also change the wall beneath them. Run-off concentrates where it did not before and shaded areas dry more slowly, which is worth anticipating before the elevation is finalised rather than discovering once the elements are up.