Where Two Different Envelope Systems Meet on One Elevation

A drained system accepts water past its visible face and returns it through a cavity to a defined exit. A face-sealed system relies on its outer surface and its laps. A bonded system has no space behind it at all. Where two of those abut, the question is not whether each works but what the drained one does with the water it is carrying when it reaches the other.

The curtain walling record frames it exactly this way: where curtain walling stops and a punched opening or a solid wall begins, two entirely different weathering philosophies meet along one line, and the drained system has to discharge at that boundary rather than into the construction it abuts.

That is the first question, and it has a direction. A cavity that is stopped by a change of construction needs a collection surface and an outlet at that level, or the stop becomes a reservoir. The junction record puts it bluntly: a collection surface with no exit holds water permanently against the wall at that level, which is worse than not collecting it at all.

The cavity wall record lists the same demand for every interruption — a lintel, a floor bearing, a change of construction, an abutment — and states that each one re-creates the requirement. A change of facade system is simply the largest instance of that.

Behind the weathering question is a continuity question. The air barrier record describes the line as passing between nominated planes — a taped sheathing board, a wet plaster coat, a membrane, a structural slab — and states that the barrier is defined less by what carries it than by whether the changeovers between them were designed at all.

It then names the failure: if the detail does not say which laps onto which and what bonds them, the line simply stops at the changeover, and the enclosure behaves as though the barrier ended there even though both planes are individually complete. The boundaries between work packages are where the line is most often left unowned, which the record treats as a project management act as much as a technical one.

Where a site-assembled metal wall meets a factory-bonded panel roof, the layers do not correspond one to one. The sheeted wall record states it directly: what arrives bonded into a single component on one side arrives as three separate operations on the other, and the eaves detail has to reconcile that.

Where the same wall meets its own roof equivalent, the demand is different but not simpler. The two build-ups have to be made continuous liner to liner, insulation to insulation and outer sheet to outer sheet, at a junction where the water on the roof is being collected and the water on the wall is running past.

The composite panel record adds the general rule for its own edges: every interruption replaces a factory-made relationship with site-made ones, and those have to reproduce weathering, thermal continuity and air control simultaneously. The field of the roof is dependable because it was made in a factory; the interruptions were not.

Where a glazed facade passes in front of every floor, the slot between the slab edge and the back of the spandrel runs unbroken round the building at each storey. The junction record lists the planes that have to be carried across it — the separation between storeys, the insulation line, the air barrier and the acoustic separation — and notes that they are not the same plane, so closing one does nothing for the other three.

It also notes the slot cannot simply be filled solid, because the slab deflects while the facade is hung from the floor above and moves on its own account. Whatever crosses it has to keep working while it opens and closes.

At the head of a facade the framing stops and the roof takes over, with a coping, an upstand and the roof's own control layers arriving from a different package. Water shed from the roof reaches that junction first, and the closure decides where it then goes. On a precast facade the same water arrives at the top of the joint system, and the coping decides whether it enters the joint or is thrown clear.

The parapet junction record adds the thermal half. The roof insulation and the wall insulation reach a parapet from two directions and at right angles, and if they stop where they arrive instead of joining round it, the wall acts as a fin along a line running the whole perimeter of the roof — not at a point, but continuously.

Transitions sit on the boundaries between disciplines. The shading record describes its own attachment detail as sitting precisely on those boundaries, which is why it is often the last thing resolved and the first thing to leak. The same is true of system-to-system lines, which are commonly designed by different parties for the same few inches of construction.

They are also reported in the wrong place. Water entering a drained system can appear internally far from its point of entry, and a break in an air line shows as draughts or condensation at an intersection rather than at the gap. Establishing what the junction is before interpreting the symptom is the practical consequence.