Ventilated Rainscreen Facade System

A rainscreen facade splits work that a solid wall does in a single plane across several separate ones. The visible skin intercepts wind-driven rain and most of the wind pressure, but nobody expects it to exclude water altogether. Behind it a cavity is held open so that anything crossing the skin runs down a defined face and leaves at a defined point, and so that air can move through the space and carry away moisture that would otherwise sit against the construction.

The nearest sibling is the brick slip cladding system, and the boundary is visible from the pavement. A rainscreen tolerates open joints because the drained cavity behind it is doing the work; a brick slip facade presents a continuously jointed face whose pointing is expected to keep most water out. Where shadow shows through the gaps between panels, the facade has already told a passer-by which of the two it is.

Behind the cavity, the backing wall holds what actually matters: the sheet or applied coating that governs water and air, and the insulation sitting outboard of the structure. The subframe carrying the cladding has to cross both of those layers, which is why the fixing arrangement is at once a structural question, a thermal question and a penetration question rather than an ironmongery choice made late.

Pressure equalisation is often described as the mode in which such a facade works: the cavity is compartmented so that pressure within it can rise towards pressure outside, easing the force that pushes water inward through joints. Whether a particular facade behaves that way depends on compartmentation, joint geometry and exposure, and is assessed by the facade designer rather than assumed from the presence of a gap. It is not the materials-library entry cladding-support-systems, which is the bracket and rail product rather than the drained and ventilated arrangement it is used within.

The concept holds only while each layer accepts a smaller job than it appears capable of. The cladding is allowed to leak, which is what makes an open joint acceptable; the cavity accepts that leakage, which is what makes drainage compulsory; the control layer on the backing wall accepts whatever reaches it, which is what makes its continuity more consequential than the fixing of any single panel. Shift responsibility one layer outward and the logic collapses.

A cavity that is not continuous stops working where it is blocked. Insulation bulging outward, dropped mortar, a squashed closure or a horizontal member with no path around it turns the drained face above into a shelf, and water that had a route down now has somewhere to stand. The same interruption halts air movement, so the wall above the blockage loses its drainage and its drying at the same moment, in the same place.

Every bracket passes through the insulation and usually through the control layer as well, so three things happen at one point: load is transferred, a path is created around the insulation, and the sheet is perforated. Whether the penetration is sealed, whether an isolating pad separates bracket from wall, and how closely brackets are grouped are decided together, because easing one of those consequences generally worsens another.

Each layer is covered permanently by the one outboard of it, so nothing inboard remains reachable. A lap or a penetration left open at the control layer cannot be got at again once cladding work is under way, and no later trade is in a position to correct it. That is why this facade tends to fail as a small number of concealed defects rather than as visible decay, and why its meaningful inspection points sit early in the programme.