Why Elevations Streak, Stain and Soil Unevenly

The render record describes a drip as the component that decides run-off leaves the face at that point rather than tracking down onto the material below. Without a drip, water returns to the wall, which is why staining so often begins directly under a sill or a stop.

The solid masonry record generalises it. Copings, sills, projections and the level of the ground at the base control the volume of water arriving on the wall, so losing an overhang, replacing a sill without its drip or raising the ground over the base course means the same masonry with the same mortar is asked to buffer far more water and to dry from a face that stays wet longer.

Concentration and shelter are two halves of the same pattern. Flow gathers at the ends of sills, below joints, beside downpipes and at any point where a projection interrupts an otherwise even sheet of water. Elsewhere, an overhang keeps a band of wall dry, a reveal shelters one side of an opening, and a recess stays dark.

Because the difference is geometric, it repeats. A detail used across an elevation produces its stain at every instance of itself, which is why weathering reads as a pattern rather than as damage, and why it can usually be traced back to a line on a drawing.

The render record notes that how far the roof edge projects governs where run-off is thrown and how much of the face below is sheltered, and that the difference shows as a weathering pattern long before it shows as a defect. On a precast facade, water shed from the roof arrives at the top of the joint system, and the coping decides whether it enters the joint or is thrown clear.

The eaves junction record adds the failure case. Water leaving a roof has to be delivered into the gutter: far enough out that it clears the fascia, not so far that it overshoots in heavy rain, with the underlay discharging into the gutter rather than behind it. When it goes wrong the water lands on the fascia, the wall or the ground at the base of the wall, and the damage appears in those places rather than at the roof.

A wall that has been wrapped in external insulation is thicker, so it no longer sits under the same overhang. The record states the consequence: the eaves either extends or the render finishes at a head detail that sheds water clear, and if it does not, run-off tracks down the face at the point where the insulation edge is most exposed.

The same thickening moves every reveal, every sill projection and every stop. So a decision taken about thermal performance arrives on the elevation as a change to how it will weather, and the two are settled at the same time or not at all.

The shading record is explicit about this. Once elements are installed they change the facade beneath them: water that used to run evenly now runs off a fin and lands in a line, so staining develops where it did not before. Shaded areas dry more slowly than exposed ones, so growth and soiling patterns differ across an elevation that used to weather uniformly.

It also notes what accumulates. Shading sits in the most exposed position on the building and collects what falls on it — leaves, dust, nesting material, salt near a coast — and what gathers on a horizontal louvre determines its appearance more than the finish originally applied to it.

Some staining is a message rather than an aesthetic outcome. On a rendered external insulation facade, a stained band above ground level usually points backwards to the starting detail at the base of the system, because water getting behind the insulation is beyond the reach of any surface repair.

On a masonry wall, efflorescence and salt damage follow from how wet the face becomes and how long it stays wet, which are consequences of exposure and detailing rather than of the units alone. The records note that similar walls on the same building can weather quite differently for exactly that reason.

The design questions the records raise are simple and early: whether every sill, stop and head has a drip that throws water clear of the face below; what weathering pattern should be expected on the exposed elevations and which details are intended to control it; and where run-off will streak the faces as the building weathers, which is decided by reveals and drips rather than by the material.

Repair follows from the same geometry. On a jointed facade a patch can be confined to a panel; on a continuous render the surrounding face has weathered, so the practical unit of repair is often a whole panel between joints, and planning where those boundaries fall is planning what a future repair will look like.