There is no single number that fits every building, and a contractor who gives you one before seeing the elevation is selling you a schedule rather than an estimate. Location decides it more than any other factor.
What makes one elevation soil faster
What explains most of the difference between two buildings in the same city:
- Proximity to heavy traffic. Exhaust carries oily particulates that bond to glass and that rain does not remove.
- A construction site next door. Cement dust is alkaline, and left on glass with any humidity it starts reacting with it.
- Which way the elevation faces. The face turned into the dust-carrying wind soils several times faster than the sheltered face of the same building.
- Height. Upper floors meet stronger wind and finer dust, which works its way into frame details.
Why deferring costs more
In the first weeks, soiling is a surface layer that comes off with water and the right product. After months of heat and humidity, salts and particulates begin reacting with the surface itself: glass loses clarity, and the coated finish on cladding goes flat. At that point cleaning no longer returns the facade to what it was, because the damage is in the material rather than on it.
Building a realistic cycle
A survey looks at the surface, what surrounds the building, and the condition the elevation is in now. The output is a schedule for your building, and it is often different for different faces of the same one. The elevation on the street needs a shorter cycle than the one at the back, and cleaning both at the same rate is money in the wrong place.
One practical signal
If the difference between the section cleaned last time and the section next to it is visible from street level, the cycle has already run long. It is the clearest signal there is, and nobody has to go up to notice it.