Does the roof get cleaned before or after the windows?

Run the windows-first order and follow it to the end of the day. The glass is washed and dried. Then the roof above it is treated with a cleaning solution, left to dwell and rinsed, and the rinse water carries spent solution and loosened growth down the slope, off the eaves and past the windows that were just cleaned.

That is the exact outcome the National Glass Association's procedure is built to avoid. Its Glass Technical Paper FB01-00 says exterior cleaning should begin at the top of the building and continue to the lower levels "to reduce the risk of leaving residue and cleaning solution on glass that has already been cleaned." NGA also asks that cleaning procedures include checking that the wind is not blowing cleaning solution and residue onto glass already cleaned, and what wind does to glass work is taken up at whether windows can be cleaned when it is windy.

NGA wrote those lines about cleaning glass, not about a roof, so applying them to a house with a roof above its windows is this page's reasoning. The reasoning is short: the roof is the top of the building. In the windows-first order the glass ends the day exposed to runoff and drift after its cleaning, and NGA's DO NOT list includes allowing water or cleaning residue to remain on the glass or adjacent materials. What a roof wash can leave on windows, from spots to film, is taken up at will roof cleaning dirty my windows.

Now run it the other way. The roof is treated, left to dwell and rinsed, and whatever it sends down has come down before anyone cleans a pane. The window cleaning is the last step, so the glass is cleaned after the roof's overspray and runoff are already on the ground.

This is NGA's top-down line applied across a whole house rather than a single facade. It is still reasoning from two sources, not a published sequence, and no roofing maker or glass association read for this page states it as the trade's rule. What it does line up with is the care guide from PGT, CGI and WinDoor, which tells owners to clean and rinse each window or door individually so cleaning agents do not permeate for long periods of time. In the roof-first order nothing from the roof is left sitting on clean glass.

In this order the soft washing on the roof is finished before the glass work starts. The same reasoning reaches the ground as well, and the order of a roof and the pavers beneath it is reasoned separately at should the roof be cleaned before or after the pavers.

If a roof wash were only water, the order would be about spots. ARMA's published shingle procedure is not only water: its technical bulletin describes lightening algae discoloration with a solution of liquid household bleach (sodium hypochlorite) and water, and asks that it be applied carefully to avoid damage to other parts of the building. The National Glass Association's list of materials that may harm laminated glass includes "Bleach (or other solutions containing sodium hypochlorite)".

Florida impact windows are laminated glass, as the window cleaning page sets out, and NGA says cleaning fluids and their vapors must be kept away from the edges of laminated glass, where its plastic interlayer is generally exposed. Why that makes overspray on impact glass a technical matter is explained under what is around the roof while the work happens.

An order is a small part of the answer. It says nothing about which panes on a given house are laminated, and it is not a cleaning method for the glass itself.

Whether a particular window is laminated or impact rated is its maker's to say. Care instructions for a given window come from that maker's own guide, the way PGT, CGI and WinDoor publish theirs, and the NGA paper sets out the general procedure for architectural glass. How impact glass is cleaned compared with ordinary glass is its own question, answered at are impact windows cleaned like regular windows.

The layout of the house matters too, as a mechanism: glass tucked under a deep overhang or directly below a valley sits in a different path from glass on a gable wall. That kind of detail, along with the roof material and what is growing on it, belongs to the conversation about what roof details matter for a cleaning estimate.