Nobody compliments clean windows. Everyone notices dirty ones. That is the awkward economics of window cleaning: done well, it disappears into the building; skipped for a few months, it becomes the first thing a visitor sees. A client walking into reception will not mention streak-free glass, but they will clock the grey film across the facade and the smudged fingerprints on the entrance doors.

There is no single correct interval for office windows. A low-rise office on a quiet residential street and a glass-fronted building on a ring road have different problems, different budgets and different standards to meet. The practical approach is to build a schedule from four inputs: how the building is used, where it sits, how much traffic passes through it, and what the seasons throw at the glass.

Start With How the Building Is Used

A back office where staff work on screens all day has different needs from a reception that clients walk through. Before deciding on a frequency, walk the building and sort the glass into tiers.

Tier one is the glass that sells the business: entrance doors, reception, the boardroom, anything that faces a client or appears in photographs. This glass should look clean most of the time, which usually means a fixed monthly interior clean plus a spot clean before important meetings.

Tier two is working glass: meeting room partitions, office fronts, corridor glazing. It can tolerate a longer cycle, typically quarterly on the inside, provided nothing is visibly grubby at eye level.

Tier three is back-of-house glass: storage areas, plant rooms, service corridors, upper windows nobody looks out of. Twice a year is often enough, and in some buildings once.

Writing these tiers down gives you something concrete to hand a contractor and something to point to when the budget is reviewed. It also prevents the most common mistake in commercial cleaning: paying for a uniform service across a building that is not uniform.

Let the Location Set the Baseline

Geography does more to set exterior frequency than anything else. Glass does not stay clean because it rains; rain leaves mineral deposits, dust runs and drying marks, particularly in the first hour after a shower.

• Quiet suburban or park-side offices: quarterly exterior cleaning is a sensible starting point, brought forward in spring when pollen is heavy.
• Town centre and roadside buildings: every six to eight weeks. Traffic film, brake dust and diesel particulates build a grey haze that no amount of rain shifts.
• Coastal sites: every four to six weeks on the seaward elevation, less often on sheltered sides. Salt film is invisible until the light catches it, and it etches if left too long.
• Industrial or construction-adjacent locations: every four weeks, with a prompt return visit after visible dust events.
• Buildings under trees: two or three visits through autumn and a thorough clean once the leaves fall. Sap and bird droppings are the two things worth removing quickly rather than letting bake on.

These are starting points, not rules. The first three months of any new schedule are a test: note what the glass looks like the week before each visit, and adjust from there.

Ground Floors, Entrances and Heavy Foot Traffic

Foot traffic affects the lower two metres of a building far more than the upper floors. Entrance doors, lobby glazing, lift lobby partitions and street-facing windows collect fingerprints, bag scuffs and hand marks faster than any contractor's standard cycle will handle.

The fix is usually a split schedule rather than more full cleans. A daily or alternate-day wipe of door glass and push plates, done by the existing cleaning team in a few minutes, keeps the entrance looking cared for. The full facade clean then runs on its own longer cycle. Buildings with heavy visitor traffic, such as clinics, showrooms, recruitment offices or anything near a transport hub, often need that touch-up twice a day at peak times.

Interior partitions near corridors and printers deserve the same treatment. One smeared panel at eye height undoes the impression of an otherwise spotless floor.

Seasonal Conditions Change the Calendar

An annual plan that treats every month the same will always be wrong somewhere. In temperate climates the pattern is fairly predictable, and it is worth planning around it rather than reacting to it.

Spring brings pollen, which binds to glass and turns into a yellow-green film after rain. A visit in late April or early May usually does more for the look of a building than one in high summer.

Summer adds dust, insects and drying marks from short, heavy showers. South- and west-facing glass can also pick up a haze from sunscreen and skin oils where people lean against it.

Autumn is the hardest season for buildings near trees: sap, leaf litter and the first storms that splatter mud up to the second floor.

Winter brings road grit, salt spray and condensation. Cold glass with heavy internal moisture shows every smear, so interior cleaning in winter needs a drier, more careful technique rather than a quick wipe.

Many offices do best with a slightly denser schedule in spring and autumn and a lighter one in midsummer and midwinter, keeping the annual spend roughly level.

Interior Glass Runs on a Different Clock

Interior glass is judged at close range and in worse light, which is why it needs its own rhythm rather than being tacked onto the exterior visit.

Meeting room partitions, glass-fronted offices and dividers are touched constantly. A monthly clean of high-contact interior glass, with a quarterly deep clean of everything else, covers most offices. Buildings with hot-desking, shared kitchens or constant meeting use should lean towards the monthly end.

Two practical notes. First, interior glass is where cleaning and privacy meet: blinds, film and frosted panels need a method agreed in advance so nothing is scratched. Second, dust and condensation settle on frames, tracks and sills as much as on the panes, and buildings with trickle vents or openable windows collect far more in those places than you would expect. Include them in the interior scope, or the clean will look half-finished.

Signs Your Current Schedule Is Off

Rather than renegotiating a contract on instinct, watch for evidence. The schedule needs tightening if:

• Staff or visitors mention the windows before you do.
• Entrance doors show visible hand marks within a day of cleaning.
• Glass looks dull in low sun, which usually means a film rather than fresh dirt.
• Bird droppings or sap sit on the glass for more than a week.
• Frames and sills look soiled while the panes are clean.
• Interior partitions show fingerprints at eye height between visits.

Sometimes the schedule is fine and the problem sits elsewhere: patchy work, the wrong method in cold weather, or exterior cleans that skip the frames. Check the standard of work before adding visits.

Putting a Workable Schedule Together

Start with a written scope rather than a frequency. List every elevation, every internal glass area and every item that should be included: frames, sills, tracks, door glass, signage, canopies. Then set intervals against that list, tier by tier.

A sequence that works well in practice:

1. Walk the building with a clipboard and note the condition of each zone at the same time of day.
2. Set exterior intervals from location, and interior intervals from how the space is used.
3. Add extra visits in spring and autumn if trees, pollen or storms affect the site.
4. Keep a short daily touch-up routine for entrance glass between full visits.
5. Review after two or three cycles, in daylight, adjusting one zone at a time.

Where access is difficult, whether that means height, sloping ground, atriums or fragile facades, take professional advice on equipment and safe methods instead of stretching a standard pole-and-ladder job. The same applies to glass soiled with bird droppings or other biological matter, which is a hygiene task and should be handled with proper protective equipment.

A good schedule is dull in the best way: predictable visits, no surprises, and glass that never becomes a talking point. Get the frequency roughly right and the rest is simply maintenance.

Photo: 652234 / Pixabay