How do you clean the outside of a roof window?

The barrel bolt, and the step nobody should skip

The bolt is not a convenience. Without it, a gust arriving up the slope can bring an inverted sash back round while you have your arms through the opening, and on an open roof window a gust arrives with the whole slope funnelling it. On the exposed elevations in the Forest of Dean and on the tops of the wolds this is a genuine event rather than a theoretical one.

Check the bolt actually engages before you let go of the handle. On older units the keeper can be worn or painted over and the bolt sits proud without dropping in. If it does not engage cleanly, that is worth sorting before the next clean, and it is one of the things looked at during a yearly check.

Cleaning a top hung sash, which does not rotate

A top hung window hinges at the head and swings outwards, so there is no rotation and no barrel bolt on the standard hardware. Most top hung ranges are built with a secondary pivot that lets the sash be rotated for cleaning after a catch is released, and where that exists it works much like the centre-pivot method, though the arc is different and there is more sash outside the plane of the roof while you do it.

Where the unit is a plain top hung with no cleaning pivot, the outer glass is reached by opening the sash to its stop and working through the gap, which is fine on a shallow rear addition roof in a Gloucester terrace and is not fine three storeys up. On those, an external clean from a pole or a cradle is the honest answer. The differences between the two designs, and what each is good at, are on centre-pivot and top hung roof windows compared.

What to use on the glass, and what damages a coating

Warm water with a little washing-up liquid, a soft cloth or a microfibre pad, and a rubber squeegee finished with a dry cloth. That is the whole recipe, and it is deliberately dull because modern roof window glass carries coatings that are easy to spoil.

The things that do damage: any abrasive cream or scouring pad, which will scratch a self-cleaning or solar control outer surface permanently; solvents and strong alkaline cleaners, which attack the coating and the gasket rubber together; a pressure washer, which drives water past gaskets and under flashings and has no business anywhere near a roof window; and a blade or scraper, which removes a coating in one stroke. Hard water is worth a thought in this county too, so drying the pane rather than letting it air-dry avoids the mineral bloom that otherwise builds up.

The sash and frame want the same soap and water. A timber unit with a factory lacquer benefits from having the surface dry rather than left wet, and any bare or dulled timber is a sign the finish wants attention, which is dealt with at can a roof window be painted.

Self-cleaning coatings, and the rain they need

A self-cleaning outer pane carries a thin titanium dioxide coating that does two things. Daylight breaks down organic material sitting on the glass, and the surface is engineered so rain sheets across it rather than beading, carrying the loosened material off in one film instead of drying into spots.

It works, within limits. It needs daylight and it needs rain, so a sheltered north slope under a large tree gets less benefit than an open south slope. It does nothing about mineral deposits, sap, or the fine grit that arrives with a Severn Vale wind. And it does nothing at all on the inside face. What it does deliver is a long interval between cleans on a window nobody can reach, which is exactly where it earns its cost: above a stairwell, high on a steep Cinderford slope, or on a Cheltenham third floor. It is worth specifying at order rather than wishing for later.

The drainage channel and the gaskets, which do the real work

While the sash is inverted, look at the parts that are not glass. The outer frame carries a drainage channel that collects the small amount of water always driven past a gasket and returns it onto the covering below the cill. If that channel is packed with moss, needles or grit, water backs up and finds the next available route, which is inward. Clearing it takes a soft brush and two minutes.

The gaskets are the next thing. They should be soft, continuous and sitting proud in their groove all the way round. Wipe them with soapy water rather than solvent, and a light silicone treatment once a year keeps them supple. Perished, flattened or shrunken gaskets that let daylight through at the edge of a closed sash are telling you the unit is near the end of its service life, which is discussed at how long a roof window lasts.

The ventilation flap in the head has a filter behind it in most ranges. It pulls out, rinses under a tap and goes back damp. In a bathroom or a kitchen it clogs faster than anywhere else.

What actually lands on glass in this county

Different parts of Gloucestershire leave different things on a roof window, and knowing which yours collects sets the interval.

In the Stroud valleys and the wooded parts of the Forest of Dean, the deposits are organic: leaf fall, sap, and lichen creeping up from the covering onto the frame and the lower edge of the glass. Under a mature tree the north side of a slope can green over in a single wet winter. Across the Severn Vale, from Tewkesbury down through Gloucester, it is fine agricultural dust in dry spells and a grey film after a run of easterly weather. On the wolds it is a mix, plus far more direct sun, which bakes anything left on the pane onto it.

Lichen at the foot of the glass is worth removing while it is soft. It roots into the junction between the glass and the sash gasket and holds moisture there permanently. Soapy water and a soft brush lifts it; a scraper takes the coating with it.

Fixed units, high units and the glass you cannot reach

Some roof windows are simply not cleanable from inside, and the specification is where that gets solved.

A fixed unit has no sash to rotate, so its outer face is reached externally, from scaffold, a tower, or a pole and brush system with filtered water. A unit above a stairwell or a double-height space has the same problem even if it opens, because nobody can safely lean out over a drop while holding a squeegee. On both of those, a self-cleaning outer coating and an electric opener with a rain sensor are worth building into the order rather than adding later. That combination is covered at electric rooflight installation.

Water-fed pole systems reach three storeys comfortably and use purified water that dries without marking, which is what a local window cleaner will normally arrive with. Ladders leaned against a roof slope are a poor idea on a Stroud valley site where there is nowhere flat to foot them, and on Cotswold stone slate a ladder against the covering breaks slates.

How often, and the best time of year

Twice a year suits most houses: once in late spring after the winter grime and once in autumn once the leaf fall has finished. A shaded slope under trees wants three, and an open slope on an estate at Quedgeley may be happy with one.

Pick a dull, dry, still day. Direct sun dries the water before you can squeegee it and leaves streaks, and wind makes an inverted sash harder to control. Do the whole job in one pass while the sash is turned: glass, frame, gaskets, drainage channel, vent filter. It takes about twenty minutes per window and it is the single cheapest thing that keeps a unit performing. Anything you notice while you are there, a stiff hinge, a gasket that has gone hard, a mark on the reveal, is worth writing down. Severn Skylights Gloucester installs and replaces roof windows across the city and thirty miles by road, and the brand-by-brand cleaning positions and pane codes are on the VELUX window installation page.