How do you clean the outside of a roof window?

Rotating the sash and locking it in position

Open the window on its control bar, then keep turning. The sash will swing past the vertical and continue until the outer face is presented to you at roughly chest height. On the side of the frame there is a small bolt, usually a slide or a hook, which drops into a slot in the sash edge and holds it there. Engage it before you let go.

That bolt is not decorative. Without it the sash can rotate back under its own weight or in a gust, and it does so quickly and with the full mass of a glazing unit behind it. On some units the bolt is at the top of the frame rather than the side. Find yours before the first clean rather than during it.

Working from inside without standing on something silly

The whole point of the rotation is that you are stood on the floor with both feet down. If the window is mounted high enough that you cannot reach the glass with the sash rotated, use a proper step, not a chair, not the edge of a bath and not a bed. A rotated sash removes the barrier between you and a hole in the roof, and that is a fall hazard from an upper storey even though the opening looks small.

Keep children and pets out of the room while the sash is rotated. Close and latch the window as soon as you are finished rather than leaving it locked open while you fetch something.

What to use on the glass

Warm water and a drop of washing up liquid, applied with a soft cloth or a microfibre, then a clean squeegee or a second dry microfibre. Nothing more sophisticated is needed and most of what is sold as glass cleaner leaves a film that shows up badly on overhead glass in low sun.

Work top to bottom. Rinse the cloth often, because roof glass carries grit and a gritty cloth is how fine scratches appear. If there is bird mess or tree sap, soak it with warm water for a minute rather than scraping at it dry.

What ruins a coating, and what to keep away from

Many modern roof windows carry a self cleaning or easy clean coating on the outer face. It is a permanent surface treatment, and it is durable, but it can be worn off. Keep abrasive creams, scouring pads, wire wool, blades and solvent based cleaners away from it. Do not use anything sold for removing limescale, and do not let cement dust or brick acid from other work land on the glass.

A coated pane cleans best with plain water and no detergent, because detergent film is exactly what the coating is designed to shed. If you have a coating, try water alone first.

The frame, the sash edge and the gap between them

With the sash rotated you have access to two surfaces that never otherwise get looked at: the outer face of the sash frame and the top edge of the outer frame. That is where moss, needles and grit collect, and it is where the drainage channel runs. Wipe the channel clear with a damp cloth and check nothing is sitting in it.

A blocked drainage channel is one of the more common causes of a wet mark appearing at the head of the reveal, because water that gets past the outer gasket has nowhere to go. It takes thirty seconds to clear while the sash is already rotated.

Do not lubricate the gasket with oil or silicone spray. If it looks dry, leave it. Do put a drop of light oil on the hinge pivots if they have started to creak.

Top-hung units and the reach problem

A top-hung sash swings outward from the head and does not rotate, so the outer face never comes indoors. On a modest opening you can lean out and reach part of the pane, which is fine on a single storey rear roof and unwise on a second floor.

Practical options are a telescopic pole with a soft head worked from inside the opening, a window cleaner with a water fed pole from the ground, or scheduling the outside clean for whenever access equipment is on site for other reasons. Some manufacturers make a top-hung unit with a secondary pivot function specifically so it can be rotated for cleaning, which is worth specifying at the order if the window is high up.

Fixed units in a pitched roof

A fixed rooflight does not open at all, so the outer face is cleaned from the roof or from the ground. On a low single storey slope a water fed pole reaches it comfortably. On anything higher it is a job for somebody equipped for working at height.

Do not walk on the glass of a fixed rooflight unless it is specified as a walk-on unit, and do not lean a ladder against the frame. The frame is not designed to take a point load and the flashing certainly is not. There is more on unreachable glazing on cleaning a rooflight you cannot reach.

How often, and when the season matters

Twice a year suits most houses: once in late spring after the pollen and blossom have finished, once in autumn after the leaves have come down. Under trees, three times is better, because sap and leaf litter both hold moisture against the glass and the frame.

Do not clean roof glass in direct sun. The water dries before you can clear it and you get streaking that is worse than what you started with. An overcast day is the right day. Clean the inside face at the same visit while the sash is already rotated, and check the air filter in the ventilation flap while you are there. The wider maintenance rhythm is on cleaning and maintaining a rooflight.

We install and replace roof windows and rooflights across Oxford and up to twenty five miles by road. Fifteen years in the trade, a ten-year workmanship guarantee, and VELUX, Fakro, Keylite and Roto units fitted.