How do you clean a roof lantern?

Twice a year suits most roof lanterns: once in late spring before the bright months, once in autumn to clear leaf fall and the summer’s film of pollen and dust. A lantern over a kitchen picks up a greasy haze faster than one over a hallway, so that one may want a third pass. If the glass has a self-cleaning coating, the rain does most of the work and you are mainly touching up the panes the weather cannot reach.

You do not need much. A bucket of warm water with a small squeeze of washing-up liquid, two microfibre cloths, a soft-bristled brush, a rubber-bladed squeegee and a telescopic pole to reach the outer slopes. Keep a separate dry cloth for the final buff. Avoid the supermarket glass sprays with added shine agents: they leave a residue that catches low sun and shows every smear on a south-facing pane.

The outside is where the dirt is, and it is also where people get hurt. A roof lantern sits on a flat or shallow roof, often one storey up, and wet glass and wet aluminium are both slippery. The safe method is to stay off the roof entirely: reach the panes with a soft brush and squeegee on an extending pole, working from a sound flat area or from a scaffold tower or platform hired for the day if the lantern is out of comfortable reach.

Wet each slope with the soapy water, brush gently from the ridge downwards to lift the grime, then pull the squeegee down in overlapping strokes, wiping the blade on a cloth between passes. Rinse with clean water so no soap dries on. Never put your weight on the glass to get at a far pane. The panes in a lantern are structural glazing, not a walking surface, and they are not designed to be stood on. If a slope genuinely cannot be reached from a safe position, that is a job for someone with the right access equipment rather than a reason to climb onto the roof covering.

The inside is easier and usually only needs doing when you can see it wants it. From a stepladder set on a firm floor, wipe each internal pane with a barely damp microfibre cloth, then buff dry with a second. Condensation over winter can leave a chalky tide mark near the bottom of each pane where moisture has run and dried; plain warm water shifts it, and a little white vinegar in the water helps if it is stubborn. Dry the rebate at the foot of each pane so water does not sit there.

The frame matters more than people expect. Wipe the internal bars and the ridge with the same soapy cloth, because dust and cobwebs gather along the top edges where nobody looks. If your lantern has trickle vents or an opening section, brush the dust out of the vent slots and wipe the gaskets so they keep sealing cleanly. On the outside, clear the drainage channels at the base of the frame with a soft brush: those channels carry rainwater off the glazing bars, and a plug of moss or leaf litter is what sends water backing up under the caps. Keeping them clear is ordinary maintenance and it is the single most useful thing you can do for the frame.

A few things do real harm, so it is worth being firm about them. No abrasive pads, no scouring cream, no wire wool, no blades: they scratch the surface and, on a coated pane, they take the coating with them. No pressure washer, however tempting on a mucky slope, because the jet drives water past the external seals and gaskets and can lift the sealant that keeps the glazing weathertight. No solvents, no acetone, no oven cleaner near the frame or the seals. And do not clean in full summer sun, when the water evaporates before you can squeegee it and dries into exactly the streaks you were trying to remove.

If you find a pane misting up on the inside of the sealed unit, between the two layers of glass rather than on the surface, no amount of cleaning will clear it. That is a failed unit, and the answer is to replace the glass, not to keep wiping it. Swapping a failed pane for a new sealed unit is a straightforward replacement, and it is the sensible moment to review the glass specification while the opening is accessible.

How you clean matters more on a coated pane, and coatings are common on lanterns round here for a reason. Southend faces south across the Thames Estuary, so a lantern over a rear extension collects sun from mid-morning until it swings west, and many carry a solar-control coating to hold down the summer heat and the glare off the water. That coating usually sits on an inner face where a cloth cannot touch it, but any self-cleaning or low-maintenance coating on the outer face is soft, and it wants plain water and a soft cloth only. Abrasives and shine-added sprays are what wear it down.

South-facing glass is also where dirt shows worst. Low morning and evening sun rakes straight across the panes and lights up every smear, every water spot and every strand of pollen, which is why a lantern that looked clean at noon can look filthy by six. Cleaning on a dull day and finishing with a dry buff is what gets you an even, glare-free pane. If the glare itself is the problem rather than the dirt, that is a glazing question, and our solar-control glazing work is about specifying the right glass in the first place.

For a routine clean, pick a cool overcast day, keep to soapy water and a squeegee on a pole, clear the drainage channels while you are up there, and stay off the glass. If the panes are out of safe reach, hire the access equipment rather than risk the roof. If a unit has misted internally or the frame is letting water in, the fix is new glazing rather than more cleaning: see our roof lantern installation page for how a replacement works, or request a quote and we will look at the whole lantern rather than just the pane in front of you.