How do you clean a roof lantern?

Outside

A pitched lantern sheds most dirt with rain, which is one of its advantages over a flat rooflight. What it does not shed is bird mess, tree sap and leaf staining.

On a single storey extension, a water fed pole from the ground reaches most domestic lanterns and is what a window cleaner will use. Twice a year is plenty for most, more under trees.

Do not walk on it. A lantern is not a walk-on unit and the panes are not rated for it.

Self cleaning glass

Worth having on a lantern that is hard to reach, within limits. The coating breaks down organic dirt in daylight and lets rain sheet it away rather than beading. It needs rain and a fall to work, so it does more on a 25 degree lantern than on a shallow one.

It reduces how often you clean rather than removing the need. It does nothing for bird mess.

Inside

The awkward one. Dust settles on the inner face of sloped glass and it is above reach. Cooking in a kitchen adds a fine greasy film that dust sticks to.

An extendable microfibre pole and a light glass cleaner is the practical answer, once or twice a year. Do not soak it: water running down the inside of the glass to the frame is not helpful.

Frames

Powder coated aluminium needs nothing but a wash. Do not use abrasives or solvents; they damage the coating, and on the coast a damaged coating is where chalking starts.

Rain does most of the outside

That is the quiet advantage of a lantern over a flat rooflight. The pitch, typically 15 to 25 degrees, means water sheds rather than sitting and evaporating, and it carries dirt with it.

A flat pane holds a film after rain, the water evaporates, and everything it was carrying stays on the glass. A lantern largely cleans itself.

The outside, when it needs it

Warm water, a mild detergent and a soft brush, rinsed off. Not abrasives, not solvents, and not a pressure washer at close range, which drives water into the perimeter seal and can damage coatings.

Access is the practical question. On a single storey extension roof it is a tower job and straightforward. On a lantern over a double height space it means a pole system with a soft head, ideally water fed.

Self cleaning glass is worth specifying at order stage on a lantern, because unlike on a near flat unit the pitch lets it work properly: the coating breaks down organic deposits and rain sheets off carrying them away.

The inside

Ordinary glass cleaner and a soft cloth, and the same access question. On a lantern above reach a pole with a soft head is the answer, not a ladder leaned against glazing.

Where the lantern has an opening vent, that panel can usually be reached more easily and it is worth cleaning the gasket at the same time.

The internal drainage channels

The part people do not know about. A well made lantern drains any water that gets past an outer gasket into channels within the glazing bars, which carry it out at the eaves.

Those channels collect dust and debris over years. Where they block, water backs up and appears inside, and it gets reported as a leak when it is a maintenance matter. Clearing them is part of a proper lantern service.

Around the outside

Keep the roof around the kerb clear. Leaves and silt collect against an upstand and there is nowhere for them to go on their own, and standing water against a seal is what kills an installation early.

Check the outlet the roof drains to at the same time.

How often

Outside, once or twice a year on an open site and more under trees. Inside, when it looks like it needs it. The drainage channels every few years, and the roof perimeter twice a year where there are trees nearby.

The order that avoids streaks

Glass first, from the ridge down, so dirty water runs onto glass you have not cleaned yet rather than over a finished pane. Frame last, because frame cleaning dislodges dirt onto the glass.

Warm water with a little washing up liquid, a soft brush or a microfibre head on a pole, then rinse with clean water and let it dry rather than wiping it. On a lantern, wiping is what leaves marks, because the pitch means the cloth is always working against gravity.

What not to use

No abrasive pads, which haze the glass permanently.

No pressure washer close to the joints. The seals between panes and frame are designed to shed rain, not to resist a jet at close range, and forcing water into a joint is how a sound lantern starts leaking.

No solvent based cleaner on the frame. Powder coating tolerates soap and water indefinitely and does not tolerate aggressive chemicals.

And nothing at all on the internal face of the glass if the unit has an internal coating, beyond water and a soft cloth.

What a self cleaning coating changes

Worth specifying on a lantern, because it genuinely reduces how often this is necessary. The coating breaks down organic deposits and lets rain sheet off rather than bead, carrying the residue with it.

It works better on a steeper lantern than a shallow one, because it needs rain to run off. And it does not eliminate cleaning, it extends the interval.