How to Clean Skylights, Inside and Out

If you want to know how to clean skylights, the answer splits in two. The inside pane you can do yourself with a pole and very little water. The outside pane is on your roof, and on anything steeper than a low pitch it is not worth doing yourself. Here is what makes skylight glass dirty, how to handle the half you can reach, and how to tell when the problem is not dirt at all.

Why skylights get dirty faster than your other windows

A wall window faces sideways, so rain runs down it and carries some of the dirt away. A skylight faces straight up. Everything that falls out of the sky lands on it and stays: pollen in May, cottonwood in June, maple seeds, oak leaf tannin in October, and the grit that washes off asphalt shingles every time it rains.

That shingle grit is the part most people miss. Every roof sheds a little of its granule surface, and on a skylight it collects along the bottom edge of the glass and down in the flashing, where it holds water against the frame.

The inside gets ordinary dust, plus more than its share of cooking grease and the film off vinyl and carpet, because warm air carries all of that up toward the ceiling. That is why the inside of a skylight usually looks worse than a window at eye level in the same room.

Cleaning the inside, and the shaft

Start dry. Lift the dust off with a dry microfiber cloth or a duster on an extension pole before anything gets wet. Skip it and you are smearing mud across the glass and dripping it on the floor.

Then use far less solution than you would think. Cool water with a couple of drops of dish soap in a spray bottle is plenty, and spray the cloth rather than the ceiling. Water running down the inside of a skylight shaft stains painted drywall, which is a worse problem than the dirt you started with. Wipe with one damp cloth, follow right behind it with a dry one, and do the edges last.

On a deep skylight the shaft itself is often what makes the room look dim. Those angled walls collect dust and the paint yellows, and wiping them down does more for the light than a perfect job on the glass. While you are up there, check the bottom corners of the inside frame for staining or soft drywall. That is water getting in, not dirt, and it needs a roofer. The habits that keep wall glass clear apply here too, and our guide to cleaning windows without streaks covers why less soap beats more.

When the haze is not dirt at all

Three things look like a dirty skylight and are not. Knowing which one you have saves you cleaning the same glass four times.

• A fogged unit. Most skylights are sealed double pane glass. When that seal fails, moisture gets between the panes and dries as a film no cleaner can reach. The unit gets replaced.
• Condensation. A skylight is often the coldest glass in the house, so it sweats first and worst. That is indoor humidity meeting cold glass, covered in why you get condensation on windows in winter.
• An old acrylic dome. The bubble style plastic skylights on flat roofs and additions yellow and craze after years of UV. That cloudiness is in the plastic itself. Cleaning does not touch it, and an abrasive pad makes it permanently worse.

The outside is roof work

Reaching the top of a skylight means getting above it, on a slope with your weight going the wrong direction and nothing flat to stand on. On a low pitch garage or porch roof that can be reasonable. On the main roof of a two story house it is not, and wet leaves on October shingles make it worse.

A water-fed pole reaches wall glass up to 40 feet from the ground, but a skylight lies back on the pitch, so there is no angle to reach the face of it from the yard. That is a real limitation worth saying plainly. If you can wash it from a ladder at the eave without stepping onto the roof, treat it like any exterior glass: wash, squeegee, dry the edges. If you cannot get at it that way, leave it. A clean skylight is not worth a fall.

Do the reachable half before the snow

Mid October is the window in the Twin Cities. The leaves are mostly down, a dry afternoon is still easy to find, and the sun is low enough now that a dirty skylight costs you real light. Once snow sits on the glass you are waiting until spring. Inside glass first, then the shaft walls, then the outside only if you can reach it safely.

Gleam Team cleans window glass inside and out, plus screens, gutters and siding. Exterior glass is done with purified water through a water-fed pole reaching up to 40 feet, so no ladder leans on your gutters, and the work is backed by our Gleam Guarantee. You can read about our window cleaning service or the areas we cover in St. Paul.

Request a free quote, or book a free 10-minute consultation, and we can sort out what is reachable and what is not.