Cleaning Skylights Safely: Access, Sealant Risks, and Why Interior Fogging Is a Different Problem

The short answer: run three tests before you buy anything

Three questions settle almost every skylight complaint. First, does it wipe? Put a damp microfiber on a pole against the room-side glass. If the haze lifts, it is dust, cooking film, or hard-water spotting, and it is a cleaning job. Second, does it come and go? Fog that shows up on cold mornings, sits on the surface you can touch, and burns off by noon is indoor humidity condensing on cold glass. That is a ventilation problem. Third, is it locked between the panes? A milky bloom, drip tracks, or a mineral ring you can see from both sides but touch from neither means the insulated glass seal has failed. On a sealed unit only two of the four glass faces are reachable. The two inner faces were sealed at the factory and nothing you spray gets to them. Sort your problem into one of those three buckets before anyone leans a ladder on your house.

Getting to it is the dangerous part, not the washing

Treat a skylight as a hole in the roof, because that is what it is. OSHA rules it that way: construction work near an unguarded skylight triggers fall protection at six feet, and a protective screen has to hold 200 pounds applied at the center. A plastic dome holds nothing. People go through skylights every year, and dirty domes are hard to see when you are moving across a roof. Step on the curb, never the glazing. Stay off shingles below 40 degrees, when asphalt is brittle, and above roughly 90, when the mat scuffs and sheds granules. Treasure Valley summers put roof surfaces well past that most July afternoons, so exterior skylight work here happens between about 7 and 11 a.m. Anything above a 6/12 pitch is rope work. On a single-story ranch with a low slope, a water-fed pole from a stable ladder or the ground beats standing over the unit.

What actually cleans skylight glazing, and what quietly ruins it

Find out first whether you have glass or plastic. Curb-mounted units from the 1980s and 1990s are usually acrylic or polycarbonate domes, and ammonia, alcohol, acetone, and most blue window sprays craze them, meaning a web of fine surface cracks that never comes out. Abrasive pads and razor blades do the same in one pass. Plastic gets soft cloths, water, and nothing else. Glass units tolerate more, but skylights sit near horizontal, so whatever you leave on them dries in place instead of running off. That is why soap matters more here than on a vertical window: residue pools and streaks. We use pure deionized water with no soap for exactly that reason. It also handles the local problem, which is that Treasure Valley tap water runs roughly 8 to 15 grains per gallon of hardness. Rinse a skylight with a garden hose on a hot afternoon, let it flash dry, and you have added spotting, not removed it.

Sealant and flashing: where cleaning turns into a leak

A skylight does not stay dry because of caulk. It stays dry because of step flashing, counter-flashing, and a drainage path that carries water around and below the unit. A homeowner pressure washer runs 2,000 to 3,000 PSI at the tip, which is enough to lift the EPDM gasket at the glass edge, drive water uphill under flashing laps, and start a leak that shows up on the drywall three weeks later. We sell pressure washing at $0.20 per square foot and soft washing at $0.18, and we still do not put either wand on a skylight. Two more things to leave alone. Do not caulk the downslope edge, because that is the exit, and sealing it traps water inside the curb. Do not let anyone smear roofing tar over the flashing as a repair. Most skylights labeled leakers are actually pine needles and cottonwood packed on the upslope side, damming water into the head flashing. Clear the debris, do not seal over it.

Interior fogging is a sealed-unit failure, and it is not cleanable

When you see haze, drip trails, or a chalky mineral ring between the panes, the insulated glass unit has lost its perimeter seal. The desiccant in the spacer bar is saturated, the argon fill is gone, and moist air now cycles in and out with every temperature swing. Insulating value drops noticeably. Here is the part that costs us a job: this cannot be cleaned, by us or anyone, and we will not take your money to try. Defogging services that drill and vent the unit can improve clarity, but they do not restore the gas fill or the seal, and once minerals have etched the inner glass face, that damage is permanent. Real options are replacing the glass pack, usually $400 to $900, or the whole skylight with a new flashing kit, commonly $1,200 to $2,500 installed. Before paying, check the date stamp in the spacer or the glass corner. Many manufacturers carry a ten-year seal warranty.

Room-side fog, yellowed domes, and when to skip the service call

Condensation on the surface you can touch is humidity, not failure. At 70 degrees and 50 percent relative humidity, indoor air has a dew point near 50, and on a 10-degree Idaho night the inside face of even a good skylight drops below that. Skylights over showers and stoves fog first. Hold winter indoor humidity around 30 to 35 percent and run the bath fan 20 minutes past the shower, and most of it stops. Two honest limits. A 20-year-old acrylic dome that has gone yellow and cloudy from UV is spent, and washing it changes nothing. And if you have one reachable skylight, a pole, and a microfiber, clean it yourself. Tubular skylights full of dead insects are usually a twist-off diffuser lens and ten minutes, not a service call. Hire it out for second stories, steep or multiple units, or exterior faces only reachable from the roof. Reflekt window cleaning starts at $199 by pane count.