How to Reseal a Skylight: Guide for Leak Prevention

Is the trim around your skylight starting to look ragged? Maybe during a heavy storm you catch the occasional drip, or you spot browning stains creeping across the ceiling. Once the original seal starts to give way, knowing how to reseal a skylight properly can spare you from expensive repairs and keep water from rotting wood and drywall.

But stopping leaks is only half the story; a tight seal also protects your home's frame against drafts and heat loss, ensuring those beautiful daylighting units remain the efficiency boosters they were meant to be. Making that extra effort today can protect both your structure and your utility bills.

Understanding Why Skylights May Need Resealing

The lifespan of roof sealant typically ranges from 5 to 20 years, but this can vary significantly based on factors like the type of sealant, the quality of application and the climate conditions.

Because skylights sit on the roof, they endure more punishment than almost any other feature of your home. Endless sun, rain, snow and hard freezes hammer the seals day after day, and over many years even high-quality materials start to break down. Ultraviolet rays can dry out low-quality sealants, while constant expansion and contraction may loosen joints.

Once you know the warning signs, spotting trouble early is fairly easy. Brown or damp stains on the ceiling near the frame show that water is sneaking through. Likewise, peeling, cracking or missing sealant around the edges gives you a clear signal that a repair is overdue.

Sealing challenges can differ depending on the skylight style. Flat skylights sit nearly leveled with the roof, so wind-driven rain and blown debris pool in the corners faster than on angled models. Framed units also add complexity because the glazing edge, frame joint and roof connection each need a reliable bead of sealant.

Frameless designs look sleek, yet they lack a protective lip, meaning the edge seal itself must be carefully maintained to block wind-driven water. With Rooflights & Skylights, you may rest assured: this issue is covered.

Essential Tools and Materials

Before starting the job, gather the correct gear so the repair looks professional and lasts as it should. You need a premium, exterior-grade sealant designed for roof work; silicone works for nearly every skylight, but polyurethane performs better in severe cold and heat.

A sharp utility blade slices through old beads and protects glass and metal from nicks. Wire brushes, stiff scrapers and clean rags clear dust, grime and loose debris before the new sealant goes on.

Safety gear is non-negotiable whenever you're working on a roof. A sturdy ladder, non-slip shoes and a safety harness reduce the odds of a fall. Gloves protect against sharp edges and caustic chemicals, while goggles prevent grit from getting into your eyes.

Before you begin, grab a tape measure, a bubble level and quality gloves. These basics will save you headaches later. For applying sealant, a caulking gun gives you steady control, though most newer formulas now come in handy tubes that work well for smaller projects.

Preparing the Skylight for Resealing

How well you prepare determines whether your new seal lasts. Clean the skylight and the area around it, clearing away dirt, leaves or moss that has collected over time. Make sure drainage channels and weep holes stay open so water can run off instead of pooling.

Remove every bit of old sealant before applying the new bead. Fresh material adheres poorly to old caulk, leaving weak spots where leaks may develop. Cut away the bulk with a utility knife, then scrub off the residue using a solvent or plastic scraper.

Check the frame and roof around the skylight for rotting wood, rust or cracks. Minor splits can be filled, but serious damage usually requires a professional or replacement of the frame itself.

Sealant performs best in mild, dry conditions, so choose a day with good weather and check the forecast. Most products need several hours of calm weather to cure properly, so always read the weather forecast before you begin.

Step-by-Step Resealing Process

Begin the resealing work at the top edge of the skylight and move downward, following the path water naturally takes. By doing this, each new seal overlaps the one below, forming an uninterrupted barrier against leaks.

First, apply a bead of sealant where the skylight frame meets the roof. The bead should fill every gap and remain smooth, so water and debris don't collect in pockets.

With framed skylights, pay special attention to the corner joints where the frame sections meet; these seams often leak first.

How you apply sealant can make or break the job. Maintain even pressure on the gun trigger so the bead stays the same width. Move the gun at a steady pace to avoid bulges or dips that could eventually crack.

Wet your fingertip or use a smoothing tool to press the bead into a shallow curve that directs water away. On kitchen skylights or other visible units, work slowly and clean up the edges for straight, professional-looking lines.

Let each section cure somewhat before working on the next to prevent fresh sealant from disturbing what you've already applied. Though most sealants form a skin in about half an hour, they may take several hours to cure completely through their full depth.

Sealing Different Skylight Types – The Importance of Having a Proper Upstande

Each skylight style has its own specific requirements during sealing. An angled upstand (from 2 to 5 degrees) is crucial for flat skylight installations to ensure proper water drainage, prevent leaks and maintain the integrity of the roof and skylight. By elevating the skylight above the roofline and creating a slope, the upstand allows rainwater to run off naturally, avoiding pooling and potential water damage.

If the upstand angle is flat, water collects along the edges of flat skylights rather than draining away, so you need to pay extra attention to the perimeter. In this case, you need to form a slight slope in the sealant that encourages water to run away from the frame; otherwise, pooling will occur.

Frameless skylights present a different challenge; they can never be installed without an upstand (2 to 4 degrees angle). Here the edge bead is critical, so apply it carefully and plan for routine inspections in the months ahead.

In kitchens or other humid areas, select a sealant that actively resists mold and mildew growth. Frequent temperature swings from cooking can stretch and compress the seal, testing its bond and durability.

When sealing opening skylights, ensure that the bead doesn't block the hinge or sliding rail while still blocking wind and water. These two goals can conflict, so test the operation several times while the compound remains workable.

Once you finish resealing and allow the sealant to cure fully, perform a quick test before calling the job complete. The most reliable proof of a solid seal is a controlled water test that saves you from waiting for the next storm.

Use a garden hose and spray around the skylight's edge, starting with a fine mist and gradually increasing flow and pressure. Have a partner inside watching for drips while you work on the roof.

Watch not only for obvious drops but also for subtle clues, a damp patch on drywall or a cool spot that suggests water is hiding behind the seal.

If problems appear, mark them and address them immediately while the weather is still dry. Small voids often disappear with another bead of sealant.

You don't want to deal with expensive resealing projects down the road, so a little regular maintenance goes a long way. Make it a habit to check your skylights twice a year (spring and fall work well) and always take a look after any major storms roll through. You're watching for things like cracked edges, water stains or those telltale moisture trails that shouldn't be there.

Here's something many people overlook: keep that glass and frame area clean. Dust, leaves and random debris love to pile up there, and when they do, they create perfect little water traps right against your seals. While you're at it, grab some pruning shears and trim back any branches or plants hanging over your skylight. They'll just keep dropping stuff on it and potentially scratch up the surface.

Don't forget to pencil resealing into your home maintenance calendar. Most quality sealants will give you anywhere from five to ten years, but Mother Nature doesn't always play fair. If you live somewhere with brutal winters, scorching summers, or wild temperature swings, you might need to reseal sooner than expected.

Look, plenty of DIY-savvy homeowners can handle basic resealing without breaking a sweat. But there are times when you want to step back and let the experts handle things. If you notice any shifting or sagging around the roof deck, frame or flashing, that's professional territory. They've got the training and tools to tackle structural issues safely.

Other red flags that scream "call a pro"? Visible cracks in the frame, deck sheathing that feels soft or spongy, or fasteners that are starting to rust. And honestly, if you're dealing with a large skylight installation or your roof has steep angles and complicated flashing, you'll probably save yourself time, money and potential headaches by hiring someone who does this for a living.

Conclusion

When you know how to properly reseal your skylight, you're protecting everything underneath (your walls, ceilings and all the stuff you care about) from water damage. Plus, you get to keep enjoying that gorgeous natural light that drew you to skylights in the first place. Stick with quality materials, take your time with the work and stay on top of maintenance: this way you ensure your skylights will keep doing their job beautifully for years to come.

At Rooflights and Skylights UK, we've seen firsthand how proper sealing makes all the difference in skylight performance over the long haul. Our team knows which materials work best for different situations and can walk you through the techniques that'll work for your specific setup. Give us a shout today and we'll help make sure your skylights stay bone dry and continue brightening up your home for years to come.