Do Skylights Leak? Causes & How Good Installation Prevents It in Cheltenham

Skylights have a reputation for leaking, but a correctly installed modern skylight should not leak. The vast majority of leaks come down to poor installation, a failed kerb or worn-out weatherproofing — not the skylight itself. Get the installation right, and a rooflight stays watertight for decades.

This is a knowledge guide. We install and replace skylights rather than repair them, so where an old or badly fitted unit is leaking, our answer is a properly installed replacement that solves the problem permanently rather than a temporary patch.

Why leaks show up in a Gloucestershire winter

If a skylight is going to leak, a Cheltenham winter is when you will discover it. Our wettest months bring weeks of persistent, driving rain rather than the occasional summer shower, and it is that sustained soaking — often combined with wind pushing water sideways against the upstand — that exposes a marginal installation. A kerb that is fractionally too low, flashing that was rushed when the extension was built, or a perished seal on a fifteen-year-old unit may sail through a dry summer and then weep steadily through January and February. This is why we get so many calls about leaking rooflights in the depths of winter: the weather is simply doing the testing that the original installation should have withstood.

The homes most often affected are the rear extensions added across Cheltenham and the surrounding villages during the building booms of the 1990s and 2000s, where rooflights were sometimes fitted quickly on inadequate kerbs. Those units are now both old enough for their seals to be failing and were frequently never weatherproofed to a standard that copes with a Gloucestershire winter. The good news is that none of it is inevitable — a correctly installed modern rooflight on a sound kerb simply does not behave this way.

Why skylights get a bad reputation

The myth that “all skylights leak” comes from the days of cheaper units and less careful fitting, where a poorly detailed opening would inevitably let water in. Modern rooflights, fitted correctly with the right kerb and flashing, are a different proposition. When a skylight leaks today, it is almost always a sign that something about the installation or the unit’s age is at fault — not an inevitability.

The real causes of skylight leaks

Poor flashing

Flashing is the weatherproof junction between the skylight and the roof covering. If it is badly fitted, the wrong type for the roof, or has lifted over time, water finds its way in. Correct flashing, matched to the roof and detailed properly, is the single most important defence against leaks.

A poorly formed or low kerb

A flat-roof skylight must sit on a raised kerb so water drains away rather than pooling against the glass. A kerb that is too low, badly built or wrongly sized invites water in. A sound, correctly sized upstand keeps the rooflight clear of standing water.

Failed seals on an old unit

Over time, gaskets and seals perish. On an older skylight, a perished seal can let water past. This is one reason an ageing unit is better replaced than patched — the seals throughout are reaching the end of their life.

Condensation mistaken for a leak

Sometimes water around a skylight is not a leak at all but condensation forming on a cold, poorly insulated unit. It looks like a leak but the fix is different. Our skylight condensation guide explains how to tell them apart.

Roof problems around the skylight

Occasionally the skylight is blamed for water that is actually entering through nearby damaged roof covering. A survey identifies the true source.

How good installation prevents leaks

A leak-free skylight comes down to getting the fundamentals right, and that is exactly where careful installation earns its keep:

• A sound, correctly sized kerb that lifts the glass clear of water on a flat roof.
• The right flashing for the roof — different kits for tile, slate, felt, EPDM, GRP or single-ply — detailed precisely.
• A tight, gap-free seal around the frame.
• A quality modern unit with sound seals and glazing.

When these come together, a skylight simply does its job and stays dry. Our flat-roof skylight installation and pitched-roof skylight installation pages explain how we detail each.

If your skylight is already leaking

An existing leak usually means the original installation, the kerb or an ageing unit is at fault. Rather than chase a temporary repair that may not hold, the lasting solution is a correctly installed replacement: a modern unit fitted on a sound kerb with the right flashing, so the problem does not come back. See our skylight replacement service for how we approach it.

Different roofs, different defences

How a leak is prevented depends a great deal on the roof, and Cheltenham’s housing stock spans the full range. On the flat-roof rear extensions that dominate the town’s kitchens, the kerb height and the way the flashing marries into the felt, EPDM or GRP covering are everything — our flat-roof skylight installation page covers that detail. On the pitched slate and stone roofs of the older Cotswold houses and the loft conversions across Gloucestershire, the right flashing kit for the roof covering is what sheds the water cleanly down the slope, and our pitched-roof skylight installation page explains how we detail those. In every case the principle is the same: water must be guided off and away from the joints, never given the chance to pool or track inward. Get that right at survey and installation, and a Gloucestershire winter holds no fear for the rooflight.

Our honest take

Skylights do not have to leak, and a well-installed modern one will not. Leaks are a symptom of poor fitting, a failed kerb or an old, tired unit — all of which a proper replacement and correct installation solve for good. If your rooflight is letting water in, a free survey lets us find the real cause and recommend a watertight, lasting fix.

Get a quote and we will assess your skylight and give you a fixed written quote for a watertight replacement after a free survey, backed by our written guarantee on our workmanship.