Leaking Velux Window Causes and Repairs for Irish Homes

Why a Leaking Velux Window Lets Water In

A leaking Velux window is usually caused by a failed or poorly fitted flashing kit, debris blocking the water channels, worn seals on the sash, a cracked or failed glazing unit, or condensation that only looks like a leak. On homes in Longford and across Ireland, most of these faults can be repaired without replacing the whole roof window.

Below we explain how each fault shows itself, how to tell a leak from condensation, what you can safely check from inside and how our Velux window repairs and replacement service deals with each problem.

Common Causes of a Leaking Velux Window

When we are called out to a leaking Velux window, the cause is almost always one of the following. Often there is more than one fault at the same time, which is why a proper inspection matters before any work starts.

• Failed or damaged flashing. Storm winds can lift the flashing, a slipped slate above the window can push water over it, and old flashing can corrode or split at the corners. Water then runs straight down the side of the frame.
• Wrong flashing for the roof. A tile flashing kit used on a slate roof, or the reverse, leaves gaps that rain is driven into during heavy weather.
• Blocked water channels. Leaves, moss and grit collect in the gutter at the top of the window and in the side channels. Water backs up and finds its way over the upstand and inside.
• Worn sash seals. The rubber gaskets around the opening sash harden and shrink with age. Rain then gets in around the edge of the glass when it is driven by the wind.
• Failed glazing unit. A cracked pane or a blown seal on the double-glazed unit lets water and moisture into the unit and around the glazing bars.
• Poor installation. A missing underfelt collar, a window set too low in the roof, or a window fitted to a roof pitch below what the manufacturer allows will all leak sooner or later.
• Damage around the window. Cracked slates or tiles, rotten battens or a torn membrane next to the window can make it look as though the window is leaking when the fault is in the roof itself.

Leaks around roof windows tend to appear in autumn and winter in Ireland. November brings the first heavy, wind-driven rain after leaves have fallen and filled the channels, so this is when many homeowners first notice a damp patch on the ceiling or the window reveal.

Telling a Leak Apart From Condensation

Not every wet roof window is leaking. Rooms in attic conversions and bathrooms produce a lot of moisture, and warm, damp air condenses on the coldest surface in the room, which is often the glass. That water then runs down onto the lower frame and the plaster below, and it looks very like a leak.

There are a few signs that point one way or the other:

• Condensation appears on cold mornings and in rooms where people shower, cook or dry clothes, whether it has rained or not.
• Condensation forms evenly across the inside of the glass, while a leak usually shows at one corner or along one side of the frame.
• A real leak gets worse during or straight after heavy, wind-driven rain, and the damp patch often spreads above or beside the window, not only below it.
• Moisture or misting between the two panes of glass means the sealed unit has failed and needs replacing.

If condensation is the problem, keeping the ventilation flap open, using an extractor fan in the bathroom and leaving a gap at the bottom of blinds so air can reach the glass will usually help. If the water is coming from outside, the window or the roof around it needs repairing.

What You Can Check From Inside

Working on a roof is dangerous and roof windows sit on steep slopes, so we never advise homeowners to climb out onto the roof. There are still some useful checks you can make from inside the house before you call a roofer.

1. Note when the water appears. Write down whether it is during rain, after strong wind, or on cold dry mornings.
2. Look at where it appears. Check the corners of the window, the head of the frame, the lining boards and the ceiling above and to the sides.
3. Close the sash fully and make sure the handle is locked. A window left slightly open on a night of heavy rain is a surprisingly common cause.
4. Look at the glass. Misting between the panes or a visible crack means the glazing unit has failed.
5. If you can safely reach the attic space beside the window, look for damp timber, stained membrane or wet insulation around the frame.
6. Photograph what you find. Photos taken during and after rain help us trace the source quickly on our visit.

In the meantime, put a towel or container below the drip and move anything valuable away from the area. Do not seal the inside of the frame with silicone, as it traps water inside the window and can make the damage worse.

How We Carry Out a Velux Window Repair

Every repair starts with an inspection from the roof. We check the flashing, the channels, the slates or tiles around the window, the sash seals and the glazing, and where possible we look at the collar and membrane from inside the roof space. Once the cause is clear, we explain what we found and what the repair involves.

Flashing repairs and replacement

If the flashing has lifted or been damaged, we refit or replace it with the correct kit for your slates or tiles. Where the wrong kit was fitted in the first place, we remove it and fit the matching type. We also replace any cracked or slipped slates and tiles around the window so water is guided onto the flashing as it should be.

Clearing and resealing

Where blocked channels are the problem, we clear the debris from the top gutter and side channels and check that water runs freely. Worn sash gaskets can be replaced so the opening part of the window seals tightly against the frame again.

Glazing and full window replacement

A cracked pane or a failed sealed unit can often be replaced on its own. If the frame is rotten, the window was fitted to the wrong pitch, or the collar and membrane around it are missing or badly damaged, replacing the whole roof window is usually the more reliable long-term fix. Damp around the window can also be a sign of a wider problem in the roof, and our roof repair service covers slates, tiles, flashing and leaks across the rest of the roof.

What Affects the Cost of Repairing a Roof Window

We price each job after we have seen the roof, because the cost depends on what has actually failed. The main things that affect the price are:

• Whether the fault is a simple clear-out and reseal, a flashing repair, a glazing replacement or a full window replacement.
• The roof covering around the window, and whether slates, tiles, battens or membrane also need replacing.
• Access, including the height of the roof, the pitch and whether scaffolding or other access equipment is needed.
• The size and type of the window and the availability of matching parts for older models.
• Any internal damage to timbers, insulation or plaster that needs attention once the roof is watertight.

Dealing with a leak early almost always keeps the cost down. Water that runs into the roof space for months can rot battens and rafters and soak insulation, which turns a straightforward window repair into a much larger job. We explain this in more detail in our article on why a small roof leak should be repaired straight away.

Getting a Leaking Velux Window Sorted

A leaking Velux window is usually down to the flashing, blocked channels, worn seals or failed glazing, and most of these faults can be put right with a targeted repair once the true cause has been found. We repair and replace roof windows for homes in Longford and across Ireland, and the sooner a leak is looked at, the less damage it does to the roof and the rooms below.

If you have a damp patch around a roof window or water coming in during heavy rain, contact Patrick Hannifin Roofing to arrange an inspection. You can call us on 085 754 7244 or email patrickhannifinroofing@gmail.com and we will get back to you as soon as possible.