In the vast majority of cases, a leak in a Velux roof window is not caused by a broken roof tile, but by worn foam strips in the ventilation flap. The solution is to have those strips professionally replaced, as long as the wood of your roof window is still sound. If you notice black granules on your windowsill, drafts at the seal, or damp spots around the window, this is almost certainly the cause, and a repair can still be done quickly and cheaply. If you wait longer, only a new roof window can resolve the problem. In the rest of this blog, you will read exactly how it works, what you can look for yourself, and when you need to take action.
Why the sponges in your skylight deteriorate
Every Velux roof window has a ventilation strip and a filter strip made of foam rubber. These ensure that your window seals against the frame in a wind- and watertight manner, even when you leave it slightly ajar to ventilate. After 10 to 15 years, this material wears out due to UV radiation, large temperature fluctuations, and condensation. You often see it before you see the water: small black granules on your windowsill or floor, as if pepper has been sprinkled. That is not dirt; that is your seal slowly crumbling.
Three ways the water comes in
As soon as the seal no longer fits properly, three problems arise simultaneously. During strong winds and driving rain, the water is no longer held back and seeps down the inside of the frame into your room. At the same time, warm indoor air condenses on the cold metal of the flap, causing extra condensation and keeping the wood around your window damp. That moisture penetrates deep into the frame and eventually causes mold and wood rot. The pulverized foam itself is also a problem. Those granules clog the side gutters where your skylight normally discharges its water. Once the water seeks another path, it often comes down meters away through your ceiling.
And what if it's not the strips?
Sometimes you don't see any black granules and the window still closes properly, yet you have a Velux roof window leak. In that case, there are a few other causes we regularly encounter. The lead flashing and guttering around the window can crack or come loose, allowing water to get under the roofing. A clogged drain caused by leaves or moss also causes water to flow in the wrong direction. In some cases, there is no actual leak at all, but rather condensation due to insufficient ventilation in the room. You can recognize the latter by water droplets on the glass and frame in cold weather, while the outside of your roof remains dry. Whatever the cause, a professional inspection will show where the water is coming from within half an hour.
When strip replacement is no longer enough
If you catch it in time, a Velux roof window leak can often be fixed with just a few hours of work. A roofer replaces the sealing strips and clears the drainage. If you have ignored the signs for years, the moisture has already penetrated the wood. If you see brown or black discoloration in the frame, or if the wood feels soft, a repair is usually no longer possible and the entire roof window must be replaced. The difference in costs between these two scenarios adds up significantly, so intervening early saves you a lot of money.
Need help with a Velux roof window leak?
Can't figure it out yourself, or are you unsure if your skylights are still sealing properly? We at VdH Dakonderhoud will come by for a inspection and tell you honestly whether strip replacement is sufficient or if more needs to be done. Feel free to call us with your question or request a quote.. That way, you'll know what to expect again before the next rain shower.
