Roof Windows – Sealing and Condensation. Complete Guide
Velux, Fakro, Roto and Dakea roof windows have specific problems not found in vertical windows. This guide explains the three condensation types, the critical difference between the window seal and the flashing collar, and which repairs are DIY-possible versus requiring a roof technician.
Velux, Fakro, Roto and Dakea roof windows have specific problems not found in vertical windows. Condensation, leaks and mechanisms work differently here. This guide explains the three condensation types, the critical distinction between the window gasket and the flashing collar, and which repairs are DIY-possible versus requiring a specialist.
Three Types of Condensation on Roof Windows
External condensation (morning dew on the outer pane): a sign of excellent thermal insulation — the outer pane is so well isolated from indoor warmth that it cools below the dew point on clear nights. Disappears with sunrise. No action needed. Internal condensation (on the room-side pane, wipes off): indicates high indoor humidity in the loft room. Improve ventilation; consider a hygro-sensitive trickle vent. See our article on window condensation causes and solutions for full detail. Between-pane condensation (inside the sealed glass unit, cannot be wiped): the unit seal has failed — moisture has entered the airspace. The only fix is glass unit replacement. Cost from 250 PLN for a small double-glazed unit, 600–900 PLN for a large triple-glazed unit.
Window Gasket vs Flashing Collar – The Critical Distinction
The most common diagnostic error with roof windows is confusing two different sealing systems. The window gasket (EPDM perimeter seal) seals the gap between the sash and the frame — it prevents draughts and rain from entering when the window is open or when the seal is compressed against the closed sash. The flashing collar (Velux: EDZ/EDP/EKP; Fakro: EFA/EFW) is the metal sheet-metal system around the window in the roof plane — it seals the joint between the window frame and the roof covering (tiles, metal sheet, felt). Rain coming in around the window frame on the roof side is almost always a flashing problem, not a window gasket problem. Flashing repair requires going onto the roof and specialist knowledge of roofing work.
Common Faults and Repair Costs
Handle mechanism failure (won't open or lock): handle replacement 80–150 PLN. Note: roof window handles are model-specific — a Velux handle does not fit a Fakro. Window won't stay open (drops under its own weight): usually a worn or broken balance spring. Replacement: 100–180 PLN. Condensation gutter blocked: the built-in condensation gutter in the bottom frame section drains internal condensation outside through a drainage hole. If blocked, water drips into the room — clean the gutter and drainage hole. Glass unit fogged: replacement 250–900 PLN depending on format and specification.
DIY vs Call a Technician
DIY-appropriate: compression adjustment with Allen key (if the manual allows), cleaning the condensation gutter, lubricating hardware with silicone spray, EPDM seal replacement (for experienced DIYers). Requires a specialist: glass unit replacement, handle mechanism repair, balance spring replacement, any work on the flashing collar (requires roof access), diagnosis when the cause is unclear.
Got a Velux, Fakro, Roto or Dakea roof window with condensation, a leak or a mechanism fault? Naprawa Okna 24 specialises in roof window repair and service — free on-site assessment including flashing and seal evaluation. Don't risk going on the roof yourself — contact us to book a service visit. Book roof window repair – contact and quote.
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Yes, the initial diagnostics and our technician's visit to assess the work are completely free. No hidden costs and no obligations. If you decide to proceed with the service, the technician will provide a clear quote on site, explain all the details, and if needed – can start work immediately and complete the repair during the same visit.
Absolutely! We provide a warranty for both the services performed and the materials used – in accordance with applicable regulations.
We cover all of Poland, with a particular focus on major metropolitan areas: Warsaw and surroundings, Kraków and Małopolska, Łódź area, Poznań and surroundings, Katowice and all of Silesia (Sosnowiec, Gliwice, Chorzów, Bytom, Zabrze, Tychy and 30+ cities). Call us – we'll call back within 15 minutes to arrange a visit.
The price depends on the type of window, the nature of the issue, and the materials needed. Upon arrival, the technician will provide an exact quote on site with no hidden fees, and you decide whether you want to proceed with the work.
Booking a free diagnostics is very simple. Just call our contact number or fill in the registration form – either way it only takes a few minutes.
In most cases, repair is sufficient: replacing seals or hardware, sealing, adjustment, cleaning and lubricating the mechanisms. This is a much cheaper solution than installing new windows.
Repair is cheaper because you don't need to buy a new window, remove the old one, dispose of it, or carry out finishing work after installing a new unit. Repair saves both time and money, being a significantly more cost-effective solution.
We service windows from all major manufacturers, including: Rehau, Veka, KBE, Schuco, Salamander, Aluplast and many others. Our technicians undergo training on the specific mechanisms of each manufacturer.
Yes, we accept all major payment cards, bank transfers and cash. Payment is made after the work is completed.
Yes, we provide services all year round. During winter, we carry out window servicing using special methods to avoid cooling down the rooms and ensure maximum comfort.
Balcony door adjustment for PVC or aluminium doors starts from 80 zł. It includes precise 3D adjustment of hinges and fittings, eliminating sagging, draughts and closing issues. Free on-site diagnostics – the technician will quote on arrival.
Yes. We specialise in sliding and HST terrace door service for all major systems: Schüco ASS 70/77, Aluprof MB-77 HS, Aliplast Imperial. We replace load rollers, repair tracks, adjust closing pressure and service drive mechanisms. From 150 zł.
A window ventilator (trickle vent) is a ventilation device fitted in or above a window frame, providing a constant supply of fresh air without opening the window. Since 2021 (Polish building regulations WT 2021), ventilators are mandatory in new buildings. We install pressure-controlled, humidity-sensitive and acoustic ventilators – from 80 zł each.
After your enquiry we call back within 15 minutes and agree a time. In most cities (Warsaw, Katowice, Łódź, Poznań, Kraków) a technician arrives the same or next working day. For urgent cases such as a fallen hinge or jammed door, we aim to arrive within a few hours.