Velux & Roof Window Installation

Roof window basics: Velux, Fakro and Keylite

Three manufacturers dominate the UK roof window market, and we fit all three. Velux (Danish, by far the largest) is the name people know — excellent build quality, widest spare parts availability, highest price, and the one we default to unless you ask otherwise. Fakro (Polish) offers very similar quality at roughly 15–25% lower cost, with excellent pivot and top-hung options. Keylite (Northern Irish) is the most affordable of the three, with integrated thermal collars as standard, good enough quality for most domestic installations.

The two common window types are centre-pivot (the frame pivots around a central horizontal axis, so the window rotates through 180° for cleaning — this is the classic Velux you picture) and top-hung (hinged at the top, opens outward like a conventional casement — better for head height and view, more expensive, good for loft conversions where you want to stand at the window). For loft bedrooms we usually spec top-hung windows at least 1200mm tall, for compliance with Building Regulations means of escape.

Fitting a new roof window

Fitting a brand-new roof window into an existing roof is a 1–2 day job that breaks down into: scaffold erection for roof access (half a day); carefully cutting back the tiles and membrane to the required opening size; cutting the rafters and installing trimmer rafters and load-bearing noggins to take the load around the new opening (this is structural work — the trimmers must be correctly sized, doubled, and bolted); installing the new window frame into the opening, seated on a layer of EPDM vapour tape; fitting the correct Velux/Fakro flashing kit (this is the crucial watertightness step and is manufacturer-specific — EDW for most profiled tiles, EDL for slate, EDJ for recessed installation); re-tiling around the window with proper overlap and making good the roof membrane; fitting internal plasterboard reveal linings back to the existing ceiling finish; and finally the internal decorative finish.

The flashing kit choice is the single most important detail. Velux and Fakro each make a specific flashing kit for every major tile profile on the UK market, and fitting the right kit for your tiles is why the window doesn't leak. We will not fit a generic universal flashing kit — the extra £40 on the materials bill is trivial compared to the cost of a leaking window inside a plastered reveal.

Replacing an existing window

Velux windows generally last 25–35 years before the seals, pivot mechanism or timber frame reaches end of life. If yours is starting to leak, fog between panes, or stick when opening, replacement is straightforward — and typically much less disruptive than fitting a brand-new one, because the rafter opening is already there.

A like-for-like replacement is usually a half-day to one-day job, with scaffold if the window is more than one storey up. We remove the old window, inspect and re-tape the membrane edges around the opening, inspect the flashing kit (usually replaced as well; generic wear happens to the flashing as well as to the window itself), fit the new window, re-flash, and make good the tiles. Internal plasterboard and reveal finishes stay in place in most cases.

One genuine upgrade to consider at replacement: go up one size. Current UK Building Regulations recommend roof-window area equal to 12% of floor area for adequate daylight. Most original 1980s–1990s Velux windows are undersized for that. A same-price upgrade to a larger window while the roof is open is one of the better interior-design moves you can make in a loft room.

Safety, Building Regulations and means of escape

If your roof window is in a loft bedroom, it almost certainly doubles as the required means-of-escape window under Building Regulations. The current minimum clear opening is 0.33m², with a minimum opening width of 450mm, and the bottom of the opening no more than 1,100mm from the floor. Most top-hung Velux GGL/GPL windows at MK04 size and larger meet this comfortably.

On conversions and new-build loft rooms we always confirm means-of-escape compliance on the quote, and the window certificate forms part of the Building Regulations completion pack. For listed buildings and conservation areas, planning permission is usually required for roof windows on visible elevations — we'll advise at quote stage.

Frequently asked questions