What a VELUX window costs to fit

Three decisions set the window line: how big, how it opens and what glass it carries.

Reading the size code

VELUX windows carry a code such as MK04 or CK02. The letters give the width and the digits give the height, so MK04 is a different shape from CK04 and from MK08. A wider and taller code uses more glass and a bigger sash, and the price follows. The code on an old window is stamped on a label on the frame, and a new window in the same code fits the same hole, which is why a swap can be priced closely from the survey.

How it opens

A centre-pivot window turns on a bar across its middle, and the top-hung type swings out from the top edge. Opening style changes the frame, the height of the handle and the position of the glass relative to the head of the opening. An electric window adds a motor and a control, and a solar-powered one adds a small panel in place of a cable.

Glass

The default pane suits a landing or a stair void. A bathroom, a kitchen or a room under heavy rain may call for different glazing, and we specify it by the room. Laminated glass holds together if it breaks, a choice that suits a window directly above a bed. Obscure glass suits a bathroom slope that neighbours might see.

Water has to be carried round the frame, and the formed kit that does it is chosen to match the tiles or slates of your roof. On a slate slope the kit lies under the slates, on interlocking tiles it follows the tile profile, and on clay peg tiles it follows the camber of each course. The pieces differ and so does the labour of lifting and relaying the covering round them.

A thicker covering raises the kit and so deepens the lining, which is a reason to treat the metalwork and the inside finish as linked lines. Our guide to roof window flashings for peg tile, slate and concrete tile takes each covering in turn.

Two roofs with the same window can therefore produce different totals, because one covering involves a few lifted tiles and the other involves a full day of cutting. The survey records the covering, and the quote names the kit for it.

The biggest division in VELUX pricing is between replacing a window that is already there and cutting one where nothing was before.

A like-for-like swap uses an opening that has already been framed. The old unit and its kit come out, the frame is checked, and the new window goes in. The structural work is small. If you want the same hole in a different size, the cost moves toward the new-opening end, as rafters may need trimming.

A new opening goes through the roof structure. A rafter or two is cut, timber is fixed across the gap to carry the load, and the opening is framed to take the window. A narrow window that fits between two rafters needs less trimming than a wide one that crosses them, and that is a reason to choose the code by the rafter spacing we measure. The ceiling below is cut too, and the insulation in the roof has to be made good around the new frame.

In a chalet bungalow or a loft conversion

In a chalet bungalow, a roof window can serve as the escape window from a bedroom in the roof when the opening is at least 0.33 m², at least 450 mm wide and 450 mm high, with the bottom of the opening no more than 1,100 mm above the floor, and the window stays open without being held. That affects which code you can choose, and so what the window costs. A loft conversion above a two-storey house works differently: its escape normally runs down a protected stair, and the roof window cannot serve for it. Both are checked at the survey.

The window is not finished when the glass is in. A frame that was set into a roof slope leaves a raw edge of timber and plasterboard, and the lining closes that gap. The lining is formed to the angle of the reveal, and it has to be plastered or boarded, sealed and painted. In a loft room, that can mean a short reveal of a few inches. In a landing under a deep roof, it can mean a boxed light well from the ceiling up to the glass.

A light well takes more finishing than a short reveal, and it is an easy part of a VELUX quote to overlook. The deeper the well, the more plaster and paint, and the more daylight it can lose if it is not splayed. We aim to splay the sides of a deep well outward at the ceiling to let more light spread across the room.

Getting to the roof

The slope has to be reached safely. A window on a rear single-storey roof may need only a ladder and a roof ladder. A window high on a three-storey terrace needs a scaffold tower or a full scaffold, and a side access might need boards across a flat roof. The method is written on the quote with the cost of hiring it.

Dust sheets, floor protection and a clean-up are part of the work, and so is taking away the old window and the tiles we cannot reuse.

A roof window takes the full sun, so a bedroom window usually wants a blind. Blinds are made to clip to the window frame, which holds them close to the glass, and blackout, pleated and roller types each have their own line. If the window is electric, the blind can often be motorised to match, with a switch beside the window, at extra cost.

Electric windows need power. A mains feed has to be run by a qualified electrician, and the route behind the lining is planned at the survey so the cable is not visible on the finished ceiling. A solar-powered window avoids the cable and carries its own panel instead. The electrician's work is a separate line; the split of jobs is set out under electrician for an electric rooflight.

A rain sensor

An opening window with a rain sensor closes itself when a shower starts. That suits a bathroom or a room where windows are often left ajar when no one is home. The sensor is another line, and it is easier to add before the lining is finished than after.

Cutting a fresh opening into the roof brings structure, energy performance and, where it applies, escape under Building Regulations. We handle the Building Control notification where the work is notifiable, and a new or replacement roof window must meet the window limit of 1.4 W/m²K, or Window Energy Rating band B at minimum. Planning is a separate matter: a roof window on a house is usually permitted development, with limits on how far the frame stands out and how high it sits. The conditions are listed in skylight planning permission, and skylight building regulations covers the rest.

The lines to expect

A quote that can be compared names the window by its size code and its opening type. It names the flashing kit by the covering it is for. It says whether the opening is new or existing, how the roof will be reached, what the lining and decoration include and what is done with the old unit. Blinds, motors and wiring are each listed or marked as not included.

We survey free before we price and then give a fixed written quote naming each of these, with a 10-year workmanship guarantee in writing. If you want to see how the lines look for your roof, send a photo on WhatsApp at 07880 284133, email info@orchardskylightsmaidstone.co.uk, or ask for a survey. Our page on how much it is to fit a VELUX window gives the short answer, and swapping an old VELUX window covers the like-for-like route.