Why two similar skylights can cost very different amounts
A fair answer to what a skylight costs starts with where it is going. A roof window slipped between two rafters on an open slate slope, with a vaulted ceiling below, is a fairly contained job from a ladder. The same window over a stairwell in a three-storey villa might need a scaffold, a cut rafter carried on new timbers and a light well boxed down through a deep loft. The unit on the invoice could be identical while the job around it is not.
That is why we price from a survey rather than a list. The rest of this page takes the main factors one at a time, so that when the written figure arrives you can see what lies behind it. If you already know which product you are after, each service has its own short cost answer, linked further down.
The unit you choose
The first factor is the product itself. A small sun tunnel, a standard roof window, a flat rooflight on a kerb, a glazed lantern, a walk-on panel and a slim conservation unit sit at very different points, and within each type the size matters. A bigger unit uses more glass and frame, and on a pitched roof it may also mean a wider opening than the rafters allow.
Frame material plays a part as well. For lanterns, aluminium gives slimmer and stronger sections while uPVC costs less, which the roof lantern installation service covers in full. Conservation rooflights, with their steel or aluminium-faced frames and a central glazing bar, are made for traditional slate and stone roofs and are priced accordingly. Brand is a factor too: we fit VELUX and other makes, and the make you prefer will change the figure.
The roof covering and how we reach it
Each roof covering needs its own way of keeping the weather out at the edge of the unit. On slate or concrete tile, a pitched roof window is weathered with a flashing kit made for that profile, and the slates or tiles around it are cut and dressed back in. On a flat roof, felt, EPDM rubber and GRP fibreglass each need their own upstand detail, and if the existing covering is tired around the opening it may be sensible to renew a section while the roof is open.
Access is a separate question. A single-storey extension can often be reached from a ladder. A two-storey terrace with a steep slope may need a tower, and a tall villa or a roof over a conservatory may need scaffold. Where scaffold is needed, it is part of the price, and we will have looked at where it can stand during the survey.
New openings and structural work
Fitting into an existing hole and cutting a new one are very different jobs. Making a new hole changes how the roof carries its weight. On a pitched roof, each rafter that is cut has its load taken by new trimmers on both sides; on a flat roof the same applies to the joists, and a large lantern opening can need a beam. The more structure is involved, the more time and timber the job takes.
Cutting a new opening is notifiable building work, and so is replacing a roof window or rooflight, and we notify Building Control for you in either case. The skylight planning and Building Regulations guide explains the rules behind it.
Making good inside the room
What happens below the roof can take as long as what happens on it. Where the ceiling follows the slope, the reveal around a roof window is short, and lining, insulating and plastering it is a modest task. Where there is a loft between the ceiling and the slope, the daylight has to travel down a light well, a boxed and insulated shaft that has to be framed, boarded, plastered and finished. A deep well over a landing is a real piece of joinery and plastering in its own right.
Sun tunnels are lighter on this side of the job, because the tube passes through the loft and only a neat ceiling ring shows in the room. Flat rooflights and lanterns need their opening lined and plastered from below. Whatever the unit, the reveal is plastered and finished as quoted, and we price that finish before we start.
Glazing, opening and controls
The glass is where much of the choice sits. Double glazing is the common starting point, with triple glazing for a cooler roof or a room you want to keep warmer. A low-emissivity coating, a gas fill of argon or krypton and warm-edge spacer bars all bring the U-value down, and solar-control coatings cut summer heat on a south-facing slope. Every unit must meet the Part L limit for its type; better than the limit costs more.
How the unit opens matters too. A fixed rooflight is the simplest. A manual roof window opens with a handle or a pole. An electric unit is worked from a wall switch or a handset, and many models carry a rain sensor that shuts them when the first drops land, which suits a high ceiling over a stairwell. Blinds, whether blackout for a bedroom or pleated for glare, add a little more. Our electric and opening rooflights page compares the controls in more depth.
Replacing a unit you already have
Swapping out a misted or tired unit avoids the structural work of a new opening when the replacement fits the same hole. VELUX size codes help here. The letter at the front of a code like MK04 stands for the width and the two digits for the height, so a matching code points to a like-for-like swap. The figure goes up when a rotten kerb needs rebuilding, when new flashing is called for, or when you would like a bigger unit, which means altering the opening after all. A replacement is priced in more depth in the cost to replace a skylight, and the misted rooflight replacement service explains when a new glazed unit alone is enough.
Cost answers for each service
If you know roughly what you want, these short answers explain the price factors for each type in more detail:
Why the figure is fixed and in writing
A survey lets us measure the rafters, the ceiling height, the depth of any loft void and the state of the roof, so the figure is based on your house rather than on an average. Once we have those measurements there is no reason for the price to drift. Your quote sets out the room, the unit and its measured size, and the figure written on it is what that work costs you.
Our method starts in the room you want brighter and works back to the roof, as our darkest room first page describes, and it means the unit is chosen for a reason you can see. The survey is free, the workmanship on each job is covered for ten years by our guarantee, and you can book a survey through the free survey and quote form.