VELUX window installation in Crawley, with the glass chosen for a quiet loft

A VELUX roof window is a glazed sash and frame set into the plane of a pitched roof, so it lies flat with the tiles or slates and lights the room under the slope. It is the most familiar skylight in British lofts, and the choices made around it decide whether the room is bright, comfortable and quiet or merely bright.

The brand has been in British roofs long enough that plenty of people use the name for any roof window. That is worth a moment, because it changes how you shop. VELUX is one maker with a coded range: a size code, an opening type, a frame material, a glazing specification, a flashing kit and a set of blinds and controls. Each of those is a decision. Each one also has a name, and once you can read the names the whole job becomes far easier to discuss with anyone who is quoting.

This page is the hub for VELUX window installation in Crawley and the 30 miles around it. It walks the decisions in the order they come up on a real job: which room and which size, which opening style, which glass, which flashing, which finish, which blinds and controls, and then what the fitting day involves. Along the way it links to the pages that go deeper on each decision. If you already own a VELUX and want to replace or upgrade it, the chapters on matching an old opening and on replacing a sash are the ones to read first.

Every VELUX roof window carries a two-letter, two-digit code that stands for its frame width and height. Once you can read it, you can compare sizes, check a replacement and understand a quote in seconds.

The first letter is the frame width class. The two digits are the height class. So a code such as CK02 is a narrow, short window, MK06 is a mid-width window of medium height, and a code beginning with S or U is a wide window. The letters and numbers map to a set of frame sizes in millimetres, and the maker publishes the full list. The page on how to read a VELUX size code sets the whole grid out, and the answer on what the size CK02 means takes a single common code apart.

The code is printed on a data plate fixed to the window itself. Finding it is usually a two-minute job, and it is the most reliable starting point for any replacement. The answer on where the data plate sits on a VELUX window shows the usual positions. Where the plate has gone, painted over or rubbed away, the window can still be identified by measurement, which the answer on finding a VELUX size when the plate is missing explains.

A roof window opens in one of a few ways, and the choice changes how you clean it, how you ventilate the room and where the handle sits. The standard form is a centre-pivot sash that turns on a horizontal axis about halfway up the frame.

The centre-pivot is the workhorse. The sash rotates, so the outer pane swings round to face you and can be cleaned from inside. The handle sits at the top edge, and the window opens outward at the bottom and inward at the top. It works on a wide range of pitches, from shallow up to steep. The answer on how to clean a VELUX window shows why the rotating sash matters for a window you cannot reach from outside.

A top-hung window is hinged at the top and pushes out at the bottom, rather like a shop awning. It gives a larger opening at the bottom edge and a better outlook when open, but it cannot rotate to be cleaned from inside in the same way. It tends to be chosen for steeper slopes, where the swing of the sash has room.

The frame comes in several finishes, each suited to a different room. The choice affects how the window looks from inside, how it tolerates moisture and how often it needs attention.

The timber frame in natural pine has a warm, traditional appearance and suits a loft with exposed beams or a country feel. It is lacquered, and it is at home in bedrooms and living spaces. White painted timber gives a cleaner, lighter look and suits a modern loft. A white polyurethane-coated frame is made for damp rooms, since the coating does not absorb water and it wipes clean, so it is the usual choice in bathrooms and kitchens. The page on VELUX pine, white painted and white polyurethane finishes compares them properly.

The codes that mark the range, such as GGL, GPL and GGU, are worth decoding before you read a quote, since each stands for a particular combination of material and opening type. The page on VELUX GGL, GPL and GGU explained reads them off.

A roof window out of reach is a window nobody opens. Electric and solar versions fix that with a remote control, and some add sensors that open or close the window for you.

An electric window, the INTEGRA range in VELUX terms, has a motor in the frame and a wall switch or remote. It is wired to the mains at a low voltage through a control unit, and that wiring is part of the installation. The page on VELUX INTEGRA electric roof windows explains the range, and the answer on whether VELUX INTEGRA windows need an electrician is useful before you plan the cabling. Our wider page on electric and opening rooflight installation covers powered rooflights of every make.

A solar window carries a small photovoltaic panel in the frame that charges the motor, so there is no mains wiring. It suits a window in a position where running a cable would mean lifting floors or ceilings. The page on VELUX solar powered roof windows sets out when that is the right choice.

Some roofs are in conservation areas, and some houses are listed. In those cases the choice of roof window is about appearance as well as performance, and the rules on what can be fitted depend on the address.

A conservation roof window sits lower in the slope, with a slim frame and a central glazing bar that echoes the look of old cast iron rooflights. It is designed to sit more flush with the roof covering, so it is less visible from the street. The answer on what a VELUX conservation roof window is sets out what the range offers and where it is used. Our broader page on conservation rooflight installation covers the planning side and the wider choice of products.

The planning position is checked for the address. Roof windows on a house are often allowed without a planning application, as long as they do not protrude beyond the plane of the roof by more than a small margin and they do not sit above the highest part of the roof. In a conservation area, on a listed building, or where the local authority has removed permitted development rights, a different set of rules applies, and an application may be needed. Crawley Borough Council and the councils around it publish guidance, and the planning portal explains the national rules at planningportal.co.uk. We check the status of your property before any work is quoted.

A new roof window is building work, and a replacement can be too. The regulations that apply cover structure, fire escape, thermal performance and ventilation, and we install to the current versions of each.

Four parts of the Building Regulations come up most often on a roof window job:

1. Part A and the structure, because cutting into a rafter needs a proper trimmer and a header that carries the load.
2. Part B and fire safety, because a loft bedroom may need a window that can be used to escape.
3. Part L and energy, because a new or replacement window has to meet a limiting thermal figure, and the glazing specification matters.
4. Part F and ventilation, because the window forms part of the ventilation of the room.

The price of a VELUX installation depends on the size, the glazing, the flashing, the access and whether structural work is needed. We give a written quote after a survey, not an estimate over the phone.

What moves the cost, in order of effect:

• the window itself, which varies with size, frame finish and glazing specification;
• the flashing kit, which depends on the roof covering;
• any structural work, such as a trimmer and header, where a rafter is cut;
• access, such as scaffolding where a roof cannot be reached safely from a ladder;
• blinds, electric operation and other accessories;
• making good inside and decoration.