Roof window installation in Exeter

A roof window is a complete window unit made for a sloping roof. It has a frame that is fixed to the rafters, a sash that opens, double or triple glazing, and a flashing kit that dresses the roof covering around the frame so water runs over it and away. The whole assembly is designed as one product, which is why the flashing for a slate roof is a different part from the flashing for a plain tile roof, even when the glass is identical.

The word skylight covers a lot of ground, and in everyday talk it can mean anything from a fixed pane in a flat roof to a window in a loft. In practice the products fall into a few families. A flat rooflight lies almost level on a kerb. A lantern rises above a flat roof as a small glass roof of its own. A sun tunnel carries daylight down a tube. A roof window is the one that follows the pitch, opens like a window and is often reachable from the room.

That reachability changes how you choose. A fixed rooflight over a kitchen island is never touched after it is fitted. A roof window in a bedroom is opened every morning, wiped on the inside and sometimes used as a way out. So the handle position, the way the sash swings, the blind fitted to it and the height of the sill all matter, and they are decisions about daily use, not only about glass.

If you are not sure which family you need, the room usually decides. A pitched roof over a room you stand in points to a roof window. A flat roof points toward a flat rooflight or a roof lantern. A dark hall or bathroom with a deep roof above it may suit a sun tunnel better than any window.

There are two main ways a roof window opens. A centre-pivot sash turns on a bar across its middle, so the lower half swings outward into the room and the upper half swings out over the roof. A top-hung sash is hinged at the top and swings out and up like an awning, leaving the bottom edge standing proud of the frame. A fixed unit does not open at all.

Each suits different positions. Centre-pivot windows are the usual choice where the sill sits at normal window height, because you can reach the handle at the top and rotate the sash fully to clean the outer pane from inside. Top-hung windows suit a sill that sits high in a room, or an opening placed where you need unobstructed headroom beneath the glass, and they also lend themselves to taller panes. Our guide to top-hung or centre-pivot roof windows goes through the trade-offs for each.

There are variations on the theme, and a few of them solve problems that are not obvious at the survey.

Pivot with a high handle

The control bar sits at the top of the sash, so the handle can be reached without leaning across a bed or a desk. It suits windows placed higher up the slope.

Top-hung with a lower handle

The handle sits at the bottom edge, which is the right place when the window is above a stair, a landing or a worktop and you reach up to it.

Fixed

A fixed unit costs less and gives slightly more glass for the frame. It suits a room that has ventilation from elsewhere, or a stairwell where height and cleaning are real obstacles.

Electric and solar powered

A motor opens the sash and often drives a rain sensor that closes it. This is worth considering where the window is out of reach, and we cover it on the electric opening rooflights page.

Whichever type you choose, a sash that opens inward and outward needs clear space. Furniture under a roof window, the swing of a blind and the path of a pole all affect how the window gets used, so we mark them on the survey and write the handle position into your finish schedule.

Roof windows are made in standard widths and heights, each designed to sit between a normal spacing of rafters. The simplest installations choose a width that fits between two existing rafters with a small allowance, so only a short length of timber is cut and the remaining rafters carry the load either side. The question of fit gets its own treatment in the answer on how wide a roof window can be between rafters.

Wider windows mean cutting through a rafter or two, and that needs trimmers: new timbers, usually doubled up, fixed across the opening to carry the load around it. Where the roof is old, the rafters may be irregular, undersized or spaced unevenly, and the opening becomes a small structural design problem. We measure before we quote, and the quote says plainly whether the window fits between existing rafters or needs trimming.

Position on the slope matters for more than looks. A window that sits low reads as part of the wall, a window that sits higher throws daylight deeper across the ceiling, and a window positioned in the middle suits most rooms. In a loft room the sill is also bound by headroom and by how near the window sits to the eaves, since a sill that is too low makes cleaning and escape awkward, and one that is too high makes it hard to open.

A roof window sits in the roof, but the part you look at is the lining: the boxed opening that carries the plane of the window down to the ceiling. In a thin roof the lining is short and shallow. In an older roof, with deep rafters, insulation and sarking boards, it can be a good deal deeper, and what you do with the sides of that opening changes the whole look of the room.

The simplest lining is straight, with sides running square from the window frame to the ceiling. It is quick, neat and right for a shallow build. A splayed lining angles the sides outward toward the room, so the opening is widest at the ceiling and narrowest at the glass. That spreads daylight onto the ceiling and walls, softens the edge between window and room, and makes a deep opening look drawn rather than cut. In a deep roof, a straight shaft casts shadows and reads as a tunnel. Our splayed lining answer explains the shape in more detail.

The material needs to suit the ceiling. A plasterboard ceiling in a 1930s semi takes a boarded and taped lining with a skim, which is quick and crisp. A lath and plaster ceiling in a Georgian terrace is more delicate, because the cut edge of old plaster can crack away from the lath. There we cut with care, secure the plaster before any structure is removed, and finish the lining in the same material as the ceiling around it. In a cob cottage or an older house with lime plaster, lime is used so the wall can go on moving and breathing.

Corners and edges are where the quality shows. A metal angle bead gives a hard, straight arris at the corner of the reveal. A stop bead or shadow gap bead where the lining meets the window frame leaves a clean line, and hides the small movement between timber and plaster. Then the surface is skimmed, sanded and either primed for you to decorate or painted in the colour you choose.

Insulation behind the lining is not decoration. A lining built from insulated plasterboard keeps the reveal from becoming a cold patch where condensation forms, which matters most in a bathroom. The detail is covered in the guide to how a rooflight is finished inside.

Planning and Building Regulations are two different checks, and a roof window needs to satisfy the second one almost every time. Planning is about how the house looks from outside and what it does to neighbours. Building Regulations are about how the work is built.

For planning, a house roof window is typically permitted development, covered by Class C, which the General Permitted Development Order sets out in its Part 1. The conditions are plain. The window may stand out 150mm at most from the roof slope, and it may not go above the ridge or other highest point. A side-facing window must be obscure glazed and fixed shut, unless the opening part is over 1.7m up from the floor. Roof windows are low profile by design, so most meet the projection limit without trouble.

The exceptions are the ones to check. Flats and maisonettes sit outside householder permitted development rights. A listed building needs listed building consent for external alterations, and a roof window counts as one. In a conservation area Class C still applies, but an Article 4 direction can remove it, and a front-facing slope on a street of terraces is where councils tend to care most. Inside Dartmoor or Exmoor national parks, some permitted development rights are restricted. In each case, speak to the planning team, which for most of our area is a district or city council, and for the moorland edge may be a national park authority. Our page on rooflight planning and Building Regulations in Devon goes further.

On the Building Regulations side, a new roof window cut into an existing roof is building work. The rafters are altered, which is structural, and the window must satisfy Part L, the conservation of fuel and power, including the limiting U-values in the 2021 Volume 1 of Approved Document L. Building Control approval is required. If you are building a loft room, the window falls under the same application.

Swapping a complete roof window, frame and glass, is notifiable too, because a window is a controlled fitting and its replacement must satisfy Part L. A new sealed glass unit in the existing frame is not notifiable. When a job is notifiable, we put in the Building Control notification, so there is nothing for you to chase. The answer on how close to a neighbour a roof window can be covers the boundary and privacy side, including Part B where a window sits near a boundary.

Roof window prices vary because the job varies. Two windows of the same size can sit at very different prices depending on the roof they go into, the structural work around them and the depth of finish inside. We give a written quote only after a survey, and it shows each part separately so you can see where the money goes.

The unit comes first. Size, opening type, glazing specification, frame material and extras such as a blind, an electric motor or a solar control coating all move the price. A fixed unit costs less than an opening one, and a pine frame with a laminated inner pane costs more than a basic white finish.

If you are comparing quotes, compare the lines, not the totals

The roof is next. A slate roof needs a skilled hand and more care than a concrete tile roof, and a high or awkward roof needs more access equipment. If the rafters need trimming or the roof is made from trusses, the structural work adds timber, time and sometimes calculations. Scaffolding is a real cost on a three-storey terrace, and it is shown as its own line.

The inside is the part that many quotes leave vague. A deep lining takes longer than a shallow one, a splayed form takes longer than a straight one, and lime plaster takes longer than a board and skim. Making good the ceiling after an old window comes out is its own task. We price each of these in the finish schedule, and our costs page gives general market ranges for each product type.

Building Control charges are separate, and where they apply they appear on the quote. So does any decoration beyond the ready-to-paint stage. If you are comparing quotes, compare the lines, not the totals, because a lower figure that leaves the lining as bare board is not the same job.

It is one page of writing, made for your room.

A single new roof window in a straightforward roof is usually a matter of days rather than weeks, with the roof opened and weathered on the first day and the lining finished after. The time depends on the covering, the structural work and the depth of finish. The survey gives a clear programme, and the finish schedule records each stage.