Roof Windows for Chalet Bungalows

Most chalet bungalows share a layout. The roof ridge runs along the length of the house or across it. On each side of the ridge the slope drops steeply, and a short vertical wall, usually called a knee wall or dwarf wall, rises from the floor to meet the underside of the slope. Behind that wall there is a low void under the eaves, often used as cupboard space. In front of it the room has its full headroom only in a strip down the middle, where the ceiling is flat or follows the ridge.

That shape decides where a window helps. A window high in the slope lights the middle of the room and the ceiling above it. A window low in the slope lights the floor and the area by the knee wall, but only people standing close to it can see out. A window that straddles both gives the most daylight and the best view, which is why a taller window is so often chosen for chalet rooms.

The slope itself matters as well. Chalet roofs are pitched steeply enough to hold rooms, and a steep slope gives a roof window a more upright face than it would have on a shallow loft roof. Each window model has a rated pitch range from the maker, and the flashing has its own range, so the survey measures your actual slope with an inclinometer and checks it against the model before anything is ordered.

Because the room is small, there is little tolerance for a poor position. A window set a hand's width too low can be blocked by a bed head or a wardrobe. One set too high leaves the lower part of the room dim and gives a view of nothing but sky. The sections that follow take those choices one at a time.

In a wall, a window sill is usually somewhere near waist height. In a roof there is no wall to set it by, so the position is chosen from inside the room. Two measurements do most of the work: how high the bottom edge of the glass sits above the finished floor, and how high the handle sits when the sash is closed.

For an adult sitting on a bed or standing at the window, the bottom of the glass should sit low enough that the view is not just sky. Where the room has a knee wall, the bottom edge often lines up with the top of that wall, so the glass begins just above it. That keeps furniture clear below the window and puts the whole pane above head height for anyone passing beside it.

The handle is the other limit. On a centre-pivot model the handle is at the top of the sash, so it must be within reach of the person who will open it. On a chalet bungalow with a steep slope and a short knee wall, a window with its bottom edge at the wall top puts the handle nearer the ridge and may need a pole or a remote. Our answer on centre-pivot and top-hung roof windows explains how the two opening styles change the reach.

A visit to the room with a tape and a chair settles this faster than a drawing. The reading that goes on the survey sheet is the distance from the finished floor to the planned bottom edge of the glass, so you can see where the window will sit before it is ordered.

Many chalet bungalows already have a dormer on the front slope, built when the loft was first converted. A dormer gives headroom and a vertical window, but it lights only the part of the room under it. A roof window placed on the same slope beside it can reach the area the dormer leaves dark, and a roof window on the opposite slope can balance the room with light from the other side.

Where there is no dormer, a pair of roof windows can do much of the same job without changing the outline. Each window in a pair keeps its own frame and its own opening, with a rafter or a strip of roof between them. A combination flashing kit dresses the pair as one group and sets the gap between the frames; separate single kits leave each window flashed on its own. Both layouts are common, and the rafters fix the positions available. The guide to roof window sizes and rafter spacing covers how rafter centres decide the width a window can have without trimming.

A new dormer is a different job from a roof window. It builds out from the slope, so it is a planning question in its own right and it alters the roof structure considerably. A roof window sits in the plane of the roof and is looked at under the rooflight rules, which are set out in the rooflight planning guide.

If your house already has dormers on the front and you want daylight at the rear, the back slope is often the better place for roof windows. It is out of sight from the road, and on many chalet bungalows the rear rooms are the ones that face the garden.

Approved Document B, the fire safety part of the Building Regulations, treats a room in the roof of a bungalow or chalet bungalow differently from a loft room above a two-storey house. Where the upstairs floor of a chalet is no more than 4.5 m above the ground, each habitable room up there can rely on an escape window, so a suitably sized roof window can do that job.

The document sets the figures for the unobstructed openable part of an escape window: an area of at least 0.33 m², at least 450 mm high and 450 mm wide, with the bottom of the openable area no more than 1100 mm above the floor. The window also has to stay open without being held. Because these limits apply to the open window, not the frame, a window that looks large may offer a smaller clear opening than expected once the sash is swung to its stop. A window chosen for escape needs checking against each of those figures.

The bottom-edge limit ties straight back to the sill height chapter. A window placed high in the slope for light may put the bottom of its opening more than 1100 mm above the floor, which would rule it out as the escape window for that room. The usual answer is a taller window with its bottom edge low enough to meet the limit, or a second window placed lower for escape and a higher one for light.

• Which rooms in the roof need a window that can be used for escape
• The floor-to-bottom-edge height for each planned window
• The clear opening width and height with the sash open
• Whether anything inside the room, such as a built-in wardrobe, sits in front of the opening

These are the readings taken at the survey for a bedroom in the roof. A two-storey house is not the same case, because a roof window cannot serve as an escape window there; that situation is covered in the Building Regulations guide.

A bedroom under a roof has a lot of surface exposed to the sun. The ceiling slope and the roof covering sit directly above the room, and a south- or west-facing roof window adds to that in summer afternoons. On a house whose rear slope faces south or west, the window that gives the best daylight can also be the one that makes the room warmest.

There are several ways to manage that without giving up the window. The glass can have a solar control coating, which cuts how much of the sun's heat passes through. An external blind or awning blind sits outside the glass and stops the sun before it reaches the room. Opening the window high up lets warm air leave, and opening a second window on the other slope can help air move through the room. Opening roof windows help ventilate, and two opening windows on opposite slopes give the air a path across the room. The answer on solar control glass covers the coating in detail.

Glare is the reverse problem. A tilted window brings in more of the sky's light than a vertical one of the same size, and with the sun low in winter it can shine straight into a bed. Blinds are the usual fix, and they are easier to specify before the window goes in, because blinds are made for particular window sizes. The question of fitting them with the window is dealt with in the blinds answer.

The number of windows follows from the room's size and use; there is no fixed formula. A single bedroom of modest size may be well served by one window, while a double bedroom with a desk or a bathroom with a shower may want two. The factors are listed in the answer on window numbers for a loft.

Chalet bungalow bedrooms are usually finished: plastered, decorated and furnished. Adding a roof window means cutting an opening in the slope, and that raises the question of whether the work is done from outside, from inside, or both. On a house with scaffold access to the roof the outside route is the normal one. Where the slope is hard to reach, working from inside can be possible with the right unit, which is the subject of our answer on fitting from inside.

The opening is formed in the rafters. A window narrower than the gap between two rafters sits between them. A wider one needs a rafter trimmed and a timber header fitted above and below the opening to carry the load. Cutting or trimming rafters is a structural alteration and needs Building Regulations approval, so this is something we record on the survey sheet and put in the quote before any cutting is planned.

Inside, the opening is finished with a lining that runs from the window frame to the ceiling and wall. The lining is angled so that light spreads into the room and does not stop at the edge of the frame, and the angle is set by the thickness of the roof build-up at that point. In a chalet roof with insulation between and below the rafters the build-up is thick, so the lining can be deep, and a wider splay gives a brighter, more open window.

Finishing plaster or paint around the lining is the last step. Floors and furniture below the opening need covering while it is cut, and a room with furniture already in it is one of the things noted at the survey so the access is planned in advance.

A chalet bungalow quote begins with the roof and the room measured together. Outside the house, the survey records the slope angle, the rafter centres and the roof covering. Inside, it records the floor-to-bottom-edge heights, the knee wall height and the position of any furniture or fixtures that limit the choice.

Those readings are used to choose a window size, a position and a flashing kit that match your roof covering. The sheet you receive lists them in writing, so the proposed position is a set of figures you can check. If you want the window a hand lower or a few centimetres to one side, that can be agreed at the survey and written on the sheet.

If you are weighing a roof window against another way of lighting a landing or a bathroom, the guide to sun tunnels and roof windows compares the two for rooms where a full window is not an option.