Do side-facing roof windows need obscure glass?

Fitting a roof window on a house is covered by Class C of the General Permitted Development Order, which grants the right to alter a roof without applying to the council. The right comes with conditions. One of them concerns any window placed in a roof slope that forms a side elevation of the house. It makes two demands. The first is obscure glazing. The second is that the window be non-opening, unless whatever opens is over 1.7 metres up, measured from the floor of the room it lights.

The aim is privacy for the neighbours. A window in a side slope tends to look across at the next house, and the rule protects against that without requiring each case to be argued. Read the condition as two separate duties joined by the word and. It does not say obscure glass only below 1.7 metres, and it does not say obscure and fixed unless high up. We cover the wider permitted development limits in our guide to planning permission for a skylight.

People often mix the two duties, so it is worth separating them. Obscure glazing is the first duty, and it has no height exception. Take a window set high on the slope, its opening part comfortably over 1.7 metres from the floor. It still has to be obscure. The height only relaxes the second duty, which is about opening.

Obscure glass is glass that lets light through but blocks a clear view, usually by frosting, texture or pattern. Manufacturers describe how obscure a pane is on a scale of levels, and the planning rule does not name a level, so ask the council if you want to be sure a particular finish will be accepted. Choosing the glass at the order stage is far cheaper than changing it afterwards, because a pane in a fitted roof window is awkward to swap. Specify the glazing on the first order, and keep the delivery note, which records what arrived.

On a simple gable-ended house, the picture is plain. The roof slopes facing the front and the back are the main slopes, and the ones that rise to the gable ends would be the side elevations. A hipped roof is harder, because it has four slopes and the small end slopes may face a neighbour, a lane or a driveway. A chalet bungalow with a dormer or a corner plot adds more questions.

The wording turns on the slope making up a side elevation of the house, so the answer comes from the face of the building concerned. If it is not obvious, send the council photographs of each slope and a plan, and ask. Doing this before the window is ordered costs nothing, whereas a window fitted against the condition can attract a letter from the enforcement team. Our survey records every slope that looks onto a neighbour or the street, so the glass we specify fits the rule from the first drawing.

If you want clear glass in a side slope, you have stepped outside what permitted development allows, and you will need to apply for planning permission. The council then decides on the merits. It will look at overlooking, the distance to the neighbouring windows and gardens, and the setting of the house. A window high on a slope looking at a blank gable or a road may be treated differently from one that looks into a bedroom next door.

Neighbours are usually told about an application and can comment. Obscure glass in a window that opens would be an easy way to avoid that, and that is why obscure panes are popular for a bathroom or landing. Where the room needs a view, a front or rear slope is simpler, because the condition applies only to side elevations. Our answer on permission to install a Velux window sets the glazing rule among the other approvals.

Class C is written for a dwellinghouse, and the Order's definition leaves out buildings containing flats, as well as the flats themselves. A flat is therefore not covered by the condition, but nor is it covered by the right, so the council has to be asked about the whole window. Listed buildings need listed building consent as well, and a local Article 4 direction can withdraw the right in a defined area. Conservation areas and the National Park do not remove Class C on their own.

Planning is one side of the question. Building Regulations apply to the window as well, including its heat-loss figure and the structure around the opening, and our guide to roof windows and the Building Regulations covers them. A plan settled early, a photographed survey and a quote in writing leave very little to guess about the glass. More on our work is under skylights and roof windows.