Do Side-Facing Roof Windows Need Obscure Glass?

A roof window on a house usually comes under Class C of the General Permitted Development Order, the class for roof alterations. Condition C.2 then adds a rule for windows on the flank slopes of the house. It has two limbs. Limb (a) says the window must be obscure-glazed. Limb (b) says it must be “non-opening unless the parts of the window which can be opened are more than 1.7 metres above the floor of the room in which the window is installed”.

Can a high side window open and be clear glass?

It can open, but it cannot be clear. The two limbs are joined by “and”, so each must be met. Limb (a) has no height exception at all. The 1.7 m figure sits only in limb (b), so a window set high enough may open, while one set lower stays shut. Neither case allows clear glass.

The purpose is privacy for neighbours, whose garden or windows may look across a narrow gap at the flank of your house. Clear glass in a loft bedroom would let anyone inside look straight down into next door's rooms and garden.

The condition bites on a flank slope, and a front or rear slope is outside it. On a semi-detached house whose ridge runs from front to back, the two slopes look out to the sides, so the condition applies. Where the ridge runs along the length of the house, the slopes look towards the street and the garden, so it does not.

What about a hipped roof or a gable end?

Hips and gables complicate it. A hipped roof has a sloping face at the end, and that can count as a slope forming a side elevation. A window in a gable wall is a wall window, not a roof window, and has its own rules. If your roof layout is not obvious, a photograph from the street helps, and we can say which slope is which when we see it.

The word dwellinghouse matters as well. In the Order it leaves out blocks of flats and any flat inside one, so flats do not use this route at all.

Class C also caps projection: a window may not stand more than 0.15 metres out from the surface of the original roof.

Designations change the picture less than people expect, but they add questions. In a conservation area, Class C carries no article 2(3) exclusion, so roof windows inside the C.1 and C.2 limits stay permitted development unless an Article 4 direction or a planning condition has removed that right.

Does a listed house keep these rights?

Listed houses keep Class B and Class C permitted development. They also need listed building consent where the work alters their character, so a roof window on a listed house goes through that route too. Put the question to Somerset Council's planning team first, or to the Park authority itself if the house is inside Exmoor.

An Article 4 direction takes rights away across a defined area. Somerset Council lists directions for a number of places, among them Wellington and Staplegrove Road in Taunton. What any one of them covers is a question for the planning team, since the list does not say. Our page on roof windows in conservation areas goes into the process.

If the house sits in the Quantock Hills, Blackdown Hills or Mendip Hills National Landscape, mention it when you ask, because the planning team will want to know.

Planning is about how the window looks and how it affects neighbours. Building Regulations are about how it is made, how much heat it loses and, in a loft room, whether it can serve as an escape window. Meeting one does not mean you have met the other.

If the window is obscure and fixed, am I finished?

For condition C.2, yes: obscure glass with a fixed sash, or with opening parts above 1.7 metres, satisfies it. You still need to check the projection limit, any listed or conservation status, and any Article 4 direction. In a loft conversion, check the escape requirement too, because a fixed window cannot serve as the escape window. Our answer on roof windows as fire escapes covers that.

The practical step is to decide which slope each window sits on before you order. Obscure glass has to be specified at the order stage, since changing it afterwards is awkward. We note the slope, the room height and the opening arrangement at the survey, so the supplier is given the right specification. A written price follows, with the pictures that back up what we found. The wider choices are on the roof windows and skylights page.