Do side-facing roof windows need obscure glass?

Class C of the General Permitted Development Order covers roof windows and rooflights on a house. Condition C.2 covers a single situation, a window put into a roof slope that forms a side elevation of the dwellinghouse. There the window must be obscure-glazed, and it must stay shut unless the parts that open are higher than 1.7 metres above the room's floor.

The plain reading is that two things are needed together. The glass is obscure, meaning frosted or patterned so you cannot see through it clearly, and the opening parts are out of ordinary reach. A window that is obscure but opens at head height does not meet the condition unless the opening lights are above that line. The condition is about preventing overlooking of the neighbouring property from a side slope.

Our guide to roof windows and planning under Class C covers all the limits together. This answer deals with just this one.

Whether a slope counts as a side elevation depends on the house, not on the compass. A typical semi-detached or terraced house has a front slope facing the road and a rear slope facing the garden, and those are not side elevations. A gable-ended house has the sloping faces at front and back and the gable walls at the sides, so again the slopes are front and rear.

The trouble comes with hipped roofs, where the roof slopes down on all four sides, and with end-of-terrace or detached houses where one slope looks along a boundary or a side passage. On a hipped roof the end slope can be a side elevation. On a cross-wing, an L-shaped plan or an extension with its own ridge, the question needs a proper look at the drawings. If in doubt, ask the council's planning team. We note slope orientation on the survey and photograph each one, so the question is answered with pictures and not memory.

There are three sensible routes. The first is to move the window to a front or rear slope, where the sideways-slope condition is not in play, and where daylight is often better anyway. The second is to keep the position and accept obscure glass, which suits a bathroom or landing but not a bedroom where you want the view. The third is to raise the window so the openable parts sit more than 1.7 metres above the floor; the glass must still be obscure, but the window can then open. In a loft with a steeply sloping ceiling, the lowest practical position for the sash may already be that high, and a tall roof window can meet the line with its opening part at the top.

In a bathroom, obscure glass is rarely a hardship, because privacy is wanted anyway, and a tall roof window high in the slope can still give a good deal of daylight. In a bedroom the trade-off is harder. Under permitted development a fixed window still has to be obscure-glazed, so do not assume that clear glass is allowed because the sash does not open; clear glass in a side slope needs planning permission. A planning application is the other route: a householder application is judged on its merits and is not bound by the permitted development conditions.

Obscure glass is a patterned or frosted pane that lets light through and blocks a clear view. Roof window manufacturers offer obscured or frosted versions of their glazing as a stock option for rooms such as bathrooms. Approved Document L still applies to the glazing, whatever its finish, so frosted glass is no way round the insulation standard: a roof window has to reach a ceiling of 1.4 W/m²K on the U-value, with Band B the lowest rating accepted on the Window Energy Rating label. Our answer on roof window U-values explains what the figures mean, and the finish does not change that requirement.

The glass does cost a little extra, so check it is covered in any quote. MyBuilder's 2026 guide gives £350 to £600 for installing a standard roof window; that is a national range, not our price, and it does not break out obscured glazing. Whichever route you take, decide before the window is ordered, because a unit delivered with the wrong glass is a costly mistake.

The Class C conditions apply only if you rely on permitted development. Listed buildings need listed building consent for most alterations to the roof, and homes under an Article 4 direction or a planning condition may need an application whatever the window does. Flats and maisonettes do not have permitted development for these works in the same way, because Class C applies to dwellinghouses.

Building Regulations are separate from planning. A loft room needs a means of escape, and a roof window only counts for escape where the loft floor sits no more than 4.5 metres above ground, with the bottom of its opening part no higher than 1,100 mm above that floor. A side-slope window opening only above 1.7 metres cannot be that escape route. Where the work is notifiable, we explain consent and deal with the Building Regulations notification. For a window on a protected building, check with Stroud District Council's planning team first, and read our answer on electric roof windows if the opening sash is out of reach and you want a motor to work it. The overall service is on the skylights and roof windows page, with a 10-year workmanship guarantee in writing.