Skylights near you

Most rooflights on most houses are permitted development. Class C of Schedule 2, Part 1 to the Town and Country Planning (General Permitted Development) (England) Order 2015 permits any other alteration to the roof of a dwellinghouse, and the government's technical guidance says Class C covers alterations such as re-roofing or the installation of roof lights and windows. The limit that matters is written into the order: development is not permitted if the alteration would protrude more than 0.15 metres beyond the plane of the slope of the original roof when measured from the perpendicular with the external surface of the original roof. The technical guidance puts it in one line, saying any protrusion from a roof, for example for a roof light or window and its frame, will be limited to 0.15 metres.

Three further limits go with it. The alteration must not result in the highest part of it being higher than the highest part of the original roof, and the technical guidance notes that under Class C height is measured against the original roof, not the existing one. Class C does not cover chimneys, flues, soil and vent pipes or solar equipment, which have their own rules. And there is a condition on side elevations: any window located on a roof slope forming a side elevation of the dwellinghouse must be obscure-glazed and non-opening unless the parts which can be opened are more than 1.7 metres above the floor of the room in which the window is installed.

Some houses have no such rights. The Planning Portal notes that the permitted development route is not available for a building containing one or more flats or a flat within such a building, nor for a house created under permitted development change-of-use rights, nor for one built as a new dwellinghouse under permitted development. A local planning authority can also remove the rights across an area with an Article 4 direction. On a listed building, national planning practice guidance is that any works to alter it in a way that affects its character as a building of special architectural or historic interest require listed building consent regardless of whether planning permission is needed, that listing normally covers the whole building inside and out, and that carrying out such works without consent is a criminal offence — there is no fee for applying, so there is no saving in skipping it.

The opening is a structural alteration, not a hole. The Planning Portal's rooflight guidance explains that installing a rooflight generally entails cutting part of one or more of the roof's rafters or joists away, and that the cut ends need new support, usually achieved by fixing two pieces of timber together spanning across the new opening on either side, which are called trimmers. It adds that the adjacent rafters or joists the trimmers are fixed to may also need strengthening, because they carry the load transferred from the cut members, and that this can be done by fixing a new rafter or joist alongside which must run the full length.

Weathering comes next, and it is where rooflights leak. The same guidance says the edges where the rooflight meets the roof require weatherproofing as well as the glass itself, commonly carried out using lead flashing or with the proprietary kits supplied with the rooflight. Those kits are made for a particular covering profile, so a flashing kit intended for slate fitted over deep concrete pantiles is a leak with a certificate. Ask which kit is being used and whether it suits the covering that is actually on your roof.

Ventilation gets forgotten twice over. The room the rooflight serves has to be ventilated, and the Planning Portal points out that this can be achieved by using the rooflight for both rapid and background venting. Separately, the ventilation of the existing roof voids has to be considered, because air must still be allowed to flow from one part to another once the new unit interrupts the space. A rooflight dropped into a cold loft or a cold-deck flat roof without thinking about the airflow will produce condensation that gets blamed on the unit.

Rooflights kill people. HSE's fragile surfaces guidance states that falls through fragile surfaces, particularly fibre-cement roofs and rooflights, account for 22 per cent of all fall from height fatal injuries in the construction industry, and that those carrying out small, short-term maintenance and cleaning jobs are over-represented in the injury statistics. Its roof work guidance names falling through fragile rooflights among the main causes of death and injury and notes that some rooflights are difficult to see in certain light conditions and others may be hidden by paint.

The law treats the risk as unavoidable-by-default. HSE's position is that all roofs, once fixed, should be treated as fragile until a competent person has confirmed that they are not, that effective precautions are required for all work on or near fragile surfaces no matter how short the duration, and that the response runs in a hierarchy: avoid the surface where possible by working from below on a suitable platform, control the remaining risk with stagings, guard rails, fall restraint, fall arrest and nets slung beneath and close to the roof, and communicate it with warning notices on the approach and trained, instructed workers.

For a homeowner this has two practical consequences. First, do not go up to investigate a leaking rooflight, clean one, or clear moss around one, however short the job looks from the ground. Second, when someone quotes for the work, ask how they are getting to it and what is protecting the opening while the unit is out, because an open rooflight aperture is a hole in a roof with a room below it.