Rooflights and skylights in Ely

Walk up Fore Hill, along St Mary's Street past Oliver Cromwell's House, or down Egremont Street and you see the pattern: brick or rendered fronts, often a Georgian face on an older timber frame behind, three storeys, a front roof slope to the street and a rear range stepping down behind. Inside, the plan is deep. The front rooms are bright; the back rooms are fine; the stair in the middle is dim on the lower floors and gloomy in winter.

A rooflight in the rear slope above the stair can change that more than any other single opening in the house, because a stairwell is a shaft. Light entering at the top falls three floors if nothing stops it. A slim conservation unit, glazed with a clear low-iron outer pane, will put daylight on the half-landing on a grey February morning. Set it over the open well of the stair, not over the top landing floor, and the light travels down instead of stopping on the carpet one floor below the roof.

Rear ranges and outshots are the second place. Many Ely townhouses have a lower wing behind, with a kitchen or a bathroom under a shallow roof. These wings often face a narrow yard and a neighbour's wall, and their one side window gives very little. A rooflight in the wing's roof sees the sky over that wall. In rooms like these we look closely at the neighbouring building heights, because a tall wall to the south can shade the slope for much of the winter, and it changes which slope is worth using.

The cathedral itself adds a local wrinkle. At Ely's latitude the midday sun in late December sits only about 14 degrees above the horizon, so any tall building throws a shadow several times its height. A house close to the north side of the cathedral, or of any taller neighbour in the precinct, can lose direct winter sun on its roof entirely for weeks. On those roofs a north-facing conservation rooflight that collects steady sky light may be the better choice, and we will say so in the light plan rather than chase sun that will not arrive.

The terraces around Broad Street, Back Hill and the roads towards the station are mostly two storeys under slate, with a rear outshot and a narrow yard. They follow the same logic as a Cambridge terrace: a long, deep ground floor, a dark middle room once the back wall is knocked through, and a loft that could become a bedroom. A rear kitchen extension with a flat roof is the obvious place for a slim flat roof rooflight or a small lantern, pushed back towards the old house so the light reaches the middle of the plan rather than the garden end, which the doors already light.

For a loft room in a terrace, roof windows in the rear slope do most of the work, and a pair set at a sensible height gives both a view and a way to purge warm air at ceiling level. Three Building Regulations points shape the layout on an Ely terrace:

• Part B keeps rooflights out of the strip 1500mm either side of a party wall, so on a narrow terrace the usable width of the slope is smaller than it looks from the street.
• Part K asks for safety glazing overhead, which in practice means a laminated inner pane on any roof window above a bed, a desk or a stair.
• Part L sets a limiting U-value of 2.2 W/m²K for a new or replacement rooflight, measured in the horizontal plane, which a good modern double or triple glazed unit meets comfortably.

The riverside is different again. Along the Waterside and Ship Lane, the old maltings and warehouses have become homes, many of them flats, with large roofs and deep floor plates. Their top floors can be superb rooms with the right roof glazing, but they sit squarely in the conservation area and near listed buildings, and a flat has no permitted development rights. These are planning applications from the start, and the light plan becomes part of the case: the officer sees exactly where each opening goes and why. The Building Regulations for rooflights page covers each part in full.

There is little between the Isle and the Wash to break a northerly or easterly wind, and in spring and autumn dry, gusting weather across the open fields can drive fine dust and rain hard against a roof. For a rooflight, that means three things. The flashing has to suit the roof covering properly: Ely has a lot of clay pantiles, whose deep profile needs a flashing kit made for it, as well as plain tiles and Welsh slate on the Victorian streets. The fixings for an opening sash need to resist the wind trying to pull it open. And an electric unit should have a rain sensor that closes it within seconds of the first drops, so it can be left open on a warm day while you are out.

Wind also affects where we put an opening. A top-hung or centre-pivot roof window on a slope facing the prevailing wind will be harder to leave open, and a sash on the sheltered slope may ventilate the room just as well. On a flat roof extension, an upstand of at least 150mm above the finished roof surface, with a fall that clears rainwater away from the frame, matters more on an exposed site than on a sheltered one. None of this is complicated, but it is easy to overlook when a rooflight is chosen from a catalogue rather than for a particular roof.

Timing matters too. A roof opened on the Isle in a spell of rough weather needs to be made weathertight the same day, so we plan the day around the forecast and keep the opening sheeted until the unit and its flashing are in.

Do I need planning permission for a rooflight in Ely?

It depends on the address. Outside the conservation area, a rooflight within the permitted development limits usually needs no application. Inside the Ely Conservation Area it may still be permitted development, unless your property falls under the Article 4 direction, in which case you apply to East Cambridgeshire District Council. A listed building always needs listed building consent, and a flat always needs planning permission.

Will a rooflight on a house near the cathedral get any sun?

In summer, yes, because the sun is high enough to clear most buildings. In midwinter the sun at midday is only about 14 degrees up, so a roof close to the north of the cathedral or another tall building can sit in shade for weeks. A north-facing unit that gathers sky light often suits these houses better, and the light plan shows which you would get.

Can I replace an old roof window in a conservation area house without a new application?

A like-for-like replacement of the same size, in the same place, with a similar profile does not normally need planning permission. If you want a larger opening, a different position, or a unit that sits higher above the roof, the planning rules apply as for a new rooflight. On a listed building, check with the council first even for a straight swap.