Fitting a skylight and rooflight to mill terraces and colliery ground at Hindley

Hindley's oldest streets were laid out for people who worked in the cotton mills and the coal pits around Wigan, and they still define the middle of the town. Red-brick terraces run in straight lines, two rooms up and two down, with a slate roof, a chimney stack at each party wall and a long back yard. Many have a single-storey kitchen or bathroom built out behind, and that extension is usually the only part of the house with a flat roof.

Hindley Green, to the east, grew in a similar way around the pits, so its terraces and the lanes between them tend to look much the same as Hindley's own, with the odd chapel, shop or mill building converted to flats. Between the wars the council added semi-detached houses on wider streets, with pitched tile roofs, hipped ends and gardens front and back. Later estates, from the 1960s onward, filled in the spaces between with bungalows, semis and short terraces, and the newest are built on ground cleared of old industry.

That is a lot of roofs of different ages, and the age tells us how to treat each. A nineteenth-century roof is slate on timber battens, often with no underlay at all beneath it, and rafters that are slighter than a modern house would use. A 1930s roof is tile on a cut timber frame that welcomes a roof window. An estate roof from the 1970s or later is more likely to be concrete tile on trusses, where an engineered opening is the norm.

Lofts are where much of the demand sits. A terrace attic reached by a steep stair or a hatch can become a bedroom or study with one or two roof windows, but the party walls limit where the openings can go, and the chimney breasts take up space on both sides. A semi or estate house usually has a wider and more regular loft, and the question there is how many windows the slope can take without crowding the ridge. Chimney stacks matter too, since a stack at each party wall leaves a narrow strip of clear rafter on either side of the loft, and a roof window has to sit in that strip without touching the flue. On the estates the roof lines are plainer, but the garage and porch roofs at the front are often too shallow for a pitched window and suit a flat rooflight better. Both start with the same visit: a ladder in the loft, a tape on the rafters and a look at what the covering is.

In a terrace loft we measure the clear strip of rafter beside each chimney stack, because that strip limits the width of a roof window. Where the rafters are slender, the opening is trimmed with doubled timbers on each side.

Wigan Council is the planning authority here, and most houses can take a rooflight or roof window as permitted development without an application, and the conditions behind that sit in the planning guide, so they are not repeated here. Flats and maisonettes fall outside those rights, which counts in a town where old mill and shop buildings have become apartments.

Listed status changes things. Whatever the roof looks like and wherever the rooflight goes, a listed house, chapel or converted mill needs listed building consent first. Wigan Council can say whether your house is listed or your street lies in a conservation area. A conservation area alone does not remove permitted development for rooflights, but the council may have added an Article 4 direction, and the front elevation is where one bites hardest. What an Article 4 direction would change is worked through separately.

Wigan Council's building control team, or a registered building control approver, is told of every job before it begins, and we deal with the notification and the energy standard it carries where the work calls for it.

In practice the paperwork follows the survey. We look at the roof, decide which unit suits it, set a price and notify the right body before work begins. Stair and escape need their own design thought when a loft is converted; a two-storey house gets a protected stair for the escape route, because an escape roof window works only for storeys within 4.5m of the ground.