Slate roofs over Royston's brick terraces and tile over its semis, lit by skylights and rooflights

Two ways down

If the room has a loft directly above it, there are two answers. A roof window brings a wide beam of light and needs a light well, a boxed shaft lined and plastered, that carries it from the glass to the ceiling. A sun tunnel needs far less space, since its tube is narrow, but it lights a smaller patch of floor, and sun tunnel against roof window sets them side by side.

What the opening takes from the loft

A light well claims a slice of loft floor that might have held boxes or a tank. Where the loft is used for storage, the well is set against the side that costs the least floor, and the shaft is boxed in plasterboard for a clean finish.

Reading the loft

In the loft we find the straight path between the slope and the ceiling of the room, and check what crosses it: a water tank, a flue, a cable run or a diagonal brace. The first position that works is rarely the first position tried. A move of a foot sideways often clears a joist.

The room that is not under the roof

On a terrace, the middle bedroom sits directly under the roof, but the middle ground-floor room has a bedroom above it. A tube would have to pass through that bedroom, boxed in a corner. Some households accept that, others decide the stair is the better place for the daylight. We set out both options and the cost in space of each.

Choosing a finish

A diffuser can sit flush or slightly domed, and the plaster round a light well can be painted any colour. White reflects the most light, so it is the sensible choice for a middle room that needs every bit of it.

Rear slope first

On a terrace the back slope looks onto the garden and is out of sight from the road. Where either slope would do, the rear one is looked at first, because it keeps the street side of the roof as the street knows it.

What the council can tell you

• Whether the house has listed status.
• Whether the street is covered by a conservation area or an Article 4 direction, either of which can remove the permitted right.
• Whether the property is a flat, which sits outside Class C and normally needs permission.

Building work and the paperwork

A new opening in a roof alters the structure, so it is controlled under the Building Regulations. (We notify Building Control, whether that means Barnsley Council or a registered building control approver.) When the work is a straight replacement of one unit with another, the notification is still made.

Why an early check pays

If a planning question turns up, it is better asked before an order goes in. The council can then respond to a defined unit, a fixed position and a stated size, all of which come from the written quote.

Putting the plan to the council

An enquiry to the council is worded around the room, the unit and its place on the roof. A photograph of the street elevation and the quote's description of the unit give the council something definite to look at.

A unit that is already in the roof

A rooflight already in a Royston roof can be replaced in the same opening. The question to the council is the same either way, since listed status can apply to a swap as much as to a new cut, and the answer is known before the work is booked.

Extensions and their own permission

A rear extension on a Royston terrace may already have planning permission that describes its roof. A lantern projects higher than a rooflight in a slope, so we read the permission, if there is one, before assuming the lantern is covered.

Boarded lofts

Where the loft floor is boarded, the boards over the route are lifted and put back, and the roof timbers are measured in place. The distance from hatch to hip is taken with a tape, never guessed from the road.

Measuring the slope

A roof window needs clear slate or tile on all four sides of its frame, plus room for the flashing above and below. We measure from the eaves to the hip and from the ridge down, then see whether a frame of the right size has room. VELUX sizes run from small to large, and the code's letter gives the width while its digits give the height.

When the slope is too short

If the frame will not sit comfortably, there are three outcomes. A narrower unit may fit. The opening may move to the long side of the roof. Or a sun tunnel takes over, because its dome is much smaller than a roof window's frame. The tube falls straight to the landing ceiling.

Using the long slope

A semi's landing often sits near the party wall, so the long slope above the stair sometimes serves it directly. A hip is usually at the end; the main slopes at the front and back are longer and take larger units.

Party walls and chimney stacks

On a semi, the party wall and its chimney stack interrupt the slope. The frame is kept clear of the stack and its flashing, and the position is set out from the wall, so the window ends up where the room below needs the light.

Light on the stair as well

A landing window lights the flight below too, when the stairwell is open. The stairs and landing page on where to place the glass above a stairwell shows how daylight is sent down the whole flight.

Matching the roof

Concrete tiles interlock in a profile, and the flashing kit is made to follow it. The tiles beside the frame come up and go back down afterwards, with a cracked one swapped for the nearest match.