Rooflights and skylights in Cherry Hinton

On a gable-ended house the rear slope is a clean rectangle. On a hipped semi it is a trapezoid that narrows towards the ridge, and the side of the house is covered by a triangular hip slope rather than a wall. That leaves less usable rear roof than the street view suggests, and the best headroom in the loft sits in a short strip under the ridge. A roof window placed too far towards the hip ends up in a corner you cannot stand in, lighting the underside of a purlin rather than the floor.

Owners converting these lofts often change the hip to a gable, sometimes with a rear dormer as well, and that is the moment to plan the roof glazing properly. Once the gable wall is up, the front and rear slopes can take roof windows at a height where you can see out while standing, and the landing below can be lit from a unit over the new stair. Our guide to rooflights, skylights and roof windows explains which type suits which part of the loft.

The hip slope itself is a trap under the planning rules. It faces the side boundary, so under permitted development a rooflight there has to be obscure glazed and fixed shut, unless the opening part sits more than 1.7m above the floor of the room. A clear, opening window on the hip that looks towards next door is a planning application, not a permitted change. We mark the side slopes on the light plan for that reason, and on a hipped semi the answer for side light is usually a small high-level unit or a sun tunnel rather than a large clear pane.

The party wall between the pair matters too. Building Regulations Part B keeps rooflights out of a band 1500mm wide on each side of it, so on a semi one edge of the rear slope is ruled out before the survey starts, and the window positions shift towards the hip. On a narrow pair that can leave a surprisingly small space to work with, which is why we measure it before anyone draws anything.

A bungalow hall is a good example. The rooms open off it on every side, each door takes a little light from its own window, and the corridor between them stays dim at noon. Because the loft space above is usually unconverted, there is a choice to make. A sun tunnel runs a reflective tube from a small dome on the roof down through the loft to a diffuser in the ceiling, and it fits between the ceiling joists without any structural work. A 250mm tube suits a bathroom or a short passage, and a 350mm tube or larger suits a longer hallway. The light it gives is soft and even, with no view of the sky.

The alternative is a proper rooflight with a lined shaft down to the ceiling. That gives a real patch of sky, more light, and the option of an opening unit to clear steam, but it means trimming rafters and ceiling joists and building a light well through the loft. In a bungalow with a shallow roof the shaft is short and works well. In a house with a deep roof void, the tube is often the more sensible answer, and our guide to skylights for dark rooms sets out where each wins.

Bathrooms in the older council-built houses are a special case. Many sit on the north side of the house with a small frosted window, and moisture is as much of a problem as gloom. An opening rooflight, or an electric opening rooflight with a rain sensor, lets warm damp air escape at the ceiling, where it collects, and it can be left ajar while the room is empty. Building Regulations Part F allows a suitably sized opening rooflight to count towards purge ventilation, which a fixed unit or a sun tunnel cannot do.

The chalk pits off Limekiln Road, part of which is now a nature reserve, are a reminder that the village was once a quarrying place, and that the ground rises gently towards the hills from here. For daylight, the rise is too slight to shade anything, so it adds nothing to the sun calculation. What it does add is exposure. Houses on the higher, eastern edge face open fields and take wind that has crossed a lot of empty land, and an opening sash on the windward slope will be harder to leave ajar. On those roofs we may put the opening unit on the sheltered slope and leave the exposed side fixed.

The airfield to the north is a different consideration. Homes close to it hear aircraft movements, and a roof is thinner than a wall when it comes to sound. If your house sits near the airfield, an acoustic laminated inner pane in the rooflight is worth pricing, because it reduces noise through the glass and also meets the Part K expectation for safety glazing overhead. The airport site is also expected to change over the coming years as redevelopment plans move forward, so the noise picture may not stay the same, but a bedroom rooflight fitted now has to suit the room as it is today.

The sun itself follows the same pattern as the rest of Cambridge. At this latitude, the midday sun climbs to roughly 61 degrees in late June and only about 14 degrees in late December, with around 38 degrees at the equinoxes. The skylight orientation guide shows what each slope gives a room through the year, and it is worth reading before the survey if your loft has slopes facing east and west rather than north and south.

Is Cherry Hinton covered by Cambridge City Council or South Cambridgeshire for planning?

Cherry Hinton is inside the Cambridge city boundary, so planning decisions are made for Cambridge City Council, through the Greater Cambridge Shared Planning service. Neighbouring Fulbourn falls under South Cambridgeshire. Check your address on the council's map, because the boundary does not always sit where the houses seem to end.

Can I put a skylight in the hip of my 1930s semi?

You can, but a hip slope usually faces the side boundary, so under permitted development the unit has to be obscure glazed and fixed, unless the opening part is more than 1.7m above the floor. A clear opening window there needs a planning application. A small high unit or a sun tunnel often does the job better.

Is a sun tunnel or a rooflight better for a bungalow hallway?

A sun tunnel is quicker and needs no structural work, and it gives soft, even light. A rooflight with a lined shaft gives more light, a view of the sky and the option to open it, at the cost of more building work. In a shallow bungalow roof, the rooflight is often the stronger choice.