Rooflights and skylights in Girton

Many houses of this period were built with hipped or part-hipped roofs, steep enough to give a usable loft but broken up by chimneys, hips and sometimes a bay or gable to the front. Every house needs measuring, but a few patterns come up. The rear slope is usually the one to use for a loft room, because it keeps new glazing off the street elevation and tends to be the larger, cleaner plane. Where the house has a hip at each end, the rear slope narrows towards the ridge, so a pair of roof windows set low enough to see out of while standing often works better than a single large unit high up.

A detached house also removes one constraint that shapes semis and terraces: there is no party wall, so the Building Regulations keep-clear zone either side of a separating wall does not apply. Boundary distance still matters for fire performance where a slope sits close to the plot edge, but on a wide Girton plot that is rarely the limiting factor. The limit is more often the structure, because an older cut roof has purlins and struts that the new openings have to respect, and trimming rafters must be done so the loads still find a way down.

These houses were built with deep plans and a central staircase, which leaves the landing and the upper hall as the darkest part of the first floor. A modest rooflight over the stair well, where the roof allows it, can change the feel of the whole middle of the house. We check whether there is a clear route from the roof to the landing ceiling, because a short lined shaft is simple, while a long one through a cold loft needs insulating and loses some light on the way down.

A south-facing roof shaded by a tall tree to the south behaves very differently in summer and winter. In June the leaves cut much of the direct sun, which can be a welcome check on heat. In December the branches are bare but the sun is so low that the trunk and limbs throw long shadows across the roof for much of the short day. A rooflight that looks ideal on a compass can end up giving soft, dappled light instead of a warm sun patch on the floor. That is not always bad, and for a study or a bedroom it can be exactly right, but it needs to be expected.

Trees also drop leaves, seeds and needles, and a flat roof rooflight under a canopy collects them. A unit with a real fall across the glass, a well-formed upstand and self-cleaning glass copes much better than a near-flat pane. For an extension roof close to a mature oak or sycamore, we would also think about access for clearing gutters and outlets, because blocked outlets can leave water sitting around the kerb.

• Deciduous trees to the south: plan for strong light in winter only if the tree is well clear of the low sun line.
• Evergreens close to the house: expect steady, softer light all year and consider a larger opening to make up for it.
• Trees to the north: little effect on direct sun, but leaf litter still reaches the roof.

Our guide to which way a skylight should face explains the compass part of this, and the survey adds the trees and neighbouring buildings the compass cannot show.

Under the permitted development rules for houses, a rooflight is generally allowed if it projects no more than 150mm from the plane of the roof, sits no higher than the highest part of the roof, and, where it is on a side-facing slope, is obscure glazed and fixed shut unless the opening part is more than 1.7m above the floor of the room. Those rules do not apply to flats, and they can be removed by a condition on an earlier permission or an Article 4 direction. A listed building always needs listed building consent for this kind of change, whatever the planning position.

We do not assume a conservation area status for any Girton address. The Greater Cambridge Shared Planning website has a constraints map and conservation area information, and that is the reliable place to check a specific house before any design is fixed. If the house does sit in a conservation area or is listed, a flush conservation rooflight on a rear slope is the kind of detail officers tend to look on more kindly. Our planning permission guide covers the rules at more length.

Building Regulations are a separate matter. New openings in a roof generally need Building Control approval, because they touch the structure, the insulation, fire performance near boundaries and safety glazing overhead. We handle the Building Control notification where the work is notifiable, and we install to current Building Regulations. The Building Regulations guide sets out which parts apply to roof glazing.

Do I need planning permission for a skylight installation in Girton?

Often not, if the house is not a flat, is not listed, and the rooflight stays within the permitted development limits for projection, height and side-facing glazing. Check the Greater Cambridge Shared Planning constraints map for your address first, because conservation area status, Article 4 directions or old planning conditions can change the answer.

Can a 1960s bungalow take a roof window on a shallow roof?

It depends on the pitch. Each roof window and rooflight has a minimum rated pitch, and some shallow roofs sit below it. Where a standard roof window will not go, a low-pitch rooflight or a sun tunnel can often be used instead, and we measure the pitch at the survey before recommending either.

Will a rooflight help with road noise near the A14?

The right glass reduces it. A laminated pane with an acoustic interlayer, and in some homes triple glazing, cuts traffic and rain noise noticeably compared with a basic double glazed unit. We would pick the glass for noise and for the orientation together, so the unit suits both the sound and the sun on that slope.