Rooflights and skylights in Cambourne

The town was planned as a group of neighbourhoods rather than grown around a green, and it still reads that way. Great Cambourne, Lower Cambourne and Upper Cambourne each have their own streets and character, and building has since carried on at the western edge. South Cambridgeshire District Council has its offices in the town, which surprises people who assume the council must sit in a historic centre somewhere. Planning applications for Cambourne addresses are dealt with by Greater Cambridge Shared Planning, the joint service that South Cambridgeshire runs with Cambridge City Council.

What this means for a skylight is practical rather than romantic. You are rarely fighting a slate roof, a sagging purlin or a conservation officer. You are more likely to be working with factory-made roof trusses, concrete interlocking tiles, a loft full of insulation and a house that was designed by a developer to a tight footprint. Those are all good things for a clean installation, but each brings its own questions, and they are different from the ones we meet in Romsey or on a thatched cottage out in the villages.

Our skylight and rooflight installation service for Cambridge and the villages plans every job by deciding where the light should land in the room first. In Cambourne that approach meets a particular set of constraints: roof structure, the planning history of the estate, and gardens that leave little room to extend. The sections below work through each one.

The national rules, known as Class C, allow rooflights on a house provided they do not project more than 150mm from the plane of the roof, do not rise above the highest part of the roof, and, where they face a side boundary, are obscure glazed and fixed shut unless the opening part is more than 1.7m above the floor. Those limits are generous for a standard roof window, which sits well inside the 150mm projection. Our guide to planning permission for rooflights covers the rules in more depth.

The catch on newer housing is that permitted development rights can be removed. When a large estate is approved, the council may attach conditions to the permission that take away some or all of those rights for certain plots, so that later changes come back for approval. We do not know which plots in Cambourne carry such conditions, and we would not guess for any named street. It may be that your house has none. The way to find out is to look at the original planning permission for your plot, which Greater Cambridge Shared Planning holds, or to ask them directly.

Separately from planning, many estate homes carry covenants in the title deeds. These can require consent from the original developer or a management company before external alterations. Whether a covenant applies, and whether it covers a roof window, depends entirely on the wording of your deeds. Flats and maisonettes are a different case again: they have no permitted development rights of this kind, and the lease will almost certainly require the freeholder's consent. We raise all three points at the survey so that none of them surprises you after the order is placed.

A kitchen or family room extension here is often only a few metres deep, with the original house wall now in the middle of a longer room. That inner wall is where the light fails. A roof lantern placed towards the back of the extension, close to the old house wall, pulls daylight into the deepest part of the room, which is exactly where the original rear windows used to do that job. A lantern placed out towards the garden end mostly lights a space that already has glazed doors.

On a low extension, a flat roof rooflight can be the better choice than a lantern. It sits lower on its upstand, which matters when a neighbour's bedroom window looks down across your roof, and its single pane reads as calmer from above. On a small roof, a lantern's ridge and hips can also crowd the space available for the kerb and falls.

Conservatories are common on this generation of housing, and many owners now want to replace a polycarbonate or glass conservatory roof with a solid insulated roof that holds its temperature better. Putting a lantern or a flat rooflight back into the new solid roof keeps a controlled amount of daylight, rather than the whole-roof glare that made the old conservatory too hot in summer. Whether that change needs Building Regulations approval depends on how the room is separated from the house, and we check it before the design is fixed.

Part L sets the thermal standard: a new or replacement rooflight should meet a U-value of 2.2 W/m2K or better, measured in the horizontal plane. Part K asks for safety glazing where glass sits overhead, which in practice means a laminated inner pane. Part B, the fire section, is where attached housing matters. Rooflights should not be placed within 1500mm either side of a party wall, because the roof there has to resist fire spreading from one home to the next. On a narrow terraced house that zone takes a real share of the roof, and the window position has to respect it even if the light plan would like it closer to the wall.

Houses set within a few metres of a boundary also bring the external fire rating of the rooflight into question. None of this blocks a well-designed opening, but it shapes where one can go, which is why the survey marks party walls and boundaries on the plan before we draw the glass. Our page on Building Regulations for rooflights covers each part in turn.

If your house is recent enough to still be inside a new-home warranty period, it is sensible to read what that warranty says about alterations to the roof before work starts. Terms differ between providers, and we would rather you checked than assumed. Once the paperwork is clear, a roof window between two trusses is usually a one-day job, and the Building Control completion follows once the inspection is signed off.

Some older installs in the town, fitted when the first phases were built, are now reaching the age where the sealed units start to mist between the panes. Replacing a unit like that is a misted rooflight replacement rather than a new opening, and it is a good moment to upgrade the glass to suit the slope. Similar new-town questions come up on our Northstowe page, where the estates are younger again.