Rooflight Loft Conversions in Cambridge

A rooflight conversion — often called a Velux conversion after the best-known make of window — only works where the loft already has the head height, because it adds no volume to the roof. Where the height is there, it is usually the cheapest and least disruptive way to turn a loft into a room; where it is not, no amount of money spent on this type will create it.

Our loft conversion costs guide carries published Cambridgeshire ranges by type and puts the difference in cost between this and a dormer in context.

Head height decides everything

Because the roof shape does not change, the room you get is the space that is already up there, minus what the build takes out of it. Two things eat into the height you measure standing in the loft today.

The first is the new floor. Existing ceiling joists were sized to hold up a ceiling, not people and furniture, so a new floor structure goes in — and it usually sits above the existing joists, raising the floor by some amount.

The second is insulation. The rafters have to be insulated to current standards, and where there is not enough depth between them, insulation goes under them too, which drops the ceiling. The figure that matters is the height after both, not before. A figure taken from a tape measure held up in an empty loft is the wrong number to plan around.

What the work actually is

The structure is the main job even though nothing changes outside. A new floor is designed by an engineer and inspected by Building Control. Where rafters are cut to take a rooflight, they are trimmed and the load carried around the opening rather than simply cut through.

Then it is insulation, plasterboard, the stair, electrics, heating and finishes — and, in most cases, fire safety work on the floors below, because the loft becomes part of a protected escape route. That last item is a Building Regulations requirement rather than an upsell, and it is the thing homeowners are least expecting. Our Building Regulations guide explains how it runs alongside the build.

The rooflights themselves

Where they go matters more than how many there are. Set them low enough in the slope and you get a view out while seated; set them high and you get daylight but a room that feels like a corridor with a skylight. Whether a rooflight also has to act as an escape window depends on the fire strategy for the whole house. In a bungalow conversion it usually does; in a two-storey house the main route is normally a protected stair, and a window on its own may not be acceptable. Your designer and Building Control will agree the escape route, alarms, doors and any other measures needed, and if a rooflight is part of that plan it sets that window’s size and sill height.

Rooflights that sit flush in the plane of the roof look considerably better from the street than ones that stand proud, and on a visible elevation that difference is worth having.

The stair problem is the same

People assume that because a rooflight conversion is the simple option, the staircase is simple too. It is not. The stair needs head height over its whole length, it has to land where it does not ruin the floor below, and on a shallow roof the head height at the top of the stair is often the very thing that is in short supply. On more than one survey the stair, not the room, is what rules this option out.

When it is the right answer, and when it is not

It is the right answer when the loft already has generous height across a decent width, when the budget is the constraint, when you want the work done with the least disruption, or when planning makes a dormer difficult — a rooflight conversion changes nothing visible in the roof line, so it is the least contentious option on a prominent elevation or in a conservation area.

It is the wrong answer when the height is marginal. Spending the money to end up with a room you can only stand up in down the middle is the most common regret in loft conversions, and it is entirely avoidable by measuring properly at the start. If the height is not there, the realistic options are a dormer, or leaving the loft alone.

Common questions

Do I need planning permission?

Usually not. Rooflights that sit within the plane of the roof normally fall within permitted development, subject to conditions, and this is the least likely of the three types to need an application. The usual exceptions are conservation areas, listed buildings and Article 4 directions; a rooflight on the front roof slope is still permitted development provided it projects no more than 150mm from the roof plane and stays below the ridge. See our permitted development guide.

Do Building Regulations still apply?

Yes, in full. Planning and Building Regulations are separate, and the fact that a job needs no planning application says nothing about the regulations. Structure, insulation, fire safety and the stair all have to comply and be inspected.

Can I do it without a proper staircase?

Not if you want it to be a habitable room. A loft reached by a ladder remains storage — it cannot be called or sold as a bedroom, and it will show up on a survey when you come to sell.

How much cheaper is it than a dormer?

Materially cheaper per square metre, because you are not building a structure outside. The loft costs guide sets out published rates for each type side by side.

How disruptive is it?

The least of the three. The roof is not opened up in the way it is for a dormer, but each rooflight still needs a smaller roof alteration, so temporary weather protection is planned for those openings, subject to the builder’s sign-off. Most of the noise is the floor and the stair opening.

The other two types

If the height is not there, a dormer conversion creates it. If your roof is hipped, a hip-to-gable conversion gives the most room of the three. The loft conversions page covers how we run all three.