Loft Conversions
Southampton

As a guide for 2026, a rooflight (Velux) loft conversion in the Southampton area typically costs £25,000 to £45,000, a rear dormer £45,000 to £70,000, a hip-to-gable conversion £55,000 to £80,000 and a mansard £65,000 to £95,000 or more. The size of the room, whether you add an en-suite, where the new staircase lands and the finish you choose move the price most. We give you a detailed written quote after a free survey.

The quick test is head height. Measure from the top of the ceiling joists to the underside of the ridge: around 2.2 metres or more usually makes a conversion straightforward. Older cut-rafter roofs are simpler to open up than modern trussed roofs, which need more steelwork. You also need room on the floor below for a staircase. A low roof or awkward roof is rarely a dead end, as a dormer or hip-to-gable can create the height, and we will tell you honestly at the survey.

Always, even when planning permission is not needed. Building control checks the structure, fire safety (a protected escape route down the stairs, fire doors to the habitable rooms and mains-wired interlinked smoke alarms), the staircase and its headroom, insulation, ventilation and sound between floors. We manage the inspections and you receive a completion certificate at the end, which you will need when you sell.

On a semi-detached or terraced house, usually yes. Cutting steel beams into the shared wall is notifiable work under the Party Wall etc. Act 1996, so your neighbours must be served notice at least two months before that work starts. If they consent in writing, no surveyor is needed. We help you serve the notices early so they do not hold up the start date.

In most Southampton streets a well-designed extra bedroom with an en-suite adds more to the value of the house than it costs to build, because buyers pay for bedroom count. It depends on the ceiling price of your street, so we will give you an honest view at the survey rather than a headline percentage.

Many loft conversions are permitted development. In England you can add up to 40 cubic metres of roof space on a terraced house and 50 cubic metres on a semi or detached house, as long as nothing extends beyond the roof slope facing the road, nothing is higher than the existing ridge, materials match, side windows are obscure-glazed and there are no balconies. Mansards, front dormers and lofts in conservation areas usually need full planning permission. Even when it is permitted development, we recommend a Lawful Development Certificate so a future buyer has written proof.

On site, a rooflight conversion usually takes six to eight weeks, a rear dormer eight to twelve weeks, and a hip-to-gable or mansard ten to fourteen weeks. Allow six to twelve weeks before that for drawings, structural calculations, approvals and any party wall notices.

Usually, yes. Most of the work is done from scaffolding outside, and we only open up the ceiling for the new staircase towards the end of the build. There will be noise and some dust during the structural stage, and we protect the stairs and landing and clean up every day.

Yes, and most of our loft clients do. The key is the waste route: the shower, basin and WC need a fall to the soil stack, so we plan the en-suite over or close to the bathroom below where we can. A loft en-suite is fitted by our own plumber and tiler, fully tanked, with an extractor fan to building regulations.

Look for a company that handles design, approvals and the build itself, uses its own trades and gives you a detailed written quote. The team behind Pure Renovation & Design has 18 years of experience building and renovating homes across Southampton, with five-star reviews on Google and the same in-house team from survey to sign-off, including the joinery, en-suite and fitted storage that make a loft room work.