Which loft conversion type suits your house?

Last updated: August 2026.

Start with the roof, not the brochure

Every loft conversion decision is really three measurements and one look out of the window. The measurements: head height at the ridge (2.2 metres minimum for anything comfortable), the roof footprint, and the pitch. The look: does your roof end in a flat gable wall or slope inwards at the side (a hip), and is there a rear outrigger behind the main house? Those four facts decide which conversion your house suits, and no amount of preference overrides them.

Velux: for lofts that already have the height

If you can stand upright at the ridge with room to spare, a Velux conversion at £15,000 to £25,000 gives you a proper room for the least money and the least disruption. Detached houses with steep pitches and older properties with tall roof voids are the natural candidates. The compromise is the sloping ceilings: furniture placement takes thought, and en-suites under a slope are tight. If head height is marginal, the money is usually better spent stepping up to a dormer.

Dormer: the default for a reason

The rear dormer at £30,000 to £50,000 is the answer for most Teesside semis and terraces because it fixes the two things a bare loft lacks: headroom across most of the floor, and a full-height window. It usually needs no planning permission, builds in 6 to 8 weeks, and the work happens mostly from the scaffold. Choose it when your loft has a reasonable footprint but not enough height to convert as it stands.

Hip to gable: built for Teesside's 1930s semis

If your semi's roof slopes down on the side as well as front and back, you have a hip, and it is stealing a third of your loft. Hip to gable at £40,000 to £55,000 (including the rear dormer that always accompanies it) squares that slope into a vertical wall and extends the ridge to meet it. On the interwar estates of Acklam, Hartburn, Fairfield and Norton this is the standard conversion, and a street where a neighbour has already done it is the strongest possible sign.

L-shaped: the terrace unlock

Victorian and Edwardian terraces with a rear outrigger, the lower back projection behind the main house, across Linthorpe, central Middlesbrough, Saltburn and the Headland have a second roof doing nothing. The L-shaped dormer at £45,000 to £65,000 builds over both roof levels, delivering a bedroom with en-suite plus a study or dressing room. The 40 cubic metre permitted development limit on terraces is tight for an L-shape, so volume calculations matter.

Mansard: maximum space, maximum process

The mansard at £50,000 to £70,000+ rebuilds the whole rear roof slope near-vertical, creating what is effectively a new storey with normal room proportions. It needs full planning permission, architect's drawings and 10 to 12 weeks on site. Choose it on larger houses where the extra space justifies the premium, or where the street already has mansard precedent.

The trussed roof caveat that applies to everything

Whatever type you choose, one structural fact can move every price above: factory trussed rafter roofs, the W-shaped timber webs standard from the late 1960s onwards and on nearly all new-builds at Ingleby Barwick and Wynyard, cannot simply be cut open. Converting them means a structural redesign with steels, adding £3,000 to £6,000. A ten-second look into your loft tells you which roof you have, and any honest survey confirms it before quoting.

Quick reference

• Good head height, tight budget: Velux.
• Standard semi or terrace, want a bedroom plus en-suite: dormer.
• 1930s hipped semi: hip to gable plus dormer.
• Victorian terrace with outrigger: L-shaped dormer.
• Large house, maximum space, planning acceptable: mansard.
• Storage only: boarding at £1,000 to £3,000, and do not let anyone sell you a conversion you do not need.