Loft conversion types explained: which is right for your home?

If you’re thinking about going up into the roof rather than out into the garden, you’ve probably already noticed that “loft conversion” isn’t one thing. There are four main types, and the right one for your house depends as much on your roof as on your wishlist. Here’s how they actually differ, in the order they usually cost — least to most.

Start with your roof, not your Pinterest board

Two things decide what’s possible before any builder draws a line:

Head height. Stand in your loft and measure from the floor joists to the ridge (the highest point). As a rough rule, you want around 2.2 to 2.4 metres of usable height. Less than about 2 metres and you’re into structural work to gain it, which changes the conversation and the budget.
Roof structure. Older Bristol homes — the Victorian and Edwardian terraces around Bishopston, Redland and Southville — tend to have “cut” roofs (timbers built up on site), which are usually straightforward to open up. Many homes built from the 1960s onward have “trussed” roofs (those W-shaped frames), which need more reinforcement to clear the space.

A good builder or structural engineer can tell you which you’ve got in ten minutes. Don’t fall in love with a design before you know.

The four types

Rooflight (Velux) conversion

The simplest. You keep the existing roof shape exactly as it is and add windows that sit flush in the slope — Velux being the brand most people know.

Best for: lofts that already have generous head height and don’t need extra floor area, and homes in conservation areas or with tighter planning constraints.
Space gained: none beyond what’s already up there — you’re making an existing volume usable, not enlarging it.
Planning: almost always falls under Permitted Development (work you can do without a full planning application), as nothing changes the roofline.
Cost: the cheapest option by a clear margin.

The honest catch: if your head height is marginal, a rooflight conversion won’t fix it.

Dormer conversion

The Bristol workhorse. A dormer is a box-shaped extension that projects out from the rear roof slope, giving you flat ceilings and proper standing room. You’ll see these across the back of terraces all over the city.

Best for: the majority of standard terraced and semi-detached homes that need real, usable space and headroom.
Space gained: significant — it turns an awkward sloped void into a square, functional room, often enough for a double bedroom and a small en-suite.
Planning: rear dormers frequently sit within Permitted Development, though there are limits on volume and rules are tighter in conservation areas. Always confirm with Bristol building control before committing.
Cost: mid-range, and usually the best value for the space you get.

Hip-to-gable conversion

For homes with a “hipped” roof — one that slopes back on the side as well as the front and rear (common on semis and detached houses, less so on mid-terraces). This type rebuilds that sloping side end into a vertical wall (a “gable”), squaring off the roof and creating volume.

Best for: semi-detached and detached homes with a sloped side roof. It’s often paired with a rear dormer (a “hip-to-gable plus dormer”) for a much bigger room.
Space gained: substantial, because you’re reclaiming the whole end of the roof.
Planning: often Permitted Development on a house, but not on a flat or maisonette, and not always in conservation areas.
Cost: more than a dormer alone, as there’s more structural rebuilding.

Mansard conversion

The biggest transformation. A mansard rebuilds an entire roof slope into a near-vertical wall (around 72 degrees) with a shallow top, usually across the rear. It looks like an added storey and gives the most space of all.

Best for: homeowners who want maximum floor area and ceiling height, and period properties where a mansard suits the street.
Space gained: the most of any type — frequently a full extra floor.
Planning: almost always needs full planning permission, as it changes the roof shape dramatically. Common on older terraces where it matches neighbours.
Cost: the most expensive, reflecting the scale of the rebuild.

The bits everyone forgets

The staircase. It has to land somewhere downstairs and meet regulations, and it can quietly eat a chunk of a bedroom below. Plan it early.
Building control. Separate from planning — this is the sign-off that the structure, fire escape, insulation and stairs are safe and legal. Every loft conversion needs it.
The Party Wall Act. If you share a wall with a neighbour (almost everyone in a terrace), you’ll likely need to serve formal notice before work starts. It’s routine, but skip it and you store up trouble.
Heating. An extra room means extra demand on your boiler and radiators. Sometimes the existing system copes; sometimes it doesn’t. It’s worth checking — our heating services can advise on whether your boiler will keep up.

So which one?

If your loft is already tall enough, start by costing a rooflight. If you need real room in a terrace or semi, a dormer is usually the sweet spot. Got a sloped side roof on a semi? Look at hip-to-gable. And if you want a whole new floor and the budget to match, a mansard delivers — with the planning effort that comes with it.

The only way to know for certain is to have someone measure up and look at your roof honestly. If you’d like that, we’re happy to come round, talk through the realistic options for your home, and put a fixed price in writing — no pressure either way. Get a free quote, have a look at our recent work, or see the areas we cover across Bristol.