Loft conversion design: dormer, mansard, hip-to-gable or rooflight conversion?

Find out how to make the most of your loft by choosing the right type of conversion for your home and budget

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Bespoke furniture from Neville Johnson has been used to maximise space in this converted loft

When you need extra space, one option to consider is a loft conversion. Building up into the roof is often the most cost-effective way to extend your home, avoid building over any of your garden area and can add significant value to your property, too.

A well-designed loft conversion with a full staircase accessed from the main hallway or landing can be made to feel as if it was always there. Providing care is taken to ensure that alterations to the roof are sympathetic to the architecture of the existing house, it can look as if it was part of the original design. Here we explain how to choose the right type of conversion, and take a look at how much each type could cost.

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Related articles: A beginner’s guide to converting your loft | Planning and costing your loft conversion | 10 great design ideas for your loft conversion | Loft conversion design ideas

Which type of conversion is best for your home?

Not all lofts are suitable for a conversion. Some roofs have very shallow pitches or an unusual shape, while others may need extensive alterations to change the structure.

In all cases, the cost of a conversion needs to be weighed up against the value and usage that the extra space will add. And remember to take into account that, usually, some existing space will be lost when you create staircase access to the new room(s).

There are four fundamental types of loft conversion and they vary in complexity and in cost. A typical loft conversion project will take four to six weeks to complete and most of the work can be done without disturbing the existing house. A more complex project that involves removing the existing roof will take eight to ten weeks.

Create a new mansard roof

This is where the roof structure is altered at the back of the house (and sometimes at the front, too) to create a far larger area with full headroom. A mansard conversion typically spans from gable wall to gable wall and is like another full storey with almost vertical tiled walls and a flat roof. This results in an addition that may appear far more a part of the property and less like an add-on than a large box dormer. Costs range from £1,500-£2,500 per m².

Mansard conversion

The cross section of a mansard loft conversion

Turn an attic into a room with rooflights

The existing loft space can be converted by simply adding rooflights, such as VELUX windows, plus upgrading the structure and adding stairs, electrics, plumbing, insulation etc. This is usually the simplest, quickest and cheapest type of conversion, as structural alterations are kept to a minimum. Costs range from £1,000-£1,750 per m².

Rooflight conversion

The cross section of a roof light loft conversion

The amount of useable space for a rooflight conversion will depend on the height and pitch of the roof. By the time the structure has been converted and insulated, only the area measuring 2.3m or more between the top of the floor joists and the underside of the rafters will have enough clear headroom for standing.

If your loft does not yield sufficient space for a simple rooflight conversion, you will need to consider one of the other design options shown on these pages to create the useable new room you need.

Try a dormer conversion

The roof structure is altered at the rear (or sometimes the sides) to add a large flat-roofed ‘box’ dormer, enlarging the amount of space with full-height headroom in the new room. The part of the roof being extended will need to be stripped and the structure rebuilt. Consequently, this option is more time-consuming and expensive. Costs range from £1,250- £2,000 per m².

Dormer conversion

The cross section of a dormer loft conversion

Choose a hip-to-gable design

This usually applies to a semi-detached house or bungalow where the roof is currently hipped (sloped) to the side, as well as to the back and front. This roof is stripped and the hipped section removed. The end wall is then built up to form a new vertical gable and a standard pitched roof. The work creates a far greater area with full headroom. Costs range from £1,500-£2,500 per m².

Hip to gable conversion

The cross section of a hip-to-gable loft conversion