Loft conversions: Choosing the right windows

Adding an extra storey to your home may be easier than you think, especially as some key planning and design rules have changed in recent years. There are three options for roof windows: dormers, rooflights and gable windows. Bringing in natural light is vitally important to the success of a loft conversion, so it is worth considering all of these designs.

ABOVE (click on gallery image to view larger picture): Rooflights, as in this A1-designed living/ home office space, are an ideal option for retaining privacy and can be combined with other solutions, as with the smaller box dormer.

There are three options for roof windows: dormers, rooflights and gable windows. Bringing in natural light is vitally important to the success of a loft conversion, so it is worth considering all of these designs.


These are vertical windows, set into the roof slope and usually projecting up, creating an area of the loft conversion that has full-height headroom or more. Although planning may not be required for a dormer, unless they face a highway, they should be carefully positioned to respect the symmetry of the building, regularly spaced – never too close to the edge of the roof – and balanced in size.

Dormers look best if they are set well in from the eaves and ridge, so a large area of the original roof is visible from outside. The pitch of the dormer’s roof should match that of the house or local architecture. The roof can be pitched with a gable end, hipped or half-hipped, flat or curved, or have a mono pitch.

Although it’s more expensive, two or more small dormer windows will usually look better than one large one. So, try not to exceed 1.2m in width. And the materials used should complement the house and surrounding architecture.

Although Building Regulations require insulation in a dormer window’s roof and walls, be careful to keep down the wall thickness by using timber framing and cladding, such as render, tile hanging, timber boarding or roof lead.


These are windows that lie in line with the slope of the roof and, although planning consent is not usually required, they need careful thought as too much glazing along a roof can detract from a house’s appearance. It is best, too, to align them and use regular sizes and spacing. Blocks of rooflights arranged in a grid can form great feature windows. For a period building or traditional-style house, conservation rooflights are worth the extra money. These are black with a vertical glazing bar and are based on an original Victorian design made from cast iron. Genuine metal conservation rooflights (as opposed to timber copies) will sit flush with the roof’s tiles.

If you have a flat roof, you can incorporate flat rooflights and there are frameless options available, too. If the loft conversion is to be used as a living room or studio, a glazed roof lantern can be an amazing-looking central feature.

ABOVE: (LEFT) A dormer like this will create additional space and headroom, and also an attractive feature. The designer, A1 Loft Conversions, covers all London postcode areas, Surrey, Middlesex and the Home Counties. (RIGHT) The gable-end wall in this guest bedroom conversion has been fitted with full-height French windows to maximise natural light and views. Restricted opening mechanisms or an exterior balconet are required by Building Regs for reasons of safety.

Gable-end windows

Most loft conversions will have at least one vertical external wall and standard window openings can be formed in these walls to bring in extra light. New windows in side elevations do not usually require planning permission if they are obscured, or are more than 1.7m above floor level.


Who should do the work?

You can commission an architect or an architectural designer to draw up your loft conversion plans. They will charge either a percentage of the build cost (7-12 per cent is common) or you can negotiate a fixed all-in fee. An engineer will also be required to provide structural calculations for the alterations and the fee for this will range from £400-£1,000. You can then put the drawings out to tender with several builders and choose from their quotes.

An alternative to using an independent designer and a contractor is to employ a specialist loft conversion company that offers a design-and-build service. If you decide go down this route, bear in mind that you will still be paying for the cost of the design, even though this is included as part of an overall package price.

Whoever you use to design and build your loft conversion, make sure they have plenty of experience and know all the planning rules and Building Regs – and all the solutions to these – inside out. Always ask around for recommendations and take references from previous customers.