Could a dormer loft conversion provide the space you need?

dormer loft conversion on terrace house
(Image credit: Simply Loft)

Dormer loft conversions are one of the most common ways for people to extend their homes skywards — offering many benefits over other types of loft conversions

Not only are dormer loft conversions a cost-effective way to expand a house, but they are also suitable for most styles of property and can be designed to suit both traditional homes as well as those more contemporary in their appearance. 

In this guide, we explain everything you need to know to get started, from how they are constructed to whether or not you are likely to need planning permission for your particular project — as well as looking into the costs you can expect to convert your loft with a dormer extension.

What is a dormer loft conversion?

Dormer loft conversions tend to be the first types of loft conversion that spring to mind for most people.

"A dormer loft conversion is when a pitched roof is converted into a box shaped structure, creating walls that sit at a 90 degree angle to the floor," explains Robert Wood, Director of Simply Loft. "This helps increase space in your loft making it more easily liveable."

Dormer loft conversions project out vertically from the slope of a pitched roof and can incorporate standard windows and even patio doors into the newly created vertical sections. 

There is more than one type of dormer loft conversion and it is useful to know all the options before you select the best one for your needs and home:

  • Flat-roofed dormer loft conversion: These are one of the most commonly seen styles, adding lots of useable extra space. They can be single or full-width and bring in lots of light. Sometimes French doors are included and a small balcony.
  • Gabled dormer loft conversion: Usually more attractive than their flat-roofed counterparts, gabled (also known as dog-house dormers or pitched roof dormers) can be located at the rear or the side of the house, with full-height glazing. They tend to be more expensive than flat-roofed dormer conversions. 
  • Shed roof dormers: Similar to flat-roofed dormers, these have a roof that slopes down at a slight angle away from the house — they are a good option for homes with a gable roof.
  • Hipped roof dormer loft conversion: These feature roofs which slope on all three of their sides. They suit traditional-style homes well, but result in less usable space than other types of loft conversion, such as a flat-roofed dormer.
  • L-shaped dormer loft conversion: An L-shaped dormer loft conversion combines two dormers, joined together to form an L shape. This is a common project with owners of Victorian terraced or semi-detached houses where there is often plenty of space for the extra dormer. The bigger of the two dormers is usually attached to the main roof, while the smaller one is attached to section of the roof that faces the neighbouring property, at a slightly lower height.

l-shaped dormer loft conversion on terrace house

This L-shaped dormer loft conversion, by Simply Loft, features standard windows as well as French doors and a Juliette balcony. L-shaped rear dormer loft conversions are common on period properties that have an outrigger at the back.  (Image credit: Simply Loft)

Is my roof suitable for a dormer loft conversion?

"The main ‘pinch-point’ with loft conversions can be summed up in a single word — headroom," says chartered surveyor Ian Rock. "To see whether your loft makes the grade, simply stand under the highest point of the roof, usually in the centre of the loft, and check whether there is at least 2.8m of clear vertical space. This may sound overly ambitious, but the available space will shrink once the new floor structure is constructed and the rafters are lined with thick layers of insulation.

"Even if the amount of full height headroom is largely restricted to the centre part of the loft, it’s usually possible to add a large box dormer to dramatically extend the usable floor area."

"A traditional roof is 2.2 to 2.4 meters high and the minimum height for a modern trussed roof is 2.4 to 2.6 meters," explains Robert Wood of Simply Loft. "The preferred level of headroom for a habitable space is 2.3 meters. This height does not need to be maintained over the whole flooring area and a lower height may be acceptable for a bathroom, corridor or kitchen."

If the height in your existing loft is lower than required, it might be possible to steal some space from the rooms below by lowering their ceilings — although this will obviously add to costs and the amount of disruption you will have to live with during the project. Alternatively, you might need to start thinking about a different style addition, such as a modular loft conversion

Do dormer loft conversions require planning permission?

Do you need planning permission for loft conversions? This is one of the first questions anyone considering this kind of project asks. 

Just as with any type of loft conversion, whether or not planning permission for a dormer conversion will be required will depend on your home and the area you live in — as well as how big you want your extension to be.

"In most cases, dormer loft conversions do not require planning permission as long as they fall within the permitted development (PD) conditions for your type of house," says Robert Wood. "If your home is a maisonette or flat or falls within a Conservation Area or heritage site then different rules apply."

How much space do dormer loft conversions add?

Dormer loft conversions can add a great deal of extra space to a house, although how much will depend on the size of addition your house can accommodate — you don't want to end up with a visually 'top-heavy' home. 

Dormer loft conversions are a great way to add an extra bedroom or incorporate a home office or a hobby room without extending the footprint of your house.

"A dormer loft conversion can add up to 50 cubic meters of additional space to your home," says Robert Wood. 

If you are trying to decide between an extension or loft conversion, bear in mind that a loft conversion is usually more limited compared to an extension when it comes to how much space you can potentially add — although this will largely depend on the outdoor space you have available. If you have limited spare garden space, a dormer loft conversion may well be the best way to gain extra internal space.  

What type of windows suit dormer loft conversions?

There are lots of different window options for dormer loft conversions, from standard vertical windows, to rooflights and even full height glazing in the form of sliding, bi fold or French doors.

"If you have side windows overlooking a neighbour’s property, these windows must be made of obscured glass to comply with conditions of permitted development," warns Robert Wood.

dormer loft conversion bedroom with large metal windows

With their vertical walls, dormer loft conversions can be fitted with many different types of windows and doors, giving the newly formed spaces great far-reaching views.  (Image credit: Simply Loft)

How much do dormer loft conversions cost?

Loft conversion costs vary wildly depending on the style, size and specification of your design — as well as where in the country you live. They will also be affected by what you plan on using the space for — bathrooms and kitchens, for example, will cost more than bedrooms as they have extra plumbing requirements to factor in. 

"The average cost of a standard dormer loft conversion starts at around £35k but a surveyor will need to visit your home and discuss your requirements in detail before providing an accurate quote," says Robert Wood.

bathroom in loft conversion

Adding a bathroom within a loft conversion is a popular idea where an extra bedroom is being created — but do factor in the extra plumbing costs involved.  (Image credit: Simply Loft)
Natasha Brinsmead

Natasha is Homebuilding & Renovating’s Associate Content Editor and has been a member of the team for over two decades. An experienced journalist and renovation expert, she has written for a number of homes titles. Over the years Natasha has renovated and carried out a side extension to a Victorian terrace. She is currently living in the rural Edwardian cottage she renovated and extended on a largely DIY basis, living on site for the duration of the project. She is now looking for her next project — something which is proving far harder than she thought it would be.