Transform a dark and dusty attic into a bright and spacious living area. 

What is a dormer loft conversion?

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Roof dormers are a popular type of loft conversion that can add valuable extra living space to your home. A roof dormer is a box-like structure that projects from a property’s existing roofline. The vertical walls and windows are a great way to bring extra headroom and daylight into a loft space. Dormer conversions are potentially suitable for almost any type of house, including terraced, semi-detached and detached.

Types of dormer loft conversion

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Dormers come in a variety of shapes, styles and sizes. Get your dormer extension design right and it can enhance the look of your home and boost its kerb appeal; get it wrong and it will be an eyesore. The challenge is to maximise internal space while making sure the dormer is in proportion to the existing house.

The main dormer types are:

Gable fronted or doghouse dormer

These feature a pitched roof with two sloping sides to form a triangle below the roofline, like a classic doghouse. Small single gables are often built for added light and visual appeal while larger ones offer extra space too.

Hip roof dormer

These are similar to a gable-fronted dormer but with three sloping sides instead of two. It gives more horizontal space than a gable dormer and more headspace than a shed dormer.

Shed dormer

On these, the roof slopes in the same direction as the main roof but at much shallower pitch. It has no peak or hip, which reduces costs. These dormers are often installed to create more space, so can be large.

Flat roof dormer

These have a box-like structure with a flat roof that is normally constructed to the rear of a property. These give the most internal space and head height as all the walls are vertical but can look a bit awkward like someone has stuck a box on the side of a property.

Mansard dormer

Named after French architect Francoise Mansard. This this is also usually built to the rear of a property, with a central flat roof and vertical sides often angled at 70 degrees. These extensions offer considerable increase in loft space.

L-shaped

This involves constructing two dormers - one over the roof of the main house and a second above a rear extension. The two dormers meet to form the L shape. Popular with owners of Victorian terraced properties.

Pros and cons of a dormer loft conversion

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The Pros:

• Dormers add head room and floorspace: A dormer can significantly increase usable floor space. A flat roof dormer may provide two additional bedrooms or a master bedroom suite with study/sitting area, for example.
• Roof dormers add light:  The vertical walls of a dormer enable the installation of standard windows in a converted attic, providing more natural light.
• Room with a view: Dormer windows offer a different view to the outside compared to Velux or roof windows. In rear dormers, it may be possible to have full height picture windows and balconies.
• Dormers add architectural interest and detail: The addition of one or two dormer windows can improve the external appearance of a property that might otherwise look a bit bland. A well-designed roof dormer can boost the kerb appeal of a home.
• Dormers enhance the interior: In addition to improving the external appearance of a home, a dormer enhances the inside space. A dormer window recess is the perfect spot for a window seat or desk where added light is required.
• Better ventilation: Rooftop windows can provide more fresh air and improve airflow throughout a house.  Hot air rises, so upper floors can become stuffy.
• Emergency fire escape: A dormer window can provide an emergency fire escape to an attic roof.  
• Versatile: Dormers come in a variety of styles.

The Cons:

• More structural work: Dormer lofts involve altering the roof of your home. You must consult with a structural engineer or qualified building professional before installing dormer windows.  . If poorly designed or constructed, a roof dormer could devalue your home.
• More labour intensive: Dormers require additional materials and time to build. There is more skilled work involved in installing a dormer loft conversion than a simple rooflight conversion.
• Planning permission may be required: Front dormers will always require planning permission. That said, many rear dormers are built under permitted development rights (no planning permission required).
• Extra cost: Building a roof dormer is more expensive than a basic rooflight attic conversion. The construction will take a bit longer because it requires altering the roof structure of the house. Costs will vary with the size and type of dormer chosen.

Is my home suitable?

Whether a loft is suitable for converting into an attic will depend on several factors, including available head height, roof pitch, structure and whether there are any obstacles, such as chimney or water tanks. Ask a building professional to visit your house and inspect your loft space.

To comply with building regulations, the minimum ceiling height required for a loft conversion is 2.2 metres. You can measure this yourself by taking a tape measure and running it from the floor to the tallest part of the roof space. Some houses with low-pitched roofs may not be suitable for a loft conversion because even adding a large flat-roof dormer won’t make up for lack of headroom.

If your roof space isn’t tall enough, there are two possible – but extremely costly – solutions. Firstly, raising the roof. While this is structurally feasible, major problems are the high cost and difficulty of getting planning permission, especially for a terraced or semi-detached house. The second option involves lowering ceilings in the rooms below to borrow some head height. Ask yourself if the space gained in the loft will make up for lower ceilings in the rooms below?

Your house will either have roof trusses or rafters depending on when it was built. Simply by lifting the loft hatch and looking inside, you should be able to tell which you have.

Traditional rafters run along the edge of the roof and leave most of the triangular space below empty. Dating from the 1960s onwards, truss frame roofs, with distinctive W-shaped trusses, take up a lot of room inside the loft. Converting a loft with trusses is possible but extra structural support is needed before the trusses can be removed.  It’s essential to consult a structural engineer before making any changes. Options include hefty steel beams, or an alternative, ingenious approach called ‘Telebeams’- extendable, lightweight aluminium beams (see our case study for more information on this approach).

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Dormers and planning permission

Rear dormers generally come under Permitted Development (PD) and since the front slope doesn’t change, your property remains largely unchanged from the street.  If the dormer window is at the front of your house, however, formal planning permission is needed. There are quite specific rules on loft conversions in terms of size and style. For example, PD allows you to extend up to 40 cubic metres for a terraced property and 50 cubic metres for a semi or detached house.  In terms of external appearance, the dormer can’t be built from materials out of character with your existing home. So, if you want to want anything bigger or a new look, you’ll need to apply for planning permission. 

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However, if you live in a flat or conservation area or national park, these PD rights will not apply, so always check with your local planning authority. 

Building Regulations and the Party Wall Act.

While many dormers loft conversions don’t require planning permission, building regulations approval is always needed. The regulations are there to ensure, for example, the structural strength of the new floor is sufficient, the stability of the roof is not jeopardised and the new loft stairs are safe. It’s a good idea to contact the building control department of your local council for further advice. If the house is semi-detached or terraced, the Party Wall Act 1996 will also come into play if the dormer conversion involved structural changes to the shared wall.

Hiring professionals, such as an architect or architectural technologist, surveyor and structural engineer, will help with the smooth running of your project. They can design your loft conversion and produce scaled drawings and calculations to demonstrate your dormer conversion complies with the latest regulations as well as secure the necessary approvals. If you want a loft conversion with extra headroom and floorspace, then a dormer may be the answer.