A guide to dormer loft conversions

This article explains all you need to know about dormer loft conversions.

As well as answering common questions, we look at the options available, their pros and cons, and tell you how to plan a loft conversion.

Let’s dive in!

Dormer windows in a row of terraced houses.

What is a dormer loft conversion?

It generally means adding a box-shaped structure onto a pitched roof, which extends upwards and outwards to provide additional useable floor space and headroom.  

Why build a dormer loft conversion?

One of the main reasons is that it’s a cost-effective way of extending your home and increasing living space with minimal disruption. It’s also usually a cheaper option than moving house or building a home extension to accommodate a growing family.

Dormer loft conversions are great for making the most of underused space in your roof where you might want an office, en suite bathroom or playroom, and if your loft space is limited, they are good for creating height and more headspace. As well as offering extra space, they also provide more natural light. A loft conversion is also a reliable way to add value to your home.

Advantages of a dormer loft conversion

They can:

  • Improve your home by adding useable space.
  • Add natural light – a standard window can be installed, or a full-length picture window to make the most of a view.
  • Add architectural detail and improve the appearance of a house.
  • Improve ventilation: as air rises, dormer windows can provide more fresh air, keeping the upper rooms cooler.
  • Provide an emergency fire escape to a roof.

Disadvantages of dormer loft conversions

  • Altering a roof requires consultation with a structural engineer or a qualified building professional.
  • A poorly designed or constructed loft conversion could devalue your house.
  • It’s a technical job, requiring more skilled work than, for instance, installing a roof light would do.
Sloped roof dormers on two sides of a house.

What to consider if you’re thinking of a dormer loft conversion

Brian Berry, chief executive of the Federation of Master Builders (FMB) said:

One of the key things to think about if you are considering a loft conversion is whether the loft itself is suitable for the conversion you are trying to carry out, as some lofts are more suitable than others. Other factors to consider include the following:

The amount of available head height.

The roof pitch – generally, the steeper your roof pitch, the easier the loft conversion will be.

The type of roof structure – the two main types are a cut roof or trussed.

Water tanks and chimney stacks located in the loft – any relocation must be factored in ahead of the planning stage.

Available head space for a staircase; many variations here will affect the cost, timescale, and the amount of work involved.

To make sure you are adding value to your house, consider a gabled dormer, where the roof has a pitched roof as opposed to a flat roof. This is more visually appealing but might be a little more expensive and limit internal headroom.

Is your home suitable?

While they are suitable for most house types, getting the right dormer loft conversion for you is important: it needs to be in proportion with your house, and if done properly it can certainly add value to your property. Generally, any house with a pitched roof and loft space that satisfies basic requirements is suitable for adding a dormer conversion.

Most common types of dormer loft conversions:

Flat roof dormer

Here, the roof sits horizontally, and while this option gives the most space internally in terms of head height, a flat roof dormer can look unsightly on the front of a house.

Shed dormer

Here, the roof slopes, either back to front or front to back and there is no ridge or hip. This style is suitable for large dormer loft conversions.

Dog house dormer

The roof here has two pitched sides like a kennel.

Gable fronted dormer

A pitched roof made up of two sloping planes is supported by a frame that’s raised vertically to create a triangular section below the roof line.

L-shaped dormer

This is an extension to the side of a house with sides extending outwards and downwards to form an L-shape, i.e., two dormers, one over the roof of the main house and a second over a rear extension and they meet to form an L-shape.

Hip roof dormer

Here, there are three sloping sides that converge at the ridge, offering more useable floor space than a gable or a shed dormer.

Hip to gable dormer

The sloping side of the existing roof is converted to a vertical gable wall to create more head space. This is useful in end-of-terrace or semi-detached houses.

Mansard dormer

Named after French architect Francoise Mansard, this style is usually constructed on the rear of a property. It has a central flat roof and vertical walls often at a 70-degree angle, offering a substantial increase in space.

Do you need planning permission for a dormer loft conversion?

Most loft conversions won’t require planning permission, depending on the scale of the work. Loft conversions typically come under permitted development rights which entitle you to extend your home without planning consent if the work meets certain criteria. Permitted development is regulated through your local authority.

You may not qualify for permitted development rights if:

  • You live in a listed building.
  • You live in a conservation area or a heritage area.
  • You have used up your permitted development rights by already carrying out building works.
  • Your dormer exceeds 40m on a terraced house or 50m on a semi-detached or detached house.
  • The height of the dormer is higher than the original roof.
  • It has a balcony (Juliet balconies are allowed).
  • The material is not in character with the rest of the house.
  • Neighbours are affected by overshadowing or overlooking.
  • Bats are present in your roof: they are a protected species and to move them requires a special licence. To check for bats, you may need a bat survey.
A large flat roof dormer conversion.

How much would a dormer loft conversion cost?

The average price in 2022 is around £45,000, according to MyBuilder.com, but costs vary depending on the size of the property and the finish of the conversion work. Other costs could include scaffolding and possibly a roof cover, a new floor, roof alterations, interior walls, insulation, installing loft stairs, windows, electric sockets, plumbing, plastering, carpentry, and a final inspection before decoration.

According to the Federation of Master Builders (FMB), the cost will depend largely on the size and scale of the conversion. Depending on the requirements, small loft conversions tend to start from £35,000 and can run well into the hundreds of thousands of pounds for larger projects. The FMB has a series of ultimate guides to home renovation, to help consumers with their building projects.

How to plan the build stages

  • Confirm whether your scheme would meet the local council permitted development criteria or if there are planning constraints.
  • Draw up plans using an architect or surveyor.
  • You must comply with building regulations and obtain building control approval before works start. Matters covered include insulation, fire safety, headroom, stair design, electrical work, and soundproofing. Think about building regulation costs; your scheme will need to be inspected by your local authority’s building regulations department to ensure it complies with matters such as fire safety, access, and floor strength. Submitting plans and on-site inspections can cost between £400-£800.
  • If evidence of bats is found at a preliminary survey and you need to have a second stage bat survey, bear in mind that these can only be carried out between May and September, so plan your timeframes accordingly.
  • You may need a Party Wall Agreement if the scheme impacts adjoining properties as your neighbours must agree to the work taking place. You will be liable for their surveyors’ costs and any damage to their home that may result from the work.
  • If your scheme went ahead under permitted development rules, you need to apply for a Lawful Development Certificate to prove that the build was legal, and to demonstrate to future buyers that the design is of good quality.

Have I missed anything?

Do you have more advice about installing a dormer loft conversion?

If you have completed a loft conversion, are you happy with the additional living space it has created?

Please leave a comment in the box below.

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