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How much does a dormer loft conversion cost?

A dormer loft conversion is a great way to open up a low roof void that lacks sufficient headroom or to add light and space to an existing loft conversion which is small and gloomy. It is no great surprise that dormer loft conversions are the most popular type of loft conversion of the different options available to choose form. The average cost of a dormer loft conversion is around £45,000 with a range of anywhere from £30,000 to £60,000 depending on the size of the conversion, the choice of internal accommodation and the number of dormer windows.

The best way to get an accurate dormer loft conversion costs is to speak with dormer experts in your area. Fill out your details below and arrange for dormer loft conversion experts to quote you - for free!

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What is a dormer loft conversion?

A dormer loft conversion is a loft conversion with dormer windows which extend out from the existing roof slope with vertical walls, creating both extra floor space and ceiling height within the loft interior. Viewed from the inside, the dormers have a horizontal ceiling and vertical walls.

Dormer loft conversions are very popular in Victorian terraces where extending at ground level is either not possible or has already been done and which tend to have lower roof spaces than later 20th-century houses. Find out more about dormer loft conversion costs below.

What are the benefits of a dormer loft conversion?

Dormer loft conversions are particularly popular for several reasons:-

  • They create not only additional floor space but also extra headroom so they are ideal for loft conversions which would otherwise not have sufficient roof height
  • They can open up existing loft conversions which are small and gloomy creating both more floor area and natural light
  • The additional headroom provides more options when it comes to the location of the staircase
  • Dormer loft conversions can improve the external aesthetics of a property rather than completely alter it in the way a Mansard loft conversion does
  • A dormer loft conversion can increase the value of your home by around 20%-25% depending on what the internal accommodation is used for – bathrooms and kitchens will always add more value than extra bedrooms. This means the cost of a dormer loft conversion could be offset by the additional value added to the property

What is the procedure for a dormer loft conversion?

The builder and the architect will consult the homeowner about their intentions and undertake a site inspection so that the architect can draw up the plans. Then it will be necessary to apply for planning permission. Your architect or surveyor must also liaise with your neighbours if you are in a terraced row or semi-detached property as you will require a Party Wall Award under the 1996 Party Wall Act and this must be in place before the work can commence. The final regulatory process before construction can start is the Building Control approval. The plans have to be submitted to the Local Authority and the Building Inspector will set up a series of site visits to check that the construction complies with current building regulations. This has nothing to do with planning permission. Only after all this is in place can work begin. This is a typical timetable for a dormer loft conversion:-

  • The loft needs to be cleared of any possessions and the water tank removed and replaced either with a sealed system or an unvented system which dispenses with the requirement for a header tank
  • Plumbing and electrical wiring are re-routed and new services installed
  • Floor joists are either reinforced or re-fitted
  • The floor is insulated and floorboards laid
  • Scaffolding is erected around the roof of the house to gain access to the external roof planes
  • The roof is opened up to accommodate the new dormer windows which are fitted, glazed and tiled
  • The new staircase is installed
  • The roof is insulated
  • Partition walls are fitted if there is to be more than one room in the new space
  • Plastering and carpentry work is completed
  • Final decoration is finished or installation of fittings for a new bathroom or kitchen are completed depending on the choice of accommodation

What can a dormer loft conversion be used for?

A dormer loft conversion can create much-needed family accommodation and avoid the requirement for a costly and undesired house move. It is also an option if the potential to extend at ground floor level has been exhausted.

Here are some popular uses for the extra room that a dormer loft conversion will create:-

  • A home working space or studio
  • One or two extra bedrooms
  • A luxury master bedroom with en-suite bathroom
  • A rooftop cinema and media room for all the family freeing up the sitting room or lounge to be used for something else like a playroom for small children or a home office or study
  • A spacious bedroom and study area for a teenager or student
  • A large dormer loft conversion can be used to create a kitchen and living/dining area. Match this up via the staircase with an en-suite bedroom on the floor below and you essentially have a self-contained annexe for an adult child, a lodger or an elderly relative

Not only does a dormer loft conversion add extra rooms but, depending on what you use it for, it can also free up other space in the home which is then available to be put to use for a different purpose.

Are there different types of dormer loft conversion? Are costs different?

There are essentially two different types of dormer loft conversion:-

  • Gable fronted dormer or gabled dormer – this is the most common type of dormer and consists of a pitched roof of two sloping planes supported by a frame which rises vertically to form a triangle shape below the roofline. These dormers resemble dog kennels and are sometimes referred to as dog house dormers.
  • Hip roof dormer – this is a roof which slopes upwards on the three sides so there are no vertical sections. The point at which the three sloping planes meet is called a hip. The term, hip bevel, refers to the degree of the slope

Why type of dormer conversion should I opt for?

Some of your decision will be based on the cost of your dormer loft conversion and practicality but what the finished conversion will look like from the outside is also important to many homeowners. Dog house dormers really suit traditional and old-style properties especially country cottages where they can sympathetically create more space without spoiling the appearance and aesthetics of an old building.

The choice of dormer and how many dormer windows to have will usually be governed by budget, the design and size of the conversion and personal taste.

How are the costs apportioned on a dormer loft conversion?

Your roofing contractors estimate will be split the cost of your dormer loft conversion between labour and materials and there will other charges such as the hire costs for the scaffolding platform and waste disposal charges.

What other dormer costs will there be?

  • You will need to employ an architect to produce the drawings and typically their fees for this type of work are between £800-£1,000 plus VAT
  • Planning permission will be required because of the structural changes to the roof and there is a set fee for this which is currently around £170
  • If the property is in a terraced row or semi-detached, your neighbours will need to be notified of the works and give their permission; this is a legal requirement under the provisions of the 1996 Party Wall Act. You might need to appoint a Party Wall surveyor (although commonly the architect who draws up the plans will perform this function). If your neighbour appoints one as they are entitled to do then you will be liable for both sets of professional fees
  • A dormer loft conversion will also require approval from the Building Inspectors who work for the local authority. They will need sight of the plans and will arrange to visit at set times during the construction process to ensure that the build is compliant with modern building regulations. They are responsible for signing off the works before the final interior fitting out and decoration is completed and issuing a completion certificate after the last inspection. This also attracts a fee which is typically in the region of £400-£800.

What else can impact on the cost of a dormer loft conversion?

It can be easy to overlook the impact that a dormer loft conversion might have on the rest of your home other than focusing on the extra accommodation it will create. There can be implications to your property which will also carry a price tag and ultimately affect the final cost.

This new part of your home will require light and heating and it may also require plumbing if you fit either a kitchen or a bathroom to the new space. All of these potentially put more pressure on your main services which could require re-routing or even upgrading:-

  • Some householders will fit a new boiler if the heating requirement is too onerous for their existing system. A couple of well-insulated bedrooms might not add too much demand but a new bathroom will
  • A loft-based water tank will need to be removed and relocated, a header tank can be replaced with an unvented system or the existing hot water system can be swapped to a sealed system
  • Fitting a staircase on the floor below may involve remodelling work and redecoration depending on its location

It may be necessary to upgrade the roof and many homeowners use a dormer loft conversion as an opportunity to refurbish their roof and undertake any other necessary upgrading or repair works whilst the scaffolding is in situ.

A traditional framed roof probably requires less work for a dormer loft conversion although the rafters may need reinforcement. A trussed roof which is usually present on more modern houses will require greater structural upgrading.

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Dormer Loft Conversion Cost Frequently Asked Questions

How do I know if my loft is suitable for conversion?

Measure from the top of the ceiling joist to the bottom of the ridge timber. The normal minimum measurement is 2.2 metres, anything smaller than this would not normally be deemed suitable. Interestingly, current Building Regulations do not state a minimum ceiling height for habitation and remain silent on this requirement so it is for the homeowner to determine with their roofing contractor and architect. Roof voids with a lower headroom are still potential candidates for conversion but the options will be much more expensive. One possibility is to lower the ceiling height in the rooms below or consider a roof lift extension which is essentially fitting a new and higher roof structure. 

How does the roof pitch impact on a dormer loft conversion?

The higher the roof effectively the more headroom you will have towards the centre of the room or rooms. Opting for a dormer loft conversion will then increase the headroom again plus provide more usable floor space.

How does a Mansard loft conversion differ from a dormer loft conversion?

A Mansard loft conversion has a flat roof with a wall sloping inwards at an angle of around 72 degrees. A Mansard loft conversion will completely change the outward appearance of the property and for some homeowners, this is not really an option. A Mansard is considered a type of dormer conversion because again, it offers maximum available headspace thus increasing the usable floor area. You can read more about the cost of a mansard loft conversion here.

How much space does a dormer loft conversion add?

How much actual space you can create will depend on the size and shape of your loft and how you choose to convert the interior. On average, a dormer loft conversion can add between 200 and 250 square feet of usable living space and used creatively, even a modest loft conversion can impact enormously on family life.

Why do I need a Party Wall Agreement?

The 1996 Party Wall Act became law to help neighbours who share walls or boundaries to cooperate with one another when it came to building works undertaken by one householder but which affect both properties. A loft conversion is a prime example of a situation which will require a Party Wall Agreement in line with the legislation; this agreement is referred to as a Party Wall Award. The agreement must be in place before the works commence and is usually organised by the surveyor or architect responsible for drawing up the plans although interestingly his position is regarded as neutral so he does not act for the homeowner who has instructed him in the first instance. The neighbour whose agreement is sought can also appoint their own surveyor and the homeowner instigating the works will be liable for these costs. It can be cheaper ultimately if you can get on with your neighbours but you should always have some sort of agreement in place regardless of this to protect you if there are unforeseen problems further down the line.

What time of year is the best time to undertake a dormer loft conversion?

Usually, the warmer months with the longer daylight hours are the most favourable although roofers are always busy at this time of year and sometimes, it can be easier to negotiate a more favourable cost if you are prepared to do the works during the autumn or winter. There will be a requirement to cover the roof and high winds and bad weather plus the shorter days can slow the works down.

Will I need planning permission for a dormer loft conversion?

Because of the changes to the structure of the roof, you will almost inevitably need to make a planning application. Some dormer loft conversions do not fall within what is described as Permitted Development or PD but more modest dormer conversions, if they do not sit forward on the roof plane and are no higher than the existing roof pitch, may fall within PD; your architect and roofing contractor will be able to advise you.

If you already have a loft conversion with roof lights or Velux windows then you may not have needed to apply for planning permission for this but if you add dormer windows to it then you will probably stray outside PD. Anything that takes the roof beyond its original size and height will require planning permission and listed houses or properties within a conservation area will always trigger a planning application.

How can I fund a dormer loft conversion?

There are a number of ways to fund your dormer loft conversion costs. Many homeowners add a further advance onto their existing mortgage if they have equity to spare in their property. Some roofing companies can offer to arrange finance for eligible customers but it can be cheaper on a monthly basis to go to your mortgage company as the payments are usually spread over the remaining term of the mortgage.

What other types of loft conversion are there?

As well as a mansard loft conversion, you'll also want to consider a Velux loft conversion. Read more about general attic conversion costs here.

How long does a dormer loft conversion take?

A dormer loft conversion takes approximately 4-6 weeks once you have all the requisite consents and agreements in place. A hip roof dormer may take a little longer.

Will my dormer loft conversion carry any guarantees or warranties?

Some of the materials used in the project will carry individual manufacturer’s guarantees plus your roofing company should add their own warranty for the entire project and the integrity of their work. An industry-standard doe this is around ten years.

If you would like a more accurate dormer loft conversion cost, get in touch with loft prices by visiting our contact form here. 

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