How to plan a loft conversion - advice for planning and costing your dream space

Could you have cash in your attic? Creating a new room at the top of the house will not only add space to your home, but can also increase its value

Need more space? How about a loft conversion? There are many good reasons to convert or extend your loft. For a start, it's possibly the largest square footage of unused space in your home, yet often the simplest and least disruptive to convert. And it's certainly more cost effective and less stressful than moving house. If you don’t have to extend, all you may need to do is strengthen the floor, insulate and add windows.

We'd always go for a loft conversion over a basement conversion. Not only will the work take a fraction of the time, it is far less expensive and and won't involve daunting structural changes, like excavating and underpinning your foundations.

Visit our project planning channel for all your home extension needs

On completion, you'll be rewarded by a light filled space and some potentially fabulous views of the surrounding neighbourhood. You might also have improved your home's insulation and cut your heating bills in the process.

Read on, to discover everything you need to know about loft conversions.

How to plan a loft conversion

living room with wooden flooring and white desk with chair

(Image credit: Mel Yates)

'Interest in loft conversions is increasing as homeowners look to add more space to their properties' explains Adrienne Minster, CEO of  Rated People (opens in new tab). 'We’ve seen demand for loft conversions surge by almost a quarter (24%) so far this year, compared to the start of 2020.'

'Converting your loft can not only provide more space, but it can also add value to your home if you decide to sell. Whilst there are many benefits, it is important that you take time to consider all factors before progressing with work. First of all, you will need to check that you are able to convert your loft space. This depends on the internal height, type of roof and the space you have available downstairs for an additional staircase.'

Is my attic space suitable for a loft conversion?

There are certain head height requirements you must adhere to in order for your loft conversion to be compliant. As a rule of thumb, you need 2.2m between the top of the floor joist of the loft to the bottom of the ridge beam. As a rule of thumb, if you can measure 210cm from the floor to the roof at the tallest part, you have sufficient head height for a loft conversion. To make for a comfortable attic bedroom or living room, at least half the loft space should be this tall. However, you could consider placing a loo or bathroom under the sloping eave, where headroom is less of a priority.

Pre-war buildings with steeply pitched roofs are often the easiest to convert, but there will always be structural considerations when turning this space and most lofts need additional support from steel beams to strengthen the floor and roof.


room with wooden flooring and bathtub

(Image credit: Alistair Nicholls)

Before beginning any construction work you will need to have architectural plans drawn up, that meet either permitted development or planning permission requirements as well as party wall agreements if your home is joined onto another at either side. Your loft conversion must also pass building control inspections for it to be compliant.

Unlike an extension, because lofts are relatively self-contained in the early stages of building, they can be accessed from the outside – meaning you can continue living in the house while the work is carried out.

What is permitted development?

The majority of loft conversions fall under 'permitted development' – in other words, you don't need planning permission to have one. This is good news, as the planning process can be a long and tricky one. However, special rules and guidelines govern conservation areas and listed buildings. If your house is listed, you will need Listed Building Consent, and if you live in a conservation area you’ll need permission for any dormers or extensions.

Whatever your situation, you will still need Building Regulations approval and possibly a Party Wall Agreement with your neighbours.

You should always ensure that:

  • No more than 50 cubic metres of space is being added to a detached or semi-detached house. For terraced houses, this figure drops to 40 cubic metres. These figures take into account any previous loft additions.
  • You're not raising the existing roof height or altering the front of the building significantly. The back can usually be changed physically and cosmetically, but it's wise to consult with your local council to be sure.
  • As mentioned above, there should be 2.1 metres of head height in the main part of the conversion.
  • You must apply for planning permission for any balcony or terrace.

Related: Attic bathroom ideas to make the most of loft conversions of all sizes

Loft conversions – know your building regulations

room with wooden flooring and white tiled walls

(Image credit: David Giles)

1. Access to your loft space

Building regulations stipulate that if the loft is to be turned into a bedroom, bathroom, study or playroom, it must have a permanent staircase. The stairs leading to it need not be as wide as the steps on the lower flights. The most minimal arrangements resemble a fixed ladder and a spiral staircase offers an attractive solution where space is tight.

When weighing up the pros and cons of converting, look at the space you will lose on the floor below to accommodate the new stairs, and check in particular the head height available.

2. Insulating a loft conversion

Part L of the building regulations insists on a good standard of insulation. The main reason for this is that loft spaces can be subject to extreme temperatures, getting very hot in summer and feeling extra chilly in winter.

For walls and ceilings, specialists generally use a rigid insulation such as Celotex insulation boards, while a fibre blanket such as Gyprock Rockwool is often used between floor joists. This insulation should be 150-250mm thick in order to satisfy building regulations for thermal, sound and fire insulation. Soundproofing is also advised.

3. Fire regulations

Fire regulations should be incorporated in your earliest plans. Building materials must comply with standards of fire resistance – your builder should have this in hand.

Find out more at the Fire Safety Advice Centre (opens in new tab)

At the very least, you will need to fit a smoke detector in the hallway. However, any building with a floor more than 7.5 metres above the ground should have a sprinkler system.

In a two-storey home, internal doors around the staircase must be replaced with fire doors to create a protected path from the attic down to the ground-floor exit. Your original doors can be upgraded by companies such as Envirograf.

If there are several rooms in your conversion, you need to provide an emergency exit to the roof. The easiest, most attractive option is to fit a fire-escape window large enough to climb through in each space.

bedroom with photoframe on white wall and wooden flooring

(Image credit: Polly Eltes)

'Whilst planning permission for loft conversions isn’t normally needed, permission will be required if you need to extend or alter the exterior roof space beyond certain limits' advises Rated People's Adrienne Minster. 'When selecting a tradesperson to take on your loft conversion, it’s a good idea to check if they are registered with an official trade body such as The Chartered Institute of Building (CIOB) and the Federation of Master Builders (FMB). And make sure that they have insurance.'

'They will be able to answer any questions you may have but you can also check the Planning Portal (the government’s online website for planning) for up to date information on regulations such as fire-resistant doors, structural floors and beams, sound insulation and more.'

Questions you should ask a loft conversion specialist

  • Do they have public liability insurance and what does this cover?
  • Are they registered with an official trade body?
  • Are they registered with a competent person scheme, and will they take care of all planning permissions / building regulation approvals?
  • Do they offer insurance-backed warranties?
  • How long have they been trading for?
  • Can they give you up to 3 references of recent work they’ve completed?
  • Do they use sub-contractors or their own employees?
  • What experience do their sub-contractors/employees have and are they covered by insurance?

What are the different types of loft conversion?

An L-shaped dormer loft conversion

sloping roof house with l shaped dormer loft conversion

(Image credit: Simply Loft)

'This type of loft conversion is built by connecting two dormers together: one on the main roof and the other on the rear roof' Rob Wood, Director of Simply Loft (opens in new tab)explains. 'The result is a much larger space, which can be used for either two bedrooms and a bathroom or one large bedroom and bathroom, or a host of other combinations. This type of conversion is particularly popular on period properties'.

What is a Hip-to-gable and rear dormer loft conversion?

house with hip to gable and rear dormer loft conversion

(Image credit: Simply Loft)

'As the title suggests, this is a combination of the two different types of conversions, resulting in a large and airy space. Planning permission may be required.'  A big factor to take into consideration for your home improvements.

What is a Hip-to-gable loft conversion?

sloping roof house with hip to gable loft conversion

(Image credit: Simply Loft)

' A hip-to-gable loft conversion can be carried out on properties that have a hipped roof i.e. a sloping side. Therefore, they are most popular on detached or semi-detached properties' Rob explains. 'The hipped end of the roof is therefore extended into a gable roof i.e. a vertical wall, extending the internal loft space.'

What is a skylight loft conversion?

sloping roof house with skylight loft conversion

(Image credit: Simply Loft)

'A skylight or VELUX window conversion is one of the simplest and most cost-effective loft conversions to build' explains Rob. Why?  'As the roof of the property is not altered in any way and only windows are added. This generally means that planning permission is not required. Space however is more restrictive than other types of conversions.' This style of loft leaves the roof in its original state, meaning the height is not extended.

What is a Dormer loft conversion?

sloping roof house with dormer loft conversion

(Image credit: Simply Loft)

'This is one of the most popular types of loft conversion as it provides a good amount of head height. It has the ability to add up to 50 cubic metres of extra space to your property. The dormer is usually built out of the slope of the roof, meaning that most of the work can be carried out from scaffolding outside. This type of conversion generally does not require planning permission.

What is a Mansard loft conversion?

sloping roof house with mansard loft conversion

(Image credit: Simply Loft)

'A mansard loft conversion alters the structure of a sloping roof to a nearly straight slope, at an angle of 72 degrees. Windows are built into the roof as small dormers or even Juliet balconies are feasible. The mansard conversion is usually erected to the rear of a property. It's often considered one of the most aesthetically pleasing types of loft conversion. Planning permission is usually required.'

How to budget for your loft conversion

bedroom with wooden flooring and photoframe on white wall

(Image credit: Colin Poole)

Loft conversions generally cost from £25,000 to £50,000, although pricing them isn't an exact science. 'All projects are different,' says London-based architect Helena Riviera of A Small Studio (opens in new tab). 'However, a loft conversion usually costs £2,500 to £3,000 per square metre, with VAT and fees on top.'  It may sound like a daunting amount but consider the cost of moving house to gain the extra space.

According to the Royal Institution of Chartered Surveyors (opens in new tab) (RICS), the cost of the average loft conversion equates to one third of the cost of moving to a property with an extra room. The institution also predicts it could increase the value of your home by 25 per cent.

Adrienne Minster, CEO of  Rated People  tells Ideal Home, 'Home buyers in the UK have indicated that they would expect to pay around £13,000 (£12,951) more for a house with a loft conversion.'

Loft conversions – does the work need to be signed off?

Whether or not it requires planning permission, your loft conversion will need to be signed off by your local council. Once the work is done, they will inspect it to check the loft complies with fire-safety and building regulations. You'll then be given a completion certificate.

Your architect or  loft insulation company can arrange for this to be done, but you must make sure you get the certificate. Without it, you could struggle to remortgage or sell your home in the future.

Loft conversion windows – what are the options?

room with loft conversion windows and white walls

(Image credit: Velux)

Choosing the right windows is crucial for any conversion, as the joy of such a space is the availability of daylight.

  • Dormer windows offer extra headroom as well as light, as the glazed units are normally set parallel to the facade of the house, and a section of the pitched roof raised to accommodate them. However, because dormer windows change the exterior appearance of a house, planning permission is sometimes required.
    For example, you might be told your dormer can only go across two thirds of the total width of the property. Or have to be sash windows, not sliding.
  • Skylights or rooflights are simple to install flat into the roof, so if you're look for a simple, fuss-free option, they may be a better bet.

If there are several rooms in your conversion, you need to provide an emergency exit to the roof. The easiest, most attractive option is to fit a fire-escape window large enough to climb through in each space. Purpose-designed windows are available from Velux (opens in new tab).

How long does a loft conversion take?

bedroom with photoframe on black wall and wooden flooring

(Image credit: Colin Poole)

A simple loft conversion can be completed in 4 to 5 weeks and is the least disruptive type of extension. More complex projects might take 15-20 weeks, plus any time it takes to get a completion certificate from the local planning office.

Scaffolding is used for access until the staircase linking the loft to the rest of the house is installed, so no materials are hauled through the house and waste can go directly down a chute into a skip outside. The work will be noisy, but won't create as much mess as a ground-floor extension.

Amy Cutmore
Amy Cutmore

Amy Cutmore is Editor-in-Chief, Homes Audience, working across the Future Homes portfolio. She works on titles including Ideal Home, Homes & Gardens, Livingetc, Real Homes, Gardeningetc, Top Ten Reviews and Country Life. And she's a winner of the PPA's Digital Content Leader of the Year. A homes journalist for two decades, she has a strong background in technology and appliances, and has a small portfolio of rental properties, so can offer advice to renters and rentees, alike.