How to plan a loft conversion

It can be difficult to know where to start when planning a loft conversion.

From deciding whether to go for a dormer, mansard or rooflight conversion, to figuring out planning permission and hiring a team to do the work, there's a lot to do.

But it doesn't need to be a complicated journey. Read on to discover how to plan a loft conversion.

Find out how much a loft conversion costs in our complete guide

Loft conversions step-by-step

There are five key steps to follow when planning a loft conversion.

1. Assessment and budget

Suitability and professional assessment: The first step is working out whether your loft can be converted, and what types of conversion you can do. You'll need to consult an engineer, but there are also a number of checks you can run yourself. Jump to Can my loft be converted?

Make a budget: Before you start any renovation, you should always work out what you can comfortably spend. Include at least 10% on top of your predicted spend to cover any unexpected costs. Read our guide to loft conversion costs to see how much you can expect to spend on different types of conversions.

2. Loft design 

Consider your needs: What type of space do you need? A home office, a playroom or a principal bedroom suite? Also consider other bug-bears in your home. For example, if you need extra storage, ensure to build more into your conversion.

Choose a type of loft conversion: Depending on your budget, the configuration of your home and planning permission, you could opt for a simple rooflight conversion, or go all in with a mansard or hip-to-gable conversion. Jump to Loft conversion types.

3. Find a contractor 

You could hire an architect and/or a builder, and you might need a structural engineer. But you could also use a specialist loft conversion company to handle the process from start to finish. 

The best place to start is to speak to a friend or neighbour who's been through the process and get their recommendations. You can also read our advice on how to find an architect or builder for an extension.

4. Permissions and regulations

Many loft conversions can go ahead under permitted development, but larger-scale conversions – or those in listed buildings or conservation areas – will require permission. All conversions are subject to building regulations, which reference everything from the staircase to ceiling height and fire-safety regulations. 

An architect or loft conversion company should be able to check all of this for you, or you can find out more in our guide to loft conversion planning permission and building regulations.

5. Pre-construction preparation

Inform your insurer: You'll need to tell your home insurance company before work begins to avoid invalidating your policy.

Prepare for disruption: Loft conversions can cause a lot of disruption, and you'll need to be available during working hours to deal with any issues that may arise. So bear in mind that this may be a stressful time, and plan work or family commitments accordingly.

Can my loft be converted?

Before you do anything else, you need to work out whether your loft space is suitable for a conversion.

You can ask a builder, architect or surveyor to visit your home and check this out for you, but there are a few assessments you can carry out yourself:

• Measure the head height: You'll need a minimum ceiling height of 2.2 metres to convert your loft.
• Look for other conversions on your street: If similar houses on your street have loft conversions, it's a good indicator that you can convert your loft as well.
• Work out if your building is protected: If you live in a listed building or an area of outstanding natural beauty (AONB), it'll be much harder for you to get permission to convert your loft.
• Make sure you can create an access point: You will need to ensure there is space for a staircase leading up to your loft. 

Types of loft conversion

There are four different types of loft conversions: rooflight, dormer, hip-to-gable and mansard. The one you choose is likely to be determined by several factors, including the type and age of house you live in, as well as your budget.

Rooflight loft conversion

• Pros An affordable option for buyers on a budget, suitable if you live in a conservation area.
• Cons Offers far less space compared to a dormer or mansard conversion.

Rooflight conversions are by far the cheapest and least disruptive option, as you won't have to make any changes to the shape or pitch of the roof. Instead, it's simply a case of adding in skylight windows, laying down a proper floor and adding a staircase to make the room habitable.

However, you'll need to have enough roof and floor space without extending for this type of conversion.

Dormer loft conversion

• Pros An option for most houses with a sloping roof.
• Cons More structural changes needed compared with a standard conversion, so can take a while to build.

A dormer loft conversion is an extension that protrudes from the slope of the roof to create more headroom. Dormers, in particular flat-roof dormers, are the most popular type of conversion. They're suitable for almost any home with a sloping roof. 

Dormer conversions are less expensive than mansard or hip-to-gable conversions, but will still add a good deal of extra headroom and floor space.

Hip-to-gable loft conversion

• Pros Generally less expensive than extending outwards and more natural-looking compared with a dormer conversion.
• Cons More expensive than a dormer conversion, not suitable for all homes.

Hip-to-gable conversions work by straightening the sloping 'hipped' roof at the side of your property to create a vertical 'gable' wall, creating more headroom in the loft. This type of conversion will only work on detached, semi-detached or end-of-terrace houses, as it requires a roof that slopes down on at least three sides. 

If you have a detached house with sloping roofs on either side, you can build out both sides to create a spacious double hip-to-gable extension.

Mansard loft conversion

• Pros Creates lots of new useable space, suitable for many different types of property.
• Cons Can be particularly expensive, doesn't look very natural due to the change in roof slope.

Mansard extensions run along the whole length of your roof and will alter the angle of the roof slope, making it almost vertical. These tend to be the most expensive type of conversion, but will result in a significant amount of extra space. 

Mansard conversions are suitable for most property types, including terraced, semi-detached and detached houses.  

Loft conversion ideas

Remember that any room that requires plumbing or a larger floor space will be more labour-intensive – and therefore expensive – than simple conversions. 

1. A principal bedroom suite: Creating a new principle bedroom with an en suite typically generates the greatest return on investment for a loft conversion. However, it does require a lot of work, particularly installing the bathroom, and you'll need a decent amount of floor space. 
2. A nursery or playroom: A nursery can be converted into a playroom as your child grows, and even a cinema room as they become teenagers. Consider clever storage solutions and stair gates.
3. Home office: With many people now hybrid working as standard, adding an office space to your home can offer a good return on investment. It doesn't require very much space, but you will need to ensure you get good wi-fi in your loft. You may wish to consider a wi-fi mesh system – find out more in our guide to the best wi-fi extenders and wi-fi mesh systems. Check out our home office ideas, too.
4. Home gym: It's unlikely you'll be able to add a full gym to your loft, but if you want a quiet space for a treadmill, exercise bike or small yoga studio, this can be a great choice. 
5. Storage space: Don't forget that you can simply convert your loft into an open storage space. Non-habitable conversions can free up a lot of space in the rest of your home, and rarely require planning permission. They also need to adhere to fewer building regulations.  

For more ways to create space, visit our guide to house extension and conversion ideas

Finding professionals to work on your loft conversion

Checking for safety and compliance

Structural engineer

Unless you're a professional, you should always consult a structural engineer when converting your loft to ensure it's safe to use. 

They will begin by assessing the suitability of your loft. Then they will calculate the structural modifications and build required for a proper conversion. 

In addition, they can ensure the conversion is carried out in accordance with building regulations and planning permission. 

When to consult: At the beginning of the process, when you have a good idea of your budget and the type of conversion you're interested in. 

Is it essential? Yes, you have to consult an engineer to ensure your conversion will be safe to use. 

Party wall surveyor

If you're making changes to a shared wall, you'll need to involve a party wall surveyor.

They will help to negotiate an agreement between you and your neighbour about the nature and amount of work that will take place. 

When to consult: In the middle of the process, when you have a fairly solid plan for your design. 

Is it essential? Yes, if you're planning to make changes to a shared wall. 

Help with design and function

Architect

If you're unsure about the best design for your conversion, you can consult an architect.

They can advise you on the best type of conversion for your home, and how to build it in an aesthetic and functional way. They can also advise on designs with the best return on investment. 

They're particularly important if you are planning a conversion with a bathroom, as they can ensure it's properly installed with good ventilation and plumbing. 

Working with an architect can offer several advantages, and even end up saving you money in the long term. Some architects can even offer end-to-end support on the project, helping you manage the stress and administration of your conversion.

When to consult: At the beginning of the process, when you have a good idea of your budget. You don't need to know what type of conversion you're interested in. 

Is it essential? Not technically, but it is a good idea to have someone at least sense-check your design. 

Completing the construction

Builder 

Unless you're very competent at DIY and are completing a simple conversion, you'll need to get a builder involved in the construction process. 

They'll build the physical structure of your conversion. 

A lot of builders can also provide recommendations for other tradespeople that you'll need to involve – such as electricians, plumbers, and plasterers – but not always. 

When to consult: Nearing the end of the design and planning process.

Is it essential? Almost always

Specialist traders (electricians, plumbers, painters)

As in any construction, you'll also need to hire specialists to complete the relevant parts. 

The traders you need will depend on the type of conversion you do. Your architect, builder or engineer should be able to offer some advice. 

When to consult: Nearing the end of construction

Is it essential? Almost always

End-to-end support

Several different types of professional can provide end-to-end support on your loft conversion. 

That means you consult with them before you've done any serious work, and they can help manage every stage of the process. 

Specialist loft conversion companies often advertise this type of support. But you can also find builders and architects who can help with this service. 

You may also consult with a Contract Administrator to help with the administrative side of the project. 

When to consult: At the very beginning of the process

Is it essential? No

Use Which? Trusted Traders to find reliable contractors for your project

Loft conversion stairs

A staircase may not be the first element that comes to mind when planning a loft conversion, but it is one of the most important.

Many people neglect to factor in changes to the floor below the loft when planning a conversion, but it's worth having a think about where the staircase is likely to go and how much room it might take up.

Even a well-designed, space-saving staircase could take up a sizeable chunk of a room, so make sure you have space you're happy to lose. Consider the flow of your home, and remember – you'll need to carry furniture up to that room.

There are also several very strict building regulations and considerations to bear in mind: 

• Headroom: Check whether you have enough space for the staircase and loft conversion. 
• Location: Where you can place the stairs and whether the location will require an alternating tread staircase or spiral staircase.
• Step height: Regulations stipulate a particular pitch or angle for your stairs, and the riser of each stair also has minimum requirements.
• Fire safety: You'll need a protected escape route and a linked fire alarm system for the whole house.
• Landings: A space as wide as the staircase is required at the top and bottom of your stairs.

How long does a loft conversion take?

Ultimately, the answer to this question depends on the trader you're using and the type of loft conversion.

• Rooflight loft conversions are usually the quickest, taking around four weeks to complete.
• Dormer loft conversions can take closer to five weeks.
• Hip-to-gable loft conversions can take around seven weeks.
• Mansard loft conversions will be closer to eight weeks to complete.

The first week or two will be spent preparing your home and gathering the materials and tools required. Work usually starts on the outside of your property. After that, the focus turns to the inside of your house and the flooring, insulation and stud walls. The final stage will deal with plastering, electrics and plumbing.

Top tips for a smooth loft conversion

Some hiccups over the course of your loft conversion are unavoidable, but there are several things you can do to keep these to a minimum and avoid any nasty surprises. We've compiled some key expert tips to help you get prepared.

• Do your research: It's best to be as clued-up as possible, so you know what to expect and can be really clear about what you want – from how you will use your conversion to how it will look.
• Budget carefully: Make a thorough budget and then factor in around 10-15% extra for contingency costs, in case something goes wrong.
• Prepare for disruption: Bear in mind that the conversion may impact your whole home (for example, you may need to relocate a water tank from the loft or get fire doors fitted).
• Make a schedule: Once you've scheduled any structural work, remember to add time for any finishing jobs, such as painting and decorating.
• Keep your neighbours on side: Set their expectations by agreeing start and finish times, and letting them know when certain parts of the building process will happen. Getting them on side will be particularly useful if you need a Party Wall Agreement (this applies if your loft wall is shared with the neighbour). It can be a lengthy and costly process if they're not happy with the plans.  
• Tell your insurer: You should tell your insurer about any changes that will alter your home’s structure, habitability, security or value. For example, a loft conversion may increase its value and this will likely affect your buildings and contents insurance premiums.

Loft conversion jargon buster

Builders finish

Typically, a builders finish involves fitting plug sockets, light fittings, skirting boards, architraves and plastering the walls. It's unlikely to include jobs such as decorating, tiling or carpeting.

If your building firm says that it will complete your conversion to a builders finish, it's worth double-checking exactly what's included.

Pitch

The pitch of a roof simply means its steepness.

Some types of loft extensions, such as mansard conversions, work by altering the pitch of the roof to create more space internally.

Rafters

Rafters are the sloping beams inside your loft that support the roof.

If you have rafters, as opposed to roof trusses (see below), your loft should be easier to convert.

Roof trusses

Roof trusses are timber frameworks that span the cross-section of your loft space and support your roof.

Typically, roof trusses will make a loft trickier to convert than old-style rafters and could double the cost of your extension.

Shell conversion

Shell conversions are part conversions, where the structural work is carried out by a building firm, but the rest is left to you.

Usually, a shell conversion involves completing all structural timber work, creating a watertight internal loft space and fitting windows and doors, chipboard flooring, a staircase and any internal stud walls.

Velux

Velux is a popular brand of skylight that has become synonymous with roof-light windows.

A Velux conversion simply involves fitting Velux rooflights, and is suitable only if your loft is already the right size and meets building regulations.

Don't forget the finishing touches – read our fitted bedroom furniture advice guides and tips on how to buy the best carpet