How to plan a loft conversion

There's a lot to think about when converting your loft. First up, you need to determine whether your home is suitable.

Assuming it is, you'll need to measure the space accurately, consider which type of loft conversion is best for your home (dormer, mansard, rooflight or hip-to-gable) and then choose a builder or architect.

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

Find out how much you can expect to pay in our guide to loft conversion costs.

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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 couple of assessments you can carry out yourself:

1. Measure the head height 
2. Identify the roof type
3. Look for other conversions on your street 
4. Work out if you need any permissions 

1. Measure the head height

The minimum height you need for a loft conversion is 2.2 metres and you can easily measure this yourself by running a tape measure from the floor to the ceiling at the tallest part of the room. 

Victorian houses tend to have lower ceilings than those built from 1930 onwards, so may not have sufficient head height.

2. Identify the roof type

Depending on when your home was built, it will either have roof trusses or rafters. By looking through your loft hatch, you should be able to tell straight away what type of roof you have.

• Rafters run along the edge of the roof and will leave most of the triangular space below hollow.
• Trusses are supports that run through the cross-section of the loft. Converting a loft with trusses is possible, but extra structural support is needed to replace the trusses and it's likely to be more costly.

3. Look for other conversions on your street

Another great way to get a sense of whether your loft can be converted is by seeing whether similar properties on your street have had loft conversions. If you spot any examples, it's more likely to be a possibility.

If you can, it's worth going a step further and asking to take a look at the loft of anyone in your street who has had it done. That way, you can get an idea of the size of the space and what can be fitted into it. 

It's also a great way to get inspiration for different layout options, and to to get an idea of how much light will come through the skylights.

4. Work out if you need any permissions

Most homes will come with an allowance for permitted development (PD), which means you can go ahead with your conversion without planning permission. 

However, if your conversion will be larger than the sizes outlined below, you will need permission:

• Terraced house – 40 cubic metres
• Semi-detached or detached – 50 cubic metres

If you live in a conservation area or your roof space isn't tall enough, it may be more complicated.  

Find out more about any permissions in our guide to loft conversion building regulations and planning permission

Loft conversion types

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 a number of 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 space without an extension 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. 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, only suits houses with a free sloping side roof.

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 free sloping side roof. 

If you have a detached house with sloping roofs on either side, you can build on both to create an even more 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.  

Read our guide to loft insulation costs and savings

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.

Expect a customised staircase to be at least five times more expensive than a standard one.

Think about

• Headroom: check whether you have enough space for the staircase and loft conversion. 
• Location: where you can place the stairs and if 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.

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 they're dealing with.

• 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.

Does a loft conversion add value to your property?

A well-designed loft conversion can add up to 20% to the value of your home.

However, this varies significantly depending on the type of conversion and where you are based.  

Adding another bedroom with an en-suite – creating a new primary bedroom – will yield the greatest returns. 

Loft conversions will add more value to your home in London and the South East, where space is at a premium, than in the North and South West. 

Should I tell my home insurance company about a loft conversion?

Yes, 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.

If you are staying elsewhere while your loft conversion is completed, you should tell your insurer about this and try to give several weeks’ notice.

In instances where you’re having serious building work done, consider specialist renovations insurance. This covers against things going wrong with the building work, materials and property owners’ liability.

Discover how home insurers score in our guide to the best and worst home insurance

Top tips for a smooth loft conversion

Some hiccups over the course of your loft conversion are unavoidable, but there are a number of 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 have scheduled any structural work, remember to add time for any additional 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 your side will be particularly useful if you need to get a Party Wall Agreement, which applies if your loft wall is shared with the neighbour – this can be a lengthy and costly process if they're not happy with the plans.  

Loft 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.