Loft conversion costs calculator

Loft conversions create additional habitable rooms in your home. These can be ideal for a new bedroom, playroom, home cinema or bathroom. This article discusses loft conversion costs in London and highlights the various design options available.

Many properties in the UK are suitable for loft conversions. Often, the changes do not require planning permission as the works can be classed as ‘permitted development’. This is, therefore, a great way to expand your home. An architect will ensure that the space is best utilised, beautiful and carefully designed. 

Architecture for London is an RIBA Chartered Practice. View our portfolio to see recent loft conversion projects, or contact us on 020 3637 4236 to discuss your project.

What are the benefits of a loft conversion?

Moving house in London may cost more than £50,000, once estate agent’s fees and stamp duty on the purchase are accounted for. This assumes that you might be buying a new house with a value of around £1m.

If, however, you are considering buying a higher-value property, these costs can increase dramatically. For a £2m house, the stamp duty alone will be in the region of £150,000. Saving these costs and extending your existing home with a loft conversion could be a more financially viable approach to owning a larger property, while potentially adding up to 20% to your house’s value.

Loft conversion in Muswell Hill by Architecture for London

The extra space gained from a loft conversion could allow you to give your teenagers their own space, install that cinema room you always wanted, or make money with Airbnb.

In addition to the financial and lifestyle benefits, the thermal performance of your home would be dramatically increased, creating comfortable internal temperatures and reducing your carbon footprint. Many existing properties have very poor roof insulation, and as part of the loft conversion works, the roof would be insulated to meet current building regulations as a minimum.

How much does a loft conversion cost in London?

Costs of construction in London are higher than in other parts of the UK, especially when working on an existing building. However, working in a loft space will often save on the time and cost of a planning application and is typically more affordable than a house extension. Additionally, there is no need to sacrifice your garden space, as with a rear extension. Loft conversion costs in London are £50,000 to £90,000 on average, excluding VAT and fees. The costs will vary depending on the size and complexity of the conversion.

Our loft conversion in Highbury has exposed brick and a dormer window

Measuring your loft

It is important to find out the rough size of the loft space to calculate your loft conversion costs. This also helps to decide if your plans are feasible in the space available. There needs to be adequate space under the ridge of the roof, ideally 2.3 metres and at least 2.1 metres of space above the location of the new stair. Along with the height, measure the full width and length of the space.

Contact us now on 020 3637 4236 for a free 30-minute telephone consultation to discuss your project.

Without a dormer

A single ‘room in the roof’ loft conversion, with a floor area of 18 square metres, without a dormer, is the most affordable option. Construction costs for a room in the roof can start at £40,000, excluding VAT and fees. This cost would normally cover new floor reinforcement, insulation, staircase, electrics, two or three roof lights, heating, fire safety measures and lighting.

As a minimum, loft conversions with roof lights only cost £1,900 per square metre, excluding VAT and fees (£175 per square foot).

Loft conversion and rear extension in Queen’s Park by Architecture for London

Dormer loft conversion costs

Dormer windows add extra light to your new room and also significant extra height. This approach might allow you to fit in both an ensuite and a bedroom. Dormers are formed from a small flat roof projecting from your existing roof with a window. The extra internal height created by a dormer can also allow the staircase to be positioned in more locations.

Adding a dormer affects the external form of the building. This approach is more likely to require planning permission if your house is in a conservation area. Speak to an architect about your budget and requirements to establish if a dormer approach is suitable.

As a minimum, loft conversions with dormers cost £2,400 per square metre, excluding VAT and fees (£200 per square foot). Total costs are likely to be a minimum of £50,000.

Depending on size, design aspirations and quality of the space that you desire, costs can increase to over £100,000 for larger homes with multiple bedrooms and bathrooms and high-quality finishes.

Our loft conversion in Brook Green has a large glazed rear dormer and a window seat.

Design costs

Architects or loft conversion specialists would normally be appointed to design your loft conversion. Involving an architect is usually the best way to maximise the potential of the space and quality of the design. Architects’ fees are usually based on a percentage of the construction cost, but can also be lump sum fees or time charged. See our guide to architects’ fees for more information.

If there are structural alterations to the roof or a new complex staircase, then the services of a structural engineer would also be required.

Loft conversion costs: Planning applications

If required, planning applications cost £234 in England. This would be for a ‘Householder application’, which is appropriate for alterations to single houses, including loft conversions. See our guide to planning application costs for more information.

Building regulations costs

Even without planning requirements, the loft conversion will need to be inspected by the local authority or an approved inspector. Approved inspectors are independent specialists who certify compliance with the building regulations. An approved inspector will check that the works are of sound construction, have good thermal performance and that fire safety requirements have been met. This costs £800 or more, depending on the scale of the project.

Party wall surveyor costs

If your home is terraced or semi-detached, then you share one or more walls with a neighbour. If your loft conversion requires this shared wall to be altered, then a legal agreement must be established between you and your neighbour. This can be as simple as issuing a party wall notice, but frequently can become more complex, with party wall awards. Party way surveyors handle the process, ensuring fairness for both parties. This costs £1,000 or more, depending on the scale of the project.

Our loft conversion in Brook Green has an ensuite bathroom under the front pitched roof.

Quantity surveyor costs

If you wish to have a clear estimate of your loft conversion costs at an early stage, we recommend appointing a quantity surveyor. A quantity surveyor manages the cost issues and ensures that you pay the builders a fair price for any variations you may make during construction. A QS might charge between 0.5% and 2% of the build cost, depending on their level of service. For an £80,000 project, this is in the range of £400 to £1,600.

Specialist survey costs

Specialist surveys may be required for some properties, such as checking for asbestos, bats (if a protected species) or damp investigations. These costs range from £500 to £2,000 per survey.

Contingency

Construction work on existing buildings is known for being unpredictable. We recommend allowing for a 10% contingency of your total building costs. Expect this cost to be used up and not just for emergencies.

Loft conversion in Queen’s Park by Architecture for London

It may not be possible to know how much of your existing roof structure can be reused when adding a dormer until the works have begun. Using a suitable contract with your builder can prevent unfair, unexpected costs.

Planning permission

Most homeowners can convert their loft without planning permission, under permitted development. However, homes within conservation areas and listed properties will require permission from your local authority.

Hiring an architect with experience in conservation areas and with listed buildings can help you navigate these sometimes complex policies. At Architecture for London, we have extensive experience with listed and conservation area properties throughout London.

Loft roof types

If your roof is steeper, then the livable space will be greater. Houses built pre-1960s are better to convert due to the space between the roof structure and the steeper pitch. After the 1960s, the pitches tend to be lower, and the new roof structure types require more work to convert.

What value is added to your home with a loft conversion?

Research from Nationwide’s chief economist shows that a full loft conversion can add 20% to the property’s value.

A large master bedroom in the loft might add 15% to the value of your home, and an ensuite bathroom 5%. The value of extending your home is not only monetary but also in the improvement to your quality of life. Investing in a good-quality, architect-designed home in London will increase its value and be a joy to live in.

Loft conversion in Brook Green by Architecture for London

Visit Architecture for London’s portfolio to see our recent loft conversions, or contact us on 020 3637 4236 to discuss your project.

Loft Conversion Costs FAQ