Loft extension by Proctor & Shaw Architects, photo by Building Narratives
Here we breakdown budget costs for typical loft conversion projects and suggest ways of saving money without losing design quality.
If you are thinking about building a loft conversion, understanding costs is probably one of your top priorities.
It’s tricky to calculate accurate costs without detailed plans, but rough estimates can be determined by drawing upon experience of similar projects and through market research.
In the article below, we breakdown the costs involved in completing a loft conversion and offer money saving tips while maintaining design quality.
More:
Dormer loft conversions – an architect’s guide
Loft conversion stairs – architects’ advice and design tips
UK loft conversion costs: analysis and money saving tips
Loft conversion costs, like other building projects, are affected by factors such as location, type, size and scale, design complexity and specification.
As a rough guide, a simple rooflight conversion (no dormer extension) of a similar size will cost on average £30,000, plus VAT, in most parts of the UK, rising to about £40,000, plus VAT, in London.
The average cost to build a low range loft dormer conversion, creating about 30-40 square metres of useable floor area, is around £40,000, plus VAT, in most parts of the UK. In London, where living costs and overheads are higher, the average cost increases to about £55,000, plus VAT.
Hip to gable conversion with rear dormer start at about £90,000, plus VAT, increasing to £115,000, plus VAT, in London.
The estimates above cover general build costs. You will also need to factor in VAT, professional fees, council fees and the cost of fixtures and fittings.
Value Added Tax
Building work is liable for 20% VAT. If you are extending a property that has been vacant for more than two years, or the works involve the conversion of an existing dwelling that is being subdivided, you may be eligible for tax relief.
Survey
One of your first tasks will be to commission a measured survey. These drawings will accurately show your property’s layout as existing and form the basis for all services thereafter. Surveyors and architects will charge about £500-1,500, plus VAT.
Architectural fees
You will need an architect or architectural designer to design the loft conversion and submit plans for council approvals.
If your property has permitted development rights, your loft will not need planning permission if it is designed to guidelines.
Architects will charge around 5-7% of construction costs for planning and building regulations approvals. If you just need help with the initial design, fees could be less than £1,000.
Structural engineer fees
In addition to architectural fees, you will need the services of a structural engineer, to provide structural drawings and calculations for building regulations approval. Fees will be in the region of £500 - 2,000.
Permitted development and planning fees
If your property enjoys permitted development rights, you can apply for a Lawful Development Certificate to ensure your loft conversion meet guidelines.
Lawful Development Certificate applications cost £103 in England, £300 in Scotland and £115 in Wales, and take up to 8 weeks to process.
If you live in a designated area, flat or maisonette you will require planning permission.
Householder approval, a form of planning permission streamlined for home improvement works, costs £206 in England, £300 in Scotland and £230 in Wales.
More: How Much Does Planning Permission Cost in the UK?
Building regulations fees
Building regulations approval is distinct from planning-related matters, including permitted development, and ensures building work is safe for habitation and meets current technical standards. All loft conversion works require building regulations approval.
Approval can be sought through your local council or a licensed private building control company. Expect to pay in around £1,000.
Party wall agreements
If you share an adjoining wall with a neighbour, you are likely to require a Party Wall Agreement. If your neighbour is supportive of the works, a simple agreement will cost about £500. If they descent, fees may exceed £1,500. If you have multiple adjoining neighbours your will need an agreement with each one.
Glazing
Design and build loft companies typically allow for standard uPVC glazing and Velux rooflights in their quotations. If you want to install something different, you will need to add it to their price.
A good quality, double glazed timber casement or aluminium window will cost about £800-1,300, plus VAT and installation.
A set of double doors with Juliet balcony to a similar specification will cost about £3,000-3,800, plus VAT and installation.
A good quality, 1 metre square flat roof skylight will cost £900, plus VAT and installation.
You will need to budget separately for installation costs with either your builder or glazing supplier.
Loft stairs
Builder quotations are likely to allow for a simple timber staircase but if you want something different, you’ll need to budget for it.
A CNC plywood staircases will cost in the region of £2,000, plus design fees. Bespoke staircases can cost in excess of £5,000.
More: Loft conversion stairs – architect advice and design tips
Internal fixtures and fittings
Builder loft quotations typically exclude interior finishes, fixtures and fittings, such as decorations, flooring, light fittings, bathroom fittings, cupboards and built-in joinery. You will need to budget for these items separately. An architect will be able to help you design and specify all aspects of your loft conversion.
Insurance
Home insurance policies do not usually cover building works. Allocate about 1% of your budget for non-negligence cover which can help protect you against most eventualities while the builders are on site.
Other costs
The costs cover expenditure for most loft conversion projects, but there could be some other expenses.
If you have a protected species in residence, for example bats, then a survey will be needed. Budget about £500 if this applies.
If there is asbestos or other harmful materials on site, it will need to be removed by a specialist. Surveys start from about £300.
And finally, consider including a contingency fund into your overall budget to protect against unforeseen costs. 10% of construction costs is usually advisable.
Loft conversion cost summary
Overall project costs can be summarised as follows.
Note, professional fees may be higher if you want a bespoke design and full project management services.
Cost factors that particularly affect roof conversion works, include:
To ensure you make the most of your budget and create the best possible loft conversion, consider the advice below.
The figures in this article are to be used as a rough guide only. They are based on market research and experience as an architect working on similar projects. To get an accurate estimate for your particular building project you will need a detailed set of plans and quotations from at least three local builders.
Appointing a skilled architect, even for just part of the way, will help you bring your project in on budget and reduce time and stress.
Best of luck!
About the author: Aron Coates is an architect with over two decades of experience, encompassing projects ranging from the restoration of historic buildings to the design of contemporary homes.
The information provided in this article is intended for general guidance and educational purposes only. At Designs in Detail, we advise you appoint a skilled residential architect to provide specific expert advice for your project.
