How Much Does a Loft Conversion Cost? A 2019 Price Guide

When considering a loft conversion, it is difficult to feel confident that you will pay a fair price for the results that you are expecting.
There can be quite large variations in price according to how complex the design is or the type of finishing you will choose. Prices can also vary a lot across the UK, almost always going up and down with the property prices. Yet it is very important to have a way to assess what a reasonable budget is.

Understanding how the costs add up enables you to make the most out of your planned investment. In this price guide we give you all the elements to make the best decisions for your loft conversion investment.


How much does a loft conversion cost?

A loft conversion can have a different cost across the UK, depending on the context, the technical and the legal constraints. Excluding finishes like windows, flooring, sanitaryware, the average cost of a standard loft conversion can be between £1,200 and £2,000 per sqm.

The variation in the cost per square meter depends on the type of loft conversion, the size of the alterations to the roof, the access, the type of finishing and the location.

Rooflight loft conversion

It requires the installation of rooflight windows in the roof to allow sunlight to enter the loft. It usually includes strengthening of the existing floor, flooring, insulation, plasterboarding and installation of rooflights. They are generally allowed under permitted development outside conservation areas and other designated areas.
With a rooflight conversion you keep the alterations to a minimum. This means the result will be basic, without budget for plumbing, extensive electrical work etc.

The average price across the UK can be between £15,000 to £25,000.

Dormer loft conversion

It consists in creating a boxed-shape structure that replaces one of the slopes of a pitched roof. The result is a flat-roofed space that allows the installation of full-sized windows and the use of full-height furniture and other appliances. They are sometimes allowed under permitted development when not in designated areas.
It is more expensive than a roof light conversion, as it requires complete rebuild of one roof pitch plus full internal works.

The average cost of a standard dormer loft extension is between £25,000 and £50,000. For an L-shaped dormer, it can go from £40,000 to £75,000.

Hip-to-gable loft conversion

In end-of-terrace or detached properties, the roof slope at the end of the terrace or of the detached house is replaced with a vertical brick wall. It is combined with a dormer conversion to maximise the space. The alterations to the roof are extensive and you need to build a brick gable wall, as opposed to the stud wall needed for the dormer conversion.

The average cost of a hip-to-gable conversion is higher than a dormer extension, and can go between £32,000 and £60,000.

Mansard loft extension

A mansard loft conversion creates a flat roof space, with four or two of the external walls gently sloped. It can go as far as to create an additional storey on top of an existing building. It is an extensive building alteration and it always requires planning permission. Overall it’s the most expensive option for a loft conversion.

The average cost of a mansard loft extension can go from £40,000 to £70,000, assuming the mansard covers the extension of the loft only.

How location can change the loft conversion cost

When talking about building works, there is no one-size-fits-all. That is true about costs, too. In general, building works are cheaper where the property market prices are lower.

A lot of this difference is due to the nature of expensive property areas: generally they are busier, more densely built and inhabited. This translates into higher costs, for multiple reasons. For example:

  • Building site access: in a busy metropolitan city, often there is no or very little space for parking, placing machinery, scaffolding, rubbish skips etc
  • Cost of labour: in a place with a higher cost of living, the workers are paid higher salaries or daily rates
  • Cost of materials and deliveries: because of the higher salaries, rent cost of commercial space, constraints in the size of transporting vehicles and distance from production plants, prices for supplies are higher in metropolitan areas.

For a better idea of the most expensive and the cheapest areas in the UK, as an average:

  • Scotland and South East England are the most expensive, with peaks in Edinburgh and London
  • Northern Ireland is the cheapest area for building costs in the UK

Explanation of the professional fees

When planning any building works, you will need to consider professional fees on top of the building costs. Consider that, even if planning permission is not required, you will still need drawings of your loft conversion to be produced for the council, the building regulation officers and for the building teams.

Having the drawings produced by a professional is often a way to save money, as they are a way to put the requirements in writing. Keep in mind that unclear requirements can cause delays and mistakes that can be very expensive to fix after the work is done.

Planning fees

Loft extensions can often be done without planning permission, you will still need to file for a Certificate of Lawfulness from your council (approx fees £100)

Fees for filing for the planning permission vary with the councils and heavily depend on the amount of work the planning authorities need to process the application. Householder applications, needed for extensions and garden buildings, are around £210.

For more information on the planning process and fees across the UK, you can visit the Planning Portal.

Design fees

For a loft conversion, you will need to produce at least building regulation drawings. For a standard loft conversion, the design fees would be between £1,000 to £2,000.

On top of this, you will need to budget for structural calculations, if a new beam or other structural alterations are needed. The fee for the structural design would go from £900 to £1,800 for a standard loft conversion.

Any design and drawings produced for a planning application of a loft conversion, if planning permission is needed, can cost between £1,000 and £3,500.

Keep in mind that the design costs vary a lot, according to the architects you appoint and whether the design is straightforward or not. A saving option is to appoint a consultant, rather than choosing an architect practice. A great solution to hire a design and build company, that will quote your loft conversion including the design fees. In some cases, the planning fees will also be included in a design and build quotation.

Party wall fees

If your loft conversion will need building work to a wall that sits astride a boundary you will need Party Wall agreements with all the neighbours that share that party wall with you.

This is very often the case in terraced or semi detached properties and if you are extending a flat in a block. The typical cost of a party wall agreement depends on whether your neighbours and you will want or need to appoint a party wall surveyor.

As an average, party wall agreements will cost £700 to £1,500 per neighbour.

Keep in mind that you can serve the notices yourself and won’t need to pay for a surveyor if your neighbour agrees on the proposed work and they don’t appoint a surveyor themselves.

Building control fees

You will need a building control certificate at completion, that certifies that all the work is in compliance of building regulations. The average cost for a loft conversion is £750 approx, depending on the size and the nature of the works.

You can liaise directly with the local authority or engage a government-approved inspection company. Both will check that the work is done in compliance and will issue the certificate at completion.


The loft cost can increase if…

Whenever a loft conversion project is not a standard one, costs can increase accordingly. The most common reasons why the budget can be higher than the average are:

  • Number of parties involved in the party wall process: the higher the number of parties involved, the higher the cost of party wall agreements. Plus, any dispute causes delays and even more additional costs
  • Complex structural design and implementation: your loft extension might need more beams or columns than the average, or the shape or the design might require specific structural solutions
  • Building access: as mentioned above, any constraint on the accessibility of the site can significantly increase the costs
  • Age and conditions of the existing building: when making structural alterations to an old building, surprises can happen while stripping out. It’s not uncommon that some of the existing joists and beam will need strengthening or replacement that cannot always be planned ahead
  • Height of the existing building: for high buildings, like blocks of flats, the cost of transporting the materials onto the site. So are scaffolding and rubbish removal
  • Finishes and interiors: any bespoke solution has an impact on the cost of a loft conversion. High end finishes also cause an increase compared to the average costs
  • Project duration: if you have tighter timelines for completion than the average, the project will need more workers on site at the same time. Delivery of materials can also be affected. This means higher logistics and organisational costs, also considering there is a maximum in the number of people who can work on a loft conversion at the same time, without interfering with each other’s work

How much should you spend on a loft conversion?

When planning building works on your property, it’s a good rule of thumb to consider how much value the alterations will add to the current property. A good practice is to consult estate agents in your area, to understand the selling price of properties in your area where a loft extension was added before selling.

Once you understand the increase in value that a loft conversion would add to your property value, you can use that figure to support many decisions in the course of the project. Design solutions, finishes, space, lighting etc can be evaluated and chosen, according to your understanding of the investment return.

Beyond budget control, this is an excellent way to stay in control of your budget and be confident that the extension is worth doing.

If you are planning a loft conversion, get in touch for questions and support; you can also book a free site visit and free quotation from our specialised teams