August 30, 2024

When calculating the cost of a loft conversion in the UK, several factors come into play that can significantly impact the final price. From the size of the space and the type of conversion—such as a Mansard or dormer extension—to additional features like en-suites or balconies, each element contributes to the overall building costs.

In this article, we’ll explore some of these variables and how they affect a project’s cost, to help you budget and plan your loft conversion.

10 Main Types of Loft Conversions

Before we take a look at the numbers, it’s important to be aware of the main options available when planning a loft conversion. Each type offers unique benefits and can significantly impact the overall cost and design of your project. Here are eight to be aware of:

1. Velux Loft Conversion – The simplest and most cost-effective option, involving the installation of Velux windows into the existing roof space without altering the roof structure.
2. Dormer Loft Conversion – Extending the roof outward to create additional space and headroom; they can be full-width or smaller, depending on the space requirements.
3. Mansard Loft Conversion – Altering the roof structure to create a near-vertical wall with a flat roof, providing maximum space and headroom.
4. Hip-to-Gable Loft Conversion – Replacing the sloping side of the roof with a vertical gable end, effectively increasing the roof space and headroom.
5. Gable-to-Gable Loft Conversion – Similar to hip-to-gable, but it extends the existing gable end across the entire width of the property. 
6. Shell Loft Conversion – Provides the basic structure and space, leaving the interior finishes and fittings to the homeowner.
7. Roof Lift Loft Conversion – Raising the entire roof structure to create additional headroom and floor space, often involving significant structural alterations.
8. Modular Loft Conversion – A prefabricated solution where sections of the loft are constructed off-site and then assembled on your property.
9. Piggyback Loft Conversion – Building an entirely new structure on top of the existing roof, effectively adding a new storey to the property
10. Standard Loft Conversion – Predominantly internal work without major changes like roof lifts or complete rebuilds.

In this article, we’ll be reviewing three loft conversion types: a standard loft conversion, a dormer loft conversion, and a Mansard loft conversion. A dormer loft conversion often comprises a single window, two windows, or the full width of the roof.

Considerations For Converting A Loft

A fully finished attic is roughly 35–50% of the house’s ground floor square meterage, so we based our calculations on a floor space of 30m2.

In addition to the total costs, we’ve also provided costs per square metre, so you can carry out your own calculations if you happen to know the dimensions you’re working with.

All our calculations are based on a loft conversion comprising the following:

• Master bedroom
• En-suite bathroom
• Eaves storage
• Landing including stairs

In terms of build specification, our BuildPartner pricing tool gives you three options (which can be revised by item at a later point):

• Basic spec is a basic finish; e.g. Leyland, Everest, Wickes.
• Standard spec is a standard finish; e.g. Dulux, Hamilton, Slim Line.
• Premium spec is a high-spec finish; e.g. Farrow & Ball, Fine Line, Siemens.

In this cost comparison article, we review projects based on a standard spec. In addition to specification, we’ve provided a range of prices to reflect the varying types of contractors:

• Low benchmark – smaller companies are generally lower cost but less specialised and with low project management function; good for low/mid-spec projects and tight budgets.

• Mid benchmark – medium-sized companies offer a balanced mix of cost-effectiveness and specialisation; good for mid-range projects for effective execution within moderate budgets.

• High benchmark – larger companies generally have a higher cost base but can handle a wide variety of specialist tasks; good for mid/high-spec projects and project management.

Standard Loft Conversion

Here’s a table showing the average costs of a standard loft conversion for a standard-spec project in the UK:

Standard Loft Conversion	Total Average Build Cost			Average Cost Per Sq Metre
	Low Benchmark	Mid Benchmark	High Benchmark	Low Benchmark	Mid Benchmark	High Benchmark
East Anglia	£47,242	£51,537	£55,831	£1,575	£1,718	£1,861
London	£55,780	£62,375	£69,410	£1,859	£2,079	£2,314
Midlands	£45,774	£49,935	£54,096	£1,526	£1,664	£1,803
North England	£45,358	£49,493	£53,618	£1,512	£1,650	£1,787
Northern Ireland	£44,087	£46,821	£50,722	£1,431	£1,561	£1,691
Scotland	£45,256	£49,370	£53,484	£1,509	£1,646	£1,783
South East	£51,317	£57,382	£63,665	£1,859	£2,079	£2,282
South West	£46,528	£52,825	£57,979	£1,575	£1,761	£1,933
Wales	£45,815	£51,229	£55,279	£1,527	£1,708	£1,843
Average	£47,462	£52,330	£57,120	£1,597	£1,763	£1,922

All costs exclude VAT.

Here’s what the data shows for the cost of standard loft conversion to a standard spec:

• It costs 23% more to convert a loft in London than in other regions.
• The minimum cost is £44,087, and the maximum cost is £69,410.
• The total average cost is £52,304, or £1,760 per square metre.

Cost Breakdown By Project Stage – London

Here’s an example of the associated costs for the different stages of a standard loft conversion for a standard-spec project – when using a mid-benchmark contractor in London:

Total	£62,375	100%
Preliminaries	£10,900	17.5%
Demolitions	£1,679	2.7%
Floor structure and lining	£3,460	5.5%
Steel and structural supports	£5,735	9.2%
External wall structure and lining	£5,524	8.9%
Internal wall structure and lining	£3,855	6.2%
Ceiling structure and lining	£3,901	6.3%
External windows and doors	£3,070	4.9%
Internal doors and frames	£1,496	2.4%
Drainage and pipework	£782	1.3%
Heating and cooling	£1,643	2.6%
Wiring and fuseboards	£1,445	2.3%
Stairs, balustrades and lifts	£2,885	4.6%
Plumbed appliances	£2,742	4.4%
Wired appliances	£2,057	3.3%
Ceiling preparation and finishes	£426	0.7%
Wall preparation and finishes	£3,720	6.0%
Floor preparation and finishes	£3,452	5.5%
Decoration	£3,177	5.1%
Fixtures and fittings	£425	0.7%

Cost Breakdown By Area – London

Here’s a breakdown of the associated costs by area for a standard-spec loft conversion – when using a mid-benchmark contractor in London:

Total	£62,375	100%
Bedroom	£8,378	13.4%
Eaves storage	£1,492	2.4%
En-suite	£11,646	18.7%
Loft conversion	£36,720	58.9%
Landing incl. stairs	£4,139	6.6%

Mansard Loft Conversion

Here’s a table showing the average building costs of carrying out a Mansard loft conversion for a standard-spec project in the UK:

Mansard Loft Conversion	Total Average Build Cost			Average Cost Per Sq Metre
	Low Benchmark	Mid Benchmark	High Benchmark	Low Benchmark	Mid Benchmark	High Benchmark
East Anglia	£61,480	£67,069	£72,658	£2,049	£2,236	£2,422
London	£71,417	£79,861	£88,602	£2,381	£2,662	£2,953
Midlands	£59,956	£65,407	£70,857	£1,999	£2,180	£2,362
North England	£59,511	£64,933	£70,343	£1,984	£2,164	£2,345
Northern Ireland	£58,129	£62,081	£67,254	£1,897	£2,069	£2,242
Scotland	£59,351	£64,746	£70,142	£1,978	£2,158	£2,338
South East	£65,704	£73,469	£80,637	£2,381	£2,662	£2,922
South West	£60,741	£68,746	£75,453	£2,049	£2,292	£2,515
Wales	£60,002	£67,093	£72,122	£2,000	£2,236	£2,404
Average	£61,810	£68,156	£74,230	£2,080	£2,296	£2,500

All costs exclude VAT.

Here’s what the data shows for the cost of carrying out a Mansard loft conversion to a standard spec:

• The minimum cost is £58,129, and the maximum cost is £88,602.
• The total average cost is £68,065, or £2,292 per square metre.

Cost Breakdown By Project Stage – London

Here’s an example of the associated costs for the different stages of a Mansard loft conversion for a standard-spec project – when using a mid-benchmark contractor in London:

Total	£79,861	100%
Preliminaries	£11,597	14.5%
Demolitions	£431	0.5%
Floor structure and lining	£3,652	4.6%
Steel and structural supports	£3,934	4.9%
External wall structure and lining	£15,478	19.4%
Internal wall structure and lining	£3,855	4.8%
Roof structure and coverings	£8,452	10.6%
Ceiling structure and lining	£1,221	1.5%
External windows and doors	£3,070	3.8%
Internal doors and frames	£1,496	1.9%
Drainage and pipework	£4,278	5.4%
Heating and cooling	£1,643	2.1%
Wiring and fuseboards	£1,868	2.3%
Stairs, balustrades and lifts	£2,885	3.6%
Plumbed appliances	£2,742	3.4%
Wired appliances	£2,057	2.6%
Ceiling preparation and finishes	£426	0.5%
Wall preparation and finishes	£3,720	4.7%
Floor preparation and finishes	£3,452	4.3%
Decoration	£3,177	4.0%
Fixtures and fittings	£425	0.5%

Cost Breakdown By Area – London

Here’s a breakdown of the associated costs by area for a standard-spec Mansard loft conversion – when using a mid-benchmark contractor in London:

Total	£79,861	100.0%
Bedroom	£8,378	10.5%
Eaves storage	£1,492	1.9%
En-suite	£11,646	14.6%
Mansard loft extension	£54,206	67.9%
Landing incl. stairs	£4,139	5.2%

Dormer Loft Conversion

Here’s a table showing the average building costs of carrying out a dormer loft conversion for a standard-spec project in the UK:

Dormer Loft Conversion	Total Average Build Cost			Average Cost Per Sq Metre
	Low Benchmark	Mid Benchmark	High Benchmark	Low Benchmark	Mid Benchmark	High Benchmark
East Anglia	£55,222	£60,242	£65,263	£1,841	£2,008	£2,175
London	£63,353	£70,844	£78,705	£2,112	£2,361	£2,623
Midlands	£53,120	£57,949	£62,778	£1,771	£1,932	£2,093
North England	£52,694	£57,485	£62,275	£1,756	£1,916	£2,076
Northern Ireland	£51,640	£56,335	£61,029	£1,721	£1,878	£2,034
Scotland	£52,624	£57,408	£62,192	£1,754	£1,914	£2,073
South East	£58,285	£65,173	£72,309	£1,943	£2,172	£2,410
South West	£53,898	£61,087	£67,046	£1,797	£2,036	£2,235
Wales	£53,166	£59,449	£64,001	£1,772	£1,982	£2,133
Average	£54,889	£60,663	£66,178	£1,830	£2,022	£2,206

All costs exclude VAT.

Here’s what the data shows for the cost of carrying out a dormer loft conversion to a standard spec:

• The minimum cost is £51,640, and the maximum cost is £78,705.
• The total average cost is £60,577, or £2,019 per square metre.

Cost Breakdown By Project Stage – London

Here’s an example of the associated costs for the different stages of a dormer loft conversion for a standard-spec project – when using a mid-benchmark contractor in London:

Total	£70,844	100.0%
Preliminaries	£12,384	17.5%
Demolitions	£2,970	4.2%
Floor structure and lining	£3,263	4.6%
Steel and structural supports	£2,465	3.5%
External wall structure and lining	£10,455	14.8%
Internal wall structure and lining	£3,855	5.4%
Roof structure and coverings	£5,907	8.3%
Ceiling structure and lining	£1,221	1.7%
External windows and doors	£3,070	4.3%
Internal doors and frames	£1,496	2.1%
Drainage and pipework	£1,575	2.2%
Heating and cooling	£1,428	2.0%
Wiring and fuseboards	£1,868	2.6%
Stairs, balustrades and lifts	£2,885	4.1%
Plumbed appliances	£2,742	3.9%
Wired appliances	£2,057	2.9%
Ceiling preparation and finishes	£426	0.6%
Wall preparation and finishes	£3,720	5.3%
Floor preparation and finishes	£3,452	4.9%
Decoration	£3,177	4.5%
Fixtures and fittings	£425	0.6%

Cost Breakdown By Area – London

Here’s a breakdown of the associated costs by area for a standard-spec dormer loft conversion – when using a mid-benchmark contractor in London:

Total	£70,844	100.0%
Bedroom	£8,378	11.8%
Eaves storage	£1,492	2.1%
En-suite	£11,646	16.4%
Dormer loft extension	£45,189	63.8%
Landing incl. stairs	£4,139	5.8%

Summary Of Loft Conversion Costs

So, how much does a loft conversion cost in the UK? Based on the three different conversions covered in this article (standard, dormer, and Mansard), you can expect a loft conversion to cost on average (when using a mid-benchmark contractor):

• Standard loft conversion – £52,304, or £1,760 per sq metre.
• Mansard loft conversion – £68,065, or £2,292 per sq metre.
• Dormer loft conversion – £60,577, or £2,019 per sq metre. 

Please remember that these costs do not include VAT, and there may be other additional costs, such as obtaining planning permission, conducting structural surveys, making unexpected repairs, and completing custom finishes.

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Frequently Asked Questions About Loft Conversions

Here are some FAQs about loft conversions.

Do I need to move out during the loft conversion?

You rarely need to move out during most loft conversions. However, there will be noise, dust, and workers coming in and out, which can be particularly inconvenient if you work from home. For a roof lift loft conversion, which involves raising the existing roof to create additional headroom, many contractors recommend staying elsewhere until the property is weatherproofed.

How much headroom is required for a loft conversion?

Building Regulations require a minimum headroom of 2.2 metres (7 feet 2 inches) for a loft conversion, taken from the floor to the highest point of the ceiling. If your loft has less headroom, you may still be able to proceed by adjusting the roofline or lowering the ceiling of the floor below.

Can I convert a loft into a terraced or semi-detached house?

Yes, but you’ll need to consider specific factors, such as shared walls with neighbours (party walls), which may require a party wall agreement. Additionally, planning permission might be needed if your conversion alters the roofline or if your property is in a conservation area. 

What fire safety regulations apply for loft conversions?

In the UK, loft conversions must comply with strict fire regulations. This includes installing fire-resistant (30-minute rated) doors on all access points to the loft, creating a protected escape route with enclosed, fire-resistant walls and doors, and fitting mains-powered, interlinked smoke alarms on each floor. Emergency escape windows or alternative exits are also required.