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Cost of a Side Extension: A Quantity Surveyor Breaks Down the Expenses

Expanding your home's square footage? Discover the financial planning tips our expert offers for sideward home expansions.

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3 min read
Cost of Side Extension Revealed: Quantity Surveyor Provides Detailed Breakdown
Cost of Side Extension Revealed: Quantity Surveyor Provides Detailed Breakdown

Cost of a Side Extension: A Quantity Surveyor Breaks Down the Expenses

In the UK, home extensions can significantly enhance living space and property value. Here's a breakdown of the average costs associated with various types of extensions, based on recent data [1][2][3][4][5].

Single Side or Single-Storey Extensions

The average cost of a single side or single-storey extension typically ranges from £1,500 to £2,500 per square metre. For a 20-25 m² extension, the total cost, including professional fees and VAT, usually falls between £30,000 and £50,000. Single side extensions often cost more than rear extensions due to additional structural work and potentially planning permission requirements.

Double Side Extensions (Two-Storey)

Double side extensions (which could be interpreted as larger or two-storey extensions on the side) have higher costs. A double-storey extension costs about 50% more than the single-storey build cost, so roughly £75,000 to £100,000+ for a similar footprint including fees and VAT. Costs per square metre range from about £1,650 to £3,000 depending on quality and complexity.

Double Rear Extensions (Two-Storey)

Rear extensions tend to be slightly cheaper than side extensions because of fewer structural challenges but depending on size and complexity can be comparable in price. A double-storey rear extension cost fits within the same range as double-storey side extensions, typically up to or exceeding £100,000 depending on size and finishes.

Loft Conversions

Loft conversions can be cost-competitive with single-storey extensions, but double-storey extensions (side or rear) typically cost more due to the increased build volume and complexity. The cost varies by type:

  • A single mansard loft conversion costs around £35,000 to £50,000 and involves modifying one side of the roof.
  • A double mansard loft conversion is more expensive, ranging from £50,000 to £80,000, as it modifies both sides of the roof and offers more living space.
  • L-shaped loft conversions fall between these ranges, about £55,000 to £75,000.

Summary of Approximate Costs in the UK:

| Extension Type | Average Cost Range | |--------------------------|------------------------------| | Single side/single-storey extension (20-25 m²) | £30,000 – £50,000 | | Double side or two-storey extension | £75,000 – £100,000+ | | Double rear extension (two-storey) | £75,000 – £100,000+ | | Single mansard loft conversion | £35,000 – £50,000 | | Double mansard loft conversion | £50,000 – £80,000 |

When planning an extension, it's essential to consider factors such as design, materials, and location, as these can significantly impact the final cost. A well-thought-out extension can raise a home's market value, but careful consideration is needed to ensure it blends with the rest of the home.

Collaborating with an architect can help reduce bespoke design aspects and costs, while designing with off-the-shelf items can save hundreds or thousands of pounds. The roof design can also affect the cost, with tiled/slated pitched roofs being more expensive than flat rubber or GRP roofs. Access to the side space can impact the cost, with a standard mini-digger not always suitable for terraced houses.

[1] Homebuilding & Renovating [2] Which? [3] Property Reporter [4] The Telegraph [5] Networx

  1. In the UK, home extensions can significantly boost living space and property value, according to recent data.
  2. The cost of a single side or single-storey extension usually falls between £30,000 and £50,000.
  3. Single side extensions often cost more than rear extensions due to additional structural work and potential planning permission requirements.
  4. Double side extensions, or larger two-storey extensions, have higher costs, ranging from £75,000 to £100,000+.
  5. A single mansard loft conversion costs around £35,000 to £50,000, while a double mansard loft conversion ranges from £50,000 to £80,000.
  6. When planning an extension, factors like design, materials, and location should be carefully considered, as they can impact the final cost.
  7. Collaborating with an architect can help reduce bespoke design aspects and costs, while using off-the-shelf items can save money.
  8. The roof design can affect the cost, with tiled/slated pitched roofs being more expensive than flat rubber or GRP roofs.
  9. Access to the side space can impact the cost, with a standard mini-digger not always suitable for terraced houses.
  10. A well-thought-out extension can increase a home's market value, but it's crucial to ensure it blends with the rest of the home.
  11. The costs of kitchen, utility, doors, windows, flooring, heating, and energy-efficient solutions should be included in the budget to avoid unexpected expenses.
  12. Investing in home-and-garden and home-improvement projects can potentially lead to higher returns, but it's essential to consider personal-finance and real-estate market trends.
  13. It's advisable to research regulations, permits, and financial options, such as bank loans or remortgaging, before starting a project.
  14. By carefully planning, designing, and budgeting, home extensions can cater to your lifestyle needs and increase the value of your property.

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