Cost of a Side Extension: Quantity Surveyor Provides Detailed Breakdown
When it comes to adding extra living space to your home, three popular options are side extensions, rear extensions, and loft conversions. Each choice comes with its own set of costs, and understanding these differences can help you make an informed decision.
Average Costs
The average cost of a side extension in the UK tends to be higher than a rear (double) extension and generally less than or comparable to a loft conversion, depending on the size, specification, and complexity.
Here's a breakdown of the typical costs:
|Type of Extension|Typical Cost|Cost Per Square Metre| |-|-|-| |Side extension|£1,650 to £3,000 per m² (double storey quality range)|£1,650–£3,000[1]| |Rear double storey extension|Around £1,000–£2,150 per m² (single/double storey range)|£900–£2,150[1][5]| |Loft conversion (mansard type)|£35,000 to £80,000 overall (depending on type and size)|Roughly £1,800+ per m² for mansard[2]| |Single storey extension|£1,500–£2,000 per m²|£1,500–£2,000[3][5]|
Factors Influencing Costs
Structural Complexity
Side extensions often require more structural work, including foundation reinforcement and alterations near boundary lines, which can increase costs relative to rear extensions[1].
Planning Permission
Side extensions more commonly trigger planning permission requirements and restrictions (e.g., being near shared boundaries), adding design and survey costs[1].
Loss of Natural Light
Side extensions may reduce natural light inside the home, sometimes necessitating skylights or larger windows, increasing expense[1].
Space Usage & Size
Loft conversions, especially mansard types, are extensive alterations that involve changing the roof structure and adding significant living space. They typically have a higher fixed cost ranging from £35,000 to £80,000, making them generally more expensive overall, but cost per m² depends on usable floor space[2].
Quality and Finishes
Higher quality materials and finishes will push costs toward the upper end of ranges for any extension[1][5].
Project Scope
Rear double extensions can be simpler, causing less disruption and generally costing slightly less than side extensions due to fewer structural complications[1].
Additional Work
Architect fees, groundwork, new plumbing, electrical installations, and compliance with building regulations add to total costs across all extension types[1][5].
Summary
- Side extensions cost roughly £1,650 to £3,000 per m² due to structural and planning complexities.
- Rear double storey extensions often cost less, in the range £900 to £2,150 per m², and tend to be simpler to build.
- Loft conversions, such as mansard types, have higher fixed costs (£35,000–£80,000) reflecting major roof modifications and can be more expensive overall though cost per usable floor metre varies.
- Single storey extensions generally cost from £1,500 to £2,000 per m².
These figures highlight how the specific location, design complexity, and size of the extension influence whether a side extension will cost more or less compared to a loft conversion or double rear extension in the UK[1][2][3][5].
It's essential to keep in mind that other factors, such as the need for Listed Building Consent and Building Regulations approval fees, can impact the overall cost of your project.
[1] The Cost of Building a Home Extension
[2] Loft Conversion Costs
[3] Single Storey Extension Costs
[4] Rear Extension Costs
[5] Planning Permission Fees
- When considering a loft conversion, homeowners might encounter costs ranging from £35,000 to £80,000 due to structural modifications required for mansard types.
- A side extension in the UK can cost around £1,650 to £3,000 per square metre, making it one of the more costly options for additional living space.
- Architect fees, groundwork, new plumbing, electrical installations, and compliance with building regulations add to the total costs of all extension types.
- Planning permission requirements for side extensions are more common, and these additional design and survey costs should be taken into account.
- While loss of natural light may necessitate skylights or larger windows in a side extension, such additions increase the overall cost.
- Side extensions often call for more structural work, including foundation reinforcement and alterations near boundary lines, which adds to the cost.
- Recommendations and guides are available to compare the costs of various extension options, offering helpful insights for personal-finance management and budgeting purposes.
- Single storey extensions generally cost from £1,500 to £2,000 per square metre, making them a more affordable choice compared to loft conversions.
- A rear double storey extension, costing approximately £900 to £2,150 per square metre, tends to be simpler to build and less expensive compared to a side extension.
- Homeowners must factor in utility costs when planning their budget for home-and-garden projects or home-improvement initiatives, such as extensions.
- Understanding the cost differences between side extensions, rear extensions, and loft conversions enables homeowners to make informed decisions about their extension projects.
- Researching ideas and designs for extensions can provide useful inspiration for home lifestyle improvements.
- Obtaining a permit is necessary for executing extension projects, and the fees associated with this process should be included in the overall project budget.
