Garden Office Cost Calculator UK 2026
Calculate the cost of a garden office or home office extension. Compare garden room vs house extension costs, planning permission requirements and ROI.
Garden Office Cost Calculator
Frequently Asked Questions
How much does a garden office cost in the UK in 2026?
A flat-pack garden room of 15m² costs approximately £8,000–£25,000 depending on specification (basic to premium). An insulated timber-clad garden office at the same size typically costs £12,000–£35,000. Brick or block-built structures range from £20,000–£45,000. SIP panel buildings offer a good mid-range option at £15,000–£30,000. Add groundworks (£2,000–£5,000), electrics (£1,500–£3,000) and internet connectivity (£500) to all options. London and South East prices are 10–25% higher than the national average.
Do I need planning permission for a garden office?
Most garden offices fall under permitted development rights and do not require planning permission, provided the building: is single-storey; does not exceed 4m in height (3m within 2m of the boundary); is not forward of the principal elevation of the house; covers no more than 50% of the garden around the original house; and is less than 30m² total floor area (for buildings over 15m² that are closer than 1m to the boundary, additional fire safety rules apply). In conservation areas, the size limit is lower. If you plan to use it as a self-contained living space, full planning permission is always required.
Is a garden office a good investment?
A quality garden office can add 1.5–5% to a property's value — on a £400,000 home that is up to £20,000. However, the added value is typically less than the build cost, so it is best justified by the utility it provides rather than pure financial return. Working from home saves commuting costs (average UK commuter spends £2,500–£5,000 per year) and can provide significant wellbeing and productivity benefits. If you can claim it as a business expense (see below), the net cost after tax relief can be substantially reduced.
Can I claim a garden office as a business expense?
If you are self-employed or a limited company director, you may be able to claim a garden office as a business expense, but the rules are nuanced. For sole traders and partnerships: HMRC generally does not allow capital cost as a deduction, but you can claim capital allowances on fixtures and fittings (computers, furniture, etc.) and a proportion of running costs (electricity, internet). For limited companies: the company can own the structure, claim capital allowances on the full build cost at 3% per year (structures and buildings allowance), and deduct all running costs. A mixed-use garden office (personal and business) requires careful apportionment.
Garden office vs house extension — which is better value?
A house extension typically costs £1,800–£2,500 per m² for a standard rear extension, putting a 15m² extension at £27,000–£37,500. A garden office of the same size can be built for £8,000–£25,000 (flat-pack to premium timber). However, a properly built extension adds more reliably to property value (typically 10–15% on house price for a well-designed kitchen extension) and may be warmer and better integrated into the home. Garden offices depreciate over time and may not add value in all markets. For pure workspace use, a garden office usually offers better value per pound spent; for living space, an extension is generally superior.