Single Storey vs Double Storey Extension: Which Is Right for You?
Deciding between a single storey and double storey extension is one of the most important choices you will make during your home improvement project. Both options have clear advantages depending on your budget, space requirements, property type and future plans. This guide breaks down the key differences to help you choose the right option.
Cost Differences Explained
A single storey extension typically costs between £1,500 and £2,500 per square metre. A double storey extension costs around £1,800 to £3,000 per square metre in total, but because the upper floor shares the same foundations and roof structure, the cost per square metre of usable space is significantly lower. For example, a 20 sqm single storey extension might cost £40,000, while a 40 sqm double storey extension on the same footprint might cost £60,000 to £70,000 — giving you double the space for only 50-75% more cost.
Planning Permission and Permitted Development
Single storey rear extensions often fall under permitted development rights, meaning you may not need planning permission at all. Extensions up to 3 metres from the rear wall (or up to 6-8 metres under prior approval) can proceed without a full application. Double storey extensions face stricter rules — they must not extend more than 3 metres from the rear wall and must be at least 7 metres from the rear boundary. Many double storey extensions require full planning permission, especially in conservation areas or on semi-detached and terraced properties.
Build Times and Disruption
A single storey extension typically takes 10 to 14 weeks to build, while a double storey extension usually takes 14 to 20 weeks. Double storey projects involve more scaffolding, structural steelwork and coordination between trades. If minimising disruption is a priority — particularly if you plan to stay in the property during the build — a single storey extension is generally less intrusive and quicker to complete.
Space, Layout and How You Use It
A single storey extension is ideal if you primarily need more ground-floor living space — a larger kitchen-diner, a garden room, a home office or an open-plan family area. A double storey extension makes sense when you need both ground-floor space and additional bedrooms or bathrooms upstairs. If your family is growing or you need a home office plus extra bedroom, a double storey extension delivers more versatility.
Which Adds More Value to Your Property?
Both types of extension add value, but double storey extensions typically deliver a higher return because they create additional bedrooms or bathrooms. An extra bedroom with an en-suite can add £20,000 to £40,000 or more to your property value depending on location. Single storey kitchen-diner extensions also perform well, particularly in family-oriented areas where open-plan living is in high demand.
Structural and Design Considerations
A double storey extension requires more structural engineering — heavier foundations, larger steel beams and careful consideration of how the upper floor connects to the existing first floor. The roof design also needs to tie into the existing roofline sympathetically. Single storey extensions are structurally simpler, with more flexibility in roof design — flat roofs, pitched roofs, lantern roofs or green roofs are all viable. If your property has limited foundation capacity or challenging ground conditions, a single storey may be more practical and cost-effective.
Impact on Your Neighbours and Boundaries
Double storey extensions have a greater visual impact on neighbouring properties and are more likely to attract planning objections. Issues around overlooking, loss of light and overbearing impact are common concerns with two-storey builds. Single storey extensions are generally less contentious with neighbours, particularly if the eaves height stays below 3 metres near the boundary. If your property shares a boundary wall and the work involves excavation or structural changes within certain distances, a party wall agreement may be required — this is more common with double storey extensions where deeper foundations and heavier structural loads are involved.
Common Mistakes When Deciding
Building a double storey without checking planning rules first is a costly mistake — discovering you need full planning permission after the design is complete wastes time and money. Other errors include not budgeting for the additional structural engineering a double storey requires, underestimating the disruption of a longer build, and not considering how a taller extension will affect light into existing rooms. Always get professional advice before committing.
Local Considerations in Worcestershire
In Worcestershire and surrounding counties, the mix of Victorian semis, 1930s detached homes, period cottages and modern estates means the right extension type varies significantly by property. Conservation areas around Worcester, Malvern and Pershore often restrict double storey extensions. Clay soils across the region may affect foundation costs. MTD Build works across Worcestershire, Herefordshire, Gloucestershire and Warwickshire and can advise on what suits your property during a free consultation.
Making the Right Decision
Consider your budget, how much space you need, your property type and local planning constraints. If you are unsure, a consultation with an experienced builder can help you weigh up the options. Use our AI-powered estimate generator to compare rough costs for both options, or book a free consultation to discuss your specific project.
Frequently Asked Questions
Is a single storey or double storey extension better value?
A double storey extension generally offers better value per square metre because the upper floor adds relatively little to the cost of foundations and roofing. However, if you only need ground-floor space, a single storey extension avoids paying for space you do not need.
Can I build a double storey extension without planning permission?
Some double storey extensions fall under permitted development, but the rules are stricter — the extension must not exceed 3 metres from the rear wall and must be at least 7 metres from the rear boundary. Many double storey projects require full planning permission.
How long does a double storey extension take compared to single storey?
A single storey extension typically takes 10-14 weeks, while a double storey extension takes 14-20 weeks. The additional time accounts for extra structural work, scaffolding and upper-floor fit-out.
Will a double storey extension overshadow my neighbours?
Potentially, yes. Planning authorities assess the impact on neighbouring properties including loss of light, overlooking and visual dominance. This is one reason why double storey extensions often require full planning permission.
Which type of extension is less disruptive to live with during the build?
A single storey extension is generally less disruptive because it involves less scaffolding, shorter build times and less impact on the upper floors of the house where bedrooms are typically located.
Does MTD Build do both single and double storey extensions?
Yes. MTD Build specialises in both single and double storey extensions across Worcestershire, Herefordshire, Gloucestershire and Warwickshire. We advise on the best option during a free consultation.