Single Storey Vs Two Storey Extensions: Pros & Cons For Hertfordshire Properties

At Wells Construction Ltd, our builders in Hertfordshire specialise in both single and two storey extensions. Our experienced team provides detailed feasibility assessments, planning guidance and construction expertise. 

Choosing The Right Extension For Your Home

Deciding between a single storey and two storey extension represents one of the most significant choices facing Hertfordshire property owners planning to expand their living space. Both options offer distinct advantages and challenges that can dramatically impact your project's cost, timeline and ultimate success. This article examines the key considerations for clients choosing between single and two storey extension projects.

Understanding Extension Options

Single storey extensions add ground-floor space only, creating additional room without increasing your property's height. These extensions typically provide areas for kitchen dining spaces, additional bedrooms, or enlarged living areas. The construction involves foundation work, single-level walls and roofing systems.

Two storey extensions provide space across two levels, doubling the floor area compared to equivalent single storey additions. The ground floor typically accommodates living spaces whilst the upper level adds bedrooms or bathrooms. These extensions require more substantial structural work, including stronger foundations and complex roofing arrangements.

Cost Comparison Analysis

Single storey extensions in Hertfordshire typically cost between £1,800-£3,000 per square metre. A 25m² single storey extension generally ranges from £45,000-£75,000 including basic finishes. Lower overall costs make single storey extensions accessible to more homeowners.

Two storey extensions offer better value per square metre, typically costing £1,750-£2,580 per square metre. A 50m² two storey extension usually ranges from £87,500-£129,000, providing double the space for less than double the cost. The cost efficiency occurs because expensive elements like foundations serve both levels.

Planning Permission Considerations

Many single storey extensions fall under Permitted Development rights, avoiding the need for full planning permission. Under these rights, you can typically build rear extensions up to 6 metres for terraced/semi-detached properties and 8 metres for detached homes.

Two storey extensions usually require full planning permission due to their greater impact on neighbouring properties. Planning fees in England cost £528 for householder applications as of April 2025. The planning process considers factors like overlooking neighbouring properties and architectural compatibility.

Construction Timeline Differences

Single storey extensions typically complete within 3-4 months from start to finish. The simpler construction process involves fewer structural complications. Reduced complexity means fewer potential delays from weather or coordination issues between different building trades.

Two storey extensions generally require 4-6 months for completion due to additional structural work, staircase installation, and upper-level services. The extended timeline reflects increased complexity, allowing for proper structural curing and coordination of building phases.

Property Extension Benefits

Single storey extensions excel at creating open-plan living areas with excellent natural light opportunities. Roof lights and large sliding doors can flood spaces with daylight. These extensions work particularly well for kitchen-dining areas and spaces requiring easy garden access.

Two storey extensions maximise floor area whilst minimising garden footprint, preserving outdoor space. Upper levels provide private spaces like bedrooms, whilst ground floors accommodate communal family areas, creating natural separation between different household activities.

Impact On Property Value 

Single storey extensions typically add significant value by creating desirable open-plan living spaces. Kitchen-dining extensions particularly appeal to buyers and can increase property values by 15-20%. The value increase depends on local market conditions and integration quality.

Two storey extensions often provide better return on investment due to additional bedroom and bathroom space. Extra bedrooms can increase property values by 10-15% per bedroom, with en-suite facilities adding further premium.

Frequently Asked Questions

Which Extension Type Is More Cost-Effective?

Two storey extensions typically offer better value per square metre, though single storey extensions have lower total project costs.

Do I Need Planning Permission For Both Types?

Single storey extensions often fall under Permitted Development rights, whilst two storey extensions usually require full planning permission.

Which Extension Adds More Property Value?

Both can add significant value when well-designed. Two storey extensions often provide better returns due to additional bedrooms.

Making The Right Choice

The decision between single and two storey extensions depends on budget, family needs and long-term plans. Single storey extensions offer simpler construction and lower costs, making them ideal for homeowners seeking ground-floor improvements.

Two storey extensions provide superior space efficiency and cost-effectiveness per square metre, making them attractive for growing families needing maximum accommodation. Contact us today to discuss your property extension requirements and receive expert advice on the most suitable approach for your property.