EXTENSIONS & CONVERSIONS
Double Storey Extensions
Double your living space and add significant property value with professionally designed and managed two-storey home extensions.
About our double storey extensions service
A double-storey extension represents one of the most effective ways to transform a property without the need to relocate. Unlike standard House Extensions that only address ground-floor needs, these projects allow for a wholesale rethink of how a home functions. They are ideal for growing families who require additional bedrooms or master suites on the first floor alongside expanded kitchen or dining areas below. For commercial landlords, two-storey additions can also be used to increase the capacity of HMOs or multi-unit dwellings. While more complex than Rear Extensions or Side Extensions, the dual-level approach offers a much better ratio of cost-to-space. These projects require precise structural engineering to support the upper floor weight and careful consideration of the existing foundations. At Design N Build, we manage the entire process, including the integration of M&E services and ensuring the new structure blends perfectly with the original character of your building.
What's included
- Architectural Planning
Full management of the planning process, including architectural drawings and submission to local authorities for two-storey approvals.
- Building Regulations Compliance
We handle all building control inspections and ensure the new structure meets the latest thermal and fire safety regulations.
- Groundworks & Foundations landscapes
Comprehensive groundworks, including reinforced foundations and drainage alterations needed to support a taller, heavier structure.
- M&E Integration
Professional installation of all plumbing, heating, and electrical systems, ensuring the upper floor has consistent pressure and power.
- Interior Fit-Out
Skilled trades for all internal works, from tiling en-suites to installing bespoke cabinetry and decorative finishes.
Key benefits
- Maximise Land Footprint
By adding floor space over two levels, you essentially double the square footage of your home without significantly impacting the footprint of your garden or outdoor areas.
- Cost-Efficiency
Adding two floors at once is more cost-effective per square metre than building two separate single-storey additions, as groundworks and roofing costs are shared across both levels.
- Substantial Value Increase
Increasing the bedroom count and ground floor living area simultaneously creates a significant uplift in market value, often providing a stronger return on investment than smaller projects.
- Internal Layout Flexibility
Two-storey builds allow for total reorganisation of your home, including moving staircases or adding en-suites, rather than simply tacking on a single isolated room.
- Enhanced Curb Appeal
A full-height addition offers the opportunity to redesign the exterior aesthetic of your property, giving an older house a modern, cohesive architectural look.
Project types we cover
- Residential Family Homes
- Terraced & Semi-Detached Houses
- Commercial Property Portfolios
- Master Suite Additions
- Open-Plan Kitchen & Bedroom Combos
- HMO Expansions
Our process
- 1Initial Consultation
Our surveyors and designers assess your property to determine structural feasibility and help you define a realistic budget for the project.
- 2Detailed Design & Planning
Detailed drawings are produced for planning applications and building control. We ensure the designs meet local authority guidelines while maximising your available space.
- 3Structural Engineering
Our engineers calculate the necessary steel reinforcements and foundation depths required to safely support the additional weight of a second floor.
- 4Construction Phase
Our site teams manage the excavation, wall construction, and roofing. We coordinate the first-fix electrics and plumbing to ensure the new levels integrate with existing systems.
- 5Finishing & Handover
After the shell is complete, we handle plastering, flooring, and joinery. A final inspection ensures everything meets our quality standards before we hand over the keys.
Why choose Design N Build Construction Company
- End-to-End Management
We offer a complete service from the first drawing to the final coat of paint, reducing the stress of managing multiple contractors.
- Technical Expertise
Our builders and engineers have extensive experience in multi-level construction, ensuring your extension is structurally sound and durable.
- Transparent Pricing
We provide clear, detailed quotes without hidden costs, helping you manage your finances effectively throughout the build.
- Quality Workmanship
We treat your property with respect, maintaining a clean site and ensuring all work meets rigorous safety and quality standards.
- Reliable Timelines
We understand the importance of sticking to a schedule, especially when a project affects both floors of your home.
Frequently asked questions
How long does a typical two-storey extension take?
A double-storey extension usually takes between 14 to 20 weeks on site, depending on the complexity of the groundworks and internal fit-out. This does not include the pre-construction phase, which involves architectural design and planning approvals that can take an additional 3 to 5 months.
Do I need planning permission for a double-storey extension?
Most double-storey extensions require full planning permission rather than falling under Permitted Development. This is due to height restrictions and the potential impact on neighbouring properties, such as overshadowing or loss of privacy. We handle the submission and liaison with your local planning department as part of our service.
Do you offer a warranty on the structural work?
Yes, we provide a standard 10-year structural warranty on all major extension works. This covers the foundation integrity, structural steelwork, and the waterproof envelope of the building. We also provide necessary certifications for gas, electrical, and building control compliance upon completion.
Can we stay in the house during the build?
While it is possible to live in the property, it can be challenging during the middle stages of construction. We often need to remove external walls and integrate new plumbing and electrical systems. Many clients choose to vacate for the most intrusive 4 to 6 weeks to avoid the noise and dust.
How does the cost compare to a single-storey extension?
Costs vary based on location and specification, but a two-storey extension typically costs about 50% more than a single-storey one, despite offering twice the space. This is because the most expensive elements, such as the foundations and the roof, are already included in the base price.
Talk to us about your project
Choosing to extend across two storeys is a significant investment that requires careful structural planning and a clear understanding of building regulations. At Design N Build, we help homeowners and developers navigate the complexities of large-scale additions, from the initial feasibility study through to the final interior finishes. Whether you are looking to add master suites, home offices, or expansive open-plan kitchens, our team provides the technical expertise to ensure your project is completed safely and to a high standard. Contact our consultants today to discuss your site requirements, budget expectations, and how a double-storey extension can best serve your long-term property goals.
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