High-quality construction, transparent pricing, and on-time delivery. We are the go-to team for house extensions in Welwyn Garden City and the surrounding Hertfordshire areas.
Get Your Free QuoteFrom compact side returns in terraced homes to large wrap‑around extensions in suburban properties, we design and build Welwyn Garden City house extensions that enhance space, flow and value.
We manage everything: design, planning, building regulations, groundworks, structure, and high‑quality internal finishes—delivered on time and to budget by our CITB certified team.
A clear, step‑by‑step process from first enquiry to final handover so you always know what is happening on your Welwyn Garden City project.
We visit your property in Welwyn Garden City to understand how you live, your space requirements, budget and timescales. We discuss options such as single‑storey, double‑storey or wrap‑around extensions.
Working with architects and structural engineers, we develop extension drawings, prepare planning or permitted development documentation and provide a detailed, fixed price for the build.
Our build team manages all aspects of construction – groundworks, drainage, structure, roof, windows, electrics, plumbing, plastering and finishes – with regular updates and site meetings.
Once complete, we walk through your new space, deal with any snags promptly and provide certificates, warranties and building control sign‑off for your Welwyn Garden City house extension.
Choose the right extension for your Welwyn Garden City home and lifestyle
Perfect for expanding ground floor living spaces. Ideal for kitchen extensions, dining areas, or family rooms with seamless indoor-outdoor flow.
Maximize space with two-storey additions. Add bedrooms, bathrooms, and living areas while maintaining garden space and adding significant value.
Combine side return and rear extensions for maximum space transformation. Create spectacular open-plan living areas with abundant natural light.
Transform your kitchen into the heart of your home. Modern kitchen extensions with island units, dining areas, and seamless garden access.
Light-filled extensions that blur the boundary between indoor and outdoor living. Modern glazed extensions with excellent thermal performance.
Convert unused loft space into bedrooms, offices, or playrooms. Dormer extensions and full loft conversions with modern amenities.
A specialist house extension contractor trusted across Welwyn Garden City and the wider Hertfordshire area for quality, safety and clear communication.
All trades on your Welwyn Garden City house extension are vetted, experienced and follow CITB and UK building regulations. Structural work, foundations, steels and roof alterations are all signed off by qualified professionals.
We provide clear, itemised quotes for your extension project in Welwyn Garden City – including labour, materials and allowances – so you know exactly what’s included before work begins.
Building Group carries full public liability and employers’ liability insurance. All major elements of your house extension are covered by written workmanship guarantees and manufacturer warranties.
From initial concept sketches to planning permission and building control sign‑off, we manage the full process for your Welwyn Garden City extension so you only deal with one contractor.
Well-designed extensions can add 15-25% to your property value, often exceeding construction cost and providing excellent ROI.
Extend your current home instead of moving. Save on estate agent fees, stamp duty, legal costs, and the stress of relocating.
Create the space your family needs to grow and thrive—open-plan living, additional bedrooms, and functional family areas.
Custom layouts, premium materials, and finishes that reflect your style and needs—designed for Welwyn Garden City homes.
Looking for trusted house extension builders in Welwyn Garden City and across Hertfordshire? Our local team delivers high–quality extensions with full project management.
Because we work across Welwyn Garden City and the wider Hertfordshire area, we understand local planning policies, typical property types and what adds real value in this market.
You can also browse all of our coverage areas on our House Extensions Near Me hub to see other locations we serve around Hertfordshire.
We cover Welwyn Garden City and surrounding Hertfordshire locations, typically within a 30–40 minute drive. This keeps our teams local and our response times quick.
From initial consultation to final handover—complete delivery in Welwyn Garden City
Professional architectural services
Full application and approval service
CITB certified professional trades
Our extension teams operate across Welwyn Garden City and neighbouring areas, bringing local knowledge and expertise to every project.
We provide comprehensive house extension services throughout Welwyn Garden City and the wider Hertfordshire area, including Welwyn Garden City, surrounding Hertfordshire villages and suburbs.
Our local Welwyn Garden City team understands the specific planning requirements, building regulations, and architectural styles common to properties in this area. We work closely with Hertfordshire planning departments to ensure smooth project approval.
Whether you're in Welwyn Garden City town centre or the surrounding suburbs, we deliver the same high standards of craftsmanship and project management that have made us the region's trusted extension specialists.
Recent feedback from homeowners in Welwyn Garden City and across Hertfordshire.
“Professional from first visit to handover. Our double‑storey extension in Hertfordshire was finished on time and to a very high standard.”
“The team did a fantastic job on our side return extension. They navigated the planning process in Welwyn Garden City effortlessly.”
“Our kitchen–diner extension in Welwyn Garden City has totally changed how we use the house. The team kept everything tidy and on schedule.”
“Honest advice and quality workmanship. Our extension in Welwyn Garden City was completed within budget and looks amazing.”
Read more detailed feedback from our house extension clients.
See All ReviewsA selection of recent house extensions we have completed across Hertfordshire, including projects close to Welwyn Garden City.
Single‑storey rear extension with structural steel installation, new kitchen, rooflights and bi‑fold doors to create a modern, open‑plan family space for a home near Welwyn Garden City.
Two‑storey side extension providing an additional bedroom, en‑suite and extended ground floor living area for a property in the wider Hertfordshire area.
Full L‑shaped wrap‑around house extension with new utility, WC, kitchen‑diner and upgraded facade, designed to maximise the plot and add long‑term value.
Clear answers to the most common questions homeowners in Welwyn Garden City and Hertfordshire ask us about planning, costs and timelines for house extensions.
Not always. Many single-storey rear extensions in Welwyn Garden City can be built under permitted development, which means you don’t need a full planning application. However, this depends on:
Before any design is finalised, we check the latest Hertfordshire council guidance, measure your existing property and confirm whether your project is permitted development or needs a planning application. If an application is required, we handle drawings, submission and liaison with the planning officer for you.
Costs vary depending on size, specification and access, but as a guide for Welwyn Garden City and the wider Hertfordshire area:
We always carry out a detailed survey and provide a fixed, itemised quotation so you can see exactly what is included: groundworks, structure, roof, windows/doors, internal finishes and professional fees where required. Value engineering options can be discussed if you have a strict budget to work to.
A typical single-storey extension in Welwyn Garden City takes around 8–12 weeks on site, while larger or double-storey projects can take 12–16+ weeks. The programme usually follows these stages:
Before we start on site, you’ll receive a clear project programme with key milestones so you always know what is happening and when each phase is due to be completed.
In most projects, yes. Many clients in Welwyn Garden City stay in their homes throughout the build. We plan the works so that:
If a short period of alternative accommodation is advisable (for example during major knock-through works), we will explain this during the planning stage so you can factor it into your arrangements.
In most cases, a well-designed extension in Welwyn Garden City adds significant value as well as improving day-to-day living. Estate agents in Hertfordshire typically see the best returns from:
We can work with you to balance build cost against likely value uplift, so your project makes sense both as a home improvement and as an investment.
Three recent extensions across Greater Manchester — from a 62m² double-storey rear-and-side, down to a focused 26m² kitchen extension on a Victorian terrace. Tap any project for the full case study.
Extension
A rear and side double-storey extension on a 1930s semi, adding an open-plan kitchen-diner downstairs and a master suite with en-suite above — finished with bi-fold doors and a steel ridge.
Extension
Single-storey side-and-rear wrap-around with a 2.5m lantern, full-width bi-folds and engineered oak flooring — transforming a tight kitchen into a 48m² family living space.
Extension
Single-storey rear extension on a Victorian terrace — structural opening into the existing kitchen, 4m roof lantern, underfloor heating, and a bespoke handle-less kitchen with quartz worktops.
Want to see the rest of our portfolio?
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