Single‑Storey Rear Extension in Belfast: A Modern Flat‑Roof Transformation at Locksley Park

How six design options shaped a fully modernised rear living space.

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A Modern Rear Extension Designed for Belfast Living

Locksley Park in Finaghy is one of Belfast’s most desirable neighbourhoods — mature gardens, solid homes, and huge potential for modernisation. This project shows how a single‑storey rear extension in Belfast can completely transform a traditional home.

Rather than jumping straight to a final layout, we explored six different design options, each refining daylight, circulation, roof design and internal flow. This design journey led to a fully modernised solution: a new flat roof across both the extension and the original kitchen, plus a fully insulated floor upgrade to bring the entire rear of the dwelling up to modern standards.

Planning Permission is currently progressing, and Building Control drawings are ready to be submitted to Building Control.

Single storey rear extension in Belfast — original AI concept by GT Building Design.

Why We Explored Multiple Rear Extension Options

Every Belfast home has constraints — boundaries, roof junctions, daylight angles and existing room proportions. Working through several options allowed us to:

• Test different kitchen and dining layouts

• Improve flow between living spaces

• Maximise natural light with rooflights

• Integrate a boot room and music/play room

• Balance budget with long‑term performance

• Modernise older fabric without unnecessary demolition

This is the difference between simply adding an extension and designing a home that works beautifully.

Option 1 — Establishing the Design Language

The first concept introduced a Trocal flat roof with a 2m x 1m Velux Flat Glass Rooflight, bringing daylight deep into the kitchen. It established the core aesthetic for this flat‑roof rear extension:

• Trocal flat roof

• Render finish

• Dark grey windows

• Clean, modern rear elevation

This option set the tone for the entire design journey.

Option 1 — Original design concept for a single storey rear extension in Belfast by GT Building Design.

Option 2 — Sliding Doors and Boot Room

Option 2 refined the rear elevation and introduced:

• Surface‑mounted sliding doors

• A dedicated boot room

• A more defined music room

• Improved kitchen circulation

This version focused on family functionality and garden connection — a key priority for many rear extensions in Northern Ireland.

Option 3 — Pocket Doors and Cleaner Flow

Option 3 introduced pocket doors, improving circulation without losing wall space. The kitchen layout tightened up, and the music room gained better proportions.

Option 4 — Dining Space Refinements

Option 4 focused on:

• A more efficient boot room

• Cleaner dining/kitchen relationship

• Improved window placement

• A more elegant rear elevation

  
  

This option was close — but not quite the final answer.

Option 5 — Final Layout Tweaks

Option 5 introduced:

• Better alignment of kitchen units

• Improved stove placement

• Cleaner circulation from hall → kitchen → dining → garden

This version delivered the best internal layout — but revealed a bigger opportunity.

Current proposal — refined single storey rear extension design for Belfast home by GT Building Design, now approaching planning approval.

The Final Decision — Fully Modernising the Rear of the Home

After reviewing all six options, the homeowners made a smart long‑term decision:

Replace the entire rear roof with a new flat roof AND install a fully insulated floor across both the extension and the original kitchen.

This achieves:

• A single modern flat‑roof plane

• Consistent ceiling heights

• Better lighting control

• A warm, energy‑efficient insulated floor

• A rear elevation that looks like a new build

• A unified, contemporary living space

This approach is increasingly popular for rear extensions in Belfast, delivering long‑term comfort, value and performance.

Exterior Finishes — Clean, Modern, Timeless

The final palette includes:

• Trocal flat roof - Anthracite grey

• Sand and cement render painted a natural colour

• Dark grey UPVC windows

• Dark grey fascias and soffits

• Black rainwater goods

A crisp, contemporary look perfect for Belfast homes.

Planning and Building Control

Planning Permission is expected to be secured without issue — the proposal is modest, neighbour‑friendly and fully compliant with Belfast’s rear‑extension design guidance.

Building Control drawings are ready to be submitted, ensuring a smooth transition into construction.

Building Control Technical Drawing 1 by GT Building Design.

Building Control Technical Drawing 2 by GT Building Design.

Why This Project Will Inspire Other Homeowners

This Locksley Park project is a perfect example of:

• How design options lead to better outcomes

• How modern flat‑roof extensions transform Belfast homes

• How upgrading old fabric (roof + floor) creates long‑term comfort

• How thoughtful design improves flow, light and usability

• How a rear extension can feel like a full renovation

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Thinking About a Rear Extension in Belfast?

If you’re considering a single‑storey rear extension — in Belfast, North Down or beyond — I can help you explore the best options for your home.

From feasibility studies to Planning Permission, Building Control and full construction packs, every project is handled with clarity, care and technical precision.

Why Choose GT Building Design

With over 40 years’ experience in residential design, I help homeowners plan extensions, conversions and internal alterations with clear drawings, practical guidance and a smooth, well‑managed process from first ideas through to approval.

I work with homeowners across North Down, Greater Belfast and the surrounding towns, supporting a wide range of projects — from small internal changes to full house extensions and larger home improvements.

You can explore my services below:

• House Extensions

• Loft Conversions  

• Garage Conversions  

• Internal Alterations

If you’re planning a home extension or thinking about improving your layout, you’re welcome to get in touch and talk through your ideas. A calm, practical chat at the start.

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FAQs

Do I need Planning Permission for a single‑storey rear extension in Belfast?

Most single‑storey rear extensions in Belfast do require Planning Permission, especially when they include flat roofs, large openings, or changes to the existing kitchen layout. Permitted Development is limited in Northern Ireland, so homeowners should expect to submit a full planning application. This Locksley Park project is currently progressing through Planning and is fully compliant with Belfast’s rear‑extension design guidance.

How much does a single‑storey rear extension cost in Northern Ireland?

Costs vary depending on size, specification and whether the existing kitchen is being modernised. As a guide, most rear extensions in Belfast range from £50,000–£70,000, with higher‑end projects reaching £85,000+. The Locksley Park design includes a new flat roof and insulated floor upgrade, which improves comfort and long‑term performance.

What are the benefits of choosing a flat‑roof rear extension?

Flat‑roof extensions are extremely popular in Belfast because they offer:

• Clean, modern lines

• Lower visual impact for Planning

• Excellent daylighting with rooflights

• Easier integration with existing structures

• High‑performance insulation options

The Locksley Park project uses a Trocal flat roof with Velux Flat Glass Rooflights to maximise natural light.

Should I upgrade the floor and roof in my existing kitchen when building an extension?

Yes — upgrading old fabric is one of the smartest decisions homeowners can make. Installing a fully insulated floor and replacing the entire rear roof creates a unified, modern living space with better thermal performance, consistent ceiling heights and improved comfort. This approach was chosen at Locksley Park to fully modernise the rear of the home.

How long does a rear extension take from design to completion?

A typical timeline for a Belfast rear extension is:

• Design options: 2–4 weeks

• Planning Permission: 8–12 weeks

• Building Control drawings: 2–3 weeks

• Construction: 10–16 weeks

Because the Locksley Park project explored six design options early on, the final layout is already optimised — reducing delays later in the process.

What internal layout changes work best with a rear extension?

The most popular layouts include:

• Open‑plan kitchen, dining and living spaces

• Boot rooms for storage and family use

• Play rooms or flexible multi‑use rooms

• Pocket doors for improved circulation

• Large sliding or folding doors to the garden