Single‑Storey Rear Extension in Moneyreagh — Full Design, Planning & Construction Case Study.

Homeowners often face the same challenge: older layouts that no longer suit modern family life. At this property in Hillview, Moneyreagh, the existing kitchen and living spaces were disconnected, daylight was limited, and the rear of the home didn’t make the most of the garden.

The clients wanted a brighter, more open family space — something warm, modern and practical — while keeping the project straightforward and cost‑effective. This case study shows how a single‑storey rear extension transformed the home, from initial concept through to detailed construction proposals, all approved under Lisburn & Castlereagh City Council.

Understanding the Existing Layout

The original ground floor layout had several constraints:

• The kitchen had a very small rear return & sitting area.

• The kitchen had poor natural light.

• Circulation between rooms felt tight and outdated.

• The garden connection was weak, with no real focal point.

The existing plans and elevations clearly showed a home with potential — but one that needed a thoughtful redesign to unlock it.

A simple design overview showing the new single‑storey rear extension layout and materials — anthracite frames, cedar cladding, and a Velux rooflight for natural light. Clean, modern look with warm tones and practical detailing.

Single‑Storey Rear Extension in Moneyreagh

The Design Solution — A Modern Family Room

The proposed extension created a new family space that connects directly to the garden through wide sliding doors.

The design focused on:

1. Light

A Velux Flat Glass Rooflight (2.5m x 1m) was centred over the new opening, flooding the space with natural light. This rooflight appears throughout the drawings, with full detailing of:

• Upstand construction

• Cavity tray integration

• Fire‑tested roof build‑up

• Insulation continuity

• Joist trimming and support

This is a premium feature that dramatically improves the feel of the room.

2. Flow

The new layout improves movement between:

• Kitchen

• Family room

• Utility

• Garden

The extension becomes the heart of the home — a warm, bright space for everyday living.

3. A clean, modern exterior

The proposed elevations show:

• Anthracite grey frames

• Sand/cement render

• Trocal/SikaPlan flat roof

• Optional Western Red Cedar cladding (from earlier concept drawings)

The result is a crisp, contemporary rear elevation that complements the existing house.

Side‑by‑side floor plans comparing the home’s current layout with the new extension design. The proposed plan adds a bright family room, dining area, and study — creating a more open, welcoming space for everyday life.

Material Choices & Why They Matter

SikaPlan Flat Roof (20‑Year Guarantee)

The detailed roof build‑up includes:

• 1.8mm SikaPlan G reinforced membrane

• Sikatherm AL PIR insulation

• Sarnavap vapour control layer

• Treated softwood firings for correct falls

• Fire test approval (BRoof T4)

This is a robust, long‑life flat roof system — ideal for NI weather.

Velux Flat Glass Rooflight

Chosen for:

• Clean modern appearance

• Excellent thermal performance

• Slim profile

• High daylight penetration

• Compatibility with flat roof systems

Render & Anthracite Frames

A natural-colour render keeps the extension bright, while anthracite frames add a modern contrast.

Gravel Margin

A simple but important detail:

• Protects render from splashback

• Improves drainage

• Reduces maintenance

• Enhances longevity of the wall base

Side‑by‑side elevation drawings comparing the home before and after the extension. The new design adds wide glass doors, a flat roof section, and clean modern detailing — creating a brighter, more contemporary look while keeping the home’s character.

Planning & Building Control

The project was submitted to Lisburn & Castlereagh City Council, covering:

• Full planning drawings

• Existing and proposed floor plans and elevations

Building Control approval followed, with clear guidance for:

• Foundation depth

• Roof structure

• Insulation levels

• Fire safety

• Ventilation

• Drainage

• On‑site inspections

The clients received a complete, compliant design package ready for construction.

The Finished Result

Although every project is unique, this single‑storey rear extension in Moneyreagh demonstrates the impact of:

• Good daylighting

• Clean modern materials

• Efficient insulation

• Thoughtful detailing

• A practical family‑focused layout

The home now feels brighter, more open, and far better connected to the garden — a transformation achieved through careful design and clear technical detailing.

---

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 can often make the whole process much easier.

---

Frequently Asked Questions

1. Do I need planning permission for a rear extension?

Most rear extensions require planning permission unless they fall under permitted development. Factors such as size, height, proximity to boundaries, roof design, and whether the property has previous extensions all affect eligibility. In this project, full planning permission was secured.

2. What size of rear extension is typically allowed under permitted development?

Permitted development in Northern Ireland generally allows modest rear extensions, but strict rules apply:

• Maximum projection from the original rear wall

• Height limits (especially for flat roofs)

• Distance from boundaries

• Restrictions on materials and appearance

  
  

  If your extension exceeds these limits — as this Moneyreagh project did — a full planning application is needed.

3. What Building Control inspections are required during construction?

Building Control will normally carry out several key inspections, including:

• Foundation excavation

• Drainage connections

• Floor slab preparation

• Damp‑proof course installation

• Structural elements (joists, beams, roof build‑up)

• Insulation checks

• Final completion inspection

4. What roof options work best for a modern rear extension?

Flat roofs with high‑performance membranes (such as SikaPlan / Trocal) are popular for contemporary extensions. They offer:

• Clean modern lines

• Excellent thermal performance

• Compatibility with flat glass rooflights

• Long‑life guarantees (SikaPlan offers 20 years) This project used a full SikaPlan build‑up with PIR insulation and a Velux flat glass rooflight for maximum daylight.

5. How can I improve natural light in a rear extension?

Rooflights are one of the most effective ways to bring daylight deep into a new space. Flat glass rooflights — like the 2.5m x 1m Velux unit used here — provide:

• High light transmission

• A sleek, modern appearance

• Excellent thermal performance

• Combined with wide sliding doors, they transform the feel of the room.

6. How long does a typical rear extension project take from design to completion?

Timelines vary, but a realistic guide is:

• Design & drawings: 2–4 weeks

• Planning approval: 12 weeks

• Building Control approval: 4–6 weeks

• Construction: This Moneyreagh project followed a smooth path through planning and Building Control, with detailed drawings ensuring the builder had everything needed for efficient construction.