House Extensions in Northern Ireland: The Four Key Stages Every Homeowner Should Know

Stage 1 - Measured Survey & Preparing Existing Drawings.

Stage 2 - Design Proposals.

Stage 3 - Planning Application.

Stage 4 - Building Control Application.

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Extending your home — whether through a rear extension, attic conversion or garage conversion — involves a clear sequence of steps. Understanding these stages from the outset helps you plan confidently, manage expectations, and make informed decisions as your project develops.

A well‑designed extension can transform how you use your home, improve day‑to‑day living, and add long‑term value to your property. With the right guidance, the process is straightforward and structured.

If you’re considering a house extension in Northern Ireland, you’re welcome to get in touch for a complimentary, no‑obligation chat about your ideas. We can look at design options, budget considerations and any potential constraints, so you have a clear picture before moving forward.

I support my clients through each stage from survey to approvals, ensuring the process is as smooth and stress‑free as possible.

Domestic extension in Donaghadee by GT Building Design incorporating a new Garden Room, Utility and sheltered Patio with a Velux flat glass rooflight.

To gain an initial understanding of your home and explore potential improvements, please provide the following information.

This will facilitate a more effective discussion of your project, after which I will send you a detailed fee proposal for my architectural services.

• Confirm your name and full address, including postcode.

• Provide your phone number and email address.

• Offer a brief summary of your objectives.

• Specify your maximum budget for extending and enhancing your home.

• Important: Confirm whether you have any existing plans or elevations of your home. These can be highly beneficial and save time. Do you have sketch plans from an estate agent? Building Control or the Planning Service might have drawings on file; please check with them early on and let me know.

Your address will help me initially view your property, garden space, front and rear elevations. This is very helpful and provides me with a brief understanding of your home.

ARCHITECTURAL FEE PROPOSAL

Upon gaining a comprehensive understanding of your project and goals, I will furnish you with a formal Fee Proposal. This document will detail my fees, the distinct stages of the project, and any additional costs or expenses that may arise.

Additional costs vary on each project and may include the following:

• Builder's estimate (provided at no charge) or Quantity Surveyor's estimate (£150 - £300). A construction cost estimate from the design drawings may be required before advancing to the next stage.

• Structural Engineer's Fee (payable to an Engineer if structural calculations are necessary).

• Planning Application Fee (payable to your local Council, £347.00).

• Building Control Plan and Inspection Fees, payable to your local Council. Fees vary, and I will confirm later. Allow £300 - £400 for an extension.

• SAP Energy Calculations, payable to others, approximately £150. Building Control rarely request this for extensions.

• Large Scale Vector from Ordnance Survey (£65.00) used to prepare the site location and site plans required by both the Planning Service and Building Control.

• Interior 3D Visualisation design drawings of your space. Optional to you and payable to others.

• Landscaping Designs including planting and paving. Optional to you and payable to others.

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STAGE 1: MEASURED SURVEY / EXISTING DRAWINGS

Upon acceptance of my written Architectural Fee Proposal, I will conduct a comprehensive measured survey of your home, typically requiring 2-3 hours.

Subsequently, I will generate existing plans and elevations utilising the latest CAD software. During the survey, I will also capture numerous photographs to aid in the creation of the existing drawings and the subsequent development of the project.

A typical measured survey drawn by hand with measurements recorded, this would also include, elevations and heights.

Architectural drawing showing existing elevations and floor plans prepared from a measured survey by GT Building Design using the latest CAD software.

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STAGE 2: DESIGN PROPOSALS

This stage involves defining your objectives for extending and enhancing your home.

• Please email your wish list, ensuring that you include your maximum budget. This helps me assess what might be accomplished.

• Differentiate between your Essential and Non-Essential items.

  
  

Your wish list will serve as a foundational inspiration for developing the initial Design Proposals, and we will begin our discussions.

Wish-list Example

🧩 Turning Your Wish List Into a Clear Design Direction

Your wish list is a bit like handing me jigsaw pieces without the picture. I can see the shapes, colours, and clues to what you’re hoping for, and my job is to start assembling those pieces into a coherent first design proposal. Sometimes everything fits together neatly. Other times, a few pieces simply don’t belong in the same puzzle — and that’s completely normal. When that happens, we explore a second option, reshaping the pieces until the overall picture feels right for you and your home.

There can be numerous ways to extend a home, but these will depend on your specific needs and preferences. I will carefully consider your wish list and prepare the initial Design Proposals (Option 1) based on my experience for your review and feedback. This is your opportunity to express what you like and dislike about the initial proposals. This is part of the process and helps me better understand your preferences.

You might like Option 1 but request adjustments. If it doesn't match your vision, we can explore additional options. Rest assured, options are drawings and can be modified or replaced according to your individual needs and preferences.

Don't worry, as I am here to assist you and I recognise that every homeowner has unique desires and circumstances. We can work closely through various options to find the perfect solution for you and your home.

Architectural design proposal by GT Building Design showing proposed ground floor plan, side elevation, material samples and reference images for a residential extension in Donaghadee.

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STAGE 3: PLANNING APPLICATION

There are two methods to obtain formal written approval from the Planning Service.

I recommend securing either Full Planning Permission or a Certificate of Lawful Development to ensure peace of mind. This will also confirm compliance with your neighbours and satisfy any requirements from a solicitor should you or your family decide to sell the property in the future.

A Certificate of Lawful Development is generally applicable for small extensions that fall within permitted development rights. Although this application requires the same preparation time, it imposes several limitations on permissible actions and, in my experience, can be restrictive.

On your behalf, I will prepare all necessary planning application documents, including:

• Application Form

• Site Location Plan

• Existing and Proposed Floor Plans & Elevations.

• Existing and Proposed Block Plans.

• Householder's Design Statement (If required by your Planning Authority)

I will submit and manage your planning application, maintaining communication with the Planning Service throughout the process and keep you updated.

Typically, a planning application for an extension takes approximately 2 to 3 months for Planning to reach a decision. I cannot guarantee approval; however, I can recommend the best approach for your home based on my extensive experience.

Architectural drawings by GT Building Design showing existing and proposed elevations and floor plans for a single‑storey residential extension submitted for planning approval in Northern Ireland.

Householder’s Design Statement by GT Building Design showing proposed elevations, floor plan, block plan, and supporting photographs for a residential extension planning application in Northern Ireland.

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STAGE 4: BUILDING CONTROL APPLICATION

This stage entails the creation of comprehensive construction drawings and a detailed specification booklet, both of which must comply with strict Building Control Regulations here in Northern Ireland.

Additionally, it often includes the Structural Engineer's Design and Calculations.

I will oversee the entire Building Regulations Application process on your behalf, coordinating with Building Control and supplying any additional information they may require to secure your Notice of Approval.

These approved drawings and specifications will also serve as a pricing package for a builder. Upon finalising construction costs, these documents will also constitute the contract between you and the builder.

Typical construction drawings prepared by GT Building Design, illustrating proposed floor plans, roof structure layout, and detailed sections used to obtain Building Control approval and form the technical basis for the contract between homeowner and builder.

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Summary - House Extensions in Northern Ireland

Many homeowners are unfamiliar with the steps involved in extending their property, which can make the process feel overwhelming. To keep things clear and manageable, it helps to focus on four primary stages:

Stage 1: Measured Survey & Preparing Existing Drawings

Stage 2: Design Proposals

Stage 3: Planning Application

Stage 4: Building Control Application

This guide is designed to give you clarity and confidence as you navigate each stage of your extension project.

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.