How Much Does a House Extension Cost in Northern Ireland? (2026 Guide

Written By Steven Ewbanks

Thinking about extending your home but unsure what it might cost? You’re not alone. One of the first questions we get asked is how much a house extension actually costs.

In this guide, we’ll give you a realistic idea based on our experience working across Northern Ireland and Dublin.

Average Cost of a House Extension

The cost of an extension can vary depending on the size, design, and level of finish, but as a general guide:

  • Small extension: £20,000 – £40,000

  • Medium extension: £40,000 – £70,000

  • Large or more complex extension: £70,000+

Every project is different, so these are ballpark figures rather than fixed prices.

What Affects the Cost?

There are a number of factors that will influence the final cost of your extension:

  • Size of the extension

  • Type of materials used

  • Groundworks and foundations

  • Structural work required

  • Internal finishes (kitchen, flooring, etc.)

  • Location and access to the property

For example, a straightforward rear extension will cost less than a more complex double-storey build.

Types of Extensions

We regularly complete:

  • Rear extensions

  • Side extensions

  • Wrap-around extensions

  • Double-storey extensions

Each type comes with different requirements and costs, depending on your home and layout.

Hidden Costs to Consider

It’s important to factor in additional costs such as:

  • Planning permission (if required)

  • Structural engineering

  • Drainage and utilities

  • Interior finishing

We always aim to be upfront about these so there are no surprises later.

Local Experience

We’ve completed a range of extension and renovation projects across Belfast, Portadown, and surrounding areas.

For example, we recently completed a rear extension for a homeowner in Belfast, including full groundwork, structure, and internal finish—delivered on time and to a high standard.

Get an Accurate Quote for Your Project

The best way to understand the cost of your extension is to get a tailored quote based on your specific plans.

We offer a free, no-obligation quote and are happy to talk through your ideas and give honest advice.

👉 Get in touch today to discuss your project

👉 Or call us directly to speak with our team

We’ll get back to you within 24 hours

Steven Ewbanks
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