How much does a house extension cost in Ireland?

A house extension in Ireland typically costs between €2,000 and €3,200 per square metre. Traditional block construction ranges from €2,000 to €2,500 per sqm, while high-performance timber frame or factory-built modular extensions range from €2,500 to €3,500 per sqm depending on finish levels and site conditions.

Do I need planning permission for a 40 square metre extension in Ireland?

No. Under Irish planning laws, a single-storey rear extension up to 40 square metres (430 sqft) is classifed as exempted development, provided it does not reduce the remaining private garden area to less than 25 square metres and adheres to specific height limits.

What is the cost of a 40 sqm extension in Dublin?

For a standard 40 square metre single-storey extension, homeowners should budget between €85,000 and €125,000 (excluding VAT of 13.5%). The total cost depends on finishing details, window configurations, plumbing, and steelwork needed to knock existing walls.

Home Improvement Guidelines

House Extensions
Ireland & UK

Planning a house extension in Dublin, nationwide in Ireland, or the UK? BuildTrade.ie provides clear cost guides, structural comparison specs, and planning permission advice to help self-builders prepare their project budget.

Direct Summary: House extensions in Ireland cost between €2,000 and €3,200 per square metre. Ground-floor rear extensions under 40 square metres do not require planning permission, provided a minimum of 25 sqm of garden area remains.

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Target Region

Extension Size (Floor Area)30 sqm (323 sqft)

15 sqm (Small Utility/Office)100 sqm (Huge Double-Storey)

Construction Method

Specification & Finish Level

Estimated Rate per sqm€2,300

Estimated Build Cost (Net)€69,000

VAT (13.5%)€9,315

Total Estimated Budget€78,315

Exempted Development Eligible: An extension of 30 sqm is under the 40 sqm threshold, meaning it can typically be built without planning permission, subject to height and garden space rules.

House Extension Prices & Cost Guidelines

Understanding building costs is essential before starting any design work. In Ireland, construction rates depend greatly on structural layout, finishes, and geographic location (Dublin build costs are generally 10% to 15% higher than rural rates due to access and logistics).

Standard Budget

€2,000+ / sqm

Standard blockwork, minimal glazing, standard fittings.

Timber Frame

€2,400+ / sqm

Prefabricated panels, excellent insulation, rapid assembly.

Modular Pod

€2,800+ / sqm

Offsite manufacturing, ready-to-plug design, premium finishes.

House Extension Rules in Ireland (40 sqm Exemption)

In Ireland, you can construct a ground-floor extension to the rear of your home without planning permission, provided it complies with the following conditions:

The 40 sqm Rule: The total floor area of the new extension must not exceed 40 square metres (inclusive of any previous extensions built since 1964).
Garden Space: The private open space remaining at the rear of the house must be at least 25 square metres.
Height Restrictions: The height of a flat-roof extension must not exceed the eaves height of the existing house. For pitched roofs, it must not exceed the ridge height of the house.
Glazing Limits: Any window at first-floor level must be at least 11 metres from the boundary they face to protect neighboring privacy.

Timber Frame vs. Modular House Extensions

With energy performance and speed taking priority, modern methods of construction are outperforming traditional block builds:

Timber Frame Extensions

Timber frame walls are built offsite in factory conditions and assembled on site within days. They offer exceptional insulation cavity depth, allowing low U-values while keeping the wall profile thinner than blockwork, preserving valuable interior space.

Modular House Pods

Modular extensions are built entirely offsite, including internal fixtures, wiring, flooring, and windows. Once the foundations are ready on site, the modular pod is crane-lifted directly into position. Ground work disruption is minimized, and installation takes only 1-2 days.

Key Facts Checklist for Extensions

1.Ground floor extensions under 40 square metres do not require planning permission in Ireland.
2.Modular pods and timber frame extensions compile up to 40% faster on site than traditional masonry.
3.Dublin construction costs average €2,400 to €3,500/sqm, slightly higher than national averages.

Successful Extensions Traced by Homeowners

"Our timber frame extension in Dublin was completed within three weeks. We stayed under the 40 sqm exemption and saved on planning permission paperwork."

Niall & Sandra

Extension in Co. Dublin

"The cost calculator gave us an accurate budget benchmark. We matched with a vetted general contractor on BuildTrade who delivered the project on time."

Eoin M.

House Upgrade in Co. Galway

House Extensions Ireland & UK