Building and renovation

House extension

Building an extension. Anything above the exempted size needs planning permission, and larger work is notifiable to building control.

Post a task House extension by county

Whether this needs a licence in Ireland

Ireland

Licence required

Building Control notification and assigned certifier

Building Control notification and assigned certifier, issued or supervised by the Local authority building control. Ask for the registration number before the work starts and check it on the public register. Check the register: www.gov.ie

Wording approved by Talqero; not yet reviewed by a solicitor

Local authority building controlwww.gov.ieChecked 11/10/2026

House extension: what the job involves

Building a single- or two-storey extension to a house: a kitchen-living room, a ground-floor bedroom, a bigger bathroom. It runs from design and the planning question through foundations, walls, roof and services to finishes, and the builder’s management of the trades is a large part of what you are paying for.

Also asked for as: kitchen extension · rear extension · single storey extension · two storey extension · builder

How the job is usually done

Brief and design: an architect, architectural technologist or engineer measures the house and draws the extension, and checks whether it is exempted development or needs planning permission.
Planning permission where needed, which takes months, and a Commencement Notice if the work is not exempt.
Tender: builders price the same drawings and specification; appoint the builder and project supervisors in writing.
Groundworks: set out, dig and pour foundations, drainage runs, block up to damp-proof course, and the floor slab with membrane and insulation.
Superstructure: walls, lintels or steel to open into the house, roof structure and covering, windows and doors — the shell is then weathertight.
First fix of electrics, plumbing and heating; insulation and airtightness; plastering and screed.
Second fix, kitchen or bathroom fitting, flooring and decoration; final certificates and snag list.

House extension: what is included

Usually included

Building work to the drawings and specification priced
Foundations, walls, roof, windows and doors as specified
Breaking through into the existing house and making good
Site management and coordination of the builder’s own trades and subcontractors
Skips and site clearance during the build

Usually not included — agree it separately

Design, planning application and engineer’s fees, unless a design-and-build price
Assigned certifier fees under BCAR
Kitchen units, sanitaryware, flooring and finishes beyond a stated allowance
Landscaping, paving and boundary walls
Moving drains or services found during digging, unless allowed for

Materials and who supplies them

Concrete, block, insulation, timber, roof covering and steel — supplied by the builder to the specification
Windows and doors — through the builder or ordered separately
Finishes such as tiles, sanitaryware and kitchen — often supplied by the customer through a PC sum

How long it takes

Usually three to six months on site for a single-storey extension, after design and any planning; two storeys, difficult ground, weather and slow decisions on finishes lengthen it.

When to book

Design and planning take months, so start in autumn or winter to build from spring; builders’ diaries fill early in the year.

House extension: the rules in Ireland

What the official sources say, checked against them on the date shown. A summary, not legal advice — follow the link to read the rule itself.

Since 27 July 2026, a rear extension is exempt from planning permission up to 45 m² in total (counting every extension since 1 October 1964), with the upper floor limited to 12 m² on a terraced or semi-detached house and 20 m² on a detached house, at least 2 m from a party boundary. It may not be higher than the house’s walls and roof, must leave 25 m² of private open space, and its roof may not be a balcony or terrace.
Applies to: the homeowner
Planning and Development (Exempted Development (Act of 2000)) Regulations 2026, S.I. 338 of 2026, Class 1 · gov.ie · Checked 9 October 2026
Under the same Class 1, windows in an exempt extension must be at least 1 m from the boundary they face at ground level and 8 m above ground level. Exemptions do not apply where the work would breach a planning condition or materially affect a protected structure, and can be restricted in an Architectural Conservation Area; side and front extensions need permission.
Applies to: the homeowner
S.I. 338 of 2026, Class 1; Citizens Information · citizensinformation.ie · Checked 9 October 2026
Work that is not exempted development generally needs a Commencement Notice lodged with the council’s Building Control Authority through the BCMS portal 14 to 28 days before it starts. An extension of more than 40 m² also needs statutory certification — a design certifier, an assigned certifier and a Certificate of Compliance on Completion — unless the owner opts out for a domestic extension, in which case the building regulations still apply in full.
Applies to: the homeowner and the builder
Building Control Regulations 1997 to 2015, including the Building Control (Amendment) Regulations 2014 (S.I. 9 of 2014) · irishstatutebook.ie · Checked 9 October 2026
An extension that creates habitable rooms must be covered by smoke and heat alarms, and in some layouts — an enclosed rear garden reachable only through a room — the fire detection and alarm system must cover the whole house.
Applies to: the designer and the builder
Building Regulations Part B — Technical Guidance Document B Volume 2, 1.3.6.4 · gov.ie · Checked 9 October 2026
Where more than one contractor works on the job, there is a particular risk (deep excavation, heavy steel, asbestos, a fall from height), or the work lasts more than 30 days, the homeowner must appoint a Project Supervisor Design Process and a Project Supervisor Construction Stage in writing, and keep the safety file. Work lasting more than 30 days or 500 person-days must also be notified to the HSA.
Applies to: the homeowner, as client
Safety, Health and Welfare at Work (Construction) Regulations 2013 — HSA, Getting Construction Work Done Safely: Guide for Homeowners · hsa.ie · Checked 9 October 2026
Ireland has no separate party wall act: work to a wall, chimney or boundary shared with a neighbour is covered by the Land and Conveyancing Law Reform Act. The owner doing the work must make good any damage and may need the neighbour’s consent, or a court works order if consent is refused.
Applies to: the homeowner
Land and Conveyancing Law Reform Act 2009, sections 43 to 47 · irishstatutebook.ie · Checked 9 October 2026

Grants

Housing Adaptation Grant for People with a Disability
Up to €40,000, or 100% of the approved cost if lower, towards works such as a ground-floor bedroom or accessible bathroom extension; the percentage paid falls as household income rises.
Who qualifies: Owners and certain tenants where a member of the household has a disability and the works are needed; applied for through the local council before work starts.
citizensinformation.ie · Checked 9 October 2026

What house extension costs, and why

What jobs on Talqero came to

Not enough comparable jobs yet to publish a range here. Talqero shows a price range only once at least five comparable jobs, agreed prices or offers exist — a range from fewer would describe a handful of jobs, not the market. Post your job and compare the offers you get.

What affects the price

Floor area, number of storeys and roof type
Ground conditions and foundations: rock, high water table, trees, drains to divert
Opening up the existing house: steel, lintels and the number of walls removed
Specification of windows, roof lights, kitchen, bathroom and finishes
Design, engineering and building-control certification
Access for machinery and materials, especially to the rear of a terraced house
VAT: building work on a home is charged at the reduced 13.5% rate by a VAT-registered builder, unless materials are more than two-thirds of the price (Revenue’s two-thirds rule)
VAT: building work on a home is charged at the reduced rate of 13.5% by a VAT-registered business — unless the materials come to more than two-thirds of the price, when Revenue’s two-thirds rule applies the goods rate to the whole job. Ask whether a quote includes VAT.

Paperwork to ask for at the end

Planning permission or a written view that the extension is exempt, with the drawings
Commencement Notice, and for certified work the Certificate of Compliance on Completion on the public register
An opinion or certificate of compliance with planning and building regulations from your architect or engineer, needed when you sell
Electrical Completion Certificate from a Registered Electrical Contractor and, for gas, the RGI Declaration of Conformance
The safety file from the project supervisor, and product guarantees

Safety

An open trench or a propped opening in your back wall is a building site: keep children and pets out.
Ask how the house will be kept secure and weathertight when the back wall is opened.
Dust from cutting block and concrete is harmful; the builder should cut wet or with extraction and seal off the house.

House extension: before you hire

Questions to ask a tradesperson

Are you pricing exactly these drawings and this specification?
What is excluded — design, certification, electrics, plumbing, finishes, skips?
How are payments staged against work done, and what is held back for snags?
Can I see your insurance: public liability, employer’s liability and contract works?
Who will be my point of contact on site each day?
Is VAT included?

What you can do yourself

Building work is not DIY, but clearing the garden, emptying the rooms affected and making decisions on finishes early saves time and cost.

What to put in your task

Roughly how big is the extension?
Single or two storey?
Do you have drawings?
What is the extension for?
Can a digger get to where the extension will go?

Photos that help

The back of the house where the extension will go, from the far end of the garden
The side access route from the road to the back
Any manholes, drains, oil tank or trees near the extension area
The rooms inside that will open into the extension

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Questions about house extension

Does house extension need a licence in Ireland?

Yes. Building Control notification and assigned certifier, supervised by the Local authority building control. Source: www.gov.ie. Ask for the registration number and check it on the public register. Wording approved by Talqero; not yet reviewed by a solicitor.

Do I need planning permission for an extension?

Not for a rear extension within the exempted development limits: since 27 July 2026, up to 45 m² in total, with limits on the upper floor, height, distance from boundaries and remaining garden. Anything bigger, to the side or front, or on a protected structure needs permission. Have your designer confirm before you build.

What is BCAR and does it apply to me?

BCAR is the Building Control (Amendment) Regulations: for an extension of more than 40 m² that needs a Commencement Notice, a registered architect, engineer or surveyor is appointed to inspect and certify the work. Owners of domestic extensions can opt out, but the building regulations still apply and you will want proof of compliance when you sell.

How do I compare builders’ prices?

Give every builder the same drawings and a written specification, and ask for a priced breakdown with exclusions and provisional sums listed. The cheapest price often has the most exclusions. Check references on jobs of a similar size.

Often booked with house extension

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