House extension planning permission in Ireland: what to check first

Write down the property type, whether it is detached, semi-detached or terraced, and whether it is a protected structure or in an Architectural Conservation Area. Gather the original house drawings if available, any earlier planning decisions, completion documents and the dates and sizes of previous extensions. A recently purchased property may have changes that are not obvious from the current room layout.

• Check the local authority planning file for earlier permissions and conditions.
• Identify every previous extension, including one that received planning permission; prior work can affect the exemption calculation.
• Measure the remaining private open space and note the position of boundaries, neighbouring windows and the rear wall.
• Record any proposed change of use, separate dwelling, roof alteration or front-facing addition as a separate question.

Ask a competent architect, architectural technologist or planning professional to review uncertain history before you commission construction drawings. A builder can describe what they can build, but that is not a substitute for a site-specific planning assessment.

The published Schedule 2 rules describe a Class 1 exemption for certain extensions to the rear of a house. They include limits covering cumulative floor area, upper-floor additions, distances from boundaries, height, window placement and the amount of private open space left after the works. An extension under a commonly quoted area threshold is not automatically exempt if another condition fails.[1]

Do not assume a side extension, a detached garden unit or an attic dormer follows the same rules as a rear extension. The proposed 2026 reforms mention changes in several of these areas, but a proposal is not permission for works on your property. Use the current regulation text and your local planning authority's published guidance when deciding what application or confirmation you need.[1][2]

• Where will the extension sit relative to the original rear wall, side walls and boundaries?
• What is the total relevant floor area after accounting for earlier extensions?
• Will any part be above ground-floor level or change the roof shape?
• What rear garden area remains exclusively available to the house?
• Could protected-structure status, a conservation area or a condition on an earlier permission restrict the proposal?

If the exemption status is uncertain, ask the planning authority about the formal declaration process rather than relying on a verbal guess. A Section 5 declaration request is a route for obtaining a written decision on whether particular proposed development is exempted development. The authority will need a clear description and enough drawings and measurements to assess the actual proposal.[3]

If permission is needed, allow for design development, application documents, statutory notices, a decision and any conditions before fixing a start date with a builder. The local authority's planning file and your designer should establish what is already approved, what is being newly proposed and which drawings are the version used for quotes.[4]

Planning status answers whether the development is permitted in planning terms. Building Regulations address how relevant work must be designed and constructed. Government building-control guidance says the regulations generally apply to extensions and material alterations; responsibility for compliance rests with the owner and the builder or designer engaged. An exempt extension still needs appropriate technical design and compliant work.[5]

Ask your designer or building-control professional which notices, inspections and certificates apply to your precise scheme. Requirements differ with the type and scale of work. Choosing an available route to opt out of statutory certification does not remove the duty to meet Building Regulations. Have this conversation before choosing a quote that leaves design or compliance responsibilities undefined.[5]

• Who is responsible for structural design and checking the existing house before an opening is made?
• Who specifies insulation, ventilation, moisture control, drainage and fire-safety details?
• Who will submit any required building-control documents and keep inspection records?
• What completion evidence will the homeowner receive and retain with the property documents?

A quote for 'a kitchen extension' can mean a weather-tight shell to one builder and a decorated, fitted room to another. Describe the desired floor area and room use, then list what is included at each boundary: demolition, foundations, structure, roof, glazing, electrical work, plumbing, heating, kitchen supply and fitting, plastering, flooring, decoration and making good outside.

• Attach the same dated drawings and specification to every request for a quote.
• Show the existing house, access route, parking, drainage and any known buried services.
• State whether the home will remain occupied and what temporary kitchen or weather protection is needed.
• Identify fixtures or finishes you will supply yourself and who measures and checks compatibility.
• Give a realistic preferred start period, without promising that planning or design work is already complete.

If you do not yet have drawings, ask for an initial consultation or indicative budget with assumptions stated. Treat that as a way to test feasibility, not as a fixed construction quote. A detailed price becomes meaningful when the scope and technical documents are stable.

Request written prices against the same documents. Compare the extent of groundworks, drainage alterations, structural steel, roof finish, glazing specification, mechanical and electrical work, waste removal, VAT treatment, provisional sums and exclusions. Clarify who will arrange specialist trades and who pays if an existing defect is uncovered.

The CCPC recommends checking recent references, seeking multiple written quotes and agreeing written scope, timing and payment terms before work begins. Stage payments should reflect defined progress, with changes priced and approved in writing. The cheapest total can become the dearest project if it excludes major items or leaves uncertain sums unexamined.[6]

'We are planning a single-storey rear extension to a semi-detached house in Kildare. The aim is an open kitchen and dining area with one rooflight and garden-facing glazing. The house has an earlier small rear extension, so planning status is being checked; we are not booking a start date until the drawings and approvals are settled. Please tell us whether you can quote from the attached drawings and specification, which groundworks and finishes you would include, your indicative programme, recent comparable projects and the documents you need to price accurately. Side access is about 90 cm and the house will be occupied.'

That description gives a builder a useful first picture while showing where more design work is needed. Once drawings are final, resend the same revision to every shortlisted builder and ask for an updated written quote rather than trying to compare prices based on different versions of the job.