Kitchen extension glossary of terms and rules
15 Irish building, structural, glazing and planning terms explained in plain English so you can compare builders' quotes.
Free, no obligation. One local builder prices it, not five.
- 15terms defined A to Z
- 45 m²exempt rear threshold
- Part LTGD 2022 U-values
- 13.5%construction VAT
Key kitchen extension terms explained
25 sq m Remaining Rear Garden Rule
Under Class 1 of the Planning and Development Regulations 2001, an exempted rear extension must leave at least 25 square metres of private open space behind the house.
40 sq m Class 1 Exempted Development
The Irish planning threshold allowing a single-storey rear extension of up to 40 square metres without full planning permission, provided no previous extensions were built after October 1964 and boundary rules are met.
Aluclad Lift-and-Slide Patio Doors
Heavy-duty triple-glazed timber-aluminium sliding doors on a flush weather-rebated floor track where turning the handle lifts the sash onto stainless steel rollers.
Assigned Certifier & BCAR Opt-Out
For extensions over 40 square metres requiring a Commencement Notice on the BCMS portal, homeowners can either appoint an Assigned Certifier under statutory BCAR or sign the statutory opt-out while retaining an engineer to inspect stages.
Box Gutter & Party-Wall Parapet
When building right up to a shared side boundary on a wrap-around or side-return extension, the eaves cannot overhang the neighbour's land, so a concealed insulated box gutter is formed inside a rendered parapet wall.
Building Control Management System (BCMS)
The national online portal where Commencement Notices are lodged at least 14 days and not more than 28 days before site work begins on a planning-approved extension.
Flat Roof Warm-Deck Construction
Placing 120mm to 150mm of foil-faced PIR rigid insulation above the structural timber roof deck beneath an EPDM rubber, GRP fibreglass or single-ply membrane so the roof rafters stay warm and condensation-free.
Mini-Piled Foundations
Steel-cased augered or driven piles sunk 4m to 9m into load-bearing strata with a reinforced concrete ring-beam on top, specified when deep made ground, peat, tree roots or a public sewer prevents standard strip footings.
Opinion on Compliance with Planning & Building Regulations
The formal certificate signed by a Chartered Engineer or Registered Architect at completion confirming the kitchen extension complies with Building Regulations and either exempted development rules or its planning grant.
Part L 2022 TGD Elemental U-Values
Irish Building Regulations Part L require new extension elements to meet maximum U-values of 0.18 W/m²K for walls, 0.16 W/m²K for pitched roofs, 0.20 W/m²K for flat roofs, 0.18 W/m²K for floors and 1.4 W/m²K for glazing.
RSJ Goalpost Steel Portal Frame
Two vertical structural steel columns bolted to concrete pad foundations supporting a horizontal universal beam across the knocked-through rear house wall to resist both vertical first-floor loads and lateral wind sway.
Section 5 Declaration of Exemption
A written certificate issued by the local county or city council within 4 weeks for an €80 fee confirming officially on the planning register that a proposed rear extension is exempted development.
Shared Foul & Surface Water Sewer Diversion
Re-routing or Concrete-encasing an existing 100mm or 150mm clay or PVC drain pipe running across the back of a terrace or semi-detached row, with new rodding access chambers placed outside the extension footprint.
Triple-Glazed Low-E Roof Lantern / Flat Rooflight
Frameless structural glass rooflights or pitched aluminium lanterns set into a flat extension roof at a minimum 5-degree pitch to throw natural daylight deep into the existing middle room of the house.
Wet Underfloor Heating (UFH) Screed Zone
A multi-loop PEX-a pipe circuit clipped into floor insulation within a 50mm to 65mm liquid anhydrite or sand-cement screed, zoned on its own manifold pump and thermostat.
Plan your extension and see the cost
Four quick taps. You see your plan build up as you go: the price range, what moves it, the planning position and the build time. Your number is only asked for at the end, if you want a real price.
A 25 m² single-storey rear extension in Ireland, mid-range, with wide glass doors and a new kitchen: €62,000 to €90,000 all in, including VAT and fees.
How this is worked out
We start from what single-storey extensions cost to build per square metre in each part of Ireland, including VAT at 13.5%, and the rates for side, wraparound, two-storey and heavily glazed extensions. Standard finishes take the lower half of the range, mid-range the upper half, and high spec or a wall of glass the glazed rate. Then we add professional fees (design, engineer, BER) and, if you want one, a new kitchen at your level of finish. Totals are rounded to the nearest €1,000. It's an estimate to plan with, never a quote: the builder prices your house after seeing it.
Questions people ask
Can I stay living in the house while a rear kitchen extension is being built?
Yes. On most single-storey rear extensions the builder builds the foundations, outer walls, roof and glazing from the garden side for the first 7 to 9 weeks before knocking through the back wall of the house. Temporary dust walls and a working sink/kettle station keep the rest of the home liveable until the new kitchen is fitted.
When should I order my new fitted kitchen and patio doors during an extension build?
Order your rear sliding or bi-fold doors and rooflights as soon as the blockwork shell starts (around Week 3 to 4) because bespoke aluclad and aluminium glazing takes 5 to 8 weeks to manufacture. Finalize your kitchen layout before first-fix electrics and plumbing (Week 7 to 8) so island power ducts, extractor ducts and waste pipes land in the exact millimetre position.
What happens if there is a shared drain pipe running across my back garden?
Nearly every Victorian terrace and 1960s-1990s semi-detached estate has a shared foul or storm drain running parallel to the back wall. Your builder either diverts the pipe around the outside of the new extension with new inspection chambers outside the room, or bridges where the pipe passes through the concrete foundation walls with lintels and rocker pipes and seals it in concrete.
Every guide, calculator and county page
Jump straight to any specification guide, our interactive calculator, the technical glossary or your county page.
Price & Specification Guides
Calculator, FAQ & Glossary
Get a free quote for your extension
Plan it in under a minute, see the cost, and one vetted builder who covers your county rings you with a proper price.