Modular Buildings questions answered in plain English

Yes, since 27 July 2026, if you meet the Class 3A conditions in S.I. No. 340 of 2026. A detached habitable garden dwelling between 32 m² and 45 m² in the rear garden of a house is exempt from planning permission provided total garden structures do not exceed 45 m², the owner lives in the main house, it connects to the main house's services, it is not sold separately or used for short-term letting, you give the local council 14 days prior written notification with your Eircode, it meets Building Regulations, and work finishes by 31 December 2030.

Class 3 (updated by S.I. No. 338 of 2026) covers non-habitable garden rooms, home offices, gyms and sheds up to 30 m² — you cannot sleep or live in a Class 3 room. Class 3A (S.I. No. 340 of 2026) covers a detached habitable garden dwelling (granny flat) of 32 m² to 45 m² with a kitchen, bathroom and bedroom.

An insulated, fitted garden office or room (12 to 30 m²) costs €18,000 to €55,000 including 13.5% VAT. A turnkey habitable 32 to 45 m² Class 3A modular dwelling with kitchen, shower room, foundations and service connections costs €65,000 to €135,000 (€2,400 to €3,200 a m²).

When a modular builder supplies and installs the building on your site (under Revenue's two-thirds rule for construction services), the reduced 13.5% VAT rate applies. If you buy a supply-only flat-pack kit with no installation, it is taxed as goods at 23% VAT.

Factory fabrication usually takes 4 to 8 weeks while your ground screws or concrete base and service trenches are prepared. On-site installation takes 1 to 3 days for a pre-assembled volumetric pod lifted in by crane, or 1 to 3 weeks for a panelised system assembled in the garden.

One vetted modular building supplier that covers your county, and only one. They review your garden access, foundation options and service runs, and give you a written turnkey price.

Class 3 (up to 30 m², S.I. No. 338 of 2026) covers non-habitable garden rooms such as home offices, gyms and playrooms where nobody sleeps. Class 3A (32 m² to 45 m², S.I. No. 340 of 2026) covers a detached habitable garden dwelling with a bedroom, kitchen and bathroom in the rear garden, subject to a 14-day council prior notification and the owner living in the main house.

Yes — while wide or open sites can take a one-piece volumetric pod lifted in by crane, properties with a narrow side passage (900mm wide) or mid-terrace access are built using factory-insulated panelised cassettes carried neatly through the side gate or house and assembled weathertight in 3 to 5 days.

A single service trench (typically 450mm to 600mm deep) is dug from the garden unit to the main house carrying an armoured SWA electrical cable from the main consumer unit, a blue MDPE mains water pipe, and a 110mm gravity foul drain (or a 32mm/50mm pumped foul line if the garden slopes away from the house sewer).

Yes — load-tested galvanised steel ground screws reach firm load-bearing subsoil 1.2 m to 2.5 m deep, keep the modular floor frame ventilated clear of damp ground, install in a single day without digger spoil skips, and cost €90 to €120 per m² compared with €140 to €220 per m² for an excavated concrete raft.

Irish pillar lenders finance standalone turnkey modular homes on their own site provided the system carries NSAI Agrément certification (or equivalent structural warranty certification), has full planning permission, and is signed off under Building Control (BCAR) by an Assigned Certifier with a 60+ year structural design life.

Under S.I. No. 340 of 2026 (in force since 27 July 2026), the 14-day prior notification window runs until 17 November 2030 and construction of the exempt Class 3A garden dwelling must be completed on or before 31 December 2030.