Foundations, plumbing and electrics for modular buildings
Ground screw foundations cost €90 to €120 a m² and go in within a day without digging up the lawn; an insulated concrete raft slab costs €140 to €220 a m². Connecting water, foul waste and an armoured ESB power cable from the main house to a Class 3A garden dwelling typically adds €3,500 to €9,500.
How your base, water, foul drainage and electrical supply are installed — and what to check before the crane arrives.
Free, no obligation. One vetted modular supplier covering your county prices it, not five.
Ground screws vs concrete raft slab compared
| Feature | Ground screw piles (€90 to €120/m²) | Concrete raft slab (€140 to €220/m²) |
|---|---|---|
| 35 m² base cost | €3,150 to €4,200 | €4,900 to €7,700 |
| Time on site | 1 day (ready to build immediately) | 3 to 5 days work + curing time |
| Sloping gardens | Levels a slope up to 1 m+ without retaining walls | Needs excavation, hardcore build-up and shuttering |
| Garden mess | No skip or concrete lorry through the side passage | Excavator, muck-away skips and concrete pump |
| Best for | Timber/SIP garden rooms and panelised Class 3A dwellings | Heavy steel volumetric pods and permanent standalone houses |
Water, foul drainage and power from the main house
- Electricity (ESB). A Class 3 garden office or Class 3A dwelling runs off the main house's MPRN via a steel-wire armoured (SWA) cable buried in a trench to a sub-consumer unit in the garden building. For a habitable dwelling with an electric shower and hob, the electrician checks your main fuse board capacity and installs a priority load unit if needed.
- Water and foul drainage. Under Class 3A, the garden dwelling connects to the main house's water and drainage. If the garden slopes away from the house's sewer manhole, a small packaged foul pumping chamber pumps waste up to the existing drain through a narrow pressure pipe.
- Broadband. Always lay two runs of external-grade Cat 6 data cable in a separate duct alongside the power trench before the lawn is closed up.
What modular buildings cost in Ireland
Our price guide by size and specification, including 13.5% VAT on supply and installation.
| Job | Typical cost | What moves the price |
|---|---|---|
| Insulated garden office or studio, 12 to 16 m² (Class 3) | €18,000 to €32,000 | Cladding, glazing, base and cable run from the house |
| Large garden room or gym, 20 to 30 m² (Class 3 max) | €28,000 to €55,000 | Up to the 30 m² non-habitable exemption limit; no plumbing or kitchen |
| Class 3A habitable garden dwelling, 32 to 37 m² (1-bed) | €65,000 to €105,000 | Kitchen, shower room, Building Regs insulation, base and service hook-ups |
| Class 3A maximum garden dwelling, 40 to 45 m² (1 to 2 bed) | €80,000 to €135,000 | Largest exempt rear-garden unit (45 m² total garden structures cap) |
| Standalone 2 to 3 bed modular home, 75 to 85 m² | €175,000 to €255,000 | Full planning permission, BCAR, foundations and site services |
| Factory shell only (weathertight exterior), per m² | €1,200 to €1,800 a m² | Excludes groundworks, internal plumbing/kitchen and service connections |
| Insulated & fitted garden room rate, per m² | €1,600 to €2,400 a m² | Includes 13.5% VAT when supplied and installed by the builder |
| Turnkey habitable modular home rate, per m² | €2,400 to €3,200 a m² | All-in with kitchen, bathroom, foundations and 13.5% VAT |
Get a modular building price in 4 taps
Tap what you want to build, the size and your county. Your request goes to one vetted modular building supplier that covers your county, and they ring you with a written specification and price.
Questions people ask
Does a Class 3A garden dwelling get its own ESB meter (MPRN) and Eircode?
No. Under S.I. No. 340 of 2026, a Class 3A garden dwelling is ancillary to the main house and must be connected to the main house's services. You give the main house's Eircode on the 14-day council prior notification.
What if my house has no side access for a crane or digger?
If your house is mid-terrace or has a narrow side passage, modular builders bring the building through in pre-insulated wall, floor and roof cassettes by hand and use portable ground-screw drivers that fit through a standard doorway.
Get a written turnkey price for your modular building
One vetted supplier covering your county checks access, foundations and service connections, and gives you a written price.