Method · checked 29 October 2026
Mini-piled underpinning
Small piles take the house down to stable ground, often more than 5 m below. Rigs fit through a front door.
Facts on this page checked against each source on 29 October 2026. Each one links to its source. How we check
Mini-piled underpinning carries the weight of the house down to stable ground through small piles, usually where that ground is more than 5 m down. The piles are normally 150 to 300 mm across, augered or driven, and rigs built for tight spaces can go through a normal domestic doorway and build piles up to 15 m deep (Wikipedia).
People also call it mini piling. One Dublin example, costed by a structural engineer in 2020, had piles going down 6 m under a semi-detached house (The Irish Times).
Where mini-piles fit
Wikipedia lists the conditions where mini-piles are most used: where the ground is variable, where access is restricted, where pollution matters, and where the structure can't be allowed to move much in service (Wikipedia).
The three main layouts
| Layout | How it works | Inside the house |
|---|---|---|
| Pile and beam | Pairs of piles either side of the wall, linked by pile caps, with reinforced concrete beams along the wall | Piles inside as well as outside |
| Cantilevered pile caps | Tension and compression piles to each cap, normally linked by a beam | Used to avoid disturbing the inside |
| Piled raft | A grid of piles and a reinforced concrete raft over the whole floor, picking up every wall | Internal floors are completely removed |
Source: Wikipedia, Underpinning.
Screw piles
A structural engineer told The Irish Times that subsidence can be remedied using mass concrete or screw pile underpinning, after a geotechnical investigation to find how far down to go (Irish Times, 2020). Your engineer will say whether screw piles suit your ground.
What it means for you
- Less digging. A mini-piling machine about half the size of a typical truck can be wheeled through the average front door, and a wall can be underpinned from the outside (Irish Times).
- Not every wall. In the cases The Irish Times described, a terraced house meant underpinning the front and back walls only, and a semi-detached house every wall except the party wall.
- Combined works. The Rathgar buyer in that article was already planning a full renovation and underfloor heating, so he was going into the ground anyway and the piling added relatively little disruption.
Questions to ask
- How deep are the piles, and what are they founded on?
- Which layout: pile and beam, cantilevered caps or a raft?
- Does anything happen inside the house?
- How will the rig get in, and where does the spoil go?
- Who is the PSDP and the PSCS?
- Will the engineer witness the piling and sign it off?
Questions people ask
What is mini piling?
Underpinning with small-diameter piles, normally 150 to 300 mm across, that carry the load of the house down to stable ground, usually more than 5 m down.
Can mini piling be done inside a house?
Yes. Rigs designed for restricted headroom and limited space can go through a normal domestic doorway. A cantilevered pile cap layout avoids disturbing the inside.
How deep do mini-piles go?
Usually more than 5 m, and rigs for tight spaces can build them to around 15 m. A Dublin example in The Irish Times went down 6 m.
What did mini piling cost in that Dublin example?
A structural engineer costed piling under one semi-detached house in Rathgar at €16,000 in 2020, at trade rates he estimated were about 20% below what most buyers would pay. It's one 2020 example, not a price list.
Related
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