Methods · checked 29 October 2026
Underpinning methods
Mass concrete, beam and base, mini-piles and injection. What each one does, where it fits, and how the engineer picks one.
Facts on this page checked against each source on 29 October 2026. Each one links to its source. How we check
Underpinning makes the foundation of an existing building deeper or wider, so it rests on firmer ground or spreads its load over a bigger area. There are four main ways to do it in a house: mass concrete, beam and base, mini-piles, and injection into the ground.
The engineer chooses the method from what is under the house, how deep firm ground is, what caused the movement and how the work can be reached. Wikipedia sets out the methods below.
Start with a chartered structural engineer. Nobody can tell from a photo or a phone call whether a house needs underpinning. An engineer looks at the cracks, the ground and the drains, then decides. This site never tells anyone their house is safe or unsafe.
The methods side by side
| Method | What it does | Where it fits |
|---|---|---|
| Mass concrete | Digs under the old footing in short bays and fills each with concrete, so the wall bears on deeper, firmer ground. | Shallow depths. The simplest form of remedial underpinning. |
| Beam and base | A reinforced concrete beam under, above or in place of the footing carries the wall to mass concrete bases at chosen points. | Base sizes and depths follow the ground. Anti-heave measures where clay may swell. |
| Mini-piled | Small piles, normally 150 to 300 mm across, carry the load down to stable ground through a cap or beam. | Variable ground, tight access, firm ground usually more than 5 m down, little movement allowed. |
| Injection | Grout or an expanding material is pumped through small holes into the weak ground under the footing. | Where the engineer judges that strengthening the ground is enough, once the cause is fixed. |
Sources: Wikipedia, Underpinning; injection as described in the Irish Examiner (2021) and by a company that offers it in Ireland, Geobear.
How the engineer chooses
- How deep firm ground is. An engineer quoted in The Irish Times says underpinning first needs a ground investigation, including digging holes, to find how far down to go (Irish Times, 2020). For soft or loose subsoils, TGD A says a site investigation is essential.
- What caused the movement. Irish engineers say leaking drains cause most subsidence they see. The drains get fixed first, or the problem comes back (Irish Examiner, 2021).
- Access. 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, 2020).
- Which walls need it. In the cases The Irish Times described, a terraced house meant the front and back walls only, and a semi-detached house all the walls except the party wall (Irish Times).
- Whether the inside can be disturbed. Cantilevered pile caps are used to avoid disturbing the inside of a building. A piled raft means taking up the internal floors (Wikipedia).
- Whether part of the house is enough. Partial underpinning is common, but on ground with low bearing capacity it can increase the risk of the underpinned and unpinned parts moving differently (Wikipedia).
What every method has in common
- It is designed by an engineer, from a survey of the house and the ground.
- The cause gets dealt with, usually the drains, before or alongside the underpinning.
- Cracks are repaired last, after the house has had time to settle on its new support. An Irish engineer puts that at six months to a year (Irish Examiner, 2021).
- Digging beside and under foundations is excavation work. The Health and Safety Authority lists deep excavations in poor soil as a "particular risk", which brings duties for you as the client (HSA). See the process.
Questions people ask
What is the most common type of underpinning?
In the UK, BRE's subsidence database found mass concrete underpinning the most common, often applied to only part of a building. We haven't found equivalent Irish figures.
How long does underpinning last?
No source we trust puts a number of years on it. Mass concrete underpinning is used where permanent support is needed. What matters later is that the cause was fixed, an engineer designed the work, and you keep the engineer's sign-off.
Can a wall be underpinned from the outside?
Yes, in many cases. A structural engineer told The Irish Times that a wall can be underpinned from the outside, with a mini-piling machine small enough to go through a front door.
Do I need to move out during underpinning?
It depends on the method. A piled raft means taking up the internal floors. Work from outside the walls can leave the inside alone. Ask the engineer and the contractor before you agree a start date.
Can old stone walls be underpinned?
TGD A notes that guidance written for new work can be unduly restrictive or impracticable for existing buildings, especially buildings of architectural or historical interest, and that approaches based on its principles may suit better. That is a job for an engineer with experience of older buildings.
Related
Keep reading
Sources (1)
Prices and facts on this page were checked against these published pages. We are not connected to these businesses.
- Geobear: residential.geobear.com
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