Beam and base underpinning supports a wall on a reinforced concrete beam that spans between separate concrete bases (pads) dug down to firm ground. Instead of digging a continuous trench of concrete under the whole wall, the load is collected by the beam and carried down at intervals. A chartered structural engineer decides whether it suits the building and the ground, sets the base positions and depths, and designs the reinforcement; we build it to that design with Building Control inspecting.
What is beam and base underpinning?
Think of it as a bridge built under your wall. The existing footing is either replaced or supported by a new reinforced concrete beam, cast beneath or alongside the wall. That beam sits on a series of mass concrete bases taken down to a stratum the engineer is satisfied with. Between the bases the beam spans the softer or less reliable ground, so the wall no longer depends on it.
It sits between two other approaches. Mass concrete underpinning fills a continuous run of bays beneath the footing, which works well where good ground is not too far down. Mini-piled underpinning carries the load much deeper on small-diameter piles. Beam and base is often considered where firm ground is deeper than is sensible to reach with continuous mass concrete, but the site or the loads do not call for piling, or where the engineer wants a stiff element to bridge a localised soft spot.
How do the main underpinning methods compare?
| Method | How the load is carried | Typically considered where |
|---|---|---|
| Mass concrete | Continuous concrete beneath the footing, dug in hit-and-miss bays | Suitable bearing ground is at a modest depth and access allows hand or small-machine digging |
| Beam and base | Reinforced beam spanning between discrete bases taken down to firm ground | Good ground is deeper, soft spots need bridging, or fewer excavations are preferred |
| Mini-piled | Small piles drilled to depth, linked by needles or a ground beam | Problem soils go deep, trees affect shallow ground, made ground or restricted access |
| Resin injection | Expanding resin fills voids and stiffens soil beneath the footing | Specific soil conditions where the engineer judges it suitable |
The table is a general guide only. The choice for any particular house comes from the engineer’s investigation, not from a rule of thumb, and our underpinning cost guide explains why method has such a large effect on the final price.
When might an engineer specify beam and base?
- Firm ground is deeper than expectedTrial pits sometimes show soft or variable ground continuing well below the original footing. Rather than digging a deep continuous trench, the engineer may prefer a limited number of deeper bases.
- A localised soft areaA backfilled hole, an old drain run or a pocket of made ground beneath part of a wall can be spanned by the beam, with bases placed either side.
- Heavier or concentrated loadsWhere a wall carries point loads, for example from a beam or a chimney breast, a reinforced beam can spread and redirect them to suitable bearing points.
- Combining with other workThe beam can also be designed to tie in an extension or a bay so that the repaired section behaves as one stiff unit, though the junction with any untouched foundation still needs careful thought.
None of this means underpinning is needed in the first place. The RICS consumer guide on subsidence says fewer than 5% of affected properties need underpinning, and that the Institution of Structural Engineers recommends it only as a last resort. In most cases the cause, such as a leaking drain or thirsty vegetation on clay, is dealt with and the cracks repaired once the ground has settled down. Beam and base comes into the conversation only when the engineer has concluded that the foundation itself must change.
What investigation comes first?
The design depends on knowing what lies below the footing. Before a scheme is drawn, the engineer will usually want soil and site investigation: trial pits beside the wall to expose the existing foundation, boreholes or probes to find where competent ground starts, and soil samples tested for things like plasticity and moisture. Where drains run near the wall, a CCTV drain survey shows whether leaks have softened or washed out the ground. In some cases a period of level or crack monitoring is recommended to see whether movement is still active.
Across Merseyside the ground varies a great deal over short distances. Parts of the area sit on glacial clay, coastal districts have sandy ground, and older neighbourhoods can have made ground or backfilled former clay pits. That is exactly why a base depth cannot be guessed from the street or the age of the house.
How is beam and base underpinning carried out?
- Design and approvals. The engineer issues drawings and calculations. Building Regulations approval is normally required for underpinning, so a Building Control application or notice is made, and party wall notices are served by a party wall surveyor if the Act applies.
- Services and preparation. Gas, water, electric and drainage runs near the wall are located. Floors may need lifting inside if the beam is to be cast internally or through the wall.
- Bases excavated in sequence. Base pits are dug one at a time or in a planned order so the wall is never left without enough support. Building Control usually inspects the bottom of each excavation before concrete goes in.
- Bases cast. Mass concrete is placed to the depth and size on the drawings.
- Beam formed. The reinforcement cage is fixed to the engineer’s schedule, checked, and the beam cast beneath or alongside the wall, sometimes with needles through the wall to pick up the load.
- Packing and reinstatement. The gap between new beam and existing masonry is dry-packed, excavations are backfilled, and floors, paths and finishes are made good.
- Sign-off. The engineer and Building Control sign off the completed work as applicable, and crack repairs and decoration follow.
Bay sizes, excavation sequence, base depth and reinforcement are always set by the engineer’s design. Digging next to or beneath a foundation without that design and proper temporary works can cause sudden collapse. Please do not attempt any excavation near your foundations yourself.
Does beam and base underpinning affect the neighbours?
Often, yes. In semis and terraces the bases may be within a few metres of next door’s foundations, and if the excavation is deeper than theirs the Party Wall etc. Act 1996 usually needs to be considered. A party wall surveyor handles the notices and, if needed, the surveyors’ binding decision. We are not party wall surveyors and do not give legal advice, but our page on party walls and underpinning explains the general process and why it can add weeks to the programme.
What affects the cost of beam and base underpinning?
We do not publish prices for this work, because every scheme is priced only after the engineer’s design exists. The main factors are:
- the number, size and depth of the bases;
- the length of wall and the size and reinforcement of the beam;
- access for spoil removal and concrete, especially on terraced streets with no rear access;
- whether floors, kitchens or fitted units must be removed and reinstated inside;
- investigation, monitoring, drain repairs or tree management needed before work starts;
- Building Control fees and any party wall surveyors’ fees;
- crack repairs, replastering and redecoration afterwards.
If an insurance claim is involved, the insurer and its loss adjuster decide on the investigation and the method, and whether underpinning is needed at all. Speak to your buildings insurer before arranging any work.
Where do we carry out beam and base underpinning?
As part of our underpinning work in Liverpool, we build engineer-designed beam and base schemes across the city and wider Merseyside. Terraced streets such as those in Walton bring tight access and shared walls; larger inter-war and Victorian houses in Allerton or Heswall often have mature gardens, extensions and longer wall runs. The method is the same; the planning around it is not.
Has an engineer recommended beam and base?
If you already have an engineer’s report or drawings, or you want to talk through whether this kind of work is likely to be relevant, call 07777 659786 or leave your details in the form. Tell us what has been noticed, the age of the house and whether an insurer, buyer or neighbour is involved, and we will call you back. You can also read more about structural underpinning across Merseyside before you call.
Frequently asked questions
Is beam and base underpinning better than mass concrete?
Neither is better in general. Mass concrete is often simpler where good ground is not far down. Beam and base can mean fewer, deeper excavations and can bridge soft spots, but it involves reinforcement and more design work. The engineer chooses based on trial pits, soil tests, loads and access at your property.
How deep do the bases go?
As deep as the engineer needs to reach ground that can carry the load reliably and is not affected by the cause of movement, such as roots or seasonal clay shrinkage. That depth is found through investigation and confirmed when Building Control inspects each excavation, so it cannot be given in advance.
Can I stay in the house during beam and base underpinning?
Many people can, particularly when the work is external. If floors must be lifted inside, or the kitchen is affected, living arrangements become harder. For insurance-funded repairs, buildings policies usually cover alternative accommodation if the home becomes uninhabitable; check with your insurer.
How long does beam and base underpinning take?
It depends on the property, the number of bases and the permissions needed. As a broad guide, MyJobQuote says most underpinning jobs take about 3 to 5 weeks on site, but investigation, Building Control and party wall matters can add several months before work begins.
Will beam and base underpinning stop all future cracking?
It is designed to stop the underpinned section moving with the problem ground. However, the junction between new and existing foundations can behave differently, and minor cracking there is something the engineer designs for. Removing the original cause, such as a leaking drain, remains just as important.