Underpinning RAMS: A Complete Guide for UK Contractors

Table of Contents

• Why Underpinning RAMS Are Complex
• Types of Underpinning Covered
• Key Hazards in Underpinning Works
• Temporary Support and Structural Stability
• Adjacent Structure Monitoring
• What Your Underpinning RAMS Must Include
• Frequently Asked Questions
• Next Steps

Why Underpinning RAMS Are Complex

Underpinning is the process of strengthening or deepening the foundations of an existing structure — typically to address subsidence, allow excavation adjacent to existing foundations, or support an increased load from an extension or additional floor. It is an inherently high-risk activity because the structure above is occupied or partially loaded while the foundations below are being altered.

The combination of confined working conditions, the risk of structural instability, exposure to contaminated ground, and the presence of unknown buried services makes underpinning one of the activities where thorough RAMS are not just a legal requirement but a genuine operational necessity. Under CDM 2015, underpinning contractors must produce comprehensive RAMS before any work begins, and these must be reviewed by the principal contractor and often by a structural engineer.

For broader guidance on RAMS in UK construction, see our complete guide to RAMS in construction.

Types of Underpinning Covered

Underpinning methods vary significantly and each has its own risk profile:

• Traditional mass concrete underpinning (pit method) — Sequential excavation of bays beneath the existing foundation, casting concrete to bear at a lower level. The most common method for residential and light commercial buildings.
• Beam and base underpinning — A reinforced concrete beam is constructed beneath the existing foundation, transferring loads to new bases at wider spacings.
• Mini pile underpinning — Small-diameter piles are installed through or adjacent to the existing foundation, transferring loads to deeper bearing strata.
• Jet grouting — High-pressure grout injection to strengthen the ground beneath and around existing foundations in situ.
• Screw pile underpinning — Helical screw piles are installed through the floor slab or at the perimeter, connected to the existing foundation by a needle beam.

Key Hazards in Underpinning Works

• Collapse of the structure above — The most catastrophic risk. If underpinning bays are excavated too quickly, without adequate propping, or in the wrong sequence, the structure above can settle differentially or collapse. Your RAMS must describe the propping and sequencing strategy in detail.
• Collapse of excavation walls — Underpinning pits are usually narrow, deep excavations in close proximity to loaded foundations. There is limited space for conventional shoring. The excavation faces must be assessed for stability and appropriate battering, shoring, or closed-face excavation methods specified.
• Contact with underground services — Services running beneath or adjacent to the existing foundations. A full service search and, where necessary, service diversions or isolation must be completed before excavation.
• Confined space entry — Deep underpinning pits may constitute confined spaces under the Confined Spaces Regulations 1997. If so, a confined space entry permit and trained rescue team are required.
• Manual handling in restricted access — Underpinning pits typically require operatives to work in very limited space. Manual handling of concrete, reinforcement, and formwork in confined conditions increases the risk of musculoskeletal injury.
• Noise and vibration affecting occupants — If the building is occupied during underpinning (common in residential subsidence repair), noise and vibration from breaking out concrete, excavation, and compaction must be managed to protect occupants.
• Contaminated ground — Particularly relevant for brownfield sites or properties with old fuel oil tanks or buried services containing hazardous materials.

Temporary Support and Structural Stability

Temporary works for underpinning must be designed by a competent Temporary Works Designer and checked by an independent Temporary Works Coordinator. Your RAMS must confirm that this design process has been completed and must describe the temporary support arrangements in detail.

For traditional pit method underpinning, the key temporary works considerations are:

• Bay sequencing — Underpinning must be carried out in a defined sequence, typically alternate bays, to ensure that at no point is more than a specified proportion of the foundation unsupported. The sequence must be designed by or agreed with a structural engineer.
• Maximum open bay length — Your RAMS must state the maximum length of open bay permitted at any time, as specified by the structural engineer.
• Props and needles — Where the structure above requires propping during excavation, the prop design must be certified. Prop loads must be calculated and verified against the structural engineer's requirements.
• Concrete specification — The concrete specification (minimum strength, mix design, admixtures) for the underpinning mass must be confirmed by the structural engineer. Your RAMS must reference this specification.
• Curing time before loading — Your RAMS must state the minimum curing time for underpinning concrete before adjacent bays can be excavated. This is typically 7 days minimum, but depends on the concrete mix and ambient temperature.

Adjacent Structure Monitoring

Underpinning works can cause settlement or movement in adjacent structures and services. Your RAMS must describe the monitoring regime:

• Pre-works condition survey — A detailed photographic and written survey of the affected building and any adjacent buildings within the zone of influence, carried out before work begins. This establishes a baseline for comparison.
• Settlement monitoring — For significant underpinning schemes, precision levelling surveys or automated settlement monitoring systems should be installed. Monitoring points should be established on the building and on any adjacent structures.
• Trigger levels — Your RAMS must specify amber (alert) and red (stop work) trigger levels for settlement and crack width. If a trigger level is reached, the monitoring data must be reviewed by the structural engineer before work continues.
• Crack monitoring — Existing cracks in the building should be marked with tell-tales before work begins. Any new cracks or extension of existing cracks must be documented and reported immediately.

What Your Underpinning RAMS Must Include

• Project details: address, type of underpinning, reason for underpinning
• Reference to the structural engineer's design and temporary works design
• Bay sequencing plan (if pit method)
• Concrete specification and curing requirements
• Propping and shoring arrangement details
• Underground service search and any diversions
• Confined space assessment and entry procedure (if applicable)
• Settlement and crack monitoring regime
• Pre-works condition survey
• Emergency procedure for unexpected structural movement
• Competency requirements for supervising engineers and operatives

Generate a complete underpinning RAMS using the RAMS AI underpinning template.

Frequently Asked Questions

Does underpinning always require a structural engineer?

Yes. Any underpinning that affects the structural integrity of an existing building must be designed by a competent structural engineer. For traditional pit underpinning, the engineer must specify the bay sequence, maximum open bay length, concrete specification, and curing times. The engineer should also review and sign off the RAMS before work commences. Operating without a structural engineer's design is a significant legal and safety risk.

When does an underpinning pit become a confined space?

Under the Confined Spaces Regulations 1997, a confined space is an enclosed or partially enclosed space that has, or is reasonably foreseeable to have, a specified risk — including reasonably foreseeable loss of consciousness, entrapment, drowning, fire or explosion, or loss of consciousness from gas, fume, or lack of oxygen. A deep underpinning pit may meet this definition, particularly if there is risk of: (i) accumulation of carbon dioxide from the concrete curing process, (ii) ingress of gas from contaminated ground, (iii) flooding from groundwater, or (iv) engulfment from pit wall collapse. Carry out a confined space assessment for each pit before entry. If it meets the definition, a full confined space procedure applies.

What insurance is required for underpinning works?

Specialist contractors insurance for underpinning works should include: employer's liability (minimum £10m), public liability (minimum £5m, often £10m for underpinning), and professional indemnity if your company also designs the underpinning scheme. You should also check whether the client's building insurance remains valid during underpinning — some insurers suspend cover or impose conditions. This is a question for the client's insurance broker, but your RAMS should acknowledge that this has been addressed.

Next Steps

Browse all trade RAMS templates on the RAMS AI trade hub — covering 22 specialist construction trades.

Underpinning RAMS require input from structural engineers, temporary works designers, and health and safety professionals. RAMS AI provides a comprehensive underpinning RAMS template that covers all the structural and safety requirements for this specialist activity.