Tayross Associates Chartered Building Surveyors | Party Wall Rates London | Party Wall Surveyor West London | Building/Structural RICS Survey London

At Tayross Associates, we regularly engage with structural engineers, architects, and contractors on complex party wall and basement projects. A recent professional discussion between Tayross Associates Ltd and structural engineer and party wall surveyor Tristan offered valuable lessons on collaboration, competence, and construction risk management under the Party Wall etc. Act 1996.

This article summarises key takeaways from that session — exploring the intersection of engineering judgment, statutory procedure, and best practice for managing structural works in London’s historic building stock.

1. Discovering Defective Underpinning

Simon raised an issue familiar to many surveyors: defective or substandard underpinning uncovered during adjoining basement works.
Common defects include:

• Gaps between underpinning pins

• Lightweight block infill used instead of mass concrete

• Poorly formed foundations deviating from design intent

Such findings highlight the risks of unsupervised or poorly executed works. Defects in underpinning can compromise stability and lead to costly disputes — reinforcing the need for early engineering involvement and vigilant site monitoring.

2. Structural Behaviour of Victorian Buildings

Tristan explained that Victorian structures are relatively forgiving of small movements due to lime mortar and traditional flexibility. However, they are highly vulnerable to vibration and disturbance, particularly during underpinning replacement or removal.

Remedial works in these buildings require carefully sequenced method statements and detailed risk assessments to protect adjoining properties. Even where works fall outside modern Building Regulations, they must still meet the test of structural adequacy and fitness for purpose.

3. Engineering Judgment and Assessment

Assessing the adequacy of decades-old underpinning is never straightforward. Engineers may recommend:

• Concrete or core testing to confirm material quality

• Load-path analysis to assess changes in use or loading

• Selective removal or replacement based on verified performance

In all cases, the decision must be grounded in engineering evidence rather than assumption.

4. Practical Engineering Solutions

Tristan shared examples from recent projects, including:

• Rebuilding defective brickwork above new underpinning using engineering brickwork for strength and durability.

• Designing temporary retaining walls that evolve into permanent foundations.

• Using corbels and chamfers to improve stability during excavation.

Both engineers and surveyors were reminded of the importance of considering temporary and permanent load paths throughout construction.

5. Contractor Shortcuts and the Importance of Supervision

Simon noted that poor workmanship often stems from time and cost pressures. Contractors may cut corners with inadequate underpinning, temporary works, or reinforcement — problems only discovered once adjoining owners raise concerns.

Regular, competent supervision is therefore not optional. Tristan recommended:

• Engineer attendance for the first underpinning stages, and

• Site visits at least every two weeks thereafter.

Under the CDM Regulations, the contractor’s Temporary Works Coordinator provides an extra layer of safety oversight, but active engineer involvement remains essential.

6. Party Wall Awards and Engineering Oversight

A key discussion point was whether Party Wall Awards should mandate regular engineering inspections. The consensus: while not a statutory requirement, ongoing engineer involvement enhances safety, reduces disputes, and gives adjoining owners confidence that structural integrity is being protected.

7. Consent and Future Enclosure Costs

When owners consent to a new party wall, questions often arise over future enclosure rights. Tristan clarified that consent need not be conditional, but adjoining owners should understand that:

• The quality and cost of the wall now affect future enclosure costs.

• A wall built in yellow stock brick, for instance, will carry a higher future enclosure cost than one built in rendered concrete block.

A practical, cost-effective specification today prevents future disagreements.

8. Temporary Works, Large Beams, and Structural Sequencing

Large beams, splices, and temporary supports are common in modern basement conversions and flat extensions. However, poor splice detailing or inadequate sequencing can lead to cracking or structural movement.

Tristan advised that:

• A temporary works method statement should accompany all significant alterations (e.g. chimney removals or deep excavations).

• A reviewing engineer may be appointed to assess the design, connections, and load paths.

• Leaving temporary works solely to the contractor or steel fabricator risks under-design or improper sequencing.

9. Improving Collaboration Between Engineers and Surveyors

Tristan offered valuable reflections on enhancing coordination:

For Engineers:

• Label drawings clearly with house numbers and section orientations.

• Identify boundaries and adjoining structures from the outset.

• Include underpinning sequences, foundation depths, and temporary works details.

• Provide practical notes to assist surveyors and avoid post-award confusion.

For Party Wall Surveyors:

• Acknowledge technical limits and bring in reviewing engineers when appropriate.

• Understand the engineering reasoning before requesting design changes.

• Engage early with the engineer to clarify sequencing, loads, and risks.

• Use structured checklists to confirm key design considerations have been addressed.

Early communication and mutual understanding greatly reduce disputes and delays.

10. Competency, Excavations, and the “45° Rule”

Surveyors were reminded of the need to recognise when an excavation warrants engineering input. The familiar “45° rule” offers only a preliminary guide — real risks depend on soil conditions, foundation type, and proximity.

Surveyors should consult local British Geological Survey data and engineers experienced with local ground conditions to make informed judgments.

11. Managing Ground Conditions and Temporary Support

Understanding ground type is fundamental:

• Good ground: dense clay, gravels, or firm undisturbed strata.

• Poor ground: soft fill, brick earth, or shallow mixed soils prone to slumping.

Temporary works such as trench boxes, shoring, or sheet piling can provide adequate short-term stability, avoiding unnecessary permanent retaining walls where rights of support are maintained.

12. Detailing Matters: Columns, Corbels, and DPCs

Even small detailing decisions carry major implications:

• Recessed columns can breach damp-proof courses, leading to moisture ingress. Columns should generally remain proud, preserving DPC integrity.

• Corbel removal adjacent to pad foundations must be limited. Small (e.g. 200mm) removals may be safe; larger removals can reduce bearing capacity and introduce eccentric loading.

13. Reviewing Engineers and Special Foundations

The session also addressed the role of reviewing engineers — often appointed by adjoining owners to assess deep excavations and special foundation proposals.

Three typical levels of review were outlined:

• Category 1: General review for coherence and reasonable care.

• Category 2: Spot checks on calculations and details.

• Category 3: Full redesign or verification of the original design.

The Bailey Rail Case was discussed as a practical example of avoiding the need for adjoining owners’ consent to special foundations. However, this method can increase cost and safety risk. From an engineering standpoint, consenting to special foundations is often more straightforward and secure.

Key Takeaways

• Competency and collaboration are vital — surveyors should seek engineering input when needed.

• The 45° rule is an early indicator, not a guarantee.

• Temporary support can often replace unnecessary permanent structures if properly designed.

• Small details matter — DPCs, corbels, and connections can have disproportionate effects.

• Regular site inspections by competent engineers protect all parties and reduce disputes.

• Clear communication between surveyors and engineers underpins safe, efficient project delivery.

Final Thoughts

This discussion reinforced the shared responsibility between surveyors and engineers: understanding each other’s disciplines, recognising limits, and communicating early. Whether dealing with Victorian underpinning, special foundations, or temporary works, the goal remains the same — to safeguard structures, uphold statutory duties, and deliver practical, safe, and efficient solutions.