Subsidence and heave are different movements
Subsidence involves downward movement; heave is upward movement associated with expansion. Uneven movement beneath a building is particularly important because different parts of the structure may move by different amounts. BGS explains that rainfall, vegetation, leaks and changes to drainage can influence shrink–swell behaviour. [1]
This is why an assessment should consider the ground and the water conditions, not only the visible roots. Ask the engineer to distinguish evidence of an existing problem from a potential hazard that must be allowed for in a new design.
London maps are a starting point
BGS produces a regional three-dimensional shrink–swell susceptibility dataset for London and the Thames Valley. It identifies potential hazards at a regional mapping scale; it is not a foundation design or a test of the soil at your exact footing position. [2]
Use available ground information to help plan the investigation. Do not interpret a map category as confirmation that a house is currently subsiding, or as proof that every plot on a street has identical ground.
What information should the team gather?
Foundation guidance identifies soil characteristics and the species, size and distance of trees as relevant. Supply information about trees on your site and nearby, including known removals, and ask what further survey or testing is required. [3]
A practical briefing record can include photographs, a site plan, the proposed building footprint, previous movement reports and available drainage information. Label uncertain information as uncertain rather than guessing a tree species or an old removal date.
Do not remove a tree as an automatic remedy
BGS recommends advice before removing mature trees that pre-date a house. Tree management and its effect on the moisture profile require assessment; removal is not automatically the safest response to a crack or a foundation-design concern. [4]
Trees can also be protected by a Tree Preservation Order or by conservation-area controls. Check with the council before instructing work, and resolve ownership and consent separately from the engineering assessment. [5]
Discuss a complete design, not just extra concrete
Ask how the proposed foundation and floor arrangement addresses the ground conditions, how any tree-management recommendation was reached, and what assumptions must be checked during construction. Request coordination between the structural engineer, ground specialist and tree adviser where their advice overlaps.
BGS's 2026 research reports changing climate-related subsidence risk. It supports attention to long-term ground behaviour, but it does not establish a new mandatory foundation depth for every London house. [6]
Where movement is already suspected, obtain a diagnosis and inform the relevant insurer or property owner rather than commissioning an unassessed landscaping fix. Keep investigation and monitoring records so later decisions are based on evidence rather than the appearance of one crack on one day. [4]