Which foundation suits your situation?
No foundation automatically suits every prefab extension. The choice depends on the ground, loads, existing house and local conditions. Discuss with the structural engineer what information and additional investigation are needed. Do not copy a neighbour’s solution without assessment: construction history, loads and details may differ even next door.
Gather existing information
Gather building drawings, earlier renovation plans and any information about existing foundations. Indicate suspected drainage, water, electricity and other service routes. Missing information is a reason to record questions for the survey, rather than guess. Photograph the garden, rear facade, safely accessible crawl space and the equipment access route.
Excavation, access and garden reinstatement
Practical preparation starts before foundation work. Discuss removals, temporary storage of soil and materials, and continued access to the house. A narrow rear passage can affect equipment and sequencing. Ask who removes paving, disposes of soil and reinstates the garden. These items sit outside the visible extension and may be included differently in quotations.
Agree connections and sequencing
Coordinate floor levels, the connection to the house, moisture protection and subsequent assembly. Make clear who checks each dimension and when work must be ready for installation. Plan around inspections and curing required by the selected construction system. A short extension assembly period does not mean investigation, foundations and finishes take the same time.
What belongs in the budget?
Request a separate scope for investigation, design, groundworks, foundations, connections and reinstatement. Identify unresolved assumptions and how changes will be handled. The configurator’s example excludes foundations and any piles. In the value calculator, therefore enter your expected whole-project budget including this work.
Record existing conditions before work starts
Gather any foundation drawings and photograph existing cracks and floor transitions. This helps discuss the starting condition with the engineer and contractor. A soil type on a regional map does not select your foundation. Measurements, loads and connections require a combined engineering assessment.