The direct answer
Start with the complete system, not one product or headline rate.
The drawings, surveys, access checks, drainage information and inspection points worth resolving before a house extension reaches excavation. A dependable plan connects the site evidence, approvals, access, installation sequence and finished reinstatement.
Confirm the approved information
Bring together planning drawings, Building Regulations information, structural design, drainage details and relevant conditions. Issue the same current revision to everyone pricing or building the work.
Survey access and protection
Record the narrowest width, turns, steps, overhead restrictions, loading position and route through the property. Decide how spoil, concrete, steel and materials will move without avoidable damage.
Locate services and drains
Plans can be incomplete. Trace relevant drains, chambers, incoming services and overhead lines, and establish whether sewer ownership or a build-over agreement affects the design.
Check the existing building
Opening-up may be needed to understand existing foundations, floor build-ups, wall construction and the structural opening. These interfaces often determine the practical sequence.
Set levels before excavation
Agree datum, finished floor, external falls, thresholds and drainage inlets. A small early level error can become an expensive problem at the door, patio or sewer connection.
Plan hold points and records
List the inspections required before foundation concrete, oversite, drainage backfill, structural steel enclosure and final completion. Photograph concealed work and retain the relevant records.
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