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Survey, Soil, Rock and Drainage Investigation

Foundation design and site cost depend on verified grades, bearing conditions, groundwater and drainage—not on a generic modular plan.

Reviewed for destination-code contextInternational with U.S. and Canadian emphasis
Permanent-home context: This guide uses “modular home” for a code-compliant building made as three-dimensional modules, transported to a permanent site and assembled on an approved foundation. It does not use the term as a synonym for a trailer, mobile home or HUD-code manufactured home.

Measure the property

A current legal and topographic survey can establish boundaries, elevations, easements and existing improvements. It gives the designer a reliable base for siting the house and planning access.

On infill lots, confirm neighbouring foundations, retaining walls and trees that could be affected by excavation or crane work.

Understand the ground

Soil bearing, frost susceptibility, expansive clay, fill, rock and high groundwater can change foundation type and excavation cost. A geotechnical report may be required by the engineer or authority.

Unexpected rock or weak fill can erase apparent factory-price savings. Allocate investigation money before finalizing the structural design.

Move water safely

Finished grades, roof drainage, foundation drainage and surface runoff must work together. The set area and temporary access also need drainage so heavy equipment does not become unstable.

Site drainage may require swales, storm connections, infiltration areas or retaining systems. These are destination-site responsibilities even when the house arrives substantially complete.

Apply this guide to a real project

For survey, soil, rock and drainage investigation, create a dated project note tied to the destination address and current drawing revision. Identify the authority, designer, factory or contractor responsible for each unresolved item. Attach the written evidence for ‘Is the survey current and suitable for design?’ and ‘Has the foundation engineer received soil and groundwater information?’ rather than recording a verbal assurance.

Before a deposit, production release, shipment or final payment, convert every open question into a named action with an owner and deadline. Keep superseded drawings and decisions in the record so later inspectors, lenders, insurers and future owners can understand why the completed house differs from an early sales plan.

Questions to resolve before proceeding

  • Is the survey current and suitable for design?
  • Has the foundation engineer received soil and groundwater information?
  • Where will roof and surface water discharge legally?
  • Can heavy transport and crane equipment operate without damaging the site?
Stop point: Pause design when bearing conditions, rock or drainage could materially change the foundation.

Primary references to check

  • Destination building department, approved plans and project contracts