The Site Survey And What It Must Show
The survey sets the floor level, the access path, the drainage and the crane position. An incomplete survey is the most common cause of a design that cannot be built as drawn.
What does a site survey need to show for a modular project?
Boundaries and easements, spot levels and contours across the site and beyond its boundaries, existing structures, trees with their trunk and canopy dimensions, all visible services and inspection points, the invert levels of drainage, kerb and gutter levels at the street, overhead powerlines with their heights, and the access route including gradients, widths and overhead clearances.
Every decision on a project traces back to the survey. The floor level, the access path, the drainage strategy, the crane position and the planning assessment all sit on it.
Which means a survey that covers the minimum produces a design that has to be revised once the real conditions are known, and the revision happens after the documentation is paid for.
What a standard survey gives you
Boundaries, levels, existing improvements and trees. All necessary and none of it sufficient for a project where a module has to be transported in and craned into position.
What a modular project also needs
**Levels beyond the boundary.** The kerb and gutter, the footpath, the road centreline and the neighbouring ground. Those decide whether an accessible path can reach the entry within gradient, and whether stormwater can discharge by gravity. A survey that stops at the boundary cannot answer either question, and both are set out in [access paths, parking and arrival](/blog/access-paths-parking-and-arrival).
**Drainage inverts.** Not just the location of a pit, the depth of the pipe in it. The invert level decides the finished floor level in many cases, because the floor has to sit high enough for the waste to run to the connection by gravity.
**Overhead powerlines, with heights and positions.** The constraint that most often moves a crane, and occasionally the one that makes a lift impossible without a shutdown. Identified on the survey or discovered on the day, and the second is expensive. This feeds directly into [crane selection and lift planning](/blog/crane-selection-and-lift-planning).
**The access route, surveyed rather than described.** Widths at the pinch points, turning radii at the corners, overhead clearances, gradients and any load limit on a bridge or a culvert. A module is an oversize load and the route is part of the design.
**Trees, with trunk diameter and canopy spread.** Both determine the protection zone, and the protection zone frequently decides where a crane can stand and where excavation is permitted. A tree shown as a dot is not usable information.
**Services, located and marked.** Every visible pit, meter, valve and inspection opening, plus whatever a service location search identifies. An unidentified service under the crane pad or the foundation is a stoppage.
**Easements, with their restrictions.** An easement that prohibits building over it changes the footprint, and one that prohibits a load over it changes the crane position.
Where surveys fall short in practice
**Levels taken on too coarse a grid,** so a localised fall or a high point is missed and appears during excavation.
**No photographic record,** which means every later question about an existing condition requires a site visit.
**Assumed invert levels,** noted as estimates and then relied upon as facts.
**A route description instead of a route survey,** usually a note saying access appears adequate.
**No height clearance dimensions** under awnings, branches, wires or structures along the route.
Why it is cheap relative to what it prevents
A thorough survey is a small line item against a redesign, a crane upgrade, a floor level change or a delivery that cannot reach the site.
The items it resolves are exactly the items that carry the largest cost movement on a project, which is the whole point of [what moves a price on a modular project](/blog/what-moves-a-price-on-a-modular-project).
When to do it
Before design, not before documentation.
A concept prepared on an incomplete survey will have to change, and the change will come after the client has approved it, which is the worst sequence available. The survey belongs at the front of the process alongside the geotechnical investigation, which is where it sits in [the eight design stages](/blog/the-eight-design-stages-explained).
What it enables
With a complete survey, the floor level is set once. The access path is designed to the real levels. The drainage runs by gravity to a known invert. The crane position is confirmed against real clearances. The planning submission is made against measured conditions.
That is what makes the rest of the programme hold, and it is why the assessment in [site constraints that decide modular viability](/blog/site-constraints-that-decide-modular-viability) can be answered with confidence rather than with caveats.
MADEmodular / MADEbetter.
MADEmodular / MADEbetter.