Topographic Survey in Seattle, WA

A Map of the Ground an Architect Can Design On

A topographic survey measures the surface of a lot and everything standing on it: contours and spot grades, the footprint and floor elevations of existing buildings, retaining walls and rockeries, driveways, visible utilities such as catch basins, manholes and meters, and the edge of the street. The deliverable is a drawing and a digital file your architect, civil engineer or landscape designer builds the project on. Everything they draw inherits its accuracy, so a topo is usually the first paid step of a new house, an addition, a backyard cottage or a townhouse project.

What Seattle Permit Reviewers Tend to Ask For

Plans submitted to the Seattle Department of Construction and Inspections need an accurate site plan, and on new construction and larger additions a topographic survey is commonly what that site plan is drawn from. The city's tree protection rules add a specific requirement: significant trees on the lot, and trees on neighboring property whose root zones reach across the line, are expected to be located and identified so reviewers can see what the design affects. Where a parcel falls inside an Environmentally Critical Area - steep slope, potential landslide, liquefaction-prone ground, wetland or riparian buffer - the survey needs to show the slope and the features that define that area with enough density for a geotechnical engineer to work from it.

Settle the Vertical Datum on Day One

Current work is referenced to NAVD 88, and horizontal positions are usually on Washington State Plane North. But a great deal of older civil drawing, sewer record and building plan across the region was produced on NGVD 29 or on legacy local datums, and the numbers differ by a few feet. Mixing them without noticing puts a finished floor or a side-sewer invert in the wrong place. We confirm with the design team which datum the project uses before fieldwork, and state it on the drawing.

Slopes, Bluffs and Canopy

The demanding sites are the hillsides: the bluffs of Magnolia and West Seattle in Seattle, the Puget Sound slopes of Shoreline, the ravines of Kirkland and the steep lake-facing lots of Mercer Island. Those also tend to be the most heavily wooded, which means more conventional instrument work and more shots to capture a surface hidden under ferns and salal. Flatter lots in Redmond and Bellevue go faster but still need utilities and trees picked up carefully. A topo pairs naturally with a boundary survey so setbacks are measured from a known line, and its control points are the same ones used later for construction staking.

How long does it take? Scales with lot size, slope and how much vegetation hides the ground. A flat city lot is quick; a wooded ravine lot takes several days in the field.

Frequently Asked Questions