Construction Layout refers to locating the areas, lines, or points where a construction activity is planned. This could range anywhere from laying out sawcuts or base plate anchor bolts, to edges of buildings and centerlines of utility piping. The more accurate the layout, the less likelihood for issues later on in the construction process.
The idea of layout is to minimize dimensional tolerance to within negligible ranges. Simple layout can be done with measuring tapes and strings, more detailed layout requires complex surveying equipment, such as a Levels, Transites, total Stations, and Theodolites. Current day Total Stations for example, have revolutionized layout to approaching levels of near perfection. Often the digital design documents themselves are uploaded to the Total Station eliminating enormous amounts of time preparing and setting up for layout.
Layout is typically done by a subcontractor specializing in such tasks. Sometimes layout is done by the actual architect or engineers field crews themselves.
‘Offset stakes’ are commonly provided by the layout crew which allow for an offset increment dimension (for example 5’) that enables the construction crews to still work off important points, without disrupting stakes. ‘Lath’ or thin wood stakes are typically used for laying out points and driven into the ground below.
If a pavement surface exists in a location that requires a layout stake, a nail is usually driven into the pavement. Sometimes ‘hub and tack’ are also provided as point layout which consist of a 2×2 stake with a nail driven into the top. The stake provides the horizontal points and the tack provides the vertical points required.
Layout must be planned and executed prior to construction activities starting, and the layout crew must make themselves well aware of the needs and requirements of the crews following who will make heavy use of the layout crews work and information.
‘Benchmarks’ are points chosen by the engineer or architect with can provide horizontal and vertical control points, which essentially control all other points on the site, which are not meant to ever change or move. Vertical control points deal in grade and elevation and fluctuate up and down based on a set benchmark point and number.
Building layout for example often uses an even number for the finish floor elevation (the planned elevation of the top of the floor of the new building). This number is commonly 100 or 600, or really any easy to remember number. Sometimes this elevation is based on relative elevation of sea level since this number can be relied on as virtually unchanged over the course of most construction projects.