This is the first in a series that will focus on the building process from the ground up, as a refresher. Here we tackle site set-out. Try the quiz at the end to see how much you already know.
Before excavating for foundations, forming building platforms or removing topsoil to cleared ground level, the proposed building must be ‘set out’. This involves working out the location and relative height and size of the building on site. There are two key steps.
Finding reference points
First off you need to establish the boundaries and roughly where the building sits. Start by finding the boundary pegs and decide on a reference point for the set-out. Then establish a datum point, or locate one referenced on the plans, for setting out the height of the building in relation to the ground or other features.
Before removing topsoil, forming a building platform or starting to dig for the building foundations and services, check for the presence of live or redundant cables, sewers, water or gas pipes. This information will normally be available from the PIM.
Once the building platform has been formed and the position and relative levels of the building have been established, the set-out of the building can be accurately carried out.
Setting out profiles
Erect profiles approximately 1.2 m (but not less than 0.9 m) outside the perimeter of the building. Brace the profiles to keep them from moving. (See Figure 1.)
Starting with the longest building face, locate each corner and then set out lines at right angles from this line to locate the other lines.
Check to ensure the building layout is square by measuring the diagonals and using the 3-4-5 rule.
Level the horizontal profile batter boards from the highest point on the site first, using a builder’s or laser level (the top is often set at the floor or top of foundation level). Then check to ensure that minimum heights and ground clearances will be achieved.
Mark set-out lines on the levelled profiles and run string lines from profile to profile to give an exact set-out.
If the site conditions are suspect, the site should be inspected by a registered engineer. This inspection will determine the soil conditions and whether foundations to NZS 3604 can be used or whether they need to be specifically designed.
Doing the calculations
It always pays to double-check when setting out.
Site coverage means working out areas, and the rules of thumb here are length × width for rectangular shapes and half the base × height for triangles. Try working out the percentage site coverage of the building shown at right. (The answers are given on page 37.)
More information on setting out is given in BUILD Dec 03/Jan 04, page 22, Feb/March 04, pages 13–15, and in the BRANZ House building guide.
NOTE: This article has been updated and replaced in 2021 by Setting out a site.
Articles are correct at the time of publication but may have since become outdated.