Construction surveying: setting out, checks, as-built surveys

Construction surveying: why a surveyor is needed on site

Construction surveying is needed so that the house stands where it is drawn and at the heights in the design. An error of half a metre in setting out means the house encroaches on the boundary setback or the building line. An error of a few centimetres in level means water runs off the terrace towards the door and the bathroom tiles do not meet the floor drain. The surveyor transfers axes and levels to the ground, checks them at every stage, and surveys what will later be covered by earth and concrete.

Setting out axes and levels

Before the excavation the surveyor transfers the corners of the house and the main axes from the design onto the plot, puts up profile boards and fixes the datum level on a permanent mark from which all heights are then measured. Beforehand we check that the setting out matches the plot boundaries and the setbacks from neighbours. On a sloping plot the levels are especially important: they decide the height of retaining walls, the falls of paths and where the water will go.

Checks during construction

• the excavation bottom and the blinding level;
• the position of piles and anchor bolts against the setting out;
• foundation and wall formwork before concrete;
• plumb of columns and frame corners;
• floor slab levels and falls of roofs and terraces.

Every pile is checked against the setting out before concreting; more on piles on the bored piles page. On a frame we check every storey: a column deviation missed on the ground floor accumulates by the third. How the frame and walls are built is described on the house shell page.

As-built surveys

Before trenches are backfilled we survey pipes, cables, chambers and drainage with coordinates and depths. Years later, when you need to plant a tree or put in a post, you will know where not to dig. The finished foundation and house are surveyed too: this data is needed to register the house in the Public Registry and to check that it was built to the design. Owners following the build from another country get diagrams and photos with levels; more on this format on the remote construction page.

Settlement and crack monitoring

If cracks have appeared in an old house, a deep excavation is being dug next door or the house stands on a slope, we install settlement markers and tell-tales and repeat the measurements every few weeks. That shows whether the house is moving and how fast, and the decision on strengthening is made on numbers, not by eye. More on such work on the foundation strengthening page.

Earthworks volumes

On a slope and with large excavations, surveys before and after the earthworks show how much soil was dug out and how much was brought in. These figures are used to check invoices for removal and fill rather than taking the number of lorries on trust. This is especially useful when earthworks are paid by volume.

How much construction surveying costs

Setting out the house axes on the plot costs from 600 ₾. An as-built survey of the foundation, frame or services with a drawing from 510 ₾, settlement and crack monitoring from 420 ₾ per cycle of measurements. An earthworks volume survey from 510 ₾, boundary staking up to 6 points from 510 ₾, a topographic survey of a plot up to 1 000 m² from 1 020 ₾. The final cost is set after a site visit and an agreed estimate.