Setting Out and Datum Confirmation Checklist

Ask what the levels on your drawings are measured from, and whether the reference is something on the site or something outside it.

The answer determines everything else, including whether the reference can be lost and whether it can be re-established.

Ask to be shown where the reference physically sits on the site, and note its position in relation to something that will still exist at the end.

A reference is only useful while it can be found, and finding it later depends on knowing what it sits next to.

Ask who established the reference, when, and whether it was set from a survey or taken from something already on site.

How a reference was established tells you how much depends on it and how easily it could be re-established.

Ask whether there is one reference for the whole project or several, and if several, how they relate to one another.

Separate references for different parts of a site are ordinary, and the relationship between them is where errors accumulate.

Ask whether the physical mark can be disturbed by the works, and what would happen if it were, before anything starts moving around it.

A reference set on something that is later removed is a recurring and entirely avoidable problem.

If the reference mark is at risk, raise it with whoever set it rather than moving or reinstating anything yourself.

Write down what you were told about the reference in plain language, and keep it with the drawings rather than only in your memory of a site conversation.

This is a single short note that stays useful for the entire life of the building.

Ask what protects the reference mark during the works, and whether anybody is responsible for checking that it is still there.

Protection is usually somebody's habit rather than somebody's task, which is why marks disappear.

Ask whether a second reference exists elsewhere on the site, so that the loss of one does not mean starting again.

A duplicate is ordinary practice and turns a lost mark from a problem into an inconvenience.

Photograph the reference mark in its surroundings, from far enough back that the picture says where on the site it is.

A close photograph of a mark tells nobody anything; the context is the useful part.

Note two or three fixed things near the mark that will survive the project, so its position can be described to somebody who has never seen it.

Descriptions relative to permanent features remain usable long after the site has changed completely.

Ask to be told if the mark has to be moved or reinstated during the works, and record what you were told about the new position.

A reinstated mark is a new fact about the project and deserves a line in the record.

Ask what the finished floor level is in each area, what it is measured to, and whether it refers to the finished surface or to something beneath it.

A level quoted to the top of one layer and a level quoted to the top of another differ by the thickness of everything between.

Ask whether the total depth of the floor build-up has been settled, and who is keeping the running total as layers are chosen.

The published material is direct that fixing a floor level before the build-up depth is known forces a later layer to be thinned.

Ask who holds the running total of the floor build-up, and whether a change of covering has been checked against it.

Ask what the external ground level is intended to be against the building, and how it relates to the internal floor.

The relationship between internal and external levels governs several things that only become visible once they are wrong.

Ask at each external door what the threshold arrangement is, and whether a step appears inside, outside, or not at all.

Thresholds are where the whole level chain meets and where small changes anywhere else become visible.

Ask what ceiling height results in each room from the levels as currently set, and note where it is tightest.

Head height is consumed from below by the floor build-up and from above by the ceiling, and the arithmetic is rarely shown to owners.

Ask where any fall towards a drain has to be formed, and whether the levels as set leave room to form it.

Falls are formed within the depth available, and the depth available is decided by the levels already fixed.

Ask what the position of the building is set out from, whether a boundary, an existing structure, or a surveyed line.

Setting out from a boundary and setting out from a building are different exercises with different uncertainties.

Ask which distances on the drawing matter beyond appearance, such as a separation from a boundary or from another structure, and note them.

Some distances are consequences of a decision made elsewhere, and moving the building moves them too.

Distances to a boundary may carry legal or consent significance; confirm them with a suitably qualified professional and your local authority rather than scaling a drawing.

Ask how certain the boundary position is taken to be, and whether it was surveyed, taken from a fence, or read from a plan.

A fence and a boundary are not the same thing, and the difference surfaces in exactly this conversation.

Where the work joins an existing structure, ask what was measured and whether the existing building was found to be square and level.

Existing buildings rarely are, and how the difference is absorbed is a decision somebody has already made.

Ask what happens if the position has to move once work starts, and who has to be told before it does.

The library is consistent that position and sizing are a single decision for foundations rather than two separate ones.

A wall moved during construction is a matter for whoever designed the structure, not an adjustment to be made on site.

Ask for a note of what was actually set out on the ground and when, rather than relying on the drawing to describe what happened.

The drawing describes an intention; the setting out is the event, and the two are worth recording separately.

Ask which trades each set part of the level, from groundworks through to the surface you will eventually walk on.

The published material names groundworks, floor, frame and paving as each setting part of the level, usually weeks apart.

Ask each of them, or ask whoever is coordinating, what reference they will work from and whether they will all use the same one.

Agreeing the datum once and recording it is what gives each trade a level to work to.

Ask where the reference is recorded on site so that each trade can see it, rather than being passed on verbally from one to the next.

Information passed verbally between trades weeks apart is the ordinary route by which a level drifts.

Ask which trade is last to set a level in each area, since that is the one that absorbs everything that went before.

Whoever is last usually has the least room, and that position is worth knowing before it is reached.

Ask what happens at the seam between two trades who each set part of a level, and who checks that the two agree.

Nobody owns a seam by default, which is the same pattern the design material describes at junctions.

Before changing a floor covering, ask what the change does to the level, the thresholds and anything already ordered against the previous arrangement.

A late change of floor finish thickness moves the level that several other things were set against.

Ask whoever is coordinating levels to confirm the effect of a covering change before it is ordered, rather than after it arrives.

Note every door that opens over a floor whose level may change, including its present undercut, before the change is decided.

Doors are made to a level, and a change reaches them whether or not anybody remembered them.

Check any stair that lands on a floor whose level may change, since a stair meets a level at both of its ends.

A change at one end of a stair arrives at the other end as well, which is easy to miss when only one room is being considered.

Ask what a level change does outside the building, at the threshold, the paving and anywhere water is meant to run away.

Internal changes reach external levels through the threshold, which is the point where the two arrangements meet.

List anything already ordered or measured against the current levels, and check each one before a change is confirmed rather than afterwards.

Made-to-measure items are ordered against a level, and they are the most expensive thing to be caught by a change.

Ask who has to agree a level change before it happens, and record who agreed and on what date.

Level changes tend to be discussed by two people and to affect many, so the agreement is worth recording.

Write a single page describing the reference, where it sits, what was measured from it, and who set it, and keep it with the project papers.

One page is enough, and it is the difference between a level that can be re-established and one that cannot.

Ask whether a record exists of the levels actually achieved, as distinct from the levels drawn, and ask for it at handover.

Drawn and achieved levels differ in ordinary construction, and the achieved set is the one a future alteration works from.

Note whether any physical reference survives on the finished property, and where, so that a future project has somewhere to start.

A surviving mark nobody knows about is the same as no mark at all.

Record the external ground level against the building as built, particularly anywhere paving or planting could later raise it.

External levels are raised by ordinary garden work over the years, and the original relationship is worth having written down.

Raising external ground against a building can affect arrangements you cannot see; ask a suitably qualified professional before changing external levels later.

Store the levels record with the drawings and the concealed-work information rather than separately, since a future reader will look in one place.

Separated records are the ones that get lost when a property changes hands.