1. CONTROL OF BUILDING SITES
THREE TIER CONTROL
THREE TIER CONTROL
SITES
CONTROL OF BUILDING

2. THREE TIER CONTROL
Primary: the network of control points coordinated in all three dimensions to give a fixed overall reference framework for the works
Secondary: local control points for construction or baselines established for structures
Tertiary: points set out at the actual positions for construction or at suitable offset positions.

3. Primary Control Points
These are the Master control points set out from national reference points
Form a closed loop
Built in redundancies for checking
Set out by specialist surveyors
Position and Level known
Official National Survey points
Primary site control points

4. Secondary Control Points
These form the control points for setting out base lines and sites grids.
Set out from the Primary control points
May have associated level value

5. Tertiary Control Points
These are the points you will be setting out
Relate to construction elements
Set out so dimensional checks can be made.