We’re aware that not all of our customers are fully conscious of how setting out works and how we process correct information. This glossary is intended to provide a little more information regarding the required drawings should show and why we need them.
These are usually produced by the architect or designer and will clearly state the points that need to be set out on site. Typically this will be a plan, stripped back of irrelevant information, with co-ordinates (easting & northing) of key junctions, corners etc. Each co-ordinate must be 9 digits (a 6 digit number to 3 decimal places, eg. E:501356.057) as this ensures we can stake out to the nearest millimetre of accuracy.
A CAD-compatible file is the most helpful to us as we can extract the key data quickly and accurately. It also allows us to check dimensions and remove any extraneous data if needed. Time spent manually imputing co-ordinates may incur additional hours to your invoice so a fully compatible CAD file will save you money and avoid difficulties.
Your architect may not have produced a setting out drawing at this stage and may feel no need to, but we highly recommend issuing one to us. It eliminates any doubt and allows us to operate under the strict instruction of the designers drawing. We cannot make assumptions or re-draw plans as this opens up the possibility of error.
This is an example of a setting out drawing, which clearly defines the co-ordinates to 3 decimal places on an accompanying table:
The above example is particularly helpful for the following reasons:
- The irrelevant information (such as levels, inspection chambers, internal details) are greyed out.
- Each setting out point is clearly defined by a unique code combined with a suitable symbol.
- An accompanying table shows all point co-ordinates to 3 decimal places, which are also aligned to a known co-ordinate system (in this instance the most common – OSGB).
- Points are only located on necessary corners and not midpoints or insignificant junctions.
- There are additional checking dimensions, useful for on-site checks with a tape.
We don’t expect all architects and designers to know what’s best to show – after all they are not surveyors and may make assumptions. It may be helpful to pass this glossary on to your designer in order to inform them for not only your project but future works.
Sometimes a pre-existing topographical survey plan for the site exists. These are often very beneficial to us as they are almost certain to include important control station positions.
Site control usually consists of nails situated outside, and sometimes inside, of the site, embedded into the pavement, road or solid ground surfaces. These will have been put in place by the original topographical surveyor and their positions measured accurately. Often, the drawing layout/sheet of the survey drawing will show the co-ordinates of these, again to 3 decimal places.
Knowing the co-ordinates of existing nails, otherwise known as control stations, can often make our lives a lot easier as we can set up our equipment correctly in relation to the site. Using triangulation, a total station (our main piece of equipment) can identify its position in relation to the existing site features such as boundaries, walls and even levels to Ordnance Datum.
If good quality setting out drawings have been issued alongside this information, it is likely the proposed building position and consequently our setting out co-ordinates relate to the original topographical survey. Having this data before we arrive can speed up the setting out process by several hours in most cases.
A combination of useful setting out and topographical survey drawings will always yield the most efficient and accurate results. If no existing site control is known, typically in instances where no topographical survey was originally undertaken, we will occasionally need to use a GPS device to set up our own control stations.
The following example is a THS Concepts topographical site survey plan showing the location and co-ordinates of control stations positioned by our surveyor:
The above example would be extremely helpful as it shows both the position of the station on site (highlighted by the red rectangle) and its co-ordinates on an accompanying table. Having 2 or more of these will allow any surveyor to establish their position relative to the site and its existing features.
Not all setting out jobs will have an original topographical survey plan and we also understand that our clients may not have these to hand. However, if one can be obtained it would be beneficial to all parties and maximise efficiently when combined with good quality setting out plans.
If you have any questions regarding our requirements please don’t hesitate to get in touch. You can call us on 0208 935 5160 or email [email protected]