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Topographical Survey - Expectation vs Reality...


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I had a Topographical Survey carried out on my 1-acre property/plot a few months ago. I kinda thought these were the gold-standard of accuracy and the foundation upon which Architects design properties and planning submissions are made. I thought that discrepancies of more than a few centimetres or even millimetres could spell planning trouble. Not sure if my expectation is too great?

 

The outcome of the Survey we had isn't quite as I expected. Granted parts of the plot were, at that time, inaccessible, but there are features on the survey that don't really add up. For example...

 

  • We have a lot of trees, but there are certainly many that have been missed and not all can be blamed on inaccessibility (a circa 40-50ft Hornbeam isn't on there, despite the fact that it is pretty much in full view)
  • There are 2 instances of trees 'double plotted' (shown as 2 trunks/canopies side-by-side, when in fact there is only 1)
  • Fence-lines that appear straight to the eye, really don't look that way on the survey

 

I ideally want the Surveyor to overlay the old plot outline measurements (that I now have but didn't before) to enable me to see if the fences are in the right place, but is this even too much to ask? I have the him coming back this week to re-look over it and I need to use his measurements to underpin at least one boundary query, so I need to know I'm working with a level of accuracy that can be depended upon, but I don't want to call this guy out if he's doing what is expected.

 

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It seems that buildings, walls, drain covers, kerbs, roofs are easy to plot with great accuracy.  There should also be spot heights around the site so you can see the levels.  The data should relate to the OS data. I think trees are more difficult, especially where there are lots.  No defined points.  You can get a tree survey done if you need an arb report.  Mention your concerns to the surveyor and see what he says.

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Bit of googling found..

 

http://www.bonningtonsurveys.co.uk/assets/samples/TSA%20Client%20Guide%20-%20Topographical%20Surveys_Issue%203_HR.pdf

 

Page 5..

 

Quote

4.3 The accuracy required


Computer aided drawing (CAD) can determine the exact distance between any two points, however all measurements will have a tolerance. In a topographical survey accuracy is related to scale e.g. a 1:100 based survey will be more accurate than a 1:200 or 1:500 scale survey.

The RICS specification for Surveys of Land, Buildings and Utility Services at Scales of 1:500 and Larger states that: “The accuracy of planimetric detail shall be such that the plan position of any well defined point of detail shall be correct to within 0.3mm r.m.s.e. at the plan scale when checked from the nearest permanent control station.”

Therefore, using this specification, a point of detail on a 1:100 survey would be accurate to 30mm r.m.s.e and on a 1:500 survey would be accurate to 150mm r.m.s.e when checked from the nearest permanent control station.
 

 

 

 

 

Edited by Temp
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It may be that the surveyor didn't properly check his  work product before issuing to you  and your greater knowledge of your plot identified some errors. Feed that back and ask him to correct these errors to your satisfaction.

Our survey had similar errors, which were obvious and really important to us for Planning Submission.  They concerned  ridge heights on the two neighbouring properties - the original submitted drawings did not appear to be correct, from just looking at the houses. Anyway, we requested that he checked and he did ( admitting that he thought he was getting some issues with his instruments when he was surveying the property) - we were correct and the ridge heights were corrected and a revised drawing issued..

The other key learning for us was ensuring the architect properly used the survey information for the site layout,  so that all subsequent drawings and plans could be overlayed and all used the same data. This came to light when the engineer responsible for designing all our BC drawings, including drainage, rainwater, and also our retaining walls,  identified that the architects layouts did not use the surveyed data.  

We then had confidence in using  surveyor to accurately layout the groundworks  (including all the underground drainage, landscaping and retaining walls,  and the insulated  foundation installed by MBC

Edited by HerbJ
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