Measuring house floor levels to the Christchurch datum

An important consideration for foundation rebuilds after the Canterbury earthquake is whether the post quake floor height meets the existing building code. The code minimum floor height is 11.4m above the Christchurch Council Datum. Christchurch City Council has stated that in flood management areas this will be increased to 11.8m in early 2011. Our guess was that our house is low lying, but how to find out? Cellphone GPS is horribly inaccurate…

I was able to borrow a Trimble S3 Totalstation to find out the current floor levels of our house. The S3 is a survey instrument that uses a laser reflected off a target prism on a pole.  I setup the TotalStation and measured to the reference elevation which was 11.42m. This reference was re-calibrated by the CCC shortly after the September 4 quake.  Reference points close to your house can be obtained via email from the CCC. Then I measured the elevation at a second point closer to our home, which became the new reference. Then I moved the Totalstation to a point between the new reference and our gate. Elevation at our gate was measured to be 10.7m. Moving the Totalstation onto our property, the floor height outside our front door comes in at 11.15m, 25cm under the current building code minimum.

An interesting exercise, the device was easy to use, hopefully compensating for the amateur surveyors! EQC will probably engage a professional…

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