Excavation, sheet piling and heavy site traffic bring vibration with them. A few months later the neighbour calls about a crack in his façade. Was it already there, or is it new? Without a record of the condition before the works, it is one person's word against another's.
A drone capture of all adjacent façades and roofs answers that question for everything visible from the outside. In Ghent we recorded 37 buildings this way in five days, for a land surveyor who was coordinating the baseline survey for a construction project in the city centre.
What a drone baseline survey records
- Façades from the street and from height. Including the upper floors, cornices and roof edges that cannot be seen from the pavement.
- Roofs and roof junctions. Tiles, zinc work, chimneys and the junction between two buildings.
- Rear façades and inner courtyards, insofar as they can be reached from the air without entering the property.
The result is an orthophoto per façade and a 3D model of the block. Every image has a date, a time and a position in its metadata. That makes it possible to look at exactly the same zone again later and compare.
What it does not prove
Be clear about this, because in a damage dispute every weakness will be used.
- It is not a joint schedule of condition. That has legal status and is drawn up by a land surveyor or architect, in the presence of or with the agreement of the owner. The drone capture is evidence that supports that schedule of condition, not a replacement for it.
- It shows nothing inside. Cracks in interior walls, ceilings or floors are out of frame. An interior schedule of condition is still needed for those.
- It does not show a crack smaller than the pixel. With a GSD of less than 1 cm, a hairline crack of half a millimetre is not visible. A new 2-millimetre crack that appears later can, however, be compared with a zone in which nothing was visible at the time.
- It does not measure settlement. Monitoring subsidence requires survey points and precise levelling.
How the drone and the schedule of condition work together
In practice it works like this: the land surveyor or architect carries out the schedule of condition inside and of the street façade, with the owners. The drone records the parts nobody can reach without an aerial lift: upper floors, roofs, rear façades. Both dossiers carry the same date and refer to each other.
That saves an aerial lift in a narrow street, and it produces a picture that is more complete than anything possible from the pavement.
What to look out for in the assignment
- Timing. Before the first excavator arrives on the construction site, not alongside it.
- Completeness. Agree in advance which buildings and which façades are in scope. A building that is missing is a building without evidence.
- Retention. Images are only evidence if they are still available after the works. We keep image and project data for 90 days after delivery. Keep the delivered files yourself, or agree a longer retention period in writing.
- Permission and privacy. In a city centre we fly under our Specific authorisation and inform residents in advance. Windows and inner courtyards are not deliberately captured.
Who it is for
Contractors and clients who want to prevent a damage dispute. Land surveyors and architects who coordinate a schedule of condition and want to document the parts that are hard to reach. Insurers who want an objective basis for comparison.
Read the case: Wall survey of adjacent buildings in Ghent