Kernrechtsfrage
Whether the architect is liable for the cost overrun under the contract of mandate despite a claimed 10% tolerance margin.
Extrahierter Entscheid
The architect was liable; the owner could rely on the accuracy of the estimate and no tolerance margin could be invoked on the facts.
Extrahierte Begründung
The only pre-construction cost information was an imprecise estimate; the architect failed to inform the owner about its accuracy and later submitted a proper detailed estimate only after construction had started. The proven breaches directly explained the overrun, so the tolerance margin did not shield the architect.