Hidden defects in house with concealed cracks

Questioner

We bought a house in 2019 that was built after 2000. Unfortunately, after a few months, cracks became visible, for which we had a structural investigation carried out. This revealed a construction error, causing the roof to sag. We held the seller liable on the advice of the building surveyor, but after the report we received a letter stating that they rejected this claim. Upon close inspection, we see subtle signs of repaired cracks, which we had not seen upon inspection and which are now only visible under certain light conditions and at a short distance. The person who drew up a valuation report did not notice this either. On the transfer form, the question "Are there (repaired) or (hidden) cracks and/or damage in/to floors, ceilings and/or walls?" is answered with 'No.' Unfortunately, we did not have a structural survey carried out in advance, nor were we advised to do so by our bank (with our current knowledge, this seems flawed to me, but it is not included as such in the law, so I cannot really blame the bank). I am familiar with the duty to investigate, which does not specify that a structural engineer must actually carry this out. I am also familiar with the duty to report, in which the selling party in this case was demonstrably negligent. I have read that in case law a structural engineer is required in disputes, despite the fact that this is not stated as such in the law, only this was in a lawsuit, in which there was no deliberate and knowing lie on the transfer form regarding repairing cracks. How would you estimate where the responsibility lies with regard to the costs of repairing the roof?

Lawyer

In this case I would have another appraisal done with attention to hiding cracks. Then there is no question of a hidden defect but in seriousness descending from fraud to error.