Unfortunately, with the "project managed" route that a lot of insurers take these days, the bin-the-claim-and-let-the-insured-argue approach occurs far too much. That is also as much to do with the capability of the adjusters, who generally are not engineers, and who are not qualified to determine cause.
Of course, they might well be correct; but, just like the rest of us, they haven't yet been issued with xray eyes and there are several potential problems that could lie below the slab, some of which are insured perils, some of which aren't.
You need to get an independent SE to look into this for you. Whilst the risk as far as fees is concerned is yours initially, if that investigation determines causation that is accepted by as an insured peril, then those fees will form part of your claim.
Moderator 6
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