Problem with floor thickness

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hi everyone,

in my designbuilder model i have following problem: I have put multiple blocks on top off each other. The Block hight ist 3,60m and the internal floor has a thickness of 0,39m (set with layers under construction). Therefore in my understanding the clearance bettween two floors should be 3,21m, while in my model it is only 2,82 and the foor has a thickness off 0,78m.

Any ideas what can cause this problem and what i can do against it?

Thank you for your help.

P.S. i am using db versin 5.4