The CLT-concrete slab solution contributes to notably improve several aspects where CLT shows some disadvantages related to its low stiffness or its low natural vibration frequency. This can affect the user’s comfort or even the structural integrity against resonance phenomena. A concrete topping working along the CLT contributes positively to mitigate these weaknesses. The current investigation work aims to analytically optimize the CLT-concrete composite floor under strength and stiffness criteria. Given the fact it is a complex and recently conceived constructive solution, there is still a lack of regulations when it comes to its calculation, which relegates the subject to a theoretical and investigation-related field. A new analytic method is proposed in this paper in order to obtain the effective bending stiffness based on the successive application of the gamma method (Successive Gamma Method or SGM) which could be used for the calculation of composite CLT-concrete sections of three, five or even more layers. In comparison with most extended methods within the scientific community, SGM provides a slightly higher bending stiffness and a similar answer when the span or the distance between supports changes. The structural, economic and environmental answers of the optimized CLT-concrete composite floor have been studied through three different study cases in Spain. The solution has been compared with a simple reinforced concrete slab and a CLT slab too. It should be noted that the composite slab solution improves the mechanical properties and, besides, it is the deformation and not the strength which results more restrictive. From an economic point of view, the simple reinforce concrete slab is the cheapest, but from an environmental perspective the composite slab improvement is notable. When dimensioning for residential and administrative use, the slenderness (span/thickness) of the composite solution varies from 26 to 33 approximately.