The determination of the costs and CO2 emissions of a model using the "Optimization & Costs / CO2 Emission Estimation" add-on is based on the member, surface, and solid elements (the latter only RFEM) that are used in the model. For this purpose, there is a method applied that is also used in practice for calculating the total costs of a model.
To simplify the task, the model is divided into units, for example, a basement ceiling, an exterior wall, a downstand beam. For these units, specific unit costs are developed, which cover all the costs to be recorded: Price per area, price per length, price per weight, and so on. The masses of the individual units (weight, solid, surface) are then multiplied by the associated unit costs. In this way, you get the partial cost for each unit. The sum of all partial costs results in the total costs of the model.
The estimation of CO2 emissions is based on the same approach.