# Wall Implementation according to TFC Layout

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We now come to a very important point that affects the entire mode of operation and the settings in the HRB editor. There are two possible modes of operation:

* The wall determines the specification: This has become the most commonly used mode of operation, as it is the most flexible and fastest. In this mode you enter your walls with the desired specification (appropriate thickness of all desired layers) and assign them the HRB pre-processing file. When assigning, a dialog box appears indicating a discrepancy between the wall and the HRB pre-processing file. Here you select the option 'Keep wall specification'. The pre-processing file must be matched to this mode of operation. For details see the section The wall determines the specification below.
* The HRB file determines the specification: This is now an outdated mode of operation that was used previously to assign walls. In this mode the thickness and layer composition of the entered wall do not matter, as they are overwritten when assigning the HRB pre-processing file. For example, you can assign a 24 cm solid wall an HRB pre-processing file and thus create a multi-layer timber frame wall. The HRB pre-processing file contains all layers and their thicknesses. However, if the thickness of a layer is to be changed or a layer is to be replaced by another (for example render replaced by formwork), the HRB pre-processing file must be modified, which is not the case with the other method—provided the pre-processing file has already been prepared accordingly.
