Thanks for your patience.
Please find below the response to this matter.
It would be more accurate to model re-used timber as having negative carbon in A1-A3 equal to the emissions in module C. This is because these emissions have been saved from the previous application, making it carbon neutral over its life (apart from transport, construction, maintenance, and deconstruction impacts). It would probably still perform slightly worse than newly-added timber from a GWP perspective, but it should be better on land use and fresh water use.
The way to model this would be to use a mock-EPD to capture the savings in A1-A3, as follows:
1. Add the design template for the timber structure in the design.
2. Offset the A1-A3 impacts of the timber structure (Please refer to Modeling Carbon Neutral Products in eTool)
3. Check the GWP of the timber structure in model C4 using the Analysis Tab (Please refer to Analysis Tab).
4. Find an EPD (incl. modules A1-A3 impacts only) that is relevant to the timber structure in the design. You can either find an EPD in our EPD library or create a new one (Please refer to Create New EPDs with Excel Templates)
5. Based on the GWP of the timber structure in model C4 and the selected EPD, you can generate a mock-EPD with the GWP of A1-A3 equal to the GWP of the timber structure in module C4 (note that the impacts of other indicators should be kept the same as the EPD specification).
6. Add the mock-EPD in the design to capture the savings in modules A1-A3.
It is important to note that the impacts of the timber element in the design template depend on the different type of timber that might be selected/specified. For example, each timber item will have slightly different end-of-life impacts. Impacts will likely change with different LCI source as well. Therefore, it will be a case of editing the GWP of the mock-EPD in each case.
I hope this helps. Please let me know how it goes with this modelling process and feel free to get in touch if you require further assistance.