Re-use of Structural Components

[Patricia6169]

Our project is retaining a large portion of the existing structural timber slabs and columns (%TBC), reducing the overall quantities of concrete and reinforcement required for the design.

We would like to confirm our approach to Reference and Proposed cases are correct.

– Reference Case will include all sq meters on the project as a brand-new building. Example: 30,000 sq m new building
– Proposed Case will include the % reduction of the structural components. Example: We reduced/delete from this 30,000 sq m the % of structural components reuse.

If this approach is correct,

1. What level of detail is expected to be provided by the structural engineers to quantify the reductions/reuse of structure?

[Fei Ngeow]

Hi Patricia,

Based on your description, yes, that’s how you’d model it to capture the benefits of reusing the existing structure.

With regards to your second question, general layout drawings that show the areas that were retained and which areas were demolished or new-built will be sufficient evidence. However the lead author should also provide some workings/material take-offs to demonstrate how you’ve arrived at the assumptions/quantities you’ve modeled in eToolLCD (i.e. your calculations on how you arrived at the % of structural components retained).

I hope that answers your question.

[Nathan7308]

Hi Fei,

Hope you’re well!

I’d like to follow up on this topic as I am currently looking into this exact question. With the retained material being Timber – the reduction in the material quantity in the proposed case has an adverse affect due to the reduction in carbon sequestration seen in timber.

We have structural engineer report stating a 93% retention level of timber floors, which means we can only claim 7% of the benefit of the timber compared to the reference case’s 100%.

Does this discourage the retention of timber structures? Or is there a metric that we can use to navigate around this? My suggestion would be to potentially:
– Alter the timber template in the reference case to exclude modules A1-A3 (leaving the negative effects for module C to accurately show the negative effects of demolishing timber), while including modules A1-A3 in the proposed case to account for the carbon sequestration?
OR
– Exclude the effects of disposal in module C for the proposed case, so the sequestration benefits are not as heavily offset by the disposal emissions.

Very interested to hear back from you soon,
Kind regards,
Nathan

[Alice Bui]

Hi Nathan,

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.

Best,
Alice