IES-VE → 1-Click LCA: mismatch in external envelope quantities and layer take-off (retrofit + Passivhaus projects)

Buildings Assessments
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I am using IES-VE (ApacheSim / ModelIT) for operational energy modelling and 1-Click LCA for whole-life carbon assessment in line with RICS WLC v2. I am working on UK residential Passivhaus / EnerPHit case studies, including both new-build and deep retrofit projects.

I am encountering consistent issues when attempting to transfer or align envelope quantities from IES-VE into 1-Click LCA, particularly for external walls, roofs, floors, and construction layers.

Observed issues:

  1. IES-VE exports or reports thermal surface areas, which do not reliably correspond to physical construction quantities needed for LCA.

  2. External wall areas appear fragmented across zones and adjacency conditions (party walls, basements, stacked zones), leading to over- or under-counting when aggregated.

  3. Construction layers (insulation, structure, finishes) are not transferred with correct quantities. Any layer quantities appearing in 1-Click LCA seem to be inferred or assumed rather than physically derived.

  4. In retrofit projects, it is unclear how to correctly distinguish:

    • retained existing structure

    • newly added layers (e.g. EWI, internal insulation)

    • demolition / replacement scope

  5. In one case, PV electricity generation data (kWh) was mistakenly interpreted as a construction material, leading to unrealistic negative A1–A3 “sequestered carbon” values and inflated A5 impacts. This highlighted how sensitive the workflow is to dataset classification.

Current workaround (manual but defensible):

  • Use IES-VE only to extract surface areas by construction type.

  • Derive material quantities externally in Excel using:

    • Area × thickness × density

  • Manually enter layer quantities into 1-Click LCA and assign lifecycle stages explicitly (A1–A5, B, C).

  • Account for onsite PV only by reducing delivered electricity in B6, while modelling PV hardware separately as products.

This approach works, but it is time-consuming and undermines confidence in any semi-automated IES → LCA workflow.

My questions to the community:

  1. Is there a recommended or supported workflow for reliably mapping IES-VE envelope geometry to 1-Click LCA quantities?

  2. Are there known limitations or guidance documents confirming that manual quantity take-off is expected when using dynamic simulation tools like IES?

  3. How do others handle retrofit boundary conditions (existing vs new fabric) when importing from energy models?

  4. Are there plans to improve interoperability so that envelope quantities reflect physical construction reality rather than thermal modelling abstractions?

Any guidance, confirmation of best practice, or references would be greatly appreciated. I am particularly interested in workflows that are robust enough for academic / PhD-level WLC analysis and professional reporting under RICS v2.

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Hi Harshul,

The IES-VE One Click LCA integration is built and maintained by the IES team, including the BOM export and how quantities are transferred. Because of that, we don’t have direct control over the logic behind the exported quantities.

I am reaching out to you via email on the specifics.

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