Chiwara Team — Quantities Module Attribution Requests¶
Status: Pending team response. This document can be sent to the Chiwara field engineering team as-is.
Context: The quantities module reverse-engineering (see quantities-spec.md and
quantities-formula-reconciliation.md) identified a set of parameters where the current
reference workbook either (a) omits a needed value, (b) uses a proxy that is methodologically
incorrect, or (c) references an unidentified source. The tool cannot be made defensible under
ISO 14071 critical review until these are resolved.
Each item below is classified:
- BLOCKED — the module raises ValueError at runtime until this is provided. No default,
no placeholder. A BLOCKED parameter means the calculation simply cannot run.
- EXPERT-JUDGEMENT — the module can run with the proxy value from the workbook, but the
result is flagged as EXPERT-JUDGEMENT in the audit trail, not SOURCED, and will be
called out in an ISO 14071 review.
Item 1 — BLOCKED: Slab mesh specification (row 51)¶
Module location: quantities, BoQ item B.II.1.b — "Reinforced concrete slab,
300 kg/m³, 10 cm thickness".
The problem: The current workbook has no rebar (Steel Rebars, column M) for this slab. Every other reinforced concrete item in the workbook (isolated footings, columns, beams — rows 9, 11, 12) includes rebar at 100 kg/m³. A 100 mm structural RC slab without any reinforcement is not structurally plausible. The Python module cannot include a rebar formula for this slab without the correct mesh specification — and it cannot safely apply the 100 kg/m³ density from the 350 kg/m³ structural recipe to a 300 kg/m³ lightly-loaded floor slab.
What we need from you: 1. The reinforcement specification for this slab: mesh type (e.g. ST30, ST40, treillis soudé), bar diameter, spacing, or equivalent density in kg/m³ or kg/m². 2. Who provided the specification (name, date, project reference). 3. Whether this specification is drawn from a standard (NF, EN, or local) or from a project-specific structural design.
Why this is BLOCKED: If we invent a rebar density, the module could understate or overstate
total project steel by ~163% (see quantities-formula-reconciliation.md §4.1). An error of
that magnitude in a material with significant embodied carbon would invalidate any comparative
assertion between this building and a conventional alternative.
Contact: Site engineer / structural engineer on the Keur Songho project.
Item 2 — BLOCKED: BBSC composition (rows 15, 17, 32, 38)¶
Module location: quantities, all BoQ items using "BBSC on header course".
The problem: The workbook models BBSC bricks using only one material output:
Rock = brick_count × 0.0002 m³/brick. No cement, no earth, no water, no binder is modeled
for BBSC. The acronym "BBSC" is never expanded anywhere in the workbook.
Working hypothesis (not confirmed): BBSC = Blocs de Béton Stabilisé Comprimé (compressed stabilised concrete/earth block), a form of CSEB. If so, its true material composition includes at minimum: earth/aggregate, stabiliser (cement, lime, or pozzolan), and water. Treating a stabilised block as pure quarried rock understates its embodied cement/binder and may significantly misrepresent its GWP. This is the same structural failure as the slab rebar omission: a material is present in the building but absent from the LCA.
What we need from you: 1. What does "BBSC" stand for? 2. The material composition per brick: earth, cement (or other binder), aggregate, water (in m³ or kg per brick, or per m³ of finished block). 3. The source of the composition data (product datasheet, manufacturer, lab test, literature). 4. Whether the 0.0002 m³/brick rock figure in the workbook has any meaning (e.g. aggregate fraction), or is a placeholder. 5. Name and date of whoever can confirm the composition.
Why this is BLOCKED: We cannot compute the LCA impact of BBSC bricks without knowing what they are made of. Using the current rock-only model would make the LCA non-compliant with EN 15804+A2 §6.3.3 ("all significant materials shall be included").
Contact: Material supplier / procurement contact for Keur Songho.
Item 3 — EXPERT-JUDGEMENT: OMPU reference document¶
Module location: Throughout quantities — every conversion factor in the workbook.
The problem: Row 72's cell note explicitly states "Not in OMPU, brief proportions" for
the Tyrolean plaster recipe. This implies that every other recipe in the workbook IS from
"OMPU" — an acronym never expanded anywhere in the source material. Every factor currently
marked PROVENANCE UNKNOWN in the spec's Factors table is presumably from OMPU.
What we need from you: 1. What is OMPU? (Full name, publisher, edition/date, where to obtain it.) 2. Is it a Senegalese BTP norms document, a company internal standard, or a university reference? Does it carry a licence that allows us to cite it? 3. Is the document available in digital form?
Why this matters: Under ISO 14071, every input parameter to a reported LCA result must have a traceable source. "PROVENANCE UNKNOWN" is acceptable during development but not in a final auditable result. Identifying OMPU would allow us to move the entire Factors table from UNKNOWN to SOURCED.
Status: EXPERT-JUDGEMENT (pending) — the tool will run and flag these as un-cited. The ISO 14071 reviewer will flag them.
Contact: Adama (referenced in the orphaned cell comment on row 43: "À vérifier avec Adama", dated 2024-02-08) or whoever assembled the original workbook.
Item 4 — EXPERT-JUDGEMENT: Anti-termite treatment reference area¶
Module location: quantities, BoQ item A.IX.2 — "Waterproofing and anti-termite
treatment in the foundation."
The problem: The workbook computes U36 = 1 × 5 L/m² × 289.15 m², where 289.15 m²
is the roof area (D35). Anti-termite treatment is applied to the foundation zone (soil
under and around the slab), not to the roof. The correct reference area is the foundation
contact area or the treated perimeter × treatment depth.
What we need from you: 1. The correct reference area for the anti-termite treatment on the Keur Songho project: - Foundation plan area (m²)? - Or: treated perimeter (m) × treatment depth (m)? 2. The product specification for the treatment (name, active ingredient, rate in L/m²). 3. Is the 5 L/m² rate confirmed from a product datasheet, or is it an approximation? 4. Name and date of whoever specified the treatment.
Status: EXPERT-JUDGEMENT (pending) — the tool currently uses roof area as the proxy.
A divergence test (test_c5_anti_termite_area_attribution) is marked XFAIL until this
is resolved.
Item 5 — EXPERT-JUDGEMENT: Steel density for fenestration¶
Module location: quantities, all window/door items (rows 60, 61, 63, 64, 65, 67).
The problem: Fenestration steel (window/door frame plates and profiles) is tracked by volume (m³) in the workbook, while structural rebar is tracked by mass (kg). There is no steel density conversion anywhere in the workbook, so the two steel streams cannot be summed or compared without assuming a density. The tool will need a density to convert fenestration steel volumes to mass for EPD impact factor application (EPD data is typically per kg of steel).
What we need from you: 1. The steel grade/type used for window and door frames (e.g. S235/S275 structural steel, or a lighter-gauge cold-formed section). 2. If you are comfortable approving a standard density: mild structural steel ≈ 7,850 kg/m³ (per EN 10025 / common reference). Can we use this? 3. Name and date of whoever can confirm.
Status: EXPERT-JUDGEMENT (pending) — the tool can use 7,850 kg/m³ if Marco approves it as the project-wide default, with named attribution in the audit trail.
Item 6 — EXPERT-JUDGEMENT: Sand density scope¶
Module location: quantities, row 72 (B.IV.4 — Tyrolean plaster).
The problem: Row 72's cell comment states "density of sand is considered → 1600 kg/m³". This is the only place in the workbook where a sand density is stated explicitly. The question is whether this value is specific to the Tyrolean plaster (a coarser plaster aggregate), or whether it should be used elsewhere in the workbook where sand mass ratios implicitly exist.
What we need from you: 1. Is 1600 kg/m³ the intended density for all sand in this project, or specific to row 72? 2. Source of the 1600 kg/m³ value (lab test, reference table, assumption)?
Status: EXPERT-JUDGEMENT (pending) — currently applied only in row 72, which is where it appears. No extension to other rows without your confirmation.
Open question: OMPU water:earth ratio for vaults (K29, K30)¶
The vault water formula uses a derived ratio 0.2585 m³ water / m³ earth, calculated from
brick dimensions (0.0043 ÷ (0.42 × 0.22 × 0.18)). The brick dimensions (0.42 m × 0.22 m ×
0.18 m) are stated in-sheet but have no external citation. Are these the standard Nubian vault
brick dimensions from a CRAterre or Voûte Nubienne Association specification, or
project-specific dimensions?
If these come from a published standard, that would allow the water:earth ratio to be classified as SOURCED rather than EXPERT-JUDGEMENT. Please advise.
How to respond¶
Please fill in answers inline under each item above, add your name and date, and return this document to the LCA team. For BLOCKED items, a response is required before the tool can compute material quantities for the Keur Songho reference project.
For questions, contact: marco.ferrario@gmail.com