NEOBIOME

CR_018: NZ model constants — veg demand, roof per dwelling, garden cost & irrigation (compiled synthesis)

Properties4
typesource
source_typecompiled_research
authorAI deep research
topicsfood_systems_agriculture, building_habitat, water_supply_treatment, nz_specific

6 min read

CR_018: NZ model constants — veg demand, roof per dwelling, garden cost & irrigation (compiled synthesis)

NZ model constants — veg demand, roof per dwelling, garden cost & irrigation (compiled synthesis)

Compiled research — upstream-referenced; mixed confidence

A Perplexity Deep Research synthesis of three model constants. Veg demand rests on the 2008/09 NZ Adult Nutrition Survey (no update since — LOW confidence). Roof is derived from floor area (medium). Garden cost is triangulated (no NZ per-ha budget exists — LOW). Irrigation is from regional-council data (medium).

Source verification (audit 2026-06-22) — ESTIMATE, NO PRIMARY

The garden cost figures (veg_capex_per_ha 125k, `veg_opex_per_ha` ~110k/ha/yr) have no underlying NZ document — confirmed: no NZ per-ha community-garden budget exists; the NZIER veg-production report gives only commercial margins ($14,384/ha GM). Both cells demoted sourced→assumed in model_design.md. Veg demand 82 kg = arithmetic from the MoH guideline (defensible); roof 170 m² = a floor-area derivation (SR501, RT_206).

Summary

Three NZ per-capita / per-dwelling constants for the NI model. (1) Per-capita vegetable demand: ~47 kg/person/yr actual consumption (2008/09 survey), ~82 kg/person/yr against the MoH 3-serving guideline, ~104–130 kg/person/yr FAO supply (incl. waste). (2) Roof footprint per dwelling: ~170 m² for recent new builds, ~202 m² for existing stock. (3) Organic community market garden: establishment ~100–150k/ha, operating ~90–130k/ha/yr (labour-dominated), irrigation ~4.5 ML/ha/yr. Fills RT_180 (③), RT_181 (③), RT_186 (④ veg cost + water coupling); feeds D02.

Key claims

- claim: "NZ per-capita fresh-vegetable demand is ~47 kg/person/yr actual consumption (2008/09 NZ Adult Nutrition Survey, ~130 g/day, excl. potatoes/kumara) vs ~82 kg/person/yr against the Ministry of Health guideline (3 servings × 75 g/day); FAO food-balance supply is ~104–130 kg/person/yr including waste."
  source_location: "§1 Constant 1 / §1.3"
- claim: "Average NZ dwelling roof footprint is ~170 m² for recent new builds (2023–24 consents, ~155–165 m² floor × ~1.12 eave factor) and ~202 m² for existing stock (~200 m² floor); the horizontal footprint (not sloped area) is the measure for PV and rainwater catchment."
  source_location: "§2 Constant 2 / §2.2"
- claim: "NZ new-dwelling floor area has fallen to ~142–156 m² (Canstar 2024; BRANZ SR501 survey 181 m², consent 188 m²; Stats NZ median 126 m²), while existing stock averages ~200–202 m²; multi-storey was 14% of new housing in 2023."
  source_location: "§2.2 Data sources"
- claim: "An organic community market garden costs ~NZD 100,000–150,000/ha to establish (fencing, irrigation, sheds, tools, propagation) and ~NZD 90,000–130,000/ha/yr to operate, dominated by labour (1.5–2 FTE; commercial market gardens run ~14 FTE/ha)."
  source_location: "§3.1 Establishment / §3.2 Operating"
- claim: "Irrigation water requirement for a year-round temperate-NZ community vegetable garden is ~4.5 ML/ha/yr (4,500,000 L/ha/yr ≈ 450 mm applied), ranging 2–3.5 ML/ha for seasonal rotation up to 5.5–6.5 ML/ha for dry east-coast regions; Nelson/Tasman ×1.0–1.1 of the central estimate."
  source_location: "§3.3 Irrigation water requirement"
- claim: "NZ community gardens typically operate well below full market-garden infrastructure — 73% pay no rent/rates, fewer than 30% have efficient watering or greenhouses (Aotearoa Community Gardens Survey 2025, University of Canterbury)."
  source_location: "§3.1 evidence base"

Model constants — recommended values

From CR_018:

CellValueTag
person_veg_demand_kg_yr (③)82 (guideline/needs basis; 47 = actual)sourced (low–med)
roof_per_dwelling_m2 (③)170 (new build) / 202 (existing stock)sourced (high new / med stock)
veg_basket establishment cost (④)**~125,000/ha** (100–150k)sourced (low–med)
veg garden operating cost~$110,000/ha/yr (labour-dominated)sourced (low–med) — see flag
veg irrigation (④b veg→water)~4,500,000 L/ha/yr (Nelson ×1.0–1.1)sourced (medium)

Neobiome Intelligence relevance

Fills three input cells. person_veg_demand_kg_yr = 82 kg/person/yr is the right denominator for the model’s ”% of vegetable needs” output (D13) — the guideline production target; 47 kg/yr is current actual consumption. roof_per_dwelling_m2 = 170 m² (new-build pilot) sizes the roof pool the model allocates to roof-PV and rainwater catchment (use the horizontal footprint). Irrigation 4.5 ML/ha/yr fills the spec’s (irrigation) veg→water coupling, previously a gap.

⚠ Model-representation flag (food-domain economics). The garden operating cost (~110k/ha/yr, labour-dominated) *dwarfs* the establishment cost (~125k/ha) — i.e. an organic community garden spends roughly its whole capex again every year, mostly on labour. The model’s veg_basket carries a capex (cost_value) and an om_%/yr, which cannot represent a labour-dominated annual operating cost. Food-domain economics will be badly understated unless operating/labour cost is modelled explicitly (not as a % of capex). Flag for the engine build.

Grounds the INT_007 practitioner benchmark. At 82 kg/person/yr, 20 people need ~1,640 kg/yr of vegetables — consistent with INT_007’s “~1 ha market garden feeds 20 people” (and a low ~1,640 kg/ha implied yield, plausible for a community-scale organic plot vs intensive commercial).

Caveat. Veg demand is the weakest constant — the last NZ nutrition survey was 2008/09 and the PHCC (2025) flags the gap. Garden cost has no NZ per-ha primary (triangulated from international + NZ proxies). Treat both as planning-grade.

Research targets

Documents to retrieve

  • BRANZ SR501 — Physical Characteristics of New Houses 2023 — the NZ floor-area/storey-mix primary behind the roof derivation. WebFetch-retrievable (BRANZ cloudfront PDF). New target RT_206 (low); firms roof_per_dwelling_m2. → RESOLVED OT_123 (BRANZ SR501 retrieved & read verbatim, 2026-07-17): Table 10 2023 = survey 181.4 m² / consent 187.8 m² and 14% multi-storey confirmed exactly, so the two SR501-attributed figures in this synthesis are now primary-verified. ⚠ SR501 is houses-only (single detached); its 181–188 m² does NOT support the ~142 m² all-dwelling-types lower bound this synthesis lists in §2.2 alongside it (that band is Canstar 2024 ~142–156 m² + Stats NZ median 126 m², not SR501) — keep the detached-house and all-forms figures distinct.
  • NZIER / Horticulture NZ (2024) — Making the economic case for vegetable production in NZ + regional-council irrigation guidelines (Waikato Aqualinc 2016, Gisborne 2012). Cross-refs for garden economics + irrigation.

Research gaps

  • No updated NZ nutrition survey since 2008/09 (PHCC 2025 flagged) — person_veg_demand_kg_yr stays low-confidence until a new survey publishes. Not closable by retrieval now. (The 2008/09 ANS macronutrient chapter is now in-corpus as RD_030 — the same-survey primary, dietary-energy shares; the veg-demand figure sits in a different chapter.)
  • No NZ per-hectare organic-community-garden budget — establishment/operating costs are triangulated; a real NZ community-garden cost study would firm them.
  • Model representation — veg_basket needs an explicit operating/labour cost term (the om_%/yr field can’t carry a labour-dominated annual cost). Engine-design note, not a retrieval target.

Connections

Links to

Sources (1): RD_030

Referenced by

Sources (8): CR_033 · CR_051 · OT_108 · OT_123 · OT_165 · OT_166 · OT_190 · RD_030

EDT domains (3): D01: Renewable Energy & Storage Systems · D02: Smart Food Systems & Agriculture · D03: Water, Waste & Circular Systems

SSI indicators (1): I02: Food Security & Sustainable Agriculture

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