OT_156: BRANZ SR391 (2018) — The Cost of Homestar (Ade — Hobsonville Point 6–10-Homestar capex case study)

OT_156: BRANZ SR391 (2018) — The Cost of Homestar (Ade — Hobsonville Point 6–10-Homestar capex case study)

Source

https://www.branz.co.nz/pubs/research-reports/sr391/ — original source (opens in a new tab; the file is not redistributed)

Summary

BRANZ Study Report SR391 (Ade, 2018) is the deepest NZ primary behind the Neobiome Intelligence ④c building_standards high-performance capex premium — the Homestar cost study that OT_085 (SR385) and CR_017 both reproduce at one remove. It is a desktop quantity-surveying analysis of 10 Building-Code-compliant stand-alone and terraced residential designs drawn from the Hobsonville Point (Auckland) submarket, none of which had considered Homestar in their basic design. For each dwelling the study prices the additional capital cost required to move from Building Code minimum up to a 6, 7, 8, 9 and 10-Homestar rating, and does so separately under three versions of the Homestar rating tool (v2, v3 and v4), all in 2018 NZD. Its headline finding is that Homestar v4 has greatly reduced the capital cost of reaching each star level versus v2/v3 — a 6-Homestar dwelling costs only ~4% more than Building Code under v4. The benefit side is deliberately narrow: only readily-quantified energy and water operating savings are counted (payback periods), explicitly excluding health, comfort, resale value, quality and carbon. For NI it upgrades the high-performance capex cell from a figure cited via a BRANZ secondary (SR385/OT_085) to one cited at origin.

Key claims

- claim: "Homestar v2 — median additional capital cost over Building Code minimum (10 Hobsonville Point dwellings, 2018 NZD, most cost-effective option): 6-Homestar $18,043 / 7-Homestar $38,549 / 8-Homestar $63,102 / 9-Homestar $75,453 / 10-Homestar $101,705; equating on the QV costbuilder base rate of $1,975/m² to +5% / +12% / +19% / +24% / +28%. Per-dwelling 6-Homestar ranged $15,031–$55,738 (median $18,043); 7-Homestar $30,189–$112,237 (median $38,549)."
  source_location: "Table 17 (p31), Table 18 (p31), Table 19 (p31), Table 28 (p37)"
- claim: "Homestar v3 — median additional capital cost over Building Code minimum: 6-Homestar $18,813 / 7-Homestar $39,625 / 8-Homestar $65,901 / 9-Homestar $93,639 / 10-Homestar $110,279; on the $1,975/m² base rate this is +6% / +12% / +19% / +26% / +32%. Per-dwelling 6-Homestar ranged $14,033–$56,279; 10-Homestar $91,763–$130,249."
  source_location: "Table 23 (p34), Table 24 (p35), Table 25 (p35), Table 28 (p37)"
- claim: "Homestar v4 — median additional capital cost over Building Code minimum (most cost-effective option): 6-Homestar $11,677 (schedule method with points; whole-method range $8,590–$46,939) / 7-Homestar $13,896 (calculation method – option 1; other 7-star methods median $16,210–$37,726) / 8-Homestar $47,372 / 9-Homestar $67,365 / 10-Homestar $85,446. Homestar v4 greatly reduced the capital cost of achieving each star level versus v2/v3, with a 6-Homestar dwelling costing approximately 4% more to construct than a basic Building Code-compliant dwelling."
  source_location: "Table 26 (p35), Table 27 (p37), Table 28 (p37); Abstract (p ii)"
- claim: "Headline median premiums: a 6-Homestar rating costs a median additional 3–5% depending on rating-tool version; a 7-Homestar rating attracts an additional 12% under Homestar v2 and v3 but only 4% under Homestar v4."
  source_location: "Executive summary (p1); Conclusion §5 (p54)"
- claim: "Homestar certification (soft) costs range from $380 to $3,800 per dwelling: ~$3,800 for a single unique one-off design (a significant portion of total 6/7-Homestar cost), falling toward ~$380/dwelling when a single design is repeated across more than 10 dwellings. Repeating one design across 1/10/50/100 homes lowers the v4 6-Homestar premium from $11,521 (3%) to $7,642 (2%) / $7,292 (2%) / $7,249 (2%); the v2 6-Homestar premium from $18,351 (5%) to $13,682 (4%)."
  source_location: "Executive summary (p1); §3.2 (p13); Table 50 (p55)"
- claim: "Simple payback on the energy/water credits only (EHC + WAT), at the survey-median electricity rate of $0.28/kWh (no discounting or price escalation): Homestar v2/v3 — 6★ 11 yr (median capital $4,675, saving $459/yr) / 7★ 27 yr ($20,769, $863) / 8★ 16 yr ($36,053, $2,113) / 9–10★ 14 yr ($49,799, $3,080). Homestar v4 — 6★ 6 yr (median capital $2,834, saving $266/yr) / 7★ 7 yr ($4,057, $548) / 8★ 51 yr ($35,396, $809) / 9–10★ 20 yr ($53,630, $2,806). Benefits counted are energy + water operating savings only — health, comfort, resale/sales price, carbon and durability benefits are explicitly excluded."
  source_location: "Table 47 (p52), Table 48 (p53); Abstract (p ii)"
- claim: "Prior NZ Homestar cost studies (which SR391 finds under-estimate costs): eCubed Building Workshop (2013), for Auckland Council, theoretical additional cost 5/6/7-Homestar = $2,223 / $5,223 / $14,337. Jasmax (2013) Auckland ($550k, 3-bed/180 m²) 5/6/7-Homestar = $3,237.50 / $6,437.50 / $16,241.50 (+0.6% / +1.2% / +3%); Jasmax (2013) Christchurch (4-bed/190 m²) = $2,260 / $3,612.50 / $27,332.50 (+0.4% / +0.7% / +5%). SR391 attributes significantly higher 6 and 7-Homestar costs than these (e.g. 7-Homestar 12% vs Jasmax 7.7%)."
  source_location: "§1 Introduction (p3), Table 1 (p3), Table 2 (p3), Table 20 (p32)"

Source-internal table inconsistency (recorded, not resolved)

SR391 reports its median-cost summary twice, with slightly different values. The analysis-body tables (Table 17 v2 / Table 23 v3 / Table 26 v4 / Table 28 overall) are the ones BRANZ SR385 (OT_085) reproduced, and are treated here as canonical (they are the figures in the key_claims above). The Conclusion Table 49 gives marginally different numbers for the same cells — v2 6★ 18,009 (vs 18,043) … 10★ 101,671 (vs 101,705); v3 8★ 65,951 (vs 65,901); and v4 6★ 11,575 / 7★ 13,794 / 8★ 47,270 / 9★ 67,263 / **10★ 92,127 (vs Table 28's canonical 85,446 — a 6,681 discrepancy, the largest gap)**, with v4 %s 3% / 4% / 13% / 21% / 26%. The differences are small for v2/v3 (~30–100, rounding/line-item drift) but material for v4 10-Homestar. Cite the analysis-body figures; flag the v4 10★ 6,681 divergence to any downstream user.

Neobiome Intelligence relevance

This is the origin primary for the ④c building_standards high-performance capex premium (context: ni, feeds D04). Until now that cell was cited via the BRANZ secondary OT_085 (SR385), which reproduces this study’s Table 1; SR391 lets the number be cited at source.

• **Firms CR_017’s high_performance ~35,000/dwelling central.** The high-performance tier (Homestar 7–8) sits inside the Ade v4 8-Homestar median (47,372) and the v2/v3 7-Homestar band (38,549–39,625), all 2018 NZD — before the ~30% inflation adjustment CR_017 applies to 2024. The bracket CR_017 and OT_085 use (e-Cubed 8★ ~21k–34k + Ade v4 8★ $47,372) is confirmed at origin.
• Homestar-based → supports the high-performance tier, NOT the Passive House premium. Like SR385, SR391 is a Homestar cost study; it brackets the passive_house premium (60k) only indirectly via Homestar 9–10 (Ade v4: 67,365–$85,446). The Passive House premium stays on its PHINZ / Basham / Jason Quinn basis.
• The spread is real and version-driven. The same star rating costs very differently by Homestar version (v4 ≪ v3 for a given star — e.g. 10★ v4 85,446 vs v3 110,279), by compliance pathway (v4 7★ ranges 13,896–37,726 across methods), and by dwelling (6★ v2 15,031–55,738). The model central is a point in a genuinely broad band — the ±-band audit should reflect this, and should note that a 2018 Homestar version is now itself dated (Homestar 5.x/HomeFit have since superseded v4).
• Certification cost is design-repetition-sensitive. The 380–3,800/dwelling certification cost, and its fall as one design is repeated across many dwellings (Table 50), is directly relevant to a Neobiome community building many like dwellings from a shared design — a real cost lever the per-dwelling premium can be reduced by at community scale.
• Payback framing. Energy/water-only simple paybacks are long at 6–7-Homestar (v2/v3 11–27 yr; v4 6–7 yr on much smaller EHC/WAT-only capital), and the study is explicit that operating-savings payback omits the health, comfort, resale and carbon benefits that actually drive above-Code building — the same “benefits must be read in a wider context” caveat carried on D04 (OT_049, LIT_044).

Scope note: a single-submarket (Hobsonville Point, Auckland), single-year (2018 NZD), 10-dwelling desktop QS analysis — regionally and temporally narrow. It is the deepest cost primary available, but the model’s high-performance premium should remain a nationally-inflated central with a wide band, not this study’s point medians read literally.

Research targets

Documents to retrieve

• None new. SR391 is itself the deepest cost primary sought (it resolves RT_283). The upstream studies it cites — eCubed Building Workshop (2013) and Jasmax (2013) — are older, superseded NZ Homestar cost estimates that this study finds under-count costs; not worth retrieving as fresher primaries.

Research gaps

• None new. A current-vintage successor (post-2018 Homestar 5.x / v4 costing) would refresh the ④c high-performance capex, but that is a pre-existing temporal gap on the cell, not one this source raises.

Notes

Authoritative BRANZ Study Report SR391 (Ade, R. 2018, 128 pp, ISSN 1179-6197, © BRANZ 2018), downloaded PDF (not AI-prepared), read verbatim via pdftotext -layout — every cited figure traces to a numbered Table (17/18/19/20/23/24/25/26/27/28/47/48/49/50) or to the Executive Summary / Conclusion / Introduction. No retrieval-provenance block required (not AI-prepared).

⚠ data_quality set high, not verified — every figure traces to the raw, but the report carries two non-identical summary tables for the same median-cost cells (analysis-body Tables 17/23/26/28 vs Conclusion Table 49; see the warning callout above). verified would imply a single unambiguous confirmed value per cell, which the source does not provide. high (authoritative BRANZ primary, all figures traced, one internal inconsistency flagged) is the honest call, and matches the sibling OT_085.

⚠ RESOLVES RT_283 — this is the exact document RT_283 sought (“Ade (2018) — the case-study analysis … that SR385 Table 1 reproduces … cite the high-performance capex premium at origin rather than via OT_085”).

⚠ Confirms, does not contradict, OT_085. The v3 medians here (6★ 18,813 / 7★ 39,625 / 8★ 65,901 / 9★ 93,639 / 10★ 110,279) and v4 medians (6★ 11,677 / 8★ 47,372 / 9★ 67,365 / 10★ 85,446) match OT_085's reproduced Table 1 figures exactly — the primary confirms the secondary. Minor citation-precision note: SR385/OT_085 attributed Ade's figures to "pp.34–35"; in SR391 the cost-summary tables are actually at pp.31–37 (the analysis body), not pp.34–35 — a page-citation nuance, not a figure discrepancy. Also: SR391's own cited eCubed study is the **2013** eCubed report (2,223/5,223/14,337 for 5/6/7★), which is a different vintage from the 2018 e-Cubed CBA that SR385/OT_085 reproduce — both are “eCubed Building Workshop” but different studies; no conflict, just distinct vintages.

Connections

Links to

Sources (4): CR_017 · LIT_044 · OT_049 · OT_085

EDT domains (1): D04: Sustainable Habitat & Building Technology

Referenced by

EDT domains (1): D04: Sustainable Habitat & Building Technology

Sources (1): OT_085