OT_123: Guerrero & Lockyer (2025) — Physical Characteristics of New Houses 2023 (BRANZ Study Report SR501)

OT_123: Guerrero & Lockyer (2025) — Physical Characteristics of New Houses 2023 (BRANZ Study Report SR501)

Source

https://www.branz.co.nz/pubs/research-reports/sr501/ — original source (opens in a new tab; the file is not redistributed)

Guerrero & Lockyer (2025) — Physical Characteristics of New Houses 2023 (BRANZ Study Report SR501)

BRANZ New Dwellings Survey (13th annual report) — the NZ floor-area / storey-mix primary behind the NI roof_per_dwelling_m2 derivation. New houses (single detached units only): 2023 average floor area 181.4 m² (survey, weighted) / 187.8 m² (consent, Stats NZ), and 14% of new housing was multi-storey (2 or more storeys) in 2023 (→ ~86% single storey). Verifies the two SR501-attributed figures CR_018 used ("survey 181 m², consent 188 m²").

Also carries the national material market shares for new houses in 2023: steel roofing 71.6%, weatherboard wall cladding 38% (down from 44%), timber wall framing 83% (down from 91%), concrete flooring 77.7%, solid-timber floor joists 66.8%, fibreglass wall/ceiling insulation ~95–96%. Read verbatim via pdftotext -layout → data_quality: verified. ⚠ SR501 is houses-only (single detached) so its floor area reads ~181–188 m² — it does not support the ~142 m² lower bound in the RT_206 note (that is an all-dwelling-types / Stats-NZ-median figure from other sources cited in CR_018, not from SR501).

Summary

BRANZ Study Report SR501 is the 13th annual output of the BRANZ New Dwellings Survey, a postal survey (running since 1998) of the builders/designers named on building consents across 31 territorial authorities, weighted by each TA’s share of building activity to give national market shares. It surveys ~5,000 new residential buildings per year and receives generally >1,200 returns; the results reported are for new houses only (single detached units). The report tracks the generic materials and design characteristics of new NZ houses — roof cladding, wall cladding, wall framing, number of storeys, flooring, floor joists, and insulation — with time series to 2023 in Appendix B. For the NI roof-pool constant, the load-bearing outputs are Table 10 (2023 average floor area: survey-weighted 181.4 m², Stats NZ consent 187.8 m²) and the Flooring section’s national storey split (multi-storey = 14% of new housing in 2023). It is the verified primary document behind the CR_018 roof_per_dwelling_m2 floor-area basis (RT_206) and it partially advances RT_304 (the roof-area-budget gap) by firming the floor-area and storey inputs, though it does not give per-building-form catchment areas or the three interim roof factors RT_304 also needs.

Key claims

- claim: "The BRANZ New Dwellings Survey (running since 1998) surveys ~5,000 new residential buildings per year by postal survey to the builder/designer named on the building consent, across 31 territorial authorities, and generally receives over 1,200 returns each year. Responses are weighted by each territorial authority's share of building activity (as indicated by building consents) to calculate the national market share. The results presented are only for new houses (i.e., single detached units). SR501 is the 13th annual report of the series."
  source_location: "Preface, p.i; §1 Introduction, p.1–2"
- claim: "Average floor area (m²) for new housing, 2023 (Table 10): survey responses (weighted for regional building activity) = 181.4 m²; Stats NZ consent data = 187.8 m². The 2023 survey sample average floor area is much lower than the consent average; over the 2006–2023 series the survey average has fallen from ~221 m² (2006) to 181.4 m² (2023) and the consent average from ~215 m² (2006) to 187.8 m² (2023)."
  source_location: "Table 10, p.15 (2023: 181.4 / 187.8); Figure 1 + §1, p.2 (sample lower than consent; 2006–2023 trend)"
- claim: "Multi-storey buildings (2 or more storeys) made up 14% of new housing in 2023. The greatest proportion of new houses built with 2 or more storeys were generally reported in areas with higher land prices such as Central Auckland and Wellington (reflecting that higher land prices encourage greater intensity of development); steeper terrain (e.g. Wellington) may also encourage multi-storey development. The number-of-storeys analysis was restricted to the 29 territorial authorities with four or more survey responses."
  source_location: "§3 Flooring, p.6 (14% multi-storey 2023); §3 Number of storeys + Figure 5, p.6 (land-price/terrain pattern; 29-TA restriction)"
- claim: "Roof claddings market share, new housing 2023 (Table 1): sheet metal 71.6% (the predominant material); tiles, metal and concrete, 27.9% (increased in 2023); other — membrane, plastic, etc. — 0.4% (decreased in 2023, mostly shingle and membrane products)."
  source_location: "§3 Roof claddings, p.4; Table 1, p.14 (2023 column)"
- claim: "Wall claddings market share, new housing 2023 (Table 2): finish bricks (clay & concrete) 30% (increased slightly); weatherboard profiles (timber, fibre-cement, PVC) 38% (down from 44% in 2022) — timber makes up just under half of surveyed weatherboard, the remainder fibre-cement and uPVC; other (aerated concrete/AAC, FC sheet, plywood, EIFS, stucco, sheet steel, etc.) 32%."
  source_location: "§3 Wall claddings, p.4–5; Table 2, p.14 (2023 column)"
- claim: "Wall framing, new housing 2023: timber framing (framing + solid timber) remains the predominant structural material, with a historical market share of around 90%; it decreased to 83% in 2023 from 91% the year prior. LVL made up only 2% of timber framing. The majority (91%) of wall framing is precut or prenailed (a slight decrease from the year prior). ⚠ Table 3, though labelled 'Wall framing market share', reproduces the Table 2 wall-cladding figures verbatim (a report error) — the framing figures are the §3 prose + Figure 4, not Table 3."
  source_location: "§3 Wall framing + Figure 4, p.5 (83% / 91% prior / LVL 2% / 91% precut); Table 3, p.14 (mislabelled — duplicates Table 2)"
- claim: "Flooring types market share, new housing 2023 (Table 4): concrete 77.7% (the prose rounds to 78%, up significantly from 64% in 2022); all other flooring (mostly particleboard and strand board) 22.3% (prose 22%, down from 36% in 2022). The percentages include upper floors (usually wood-based) so are affected by the shift to multi-storey buildings."
  source_location: "§3 Flooring, p.6; Table 4, p.14 (2023 column)"
- claim: "Floor joists market share, new housing 2023 (Table 5): solid timber 66.8% (prose ~67%, down from 70% in 2022); other (proprietary wood/steel composite joists and heavy-gauge steel joists) 33.2% (increased slightly)."
  source_location: "§3 Floor joists, p.7; Table 5, p.14 (2023 column)"
- claim: "Insulation market shares, new housing 2023: wall insulation — fibreglass 94.9% (prose 95%, unchanged), other (mainly polyester) 5.1% (Table 6); ceiling insulation — fibreglass 96.1% (prose 96%), other (mainly polyester) 3.9% (Table 7). Builders commonly use the same material/brand for wall and ceiling cavities, so the two move together."
  source_location: "§3.7.1 Wall insulation + Table 6, p.8/15; §3.7.2 Ceiling insulation + Table 7, p.8/15 (2023 columns)"
- claim: "Concrete-slab floor insulation, new housing 2023 (Table 8): underslab full/partial insulation 57.7% (the most common form for concrete slabs); perimeter edge 3.5%; under footing 0.0%; total insulated 61.2%. Timber floor insulation, 2023 (Table 9): polystyrene 86.3% (the dominant material), fibreglass & polyester 13.7%, foil 0.0% (foil was banned in 2016 and has been non-existent as a timber-floor insulator since 2018). Timber subfloors are much less common than concrete slabs in new housing, so the timber-floor shares are susceptible to large year-to-year swings."
  source_location: "§3.7.3 Floor insulation, p.9; Table 8, p.15 (concrete slab 2023); Table 9, p.15 (timber floor 2023)"
- claim: "The territorial-authority sample sizes for the 2023 number-of-storeys analysis (responses in brackets, Figure 5) show the survey is thin in many TAs — e.g. Waimakariri 74, Tasman 71, Christchurch 63, New Plymouth 56, Queenstown 42, Marlborough 35, Waikato 37, Waipa 33 at the high end, but Manukau 1, North Shore 1, Gisborne 2, Rotorua 2, Hutt 3, Kapiti 3, Waitakere 3 at the low end. A limitation of the survey is that it does not ask why materials are selected, and it is subject to sampling noise that can cause short-term fluctuations at variance to long-term trends."
  source_location: "Figure 5, p.6 (response counts); §1 Introduction, p.2 (limitation / sampling noise)"

Neobiome Intelligence relevance

This is the NZ primary document RT_206 was raised to retrieve — the floor-area / storey-mix source that sits behind the NI roof_per_dwelling_m2 derivation, previously held only through the AI-compiled synthesis CR_018. Its value to NI is three-fold.

• Verifies the roof-pool floor-area basis (D01 roof-mount + D03 roof-catchment). CR_018 attributes to SR501 “survey 181 m², consent 188 m²”; the raw confirms this exactly — Table 10, 2023: survey-weighted 181.4 m² / Stats NZ consent 187.8 m². The roof param roof_per_dwelling_m2 (170 default) is derived from this floor area (CR_018 applies ~1.12 eave factor to a ~155 m² figure); SR501 firms the primary behind that derivation, so the roof constant’s provenance can be upgraded from “CR_018 (compiled, medium)” to “CR_018 + SR501 (verified BRANZ primary for the floor-area/storey basis)”. The roof footprint drives both the roof-PV mount area (D01, roof_mount_per_dwelling_m2) and the rainwater-catchment area (D03, roof_catchment_per_dwelling_m2) — the load-bearing catchment side of the Earthsong water-SSI validation.
• Firms the multi-storey fraction — the storey-to-footprint correction (D01/D03). SR501 gives 14% multi-storey / ~86% single-storey (2023) nationally. This is the correction that separates floor area from roof footprint: for single-storey houses roof footprint ≈ floor area, but for the 14% multi-storey stock the ground-floor footprint (and hence roof catchment) is smaller than the total floor area. The report also documents the storey-intensification driver (higher land prices / steeper terrain → more multi-storey), consistent with the compact-form Earthsong caveat that pushed the roof-catchment split (~110 m² compact vs 170 default → water SSI −0.18).
• National new-house material market shares (adjacent D04 building evidence). Steel roofing 71.6%, timber wall framing 83%, concrete flooring 77.7%, fibreglass wall/ceiling insulation ~95–96%, polystyrene timber-floor insulation 86.3% — a verified snapshot of what NZ new houses are actually built from. This is directly relevant to the sustainable-habitat/building domain (D04) materials and embodied-carbon discussion (cf. OT_045, CR_049).

⚠ Scope caveat (do NOT over-read the floor area): SR501 measures new houses = single detached units only. Its 181–188 m² sits at the upper end of the RT_206 note’s “~142–188 m²” range; the ~142 m² lower bound is an all-dwelling-types / Stats-NZ-median figure (CR_018 cites Canstar 2024 ~142–156 m² and Stats NZ median 126 m²), not from SR501. Townhouses/apartments — increasingly a large share of new consents — are excluded here, so SR501 is the right basis for a detached-house roof constant but understates the roof-pool shrinkage if a community’s built form is medium-density.

Research targets

Resolved

• RT_206 (RESOLVED → this page): BRANZ SR501 Physical Characteristics of New Houses 2023 retrieved, read verbatim and ingested. It is the specific doc target (retrieve-and-ingest) and the document is now held. Scope of resolution: it delivers the 2023 new-house floor area (survey 181.4 m² / consent 187.8 m²) and the national storey split (14% multi-storey), verifying the two SR501-attributed figures in CR_018. It does not itself give a roof-catchment area (that is a floor→footprint derivation) nor per-building-form catchment areas — so it firms the inputs to the roof constant, not the constant directly.

Research gaps

• RT_304 (ADVANCED, remains open): the roof-area-budget gap references SR501 for “per-building-form catchment areas”. SR501 advances it — it firms the national average floor area (181.4/187.8 m²) and the national storey split (14% multi-storey) — but does not break floor area out by storey count/building form, and does not touch the three interim roof factors RT_304 centres on (roof_usable_frac 0.40, pv_m2_per_kwp 6.0, pv_ground_kwp_per_ha 150). Keep RT_304 open; annotate that its floor-area/storey inputs are now firmed by SR501 while the form-specific catchment areas and the PV roof factors remain unresolved. The medium-density (townhouse/apartment) all-forms floor-area series is folded into RT_304’s “per-building-form catchment areas” ask.

Notes

Primary source: BRANZ Study Report SR501, Physical characteristics of new houses 2023, Guerrero, N. & Lockyer, O. (2025), BRANZ Ltd (© BRANZ 2025, ISSN 1179-6197, 20 pp). The 13th annual report of the BRANZ New Dwellings Survey. Read verbatim via pdftotext -layout → data_quality: verified; every quantitative claim is traceable to a named Table/Figure/section (Appendix B carries the full 2006/2010–2023 time series behind the charts). context: ni — the calibration value is the floor-area + storey data behind the roof constant.

⚠ Data vintage vs publication year: the report is dated 2025 (year: 2025, per its own Reference and © line) but reports the 2023 data set. Cite figures as 2023-vintage. The Appendix B tables also carry the 2006/2010–2022 history for trend context.

⚠ Report table error (Table 3): Table 3 is labelled “Wall framing market share” but its cell contents are an exact duplicate of the Table 2 wall-cladding data (finish bricks / weatherboard / other). The genuine wall-framing figures (timber 83% in 2023, down from 91%; LVL 2% of timber framing; 91% precut/prenailed) come from the §3 “Wall framing” prose and Figure 4. Do not read Table 3 as framing data.

⚠ Houses-only scope (repeated — the most likely mis-use): “new houses” = single detached units. The 181–188 m² floor area and all material shares exclude townhouses/apartments. SR501 does not support the ~142 m² figure in the RT_206 note; that came from all-dwelling-types / median sources in CR_018 (Canstar, Stats NZ median), not SR501.

Corpus fit: joins the BRANZ evidence cluster (all ot_): OT_036, OT_037, OT_042, OT_057, OT_105 — and is the verified BRANZ primary that backfills the floor-area/storey basis of CR_018’s roof-per-dwelling constant.

Connections

Links to

Sources (8): CR_018 · CR_049 · OT_036 · OT_037 · OT_042 · OT_045 · OT_057 · OT_105

Referenced by

Sources (2): OT_130 · OT_144

EDT domains (2): D01: Renewable Energy & Storage Systems · D03: Water, Waste & Circular Systems