OT_134: BRANZ Bulletin 682 (2023) — Specifying Glazing (glazing types, low-E / solar-control, overheating & SHGC)

OT_134: BRANZ Bulletin 682 (2023) — Specifying Glazing (glazing types, low-E / solar-control, overheating & SHGC)

Source

https://www.branz.co.nz/pubs/bulletins/bu682/ — original source (opens in a new tab; the file is not redistributed)

BRANZ Bulletin 682 (2023) — Specifying Glazing

The glazing / window-element companion to the H1 5th-edition thermal-envelope family already in the corpus ( OT_043 element schedule, OT_044 calculation method, OT_057 the guide, plus the roofs/floors siblings). A qualitative overview of glazing types (clear/low-iron float, safety, low-E / solar-control, tinted, reflective, sound-reducing, security, acrylic/polycarbonate) and their specification — it deliberately does not carry the H1 glazing R-values (those live in Bulletin 670, now held as OT_131) nor IGU construction detail (Bulletin 680, not yet ingested). Its NI-load-bearing content is the overheating caution (higher-R + large glazing + airtightness → overheating; solar radiation through glazing is currently unregulated), the four Low-E tiers (Low-E1–Low-E4 in H1 Appendix E), the SHGC concept, and the supply-chain fact that float glass is not made in NZ and is all imported. No cost/currency data. Read verbatim (pdftotext -layout) → data_quality: verified. ⚠ The raw filename (Bulletin682_Selecting_glazing_WnbzJUF.pdf) says "Selecting"; the bulletin title is "Specifying glazing".

Summary

BRANZ Bulletin 682 “Specifying glazing” (Issue 682, March 2023) is a practical overview of the glazing types available in New Zealand and how to specify them, written against a backdrop of “changing government regulations and the development of new technology” — chiefly the H1 5th-edition Building Code requirements that have pushed most new windows, doors and skylights from a single sheet of “glass” to a multi-sheet “glazing” system (an IGU, often with low-E coatings). It is deliberately scoped: it does not detail IGU construction or the R-values glazing must achieve to comply with clause H1 (those are Bulletin 680 and Bulletin 670 — the latter now held as OT_131), and it carries no cost data. What it does carry, and why it matters to Neobiome Intelligence, is (a) the overheating message — BRANZ research finds many new NZ houses at risk of overheating, the higher H1 thermal performance is likely to contribute to that risk, and solar-radiation heat gain through glazing is currently unregulated (expected in a future Code update); (b) the semi-quantitative glazing performance handles — the four Low-E1–Low-E4 tiers in H1/AS1 Appendix E, the solar heat gain coefficient (SHGC, 0–1) which is independent of R-value, and the G7 natural-light cut-off (visible light transmittance < 70% cannot use G7/AS1); and (c) a self-sufficiency-relevant supply fact — float glass is not manufactured in New Zealand and is all imported (closest manufacturer in Australia). It sits in the D04 H1 thermal-envelope cluster as the glazing-element context alongside OT_043 / OT_044 / OT_057, refining the window/glazing understanding without adding a new baseline R-number.

Key claims

- claim: "The bulletin gives an overview of the different types of glazing available today and provides guidance around specification, as changes in technology and government regulations — especially the requirements in the compliance documents for NZ Building Code clause H1 — are substantially transforming the glazing in new windows, doors and skylights. What sits inside the frames of most new windows, doors and skylights today is two or three sheets of glass (an IGU, insulating glass unit) that can incorporate low-E coatings — so the part we look through is less likely to be a single material ('glass') and more likely a system ('glazing'). The bulletin does NOT go into detail about the construction of IGUs nor the R-values that glazing must achieve to comply with clause H1 — for those, see Bulletin 680 (Insulating glass units) and Bulletin 670 (Specifying windows and doors under H1)."
  source_location: "§1.0.1–1.0.5 (p.1)"
- claim: "Flat window glass is called 'float glass'. Silica sand (the main ingredient) is mixed with lime and soda and heated to approximately 1,500°C, typically using natural gas; the molten glass floats over a bed of molten tin (at 1,000°C) and is cooled in a controlled manner to form a continuous sheet. Float glass is normally manufactured in thicknesses of 2–25 mm. Recycled glass ('cullet') can be added, reducing the energy required in the process. Glass for construction can be grouped as: clear float; low-iron (extra-clear) float; body-tinted float; coated (reflective and/or low-E) float; patterned; obscure (privacy); and bent/curved glass."
  source_location: "§2.0.1–2.0.2 (p.1)"
- claim: "Float glass is not currently manufactured in New Zealand and is all imported — the closest manufacturer is in Australia. Glass is processed in New Zealand to meet specific performance requirements (cutting, drilling, edge working, laminating, toughening and heat strengthening, IGU manufacture, ceramic-screen/digital printing, colour and mirror coating, surface etching)."
  source_location: "§2.0.2, §2.0.4 (p.1)"
- claim: "The production of glass requires high furnace temperatures and so uses considerable energy. In November 2021, Nature magazine reported that worldwide glass manufacturing produces at least 86 million tonnes of carbon dioxide every year, but that glass 'could be the star of a net-zero carbon economy' because it can theoretically be recycled infinitely without losing its properties and recycling produces far less carbon dioxide than new manufacture. There are technical/logistical barriers — only clean, clear recycled float glass can go back into float-glass production — and a lot of building glass currently ends up in landfill."
  source_location: "§2.1.1 (p.2)"
- claim: "In New Zealand a considerable portion of window glass from processors and window manufacturers is recycled by 5R Solutions (regional facilities feeding two processing centres), and the processed glass is used to manufacture glass wool insulation. The BRANZ carbon tool CO2NSTRUCT gives embodied carbon and embodied energy data for clear float glass based on an environmental product declaration (EPD) from an Asian manufacturer."
  source_location: "§2.1.2–2.1.3 (p.2)"
- claim: "Clear float glass offers high clarity and low distortion and is the most widely used type of glass in construction, typically available in thicknesses of 2–19 mm; its visible light transmission is around 80–90%, but this falls with glass thickness. Standard float glass commonly has a slight green tint from iron in the sand; low-iron (extra-clear) float glass has almost none, typically achieves the highest visible light transmission (over 90% is possible, remaining almost constant with thickness) and is available in thicknesses of around 4–19 mm."
  source_location: "§3.1.1–3.1.2 (pp.2–3)"
- claim: "Safety glass must be tested and comply with AS/NZS 2208:1996, BS EN 12150-2:2004, BS EN 14449:2005 or ANSI Z97.1-2015. In NZ the widely available safety glass falls into two categories: toughened glass (breaks into small cube-like pieces; made by heating float glass to around 620–650°C then cooling it very quickly; available around 4–20 mm; cannot be recut once toughened; should not be used where fire resistance is required; a post-toughening 'heat soaking' process greatly reduces the rare risk of spontaneous shatter) and laminated safety glass (a vinyl interlayer between two sheets holds the glass together if broken; available around 6–20 mm). NZS 4223.3:2016 specifies minimum requirements for glass in locations where people are at risk of injury and provides a means of compliance with Building Code clauses B1, F2 and F4 — requiring safety glass in, among others, bathrooms/ensuites/spa rooms within 2 m of the floor, glazing near swimming/spa pools, and doors (with a few exceptions)."
  source_location: "§3.2.1–3.2.5 (pp.3–4)"
- claim: "Low-E (low-emissivity) glazing has a microscopically thin transparent metal coating that lets light through both directions but reflects long-wave infrared radiation and heat back, keeping a house warmer in winter or cooler in summer. H1/AS1 and H1/VM1 5th edition amendment 1 include FOUR levels of low-E glazing in the generic windows in Appendix E — Low-E1 to Low-E4 — the numbers indicating thermal performance from basic to very high. Low-E coatings are applied as a durable hard-coat (while the glass is molten) or a more vulnerable but more heat-reflective soft-coat (after manufacture). All solar-control glass reduces the light entering a building, so a disadvantage is that in winter it reduces the solar gain available to heat the interior; solar-control films may reduce heat gain by up to 80%."
  source_location: "§3.3.1–3.3.4 (p.4)"
- claim: "Any glazing with visible light transmittance of less than 70% cannot use the G7/AS1 (Natural light) compliance pathway and will need to use G7/AS2 or an alternative method — so designers/specifiers must watch the light-transmission impact of added films, coatings and tints. Tinted glass is most commonly made with metal oxides (grey the most common NZ tint); the most commonly used tint, 5 mm grey, has a visible light transmission of 49% compared to clear glass at 80%."
  source_location: "§3.3.5, §3.4.1–3.4.2 (p.4)"
- claim: "For a number of years BRANZ research has identified that many new houses are at risk of overheating — large areas of glazing (for views and indoor-outdoor living) together with greater airtightness in construction have contributed to this — and it is likely that the enhanced thermal performance required of new buildings under the H1 compliance documents will contribute to the overheating risk. The increase in R-values for insulation addresses conductive heat flow, but there is currently NO regulation around radiation of heat through glazing into homes from the sun (this is likely to be addressed in future Building Code document updates)."
  source_location: "§4.0.2–4.0.3 (p.5)"
- claim: "The amount of heat that can pass through glazing by radiation is measured by the solar heat gain coefficient (SHGC), a figure from 0–1 where 1 is 100% heat flow through the glazing. The SHGC is independent of the R-value of glazing — two windows with the same construction R-value can have different SHGC figures — so where overheating is a risk, designers should consider the most appropriate SHGC (generic-glazing SHGC figures are given in Table 2 of Bulletin 670). Beyond glazing choice, designing appropriate shade devices (especially eaves on the north side, and control of late-afternoon west sun) and ventilation paths is a key part of preventing overheating."
  source_location: "§4.0.4–4.0.5 (p.5)"
- claim: "Thermal-stress failure: clear float glass very rarely cracks from thermal stress because it absorbs little heat and pane temperature differences are usually less than 40°C; but solar-control glass that absorbs more than 60% of visible solar energy (an SHGC of less than 0.4) is likely to have temperature gradients greater than 40°C and, if used in high sun-exposure situations, should be toughened or heat-treated to resist thermal-stress cracking. As glazing alternatives to float glass, acrylic sheet weighs less than glass but has much greater impact strength and similar or greater visible light transmission (90% or more), and polycarbonate has greater structural strength and impact resistance than both glass and acrylic (used where security is a priority)."
  source_location: "§6.0.1–6.0.3, §7.0.1 (pp.5–6)"

Neobiome Intelligence relevance

This is the glazing / window-element companion to the model’s ④c building_standard H1 baseline (context: ni, feeds D04). Unlike the roof/floor siblings it carries no new R-value — it explicitly defers the H1 glazing R-values to Bulletin 670 — so its value is qualitative design-context and three specific hooks.

• Overheating is the load-bearing NI signal — the passive-solar glazing lever has a downside R-value cannot see. BRANZ research finds many new NZ houses at risk of overheating, and the higher H1 thermal performance is likely to contribute: R-value increases address conductive heat flow, but solar-radiation gain through glazing is currently unregulated. This qualifies the model’s high-performance / passive-solar glazing path (the calculation-method glazing trade-off in OT_044 / OT_057 and the passive-solar thermal-mass design in LIT_018): a bigger glazing area for winter solar gain buys a summer-overheating risk that the H1 R-value envelope does not capture. The controlling metric is the SHGC (0–1), which is independent of R-value — so a Neobiome high-performance build must specify both a window R-value (warmth) and an SHGC (overheating control), not R-value alone, and pair the glazing with north-eave shading and ventilation.
• The four Low-E tiers frame the above-baseline window leg. H1/AS1 Appendix E defines Low-E1 → Low-E4 generic-window levels (basic to very high thermal performance) — the graded steps by which a build lifts the window/glazing leg of the envelope above the standard baseline (window R0.46+, per OT_043 / OT_057) toward the high_performance / passive_house tiers (CR_017). This page names the tiers; the actual per-tier R-values and SHGCs live in Bulletin 670 — now held in the corpus as OT_131.
• Supply-chain / self-sufficiency fact — glazing is an unavoidably imported element. Float glass is not manufactured in New Zealand and is all imported (closest manufacturer in Australia). For a remote / off-grid self-sufficient community this is a genuine resilience constraint (D04 → I06 resistance to external shocks): unlike timber framing, earth walls or NZ-made insulation, the transparent envelope depends on an offshore supply chain, so glazing quantity is a point of external dependence in an otherwise locally-sourceable build. NZ processing (cutting, toughening, IGU manufacture, and recycling by 5R Solutions into glass-wool insulation) is domestic, but the base float glass is not.
• Materials-footprint / circularity context (I09), no NZ number. Worldwide glass manufacturing emits at least 86 Mt CO₂/yr (Nature, 2021); glass is theoretically infinitely recyclable, and NZ window-glass offcuts are recycled by 5R Solutions into glass-wool insulation — a closed-loop materials note that complements the embodied-carbon strand on D04 (OT_045, CR_049, OT_047). BRANZ CO2NSTRUCT holds an EPD-based embodied-carbon figure for clear float glass, but this bulletin does not reproduce it — so it is context, not a data cell.
• Scope note — no cost/currency data, no glazing R-values. An envelope specification overview: it firms the qualitative glazing understanding and the overheating caution, not a price or a baseline R-number. Glazing R-values and generic SHGCs are in Bulletin 670 (OT_131); IGU construction is in Bulletin 680 (RT below); glazing/window CapEx stays a corpus gap.

Research targets

Documents to retrieve

• ✅ BRANZ Bulletin 670 “Specifying windows and doors under H1” — the window/door leg authority this bulletin repeatedly defers to (the H1 glazing R-values, the generic-glazing SHGC figures (Table 2), and the Low-E1–Low-E4 generic-window performance data) — is already held as OT_131. It completes the window leg of the ④c standard baseline exactly as the roofs (Bulletin 677 / OT_133) and floors (Bulletin 672 / OT_132) siblings complete theirs.
• RT_375 (doc, low) — BRANZ Bulletin 680 “Insulating glass units” — IGU construction detail (gas fills, spacers, edge seals, U-values), the IGU counterpart this bulletin excludes. Lower NI priority (construction detail, not baseline numbers). → D04.

Research gaps

• The window/glazing leg of the ④c building_standard baseline (per-zone window R-values + SHGC by Low-E tier) is not yet held as a dedicated authority — it exists only as the summary R0.46+ on OT_043 / OT_057. This is now held by OT_131 (Bulletin 670 — the by-zone window/door R-values + Table 2 SHGCs), so it is no longer an open gap.
• The overheating / summer-cooling load is a standing model gap: H1 (and this bulletin) regulate winter heat loss but not summer solar gain, and NI’s heat-demand model is winter-space-heat-centric. Not re-opened here — flagged as a design boundary the SHGC data (via OT_131 / Bulletin 670) would begin to quantify.

Notes

• Primary BRANZ technical bulletin (Issue 682, March 2023, ISSN 2537-7310, © BRANZ 2023, 7 pp), downloaded PDF (not AI-prepared), read verbatim via pdftotext -layout — every figure (temperatures, thicknesses, VLT %, SHGC range, 86 Mt CO₂, standards references) traces to a numbered paragraph → data_quality: verified. No retrieval-provenance block required (not AI-prepared). BRANZ documents are classified ot_ (cf. OT_043 / OT_044 / OT_057 / OT_102).
• Filename discrepancy flagged: the raw is Bulletin682_Selecting_glazing_WnbzJUF.pdf (“Selecting”); the bulletin’s own title is “Specifying glazing”. The slug/page use the correct “specifying” form. Recorded so the mis-named raw does not cause a later mis-file. (Companion titles in the same family use “Specifying”: Bulletin 670 windows/doors, 672 floors, 677 roofs.)
• Siblings in corpus: OT_043 (Bulletin 676 — H1 overview + element schedule), OT_044 (Bulletin 678 — calculation method), OT_057 (House Insulation Guide 6th ed), plus the roofs (Bulletin 677 / OT_133) and floors (Bulletin 672 / OT_132) siblings. Bulletin 670 (windows/doors) is now held as OT_131, completing the window leg; Bulletin 680 (IGUs) remains referenced but not yet ingested (RT_375 above).
• No cost/currency content — envelope specification only; adds no NZD cost or new baseline R-value. Its NI-load-bearing content is the overheating caution + SHGC concept + the four Low-E tiers + the “float glass is all imported” supply fact.

Connections

Links to

Sources (11): CR_017 · CR_049 · LIT_018 · OT_043 · OT_044 · OT_045 · OT_047 · OT_057 · OT_131 · OT_132 · OT_133

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

Referenced by

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