Timber windows: selection, installation, and maintenance
Timber window selection, species durability, AS 2047 compliance, NCC 2022 energy rules, installation in timber framing, and maintenance regime for Australian builders.
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Timber windows cost $1,200 to $2,500 per standard window supplied and installed (2026, ex-GST), roughly double the entry-level aluminium equivalent. That premium buys natural thermal performance, heritage character, and a product that can be repainted indefinitely, but it costs you in maintenance: a repainting or restaining cycle every 3 to 7 years depending on exposure and species. The compliance path is identical to aluminium: every timber window must be tested and rated to AS 2047:2014 for the site’s wind classification, and installation follows ABCB Housing Provisions Part 8.2. The species choice is the decision that drives long-term performance: western red cedar (DC2 above-ground per AS 5604:2022) is stable, readily finishable, and the premium market option; meranti (DC3 above-ground) is the workhorse budget hardwood. The most common site failure with timber windows is the one shared with every other frame material: installing a product rated for a lower wind class than the site, or skipping the 10 mm clearance above the head that keeps structural loads off the frame.
When you do this
Timber windows are ordered and installed in the same build sequence as any other window product. On a typical Class 1 timber-framed house:
- Frame erected and inspected
- Structural drawings confirmed with wind classification and lintel schedule
- Window orders placed with manufacturer (lead times of 6 to 12 weeks for custom-made timber windows)
- Windows installed after frame inspection, before external cladding commences
- Flashing and weatherproofing completed as part of the cladding sequence
- Internal trims (reveals, stools, sashes) fitted at second-fix stage
Long lead times on custom-made timber windows are the main scheduling risk. Meranti and cedar windows made to order by Australian joinery manufacturers (Stegbar Timberaul, Trend, Cedar West) are not off-the-shelf products. Order early: if you discover the wind-class rating on the windows is wrong after they arrive, the remediation options are limited to return, replacement, or a structural alternative.
Who’s involved
| Role | Responsibility |
|---|---|
| Builder (principal contractor) | Hold point sign-off, confirm wind classification matches windows ordered, coordinate sequence with cladding subcontractor |
| Chippy | Frame window opening to correct size and squareness, install lintel per AS 1684.2:2021, fix window unit into frame |
| Window manufacturer / supplier | Supply windows rated to the correct AS 2047 wind class; provide the performance label |
| Glazier | Where glazing is separate from the frame supply (uncommon in pre-glazed timber units), install glass per AS 1288 |
| Structural engineer | Set wind classification on drawings; specify lintel sizes for openings exceeding AS 1684.2 span tables |
Species selection
The two dominant species in the Australian custom timber window market are western red cedar and meranti. Engineered alternatives (LVL-cored, Accoya) are also available for performance applications.
Western red cedar
Western red cedar (Thuja plicata) is the premium joinery timber for Australian residential windows. Under AS 5604:2022 it rates DC2 above-ground (high durability, 15 to 40 years heartwood service life without treatment). Key properties for window manufacture:
- Low density (around 370 kg/m3) keeps unit weights manageable in large sashes
- Fine, straight grain accepts paint, oil, and clear finishes equally well
- Natural oils provide inherent resistance to moisture absorption and decay
- Dimensionally stable: lower movement on moisture cycling than most softwoods
Western red cedar does not require preservative treatment for above-ground window joinery, but factory-applied primer and site-applied finish coats are essential to protect the exposed sapwood (which has lower natural durability than the heartwood).
Source: Mortlock Timber, Timber Durability Classes Explained (verified 2026-05-10); Stegbar, Timberaul timber windows range (verified 2026-05-10).
Meranti
Meranti is the name applied to a large group of related South-East Asian dipterocarp species, most commonly dark red meranti (Shorea spp.) in Australian window manufacture. Under AS 5604:2022, dark red meranti rates DC3 above-ground (moderate durability, 7 to 15 years heartwood service life without treatment) (verified 2026-05-10, Standards Australia AS 5604:2022).
Because meranti includes multiple species with varying durability, AS 5604 requires that where the particular species cannot be confirmed, the lowest rating for the genus should be applied. For manufactured windows, the major suppliers (Stegbar, Trend) specify the meranti grade and source used in their products.
Meranti accepts paint readily and provides good dimensional stability. It is more susceptible to fungal staining than cedar if surface coatings are allowed to fail, so the maintenance interval is shorter in coastal or high-humidity applications.
Treated pine and other softwoods
Finger-jointed or solid radiata pine is sometimes used for budget timber window frames, particularly in Victoria and SA. Radiata pine has no natural durability for exposed applications: for above-ground window joinery it must be preservative-treated to H3A under AS/NZS 1604.3 (light organic solvent preservative, above-ground, exposed, predominantly vertical with regular paint maintenance) (verified 2026-05-10, AT Pine, Treated Pine Timber Guide). H3A-treated pine provides fungal and insect protection suitable for window joinery provided the paint maintenance regime is maintained.
Engineered timber (LVL-cored, Accoya)
Some manufacturers offer LVL-cored frames (engineered laminated veneer lumber) or Accoya-modified radiata pine. LVL core increases dimensional stability and allows larger-section profiles without the risk of twist or bow associated with solid timber in wide openings. Accoya is acetylated (chemically modified) pine rated for external above-ground use with extended maintenance intervals. These are premium products and appropriate for large openings or demanding exposures.
AS 2047 compliance: same rules, different frame material
AS 2047:2014 (Amd 2:2017) covers all framed external windows regardless of frame material: aluminium, timber, uPVC, or composite. The standard’s structural and weatherproofing tests (wind deflection, ultimate strength, water penetration resistance, air infiltration, operating force) apply equally to timber-framed products.
Timber window manufacturers who supply products rated under AS 2047 are typically members of AGWA (Australian Glass and Window Association) and test their designs in NATA-accredited laboratories. Each product line carries a permanent performance label showing the wind class rating (N1 to N6 for non-cyclonic, C1 to C4 for cyclonic regions per AS 4055:2021).
On delivery, check:
- Performance label is present and legible on every unit
- Wind class on the label matches the wind class on the structural drawings
- Units are undamaged: check frame corners, seals, and glass for transport damage before installation
- Priming or factory coating is intact; any damage to factory coating on timber must be made good before installation, as exposed timber begins absorbing moisture immediately
AS 2047 also includes a generic timber window detail in Appendix F, which allows small joinery manufacturers (custom regional joineries) to supply AS 2047-compliant timber windows without individual laboratory testing of each design, provided the product follows the generic detail exactly (verified 2026-05-10, Cedar West, What is AS 2047).
NCC 2022 energy efficiency
The NCC 2022 mandates a minimum 7-star NatHERS shell energy rating for new Class 1 residential buildings (effective 1 May 2023 in most states). Windows are a key variable in NatHERS modelling, contributing thermal performance data via U-value and SHGC (Solar Heat Gain Coefficient) (verified 2026-05-10, ABCB NCC 2022 Volume Two H6 Energy efficiency).
Timber frames provide inherently lower thermal conductivity than standard aluminium frames. A timber frame conducts significantly less heat than an unbroken aluminium frame, which translates to better U-values at the frame level. However, the glazing specification (single vs. double, Low-E coating, gas fill) dominates the whole-window U-value in practice.
The WERS (Window Energy Rating Scheme), administered by AGWA, provides rated U-values and SHGC values for registered window products, formatted for direct input into NatHERS accredited software (AccuRate, FirstRate5, BERS Pro). Timber window products from major manufacturers are registered on WERS. Stegbar Timberaul double-glazed timber windows achieve U-values as low as 1.5 W/m2.K (verified 2026-05-10, Stegbar Timberaul timber windows), placing them among the better-performing residential window products available in the Australian market.
For the energy rater to use WERS data, the product must be supplied as rated: substituting a different glazing unit or frame profile invalidates the WERS rating and may require re-modelling.
Installation in timber-framed construction
Installation requirements under ABCB Housing Provisions Part 8.2 apply regardless of window frame material (verified 2026-05-10, ABCB Housing Provisions 2022 Part 8.2):
Frame opening preparation
The rough opening in the timber frame is sized by the carpenter to the manufacturer’s specified rough opening dimensions, typically 10 to 15 mm larger than the window unit on each side to allow for plumb and level adjustment and packing. AS 1684.2:2021 governs the lintel size over the opening and the trimmer stud arrangement; the minimum lintel bearing to each side is typically 50 mm for standard openings under AS 1684.2, with engineer-specified lintels for openings wider than the span tables permit (verified 2026-05-10, HIA, Using AS 1684 for Timber Framing; Standards Australia AS 1684.2:2021).
Structural load isolation
No structural loads may be transferred to the window assembly. This is a hard requirement under Housing Provisions Part 8.2. The lintel above the window opening carries the imposed loads; the window unit sits below and is not part of the structural load path. Consequences of structure bearing on the window frame include:
- Frame distortion, preventing sashes from operating correctly
- Seal failure at the head, creating water ingress paths
- Glazing pressure, potentially causing glass failure
Clearance at head
A minimum 10 mm gap must be provided between the top of the window assembly and any loadbearing framing element above it (Housing Provisions Part 8.2). This gap may need to be increased over wide openings where frame deflection under load is expected. The gap is typically filled with compressible foam backer rod and sealant (not hard packing) so the space remains flexible.
Packing and setting
Packing between the rough opening and the window unit must be:
- Located along the sides and bottom of the frame only (never at the head)
- Fixed to hold the unit in position and prevent the sides and sill from bowing
- Clear of any flashing material
- Compatible with both the window frame and the surrounding structure
For timber windows, avoid packing materials that trap moisture against the frame. Treated timber or plastic packers are preferable to untreated timber or materials that absorb and retain water.
Square and true
Install the window unit square and plumb. Check both diagonals: if they are equal, the unit is square. A twisted or racked timber window frame causes sashes to bind, seals to lift at corners, and water to track along the distorted joint line. Verify with a spirit level on both jambs and across the head.
Flashing at head and jambs
Head and jamb flashing is governed by the external wall cladding requirements, not solely by Part 8.2. The general principle is the shingle rule: upper layers of flashing lap over lower layers to shed water to the outside. For timber-framed walls with timber windows, the head flashing must turn over the top of the window frame to direct water away from the head joint; the jamb flashing must cover the gap between the frame and the surrounding substrate.
Timber to masonry substrate junctions require an isolating layer between the window sill or frame and any masonry element to prevent galvanic corrosion or direct moisture transfer (Housing Provisions Part 8.2 explanatory guidance).
Tolerances and acceptance
Workmanship tolerances for window installation in residential construction refer primarily to the HIA Guide to Materials and Workmanship.
| Element | Standard | Requirement |
|---|---|---|
| Frame squareness (diagonal differential) | HIA Guide | Per current HIA Guide to Materials and Workmanship. Verified numerical value pending HIA member access. [HIA-104] |
| Frame plumb (jamb vertical alignment) | HIA Guide | Per current HIA Guide to Materials and Workmanship. Verified numerical value pending HIA member access. [HIA-105] |
| 10 mm head clearance | NCC 2022 HP Part 8.2 | Minimum 10 mm gap between top of window assembly and any loadbearing framing; may increase for wide openings |
| Performance label match | AS 2047 | Wind class rating on label must match wind class on structural drawings |
| Lintel minimum bearing | AS 1684.2:2021 | Minimum 50 mm bearing each end for standard residential openings; engineer-specified for wider openings |
Maintenance regime
The maintenance regime is the primary ongoing cost distinction between timber and aluminium windows. A properly designed and installed timber window can last 30 to 50 years or more with consistent maintenance (verified 2026-05-10, Heritage Specialists Australia, How to Restore Timber Windows).
Recoating intervals
| Species / exposure | Typical repainting or restaining interval |
|---|---|
| Western red cedar, sheltered (eaves coverage) | Every 5 to 7 years |
| Western red cedar, exposed (no eave protection) | Every 3 to 5 years |
| Meranti, sheltered | Every 3 to 5 years |
| Meranti, exposed or coastal | Every 2 to 3 years |
| H3A treated pine | Every 2 to 3 years (paint maintenance is part of the H3A service regime) |
Source: general industry guidance from multiple Australian timber suppliers and Wideline (Timber vs Aluminium windows, verified 2026-05-10). Specific intervals depend on paint system quality, climate, and UV exposure. Establish the actual interval with the timber manufacturer for the specific product and finish system specified.
What happens without maintenance
If surface coatings are allowed to fail:
- Moisture ingress causes timber swelling and eventual rot, particularly at sill joints and end-grain sections
- Sashes bind and seals lift as frames swell
- Fungal staining appears first as surface discolouration, then as deeper structural degradation
- At the point of structural rot, the only remedy is component replacement
Early intervention (recoat when the paint begins to chalk or crack, before substrate is exposed) is substantially cheaper than rot remediation or unit replacement.
Timber vs aluminium: practical comparison
| Factor | Timber | Aluminium |
|---|---|---|
| Supplied and installed cost (standard window) | $1,200 to $2,500 ex-GST | $600 to $1,500 ex-GST |
| Frame thermal conductivity | Low (natural insulator) | High without thermal break; low with thermally broken frame |
| U-value (double glazed, indicative) | 1.5 to 2.2 W/m2.K | 2.0 to 4.0 W/m2.K (standard); 1.5 to 2.0 W/m2.K (thermally broken) |
| Maintenance | High: recoat every 2 to 7 years | Low: clean only |
| Lifespan with maintenance | 30 to 50+ years | 30 to 50 years |
| Custom profiles | Extensive: joiners can match heritage profiles exactly | Limited to manufacturer’s extrusion range |
| Coastal performance (unpainted) | Poor (requires coating) | Good (anodised or powder-coated) |
| NCC energy compliance | Yes (WERS rated products) | Yes (WERS rated products) |
Source: Wideline, Timber vs Aluminium windows (verified 2026-05-10); Stegbar, Timberaul timber windows (verified 2026-05-10).
Common defects
| Defect | Cause |
|---|---|
| Water ingress at head | Missing or incorrectly lapped head flashing; sealant substituted for flashing |
| Sash binding or sticking | Frame installed out of square; structure bearing on head |
| Timber swelling at sill | Sill in standing water; no drainage slope; coating failed at sill joint |
| Rot at end grain | Insufficient priming of end-grain sections before installation; factory coating not restored at site cuts |
| Frame twist or bow | Timber stored incorrectly before installation (unsupported, on uneven ground); wide opening without LVL-core reinforcement |
| Glass failure | Product rated below site wind class; incorrect glazing specified |
| Fungal staining without structural damage | Surface coating failed; moisture absorbed but not yet rotting; early-intervention recoat point |
Documents needed
- Structural drawings showing wind classification (AS 4055:2021) and lintel schedule
- Window supplier’s performance certificate and WERS data sheet (for NatHERS input)
- Manufacturer’s installation guide and rough-opening schedule
- AS 2047 performance label verification sheet (or photo record on delivery)
- SWMS for any work at height during installation
References
- Standards Australia, AS 2047:2014 Amd 2:2017 Windows and external glazed doors in buildings. https://store.standards.org.au/product/as-2047-2014-amd-2-2017 (verified 2026-05-10).
- Standards Australia, AS 5604:2022 Timber, Natural durability ratings. https://store.standards.org.au/product/as-5604-2022 (verified 2026-05-10).
- Standards Australia, AS 1684.2:2021 Residential timber-framed construction, Part 2: Non-cyclonic areas. https://store.standards.org.au/product/as-1684-2-2021 (verified 2026-05-10).
- Australian Building Codes Board, ABCB Housing Provisions Standard 2022, Part 8.2 Windows and external glazed doors. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/8-glazing/part-82-windows-and-external-glazed-doors (verified 2026-05-10).
- Australian Building Codes Board, NCC 2022 Volume Two, Part H1 Structure, clause H1D8. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two/h-class-1-and-10-buildings/part-h1-structure (verified 2026-05-10).
- AT Pine, Treated Pine Timber Guide: Hazard Treatments H1-H6. https://www.atpine.com.au/treated-pine-timber-guide/ (verified 2026-05-10).
- Stegbar, Timberaul timber windows. https://www.stegbar.com.au/windows/timber-windows/ (verified 2026-05-10).
- Cedar West, What is AS 2047. https://cedarwest.com.au/info/what-is-as2047 (verified 2026-05-10).
- Wideline, Timber vs Aluminium windows. https://www.wideline.com.au/blog/timber-vs-aluminium-windows/ (verified 2026-05-10).
- Mortlock Timber, Timber Durability Classes Explained. https://www.mortlock.com.au/learning/timber-durability-class/ (verified 2026-05-10).
- HIA, Using AS 1684 for Timber Framing. https://hia.com.au/resources-and-advice/building-it-right/australian-standards/articles/using-as-1684-for-timber-framing (verified 2026-05-10).
- Heritage Specialists Australia, How to Restore Timber Windows. https://www.heritagespecialists.com.au/2026/01/19/how-to-restore-timber-windows/ (verified 2026-05-10).
Related
- AS 2047: windows and external glazed doors
- AS 1684: residential timber framing
- AS 4055: wind loads for housing
- Durability class
- WERS: Window Energy Rating Scheme
- Flashing
- First fix and second fix sequence
- NCC energy efficiency
See also
- Lintel
- H3 treated timber
- Galvanic corrosion
- SHGC
- NatHERS
- Thermal break
- Workmanship
- HIA Guide to Materials and Workmanship
- Wind region
- AS 1288: glass in buildings
Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency: check current AS 2047 and AS 5604 edition status at Standards Australia; confirm NatHERS 7-star effective dates in each state.