Roof Timber Sizes Australia: Rafters, Joists & Ridge Beams
Standard roof timber sizes used in Australian residential construction. See common rafter, ceiling joist and ridge beam dimensions with their typical spans and applications — useful for builders, drafters, and homeowners planning a new roof, extension, or renovation.
How Australian Roof Timber Sizes Are Specified
In Australia, structural roof timber is specified as depth × thickness in millimetres — for example 90 × 45 means 90 mm deep and 45 mm thick. Most residential rafters and ceiling joists are made from MGP10 pine or F7 hardwood, while ridge beams and longer spans are usually engineered timber such as LVL or Glulam.
Common stock sizes you will find at AU timber yards include 70×35, 90×35, 90×45, 120×35, 120×45, 140×45, 190×45, and 240×45 mm. Less common sizes (240×45+) are usually engineered or special-order.
Important — indicative reference only, not engineering advice
This page is educational and does not reproduce the official AS 1684 span tables, which are copyright Standards Australia. It shows which timber sizes and grades are commonly used for each member — it does not give allowable spans. Every actual span must be read from the published AS 1684 tables for your wind classification, roof type, spacing and loading, and confirmed by a qualified structural engineer before specifying or building. This is not engineering or certification advice.
| Size (mm) | Common Use | Typical Span | Notes |
|---|---|---|---|
| 70 × 35 | Light patio rafters, eaves, short pergola spans | Verify against AS 1684.2 | Generally too small for habitable roofs |
| 90 × 35 | Short residential rafters, garage roofs | Verify against AS 1684.2 | Common for short pitched roofs |
| 90 × 45 | Standard residential rafters, garages, sheds | Verify against AS 1684.2 | Most common small-rafter size in AU |
| 120 × 35 | Mid-span rafters in single-storey homes | Verify against AS 1684.2 | Lighter alternative to 120×45 |
| 120 × 45 | Standard pitched-roof rafters | Verify against AS 1684.2 | Workhorse rafter size for AU homes |
| 140 × 45 | Larger residential rafters, longer spans | Verify against AS 1684.2 | Common for cathedral / vaulted ceilings |
| 190 × 45 | Long-span rafters, exposed structural rafters | Verify against AS 1684.2 | Often used in architectural / open-plan roofs |
| 240 × 45 | Heavy-load or very long-span rafters | Verify against AS 1684.2 | Engineered solutions often preferred at this size |
- 70 × 35
- Common Use
- Light patio rafters, eaves, short pergola spans
- Typical Span
- Verify against AS 1684.2
- Notes
- Generally too small for habitable roofs
- 90 × 35
- Common Use
- Short residential rafters, garage roofs
- Typical Span
- Verify against AS 1684.2
- Notes
- Common for short pitched roofs
- 90 × 45
- Common Use
- Standard residential rafters, garages, sheds
- Typical Span
- Verify against AS 1684.2
- Notes
- Most common small-rafter size in AU
- 120 × 35
- Common Use
- Mid-span rafters in single-storey homes
- Typical Span
- Verify against AS 1684.2
- Notes
- Lighter alternative to 120×45
- 120 × 45
- Common Use
- Standard pitched-roof rafters
- Typical Span
- Verify against AS 1684.2
- Notes
- Workhorse rafter size for AU homes
- 140 × 45
- Common Use
- Larger residential rafters, longer spans
- Typical Span
- Verify against AS 1684.2
- Notes
- Common for cathedral / vaulted ceilings
- 190 × 45
- Common Use
- Long-span rafters, exposed structural rafters
- Typical Span
- Verify against AS 1684.2
- Notes
- Often used in architectural / open-plan roofs
- 240 × 45
- Common Use
- Heavy-load or very long-span rafters
- Typical Span
- Verify against AS 1684.2
- Notes
- Engineered solutions often preferred at this size
| Size (mm) | Common Use | Typical Span | Notes |
|---|---|---|---|
| 70 × 35 | Short ceiling spans, light loads | Verify against AS 1684.2 | Limited residential use |
| 90 × 35 | Standard residential ceilings | Verify against AS 1684.2 | Common for hallways and small rooms |
| 90 × 45 | Standard ceiling joists in living areas | Verify against AS 1684.2 | Workhorse ceiling-joist size |
| 120 × 35 | Mid-length ceiling joists | Verify against AS 1684.2 | Good lightweight option |
| 120 × 45 | Larger rooms, no ceiling load | Verify against AS 1684.2 | Standard for bedrooms and lounges |
| 140 × 45 | Long-span living rooms | Verify against AS 1684.2 | Common for open-plan ceilings |
| 190 × 45 | Very long ceiling spans | Verify against AS 1684.2 | Often used with strongbacks/blocking |
- 70 × 35
- Common Use
- Short ceiling spans, light loads
- Typical Span
- Verify against AS 1684.2
- Notes
- Limited residential use
- 90 × 35
- Common Use
- Standard residential ceilings
- Typical Span
- Verify against AS 1684.2
- Notes
- Common for hallways and small rooms
- 90 × 45
- Common Use
- Standard ceiling joists in living areas
- Typical Span
- Verify against AS 1684.2
- Notes
- Workhorse ceiling-joist size
- 120 × 35
- Common Use
- Mid-length ceiling joists
- Typical Span
- Verify against AS 1684.2
- Notes
- Good lightweight option
- 120 × 45
- Common Use
- Larger rooms, no ceiling load
- Typical Span
- Verify against AS 1684.2
- Notes
- Standard for bedrooms and lounges
- 140 × 45
- Common Use
- Long-span living rooms
- Typical Span
- Verify against AS 1684.2
- Notes
- Common for open-plan ceilings
- 190 × 45
- Common Use
- Very long ceiling spans
- Typical Span
- Verify against AS 1684.2
- Notes
- Often used with strongbacks/blocking
| Size (mm) | Common Use | Typical Span | Notes |
|---|---|---|---|
| 190 × 45 LVL | Standard residential ridge beams | Verify against AS 1684.2 | Engineered timber, consistent strength |
| 240 × 45 LVL | Mid-span ridges, longer rafters | Verify against AS 1684.2 | Popular for hip and pitched roofs |
| 300 × 63 LVL | Cathedral ceilings, exposed ridges | Verify against AS 1684.2 | Often used as feature beam |
| 360 × 63 LVL | Long-span open-plan roofs | Verify against AS 1684.2 | Engineered design recommended |
| Custom Glulam | Architectural / heavy timber roofs | Engineer-specified | Made-to-order; specify by engineer |
- 190 × 45 LVL
- Common Use
- Standard residential ridge beams
- Typical Span
- Verify against AS 1684.2
- Notes
- Engineered timber, consistent strength
- 240 × 45 LVL
- Common Use
- Mid-span ridges, longer rafters
- Typical Span
- Verify against AS 1684.2
- Notes
- Popular for hip and pitched roofs
- 300 × 63 LVL
- Common Use
- Cathedral ceilings, exposed ridges
- Typical Span
- Verify against AS 1684.2
- Notes
- Often used as feature beam
- 360 × 63 LVL
- Common Use
- Long-span open-plan roofs
- Typical Span
- Verify against AS 1684.2
- Notes
- Engineered design recommended
- Custom Glulam
- Common Use
- Architectural / heavy timber roofs
- Typical Span
- Engineer-specified
- Notes
- Made-to-order; specify by engineer
1. Measure the span — the unsupported distance between bearing points (wall plates, beams).
2. Confirm the spacing — most AU homes use 450 or 600 mm centres for rafters and joists.
3. Pick a timber grade — MGP10 for general framing; F17 hardwood for higher loads or longer spans.
4. Check loading — tile roofs need shorter spans than sheet metal roofs.
5. Verify with span tables — match size, grade and spacing against AS 1684.
Undersizing for tile roofs — heavy tile loads often need 140×45 instead of 120×45.
Forgetting wind load — N3 and N4 wind zones (coastal, cyclonic) increase requirements.
Using F-grade vs MGP wrong — F7 pine and MGP10 perform differently despite similar names.
Over-spacing rafters — going from 600 to 900 mm spacing significantly reduces allowable spans.
Using sawn vs dressed sizes — quoted sizes (90×45) are dressed; rough-sawn is slightly larger.
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Frequently Asked Questions
What size are standard roof rafters in Australia?
The most common roof rafter sizes for Australian homes are 90 × 45 mm and 120 × 45 mm. For longer spans or cathedral ceilings, 140 × 45 mm and 190 × 45 mm are typical.
What size timber is used for ceiling joists?
Standard ceiling joists in Australian residential construction are usually 90 × 45 mm or 120 × 45 mm, in MGP10 pine. Longer spans typically step up to deeper sections such as 140 × 45 mm or 190 × 45 mm — read the allowable span for each size from the published AS 1684.2 table.
What size ridge beam do I need for a long span?
Longer ridge-beam spans usually call for an engineered solution such as an LVL or glulam beam, with the exact section depending on roof load (tile vs sheet) and rafter span. Ridge beams at this scale are engineer-specified — always confirm the member with a structural engineer for your specific design.
Is 90 × 45 timber strong enough for roof rafters?
90 × 45 MGP10 pine is a common small-rafter size for short spans under typical sheet-roof loads. For tile roofs or longer spans, step up to 120 × 45 or 140 × 45. Confirm the allowable span for your size and spacing against the published AS 1684.2 table.