How to choose structural timber grades for framing

How do you choose structural timber grades for framing in Australia?

🪚 Choosing structural timber grades for framing is about matching the correct strength class, treatment level and product type to the load path, exposure conditions and compliance requirements of the build. For Australian trade professionals, the key is understanding where MGP, F-grades, machine-graded versus visually graded timber, and treated versus untreated framing fit under AS 1684 Residential Timber-Framed Construction and related product standards.

This guide sets out a practical site-and-ordering workflow for selecting framing timber for wall frames, floor systems and roof members, so you can specify the correct 90x45, 140x45, 190x45 or larger section in the right grade, with fewer ordering errors and less risk of non-compliant installation.

What skill level is required for selecting structural timber grades?

Intermediate — Estimated time: 1.5–3 hours for assessment, take-off review and supplier confirmation

What tools are essential for selecting and verifying structural timber grades?

What common structural timber materials are used for framing in Australia?

🪵 Materials

Safety Requirements

⚠️ Safety

Step-by-Step Guide

Step 1: Identify the framing application and load path

1️⃣ Define the structural role

Start by identifying exactly what the timber is doing: non-load-bearing stud wall, load-bearing external wall, floor joist, bearer, rafter, ceiling joist, lintel support framing or truss-related framing. Grade selection is only correct when tied to the actual structural function.

Review the architectural set, structural plans and engineering notes together. A 90x45 mm stud in an internal partition has a different requirement to a 90x45 mm stud carrying roof and upper-floor loads. Likewise, a 140x45 mm member may be acceptable as a wall plate or nogging but unsuitable as a floor joist at the same grade and span.

💡 Do not select grade by section size alone. The same section can have very different allowable capacities depending on grade, species, moisture condition and restraint.

Step 2: Check the governing standard and design method

2️⃣ Confirm the compliance pathway

For most housing work, use AS 1684 as the primary reference for residential timber-framed construction. The span tables and framing provisions in AS 1684 guide member size and grade selection for standard housing loads and configurations.

Where the project falls outside AS 1684 assumptions—such as unusual point loads, concentrated girder trimmers, large openings, high wind classifications, stacked loads, or non-standard geometry—refer to the structural engineer and AS 1720 Timber Structures. Engineered designs override rule-of-thumb ordering.

If the drawings call up a specific grade such as MGP10, MGP12, F7 or F17, match that exactly unless a formal substitution is approved.

💡 Supplier “equivalent” substitutions are not automatic. A change from one grade system to another still requires verification against the design capacity.

Step 3: Understand the difference between MGP and F-grades

3️⃣ Select the correct grade system

In practical trade terms:

When ordering, never assume MGP10 = F7 or similar. They are not interchangeable by label alone. Use the span tables, engineering schedule or supplier structural data.

💡 For pine framing in project homes, MGP10 90x45 mm is common, but floor and roof applications often step up in either depth, spacing control or grade depending on the span table outcome.

Step 4: Determine whether the timber is machine graded or visually graded

4️⃣ Verify how the product has been graded

Machine grading and visual grading are different quality systems. Machine-graded pine typically carries a marked MGP classification and supplier branding. Visually graded timber carries an F-grade and is assessed by allowable natural characteristics and manufacturing quality.

On delivery and during take-off review, check:

Do not accept unmarked structural framing as compliant structural stock unless the supplier provides clear certification and traceability. For inspections and QA, bundle tags and delivery dockets matter just as much as the timber itself.

💡 If the grade stamp is unclear after cutting, retain offcuts with visible branding until inspection sign-off is complete.

Step 5: Match member size and grade to span, spacing and loads

5️⃣ Use span tables properly

Once the application and grade system are clear, check the member depth, thickness, spacing and span against AS 1684 or engineering documentation. A timber grade is only part of the selection; 90x45 mm MGP10 and 90x45 mm MGP12 may both be structural, but allowable spans differ.

Confirm:

For example, a wall stud may satisfy compression requirements at 90x45 mm MGP10, but a floor joist over the same length may require 190x45 mm MGP12 or an engineered alternative.

💡 Trades regularly undercall timber by checking only span and ignoring spacing. The difference between 450 mm and 600 mm centres can change the required section or grade.

Step 6: Decide between treated and untreated framing timber

6️⃣ Specify treatment to suit exposure and termite risk

Treatment selection is based on hazard class, exposure location and local compliance requirements.

General framing rules:

In many Australian regions, internal framing still requires termite risk consideration even where the member is not weather-exposed. Treatment is not about strength grade; it is a separate requirement from structural capacity.

Do not confuse treated with structural. A member must satisfy both:

💡 A common compliant order description is: 90x45 mm MGP10 H2F pine framing, which identifies size, strength class and treatment in one line.

Step 7: Check seasoned, unseasoned and moisture requirements

7️⃣ Confirm timber condition and stability

Most modern framing supply is seasoned or kiln dried for dimensional stability. This matters for shrinkage, straightness, lining performance and frame movement. For internal wall framing, seasoned material is generally preferred and often expected.

Verify whether the project or supplier is providing:

Moisture condition can affect serviceability outcomes, especially for cabinetry interfaces, plasterboard cracking risk and frame movement around openings.

💡 For straight wall framing and reduced callbacks, confirm moisture content and reject badly bowed or twisted members before installation, even if they carry the correct grade.

Step 8: Confirm species, durability and project-specific constraints

8️⃣ Select the right timber product for the environment

Not all framing is plantation pine. Some work still uses seasoned or unseasoned hardwoods, particularly in repair work, tie-ins to older structures, or where specified by engineer or architect. Species selection can affect:

For residential framing, plantation pine in MGP10 or MGP12 is the standard supply line in many markets. Hardwood F-grades are typically used where higher strength, matching existing construction, or specific engineering requirements apply.

Where durability and exposure are major factors, consider whether a standard framing product remains appropriate or whether LVL, preservative-treated hardwood or another structural product is a better solution.

💡 In remedial work, matching existing hardwood framing with lightweight pine without engineering review can create differential movement and fixing issues.

Step 9: Review substitutions, engineered products and supplier equivalents

9️⃣ Manage changes properly

If standard sawn framing is unavailable, the next step is not guesswork. Check whether the engineer permits substitution to:

Document every approved change. Keep the supplier’s structural literature and confirmation emails on file. On commercial or certifier-sensitive residential work, that record can save substantial rework.

Do not allow site substitutions based solely on “it looks stronger” or “that is what was available in the yard.”

💡 Higher grade does not automatically solve every issue. Serviceability, connection detailing, thickness compatibility and fastening schedules still need checking.

Step 10: Order timber with a full structural description

🔟 Write the order correctly

A professional timber order should clearly identify:

Examples:

This reduces supplier interpretation errors and ensures the delivered stock matches design intent. Include project area references if practical, such as “Level 1 external walls” or “Garage roof framing”.

💡 If the order value includes specialist saws, lasers or moisture meters above $300, check whether current EOFY instant asset write-off rules may assist the business at tax time.

Step 11: Inspect delivered timber before installation

1️⃣1️⃣ Carry out receiving QA

When the delivery arrives, inspect bundles before dispersing them around the site. Confirm:

Segregate non-conforming stock immediately and photograph tags and defects. It is far easier to reject a bundle before cutting than to argue compliance once installed.

💡 Keep one photographed tag from every timber pack as part of the job QA file.

Step 12: Record compliance for certifier and handover

1️⃣2️⃣ Maintain documentation

Retain:

This is particularly important for structural inspections, termite-related compliance, warranty matters and future rectification works. Good recordkeeping is part of professional framing practice, not administration overhead.

Common Mistakes to Avoid

Pro Tips

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