Construction Timber Specifications: Stress Grades

Whether you need timber for general construction, timber fencing or timber decking for your home, stress grades are important. Stress grades are issued in conjunction with strength grades. Unseasoned timber is graded from S1 through S7 with S1 being the strongest. Seasoned timber is graded from SD1 through SD8 with SD1 being the strongest.

Stress grading is used primarily for structural components as pursuant to Standards Australia 1997a: AS-1720.1-1997 Timber structures—design methods. They are also in Building Code of Australia (Queensland Building Act 1975) and AS 1684 Series Residential timber—framed construction parts 2 and 3, as seen in Standards Australia 2006a,b.

There are three ways in which stress grades are assigned. The first is by full-size, in-grade testing as pursuant to Standards Australia 1992 (AS 4063-1992 Timber—stress graded—in-grade strength and stiffness evaluation). The second is to use in-grade testing to confirm traditional F-grades as pursuant to AS 4063-1992 as seen above. The third method is using the traditional F-grades determined by testing on small, clear properties.

Common Stress Grades Determined by In-Grade Testing

• White Cypress (Seasoned or Unseasoned): F4, F5 or F7
• Seasoned Hoop Pine: F5, F7 or F8
• Seasoned Pinus Species (Caribbean, radiata, slash and maritime pines): SP1-SP4, MGP10, MGP12 and MGP15
• Victorian Ash (Seasoned): A17

Common Stress Grades Adjusted or Confirmed by In-Grade Testing

• North-Eastern Australian Hardwoods including ironbark, blackbutt, spotted gum
• Spruce-pine-fir
• North American Douglas Fir
• Plantation Pinus species mentioned above, grown in Australia

Call Narangba Timbers Today

We hope our series on timber specifications is helpful. It is meant as background information to help you understand why ratings are important. Whatever project you have in mind, from a full home to timber decking to timber fencing for you home, Narangba Timbers has everything you need to make that project something you can be proud of. We can help you select the correct timber for any task. We only carry high-quality, ethically-sourced timber. To learn more, call us today on 1300 477 024.