Question 1

What is the maximum span for a 90×45 MGP10 ceiling joist at 600mm spacing?

Accepted Answer

The maximum allowable span depends on your wind classification, roof type and loading category. Rather than rely on a single quoted figure, look up the 90×45 mm MGP10 ceiling joist row in the published AS 1684.2 table for your conditions, or have a structural engineer confirm the span for your specific project.

Question 2

What span tables apply to Australian residential roofing timber?

Accepted Answer

AS 1684.2:2021 (non-cyclonic) and AS 1684.3 (cyclonic) cover residential timber-framed construction in Australia, with simplified tables in AS 1684.4. NZS 3604 is the New Zealand equivalent and uses the same MGP and F-grade designations.

Question 3

Can MGP10 be used for rafters as well as ceiling joists?

Accepted Answer

Yes — MGP10 is suitable for both rafters and ceiling joists in residential roofing under AS 1684. Rafters carry roof load and span less than ceiling joists of the same size; published AS 1684.2 rafter tables give the maximum allowable span for each combination of size, spacing and wind classification.

Question 4

What is the difference between F17 and MGP10 timber?

Accepted Answer

F17 is a stress grade for seasoned hardwood (typically Spotted Gum, Blackbutt or Sydney Blue Gum), while MGP10 is a machine-graded structural pine softwood. F17 generally achieves longer spans than MGP10 of the same size, but is heavier, costs 2–3× more, and is harder to fix.

MGP10 span tables for Australian roofing timber