What timber for exterior stair stringers?

Question

Is 290mm x 45mm treated pine suitable for external stair stringers?

Currently in the process of building a deck which contains a upper and lower section.

I have Engineering for the deck and the certifier has signed off on the goings and rise of the stairs although no detail for the stair stringers.

Would 290mm x 45 treated pine work for these measurements.

Thanks in advance for the expertise.

Nailbag · Answer

Hi @Scottydont85

I've only built from scratch a couple of 3-tread steps both of which were 290mm x 45mm. One was Merbau and the other TP to match the tread material. Both worked fine dimensional wise.

Nailbag

EricL · Answer

Hello @Scottydont85

My apologies that I can’t provide a more definitive answer on this one. As this is a certified build with engineering specifications already in place, I think the best approach would be to send this exact drawing to your engineer and ask them to nominate the appropriate stringer size, structural grade, number of stringers and fixing arrangement. It should be a relatively straightforward detail for them to confirm, and it takes the guesswork out of the build while also giving your certifier something definitive to work from.

From a safety and compliance point of view, I’d also recommend having both your engineer and certifier sign off on the stair construction. That way, you can move ahead with confidence knowing the stairs have been designed appropriately for your particular deck. It also means that if the build is ever inspected by your local council, you’ll have the documentation showing that the stair assembly was properly designed, approved and constructed to the required specifications.

Let me call on our experienced members @Nailbag and @DIY4Knuckleheds for their recommendations.

If you need further assistance, please let us know.

Eric

Scottydont85 · Answer

Thanks @EricL,

I need to cut these as my rise and run have been set and signed off by the Certifier.

The steps are also 4400mm wide. Will using 290mm treated timber work for these stringers?