What timber for outdoor staircase rebuild?

[ddel]

Hi all, 

I need to re-build my staircase landing and staircase to the ground. Rotten wood and other issues are the cause.

I pretty much know in theory what to do and this is my first time...I am a DIYer.

I am stripping down the stair treads and will replace them with this : https://www.bunnings.com.au/peak-black-5-tread-steel-stair-stringer_p0083614

Now my question is I do not know what sort of wood is suitable for some specific part. All I know is it has to be H4. 

Could someone help me with this. Images to simplify my lack of technical terms I used here. 

[MitchellMc]

Hi @ddel,

When it comes to selecting the right timber, you'll need to use structurally rated timber that's appropriate for outdoor and elevated applications. If you're planning to use pine, look for either F7 or MGP-10 grading. Posts that go into the ground must be H4 treated to withstand ground contact, while any timber used above ground, such as framing for the landing, should be H3 treated, which protects against the elements but isn't suitable for direct soil contact.

For your support posts, 90x90mm H4 treated F7 timber is commonly used. For the frame of the elevated platform, something like 140x45mm H3 treated MGP-10 timber would typically be suitable. This same size timber is also ideal for your joists that run across the landing.

Given that this is an elevated structure supporting stairs, it's essential that the platform is properly designed to meet structural requirements and safely carry the load. The platform must not only support itself but also securely anchor the top of the steel stringers. For this reason, it’s strongly recommended you consult with an engineer, a licensed builder or a carpenter to ensure your structure is compliant with local building codes and safe for use. 

Please let me know if you have any questions.

Mitchell

[ddel]

Thank you Mitchell.

I will look for one.