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I'm planning on building a pergola with posts sized 200mm x 150mm.
Hardwood post of this size is quite expensive and so instead, I'm thinking of putting (laminating) together three(3) 200mm x 50mm Sleepers (Ironwood H4 Sienna MicroPro) to come up with a single 200mm x 150mm post.
https://www.bunnings.com.au/200-x-50mm-3-0m-sleeper-h4-sienna-micropro_p8423134
However, I'm not 100% sure if it will be structurally sound for a pergola post. But I think it would be given that the pergola roof is light-weight. My other concern is the possibility of the laminated sleeper post warping over time.
I would appreciate to get some comments from the group.
Regards.
Welcome to the Bunnings Workshop community @ianm64. It's fantastic to have you join us, and many thanks for your question about building a pergola.
Unfortunately, sleepers are not structurally rated and can't be used for weight-bearing purposes. They're purely for retaining walls and garden beds.
What was the reasoning behind using a post of that size? It appears exceptionally large for your proposed use. Is it for aesthetical reasons? If so, I'd suggest you use standard 90 x 90mm 3.0m Post GL17 Merbau Laminated DAR or 90 x 90mm 3.0m Post F7 H4 Treated Pine Premium KD posts and clad them with your sleepers.
If the use of such large calibre timber is due to its weight-bearing characteristics, it's a good indicator that more posts need to be added to the design instead of upping the size of the post.
Check out this helpful step-by-step guide: How to build a pergola frame.
I'm looking forward to hearing more about your design choices. Please let me know if you have any questions.
Mitchell
There is a good chance of them warping @ianm64. To be clear, you shouldn't use sleepers as the posts for your pergola. Not only do they not comply with building codes and council regulations, they would also be dangerous.
Mitchell
