How to build a DIY pergola?

Amal108

Hi everyone,

I’m planning to build a pergola and I’m trying to decide between using 100x100mm posts or 90x90mm posts. The 100x100s are actually cheaper which makes me wonder if they’rhe better option.

A couple of questions I’d love advice on:

1. Is there much difference structurally between 90x90 and 100x100 posts for a pergola?

2. Since 100x100 is cheaper, is there any reason I should stick with 90x90 instead?

3. What’s the maximum recommended distance between pergola posts? I want to make sure I don’t end up with sagging beams or an unstable frame.

Appreciate any guidance or experience from those who’ve built similar structures!

JacobZ

Hi @Amal108,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

The first thing to do with any pergola project is to check with your local council what rules they have around their construction, and whether you will require building approval. A quick Google search or phone call to your local council can certainly help guide the process.

Assuming the grade and type of timber are the same, a 100x100 post would be stronger than a 90x90 post, so I would go with the 100x100.

The recommended distance between posts would depend on the type and size of timber used to span those posts, the spacing of the rafters running perpendicular to the beams and whether there was going to be any roofing material on top of those rafters. For example, a 190x45 beam would be able to span further between posts than a 140x45 beam would. 

I would need to know a few more details to give you a firmer recommendation. If you could provide a basic sketch of the pergola showing the size and basic design, I would be happy to find you some relevant resources and make some recommendations.

Let me know what you think. Once I have more details, I will assist further.

Jacob