How to build a 3x4 pergola?

jmm10

Hi, I'm planning to DIY a 3x4 garden pergola, and i just want to know the timber specs that i should use for the post and frame? My initial plan is to install a 4 post using 100x100mm H4 treated timber and having a square frame around using either 200x50mm H3 treated or 140x45mm H4 treated timber.

JacobZ

Hi @jmm10,

Cypress is a good option as long as it is structural grade.

Keep in mind that the weight can be a bit deceptive as posts are often full of water. If the weight is heavier, it does not necessarily mean it is denser, it could just be full of water. If density and strength is what you are after, then you would be better off using hardwood posts.

Without the input of a structural engineer, I would not advise using stirrups. Concreting in your posts so that 1/3 the overall height of the posts is embedded, will ensure they are adequately anchored and up to the task. For example if the posts sit 2.4m out of the ground, then you will need to use 3.6m posts so that 1.2m can be embedded in concrete.

Cypress can be used in ground if you choose to do so, however you should coat the in-ground portion of the post with bitumen membrane to help protect it from water in the concrete.

If you are painting the structure, make sure you use a quality exterior paint such as Dulux Weathershield or Taubmans Sunproof.

Let me know what you think and if you have any further questions, please don't hesitate to ask.

Jacob

jmm10

Update. After a long planning i already finished my DYI project by my self, from posts digging up to painting. All materials and tools are all from bunnings. Thank you everyone for sharing ideas. Thank you and more power...

JacobZ

That looks like an extremely solid pergola with some beautiful accents. It looks like a great place to sit and enjoy time with your friends and family.

You have done a brilliant job turning your vision into a reality and I am so glad to know I could help, even in a small way.

Thank you for sharing @jmm10.

Jacob