How to build a pergola attached to the house?

[pasquaj]

Hello Bunnings

I am researching a project that I am going to undertake shortly. I am wanting to attach a timber pergola to a house. The pergola will be

have width of approx. 5.4m x depth of 2m

a) A H3 ledger board of 190mm x 45mm x 5,4m will be attached to the house with appropriate bolts.

b) Two (or more if required) H4 posts will be concreted into the ground and will have a final height of 2.4m.

c) A main H3 beam will be attached to these two posts (or more), I am thinking 240mm x 45mm x 5.4m.

d) The posts do not necessarily have to be positioned at the ends of the 5.4m main beam.  They can be positioned in for some overhang of the main beam.

e) 140mm x 45mm H3 rafters will be attached across the ledger board to the main beam.

f) H3 purlins 70mm x 35mm will be attached  across the rafters.

g) A lightweight polycarbonate roofing will be installed. 

h). The pergola will have a 5 degree pitch.

It’s a little confusing trying to decipher span tables. For this project I have 3 questions

     
1. What size posts should I use?

2. How many posts should I use. (I note two above ? need an additional post). 

3. Is a 240mm x 45mm x 5.4m main beam suitable for attachment to two posts (or more required).

Hoping you can advise.

Regards John

[EricL]

Hello @pasquaj 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your pergola project.

Your pergola project sounds great! I’m happy to offer some advice to help you get started, but keep in mind that for a structure like this, it’s always best to have it certified by a draftsperson or engineer. They’ll make sure everything is structurally sound and meets council requirements. It’s also a good idea to check with your local council about any size or home attachment rules. If you’re looking for a simpler approach, building it as a free-standing pergola might save you some extra approvals and planning headaches.
 

For the posts, I propose something like 100mm x 100mm H4-treated timber should be a solid choice but double-check based on your final design. As for the number of posts, having just two over a 5.4m span might not be enough, so adding a third post in the middle would give the beam extra support and help prevent sagging.
 

Your main beam at 240mm x 45mm is strong, but over a 5.4m span, it might need extra reinforcement if only using two posts. I recommend going with three posts, to make it more stable.

Since you’re using lightweight polycarbonate roofing, the load won’t be as heavy as other materials, but it’s always good to get professional confirmation on spans and fixing methods.

If you need further assistance, please let us know.

Eric