Hi @Crash76,
Thank you for your question about post-hole dimensions for your verandah.
Unfortunately, due to the complex loads that are applied to roofed structures like verandahs, there is no standard sizing for concrete piers that I can point you to.
There are a number of variables that will be taken into consideration when designing a suitable method of anchoring your verandah. These variables include the overall size of the structure, the wind rating in your area and the type of soil it will sit on. Unfortunately, the only people qualified to provide advice on this are engineers.
The way I'd approach your design, not being an engineer myself, is to budget and plan for the higher end of what's likely, then take this plan to your engineer and ask if you can reduce the size of your concrete piers and the calibre of post anchors.
Concrete piers will often be 450-600mm in diameter depending on the specific requirements of the project. They can be larger than this, but I can't imagine anything smaller than this would be sufficient. If you assume all piers need to be at least 450mm in diameter and plan accordingly, you could take your design to the engineer later in the process for their approval.
Again, the Pryda post supports would need to be approved by an engineer, but these Pryda 600 x 100mm M12 High Wind Post Anchors are often used in high-wind areas and are on the higher end of what may be required. For budgeting purposes, it would be worthwhile factoring these into your design and during your consultation, asking your engineer if you need to go to this extent.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
