Concrete for Pergola Post Footings
Pergola posts support roof structures that must withstand wind loads, their own weight, and potentially climbing plants or attachments. Proper footings are essential for structural integrity and long-term stability. Here's how to calculate concrete for a standard four-post pergola.
Typical Pergola Post Requirements
Most residential pergolas use 100mm posts in 350mm diameter holes at 700mm depth. This specification suits pergolas up to approximately 4x4 metres with open-roof designs. Larger pergolas, covered roofs, or pergolas in high-wind areas may require engineering assessment for specific footing requirements.
Four-Post Concrete Volume
Each 350mm × 700mm hole requires approximately 0.065 cubic metres of concrete after accounting for the post. Four posts therefore need roughly 0.29 cubic metres including wastage, equivalent to 31-32 bags of premix. This quantity is manageable as a bag-mixing project but substantial work.
Post Positioning Strategy
Accuracy in post positioning determines whether your pergola is square and your roof components fit correctly. Set out positions carefully using the 3-4-5 triangle method to verify right angles. Dig all holes before setting any posts, allowing final verification of positions.
Height Coordination
All posts must finish at the same height for level roof installation. Set one reference post first, then use a builder's level or laser level to transfer heights to remaining posts. Account for any slope in the ground when calculating hole depths to achieve level tops.
Bracing Requirements
Unlike quick-set fence posts, pergola posts require bracing while concrete cures. Install temporary braces to hold posts plumb in two directions. Leave braces in place for minimum 48 hours, longer in cool weather. Don't attach any roof components until concrete has achieved adequate strength.
Building Approval Considerations
Pergolas attached to houses typically require building approval. Even freestanding pergolas may need approval if they exceed certain sizes or are located within specific distances of boundaries. Verify requirements with your local council before commencing work.
Need Different Specifications?
Use our post hole calculator to enter your exact hole dimensions and post size. You can also explore our slab calculator or footing calculator for other concrete projects.