How deep should my deck post holes be?

[RyanW8]

I've read a lot online that deck posts should be a minimum of 750mm deep to be below the frost line to prevent movement in freeze/thaw cycles. I'm planning on using 2 bags of postcrete on each post but 750mm deep seems quite overkill to me. Is postcrete affected the same way as normal concrete when frozen?

 

[mikeey84]

That's more of an issue in the US, where frost heave occurs as it gets much colder than here in Blighty

400mm should be fine, depending on ground conditions

 

[RyanW8]

That's more of an issue in the US, where frost heave occurs as it gets much colder than here in Blighty

400mm should be fine, depending on ground conditions

yeah I did think so. So far I’ve managed to get 300mm down but it seems there is solid rock below that so might just stick with 300mm. Spoke with my uncle who’s a builder and he said it’s plenty. Houses are built on 800m deep foundations so 300 is plenty

 

[mikeey84]

Sounds like a good plan