DIYbanter - View Single Post

wrote:
So, what are you saying? Two feet is not deep enough?

The lumber store told me it was ok at that depth if using concrete.

I am sorry but I think a 4 foot hole is overkill.

Surprised to see this thread still going. You need a system to resist horizontal
loads. If the poles are not deeply embedded then you will need a system of
diagonal braces in every plane (including the roof plane(s)). Even with diagonal
bracing to resist horizontal loads, you will still need a system to resist
uplift. This will usually be concrete footings for the posts. The amount of
concrete needed depends on the weight of the building and the roof area
supported by each pole. In high wind areas in NZ (55 M/s) the requirement is to
design for a uplift of 100Kg/sqr. metre. If the poles are to resist horizontal
loads without diagonal bracing then they are working as cantilevered piles and
the theoretical resistance to movement at the top of the pole goes up as the
square of the depth of embeddment. Deeper is much better. My guess is that 3 or
4 feet of embedment with a concrete collar around the top third of the pole
would be about right. Don't underestimate wind loadings, wind loading goes up
exponentially with wind speed. One useful trick is to set a small concrete
culvert vrtically in the post hole, pack earth and rubble around this to hold it
in place and then you have room to manuever heavy posts into exact alignment
without crud dropping into the post hole as you do so. When you have the post
properly positioned inside the culvert, wedge it in place and and fill the
culvert with concrete. Hey presto!.