To change over to a wooden subfloor would be a large change to the overall house design and would cost significantly more than simply putting driven piles in under the ribraft. In this case I believe that they put the driven piles in essentially as a means of ground improvement. Essentially, they had a standard ribraft design that they didn't want to mess with, and the geotech came back with poor ground results (the top couple metres were not suitable for founding). They can just throw the driven piles underneath the ribraft and continue with minimal redesign. In some cases liquefaction is the major concern (we have that issue up the Kapiti coast a lot), and in that case piles driven to specific bearing layers is often required (depending on CPT results). Houses in Kapiti often have to be raised for flooding risk (depending on location, but generally is the case in areas where liquefaction is a concern). So the best option there is usually a timber subfloor on driven piles.

Piled timber piles never connect to a slab buddy, there's to many gravity loads, and lateral loads, the resistance load to the connection of a slab would comprise the dead load. Hope that helps.

There no such thing as standard piles, there are either anchored, braced, ordinary or driven, they all have effects for dead loads, live loads, and dynamic loads. Learn the above first, then talk about the expenses.

@@shalimar7100 you seem very smart mate, tell me more about it.....please.

That’s a ‘how long is a piece of string’ question, as these kinda piles get done in this way for a specific reason. I’d consider the extra engineering/compliance reports, machinery/operator hire and materials used to give you an idea of cost on top of what you’d see in an average timber-pile house

Sounds silly in my experience you are cutting the pile for water run off, chainsaws are pretty good, sabres will do, but a handsaw is the worst

@@shalimar7100 I was asking what they do with the off-cuts.

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