Pole and Pile Foundations for Residential Housing in New Zealand

Pole and pile foundations have been in vogue in New Zealand for only 5 years but already are used in over a third of all new residential housing. The appeal of pole housing lies in site and construction cost savings. In addition there are opportunities for architectural innovation particularly on steep lots which hitherto have been too costly and difficult to develop and where the setting can be quite dramatic. Short pile foundations provide the cheapest type of foundation on flat or gently rolling country where they have been adopted by large companies in the low cost, offsite, and modular housing field. Radiata and Corsican pine have a characteristically wide, readily treatable sapwood band; they are of good form and readily available. With CCA preservation, roundwood of these species is expected to last at least 80 years, well beyond the economic life of a house. Engineering design requires particular attention to site stability, pole embedment and spacing, and joint detailing. It is important to be aware of and minimize any possible discomfort that might arise if the pole house were not stiff enough to avoid slight movement in high winds. Practical problems that can occur during construction are discussed. Some suggestions are offered on excavation of holes, pole setting and alignment, and framing up. Finally, the tremendous potential, still not fully realized, of the driven timber pile system is noted. Piles can be placed easily and cheaply to give a level grade for prelaying the floor and framing up–only hours after starting on the site.

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