the first architect said we needed raft foundations because we are 7.4m from a belt of trees(nearest). the trees are ash, about 200 to 300mm diameter. then he declined not to do the work. the next architect designed using raft as first proposed then said a strip foundation with 1.4m founds will be sufficient and cheaper. who is right??

  • Mark Brinkley

    A good question! There is no right or wrong here, just opinions based on experience plus a little guidance from sources such as the NHBC tree table. Normally architects don’t even make such judgements but defer to the likes of building inspectors and structural engineers. A building inspector may advise there and then on the spot: an engineer is likely to make a recommendation backed up by their insurance policy and is therefore going to err on the conservative (i.e. expensive) side.

    You pays your money, you take your choice. Ash (moderately thirsty) at 7m (a little bit closer than you’d like, esp for a tree which grows above 20m in height) is pretty marginal – hence probably the conflicting advice you are getting. Bare in mind also that ash as a species is currently at blight risk from die back disease and the trees may not be around for long.

    What no one wants is for the foundations to move (i.e. fail) in future.

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