Wood : black locust (US sourced, not the eastern European stuff everyone seems to use), Accoya and other heat/chemical treated wood (some of them are now building US plants); in general lumber that isn’t shipped to Canada to be processed and brought back down; reused timbers
Stone: local (though often more costly than Chinese, both for transportation impact concern and Asian longhorn beetle import concerns)
Steel: generally this doesn’t seem to be an issue as US steel is of good quality and competitive priced (as well as recycling when possible – presumably for cost reasons)
Soil: local, using local compost in lieu of chemical treatment
Plants: locally grown natives usually hold up better than from long distances or foreign; but where conditions dictate, non-native adapted species often are a better long term solution. Often try to select for habitat considerations (whether wildlife is desired or best deterred).
Usually stick to HDPE to avoid chemical reactions with PVC.
An interesting one is recycled content in concrete, and the impact it has on strength/chemical reactions.
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