The bulk of 'old growth' Redwood from the US west coast has long since been harvested, and now most Redwood is from second growth forests, most of which are more sustainably managed than they were in the past.
There is a limited amount of New Zealand grown Redwood available, and some US grown Redwood imported into the country.
Redwood heartwood is durable and compliant as an acceptable solution for use as weatherboards or exterior cladding under NZS 3602.
The sapwood of Redwood - easily recognisable by its creamy white colour is not durable and is not suitable for use in exterior applications
The sapwood of Redwood contrasts quite obviously with the pink - red heartwood.
Beware of companies selling local or imported Redwood with a high sapwood content, it is unlikely to conform with the New Zealand Building Code.
Ensure Redwood is fixed with stainless steel of silicon bronze nails, as bright steel or even galvanised nails can stain the wood.
The above image shows non compliant Redwood containing significant sapwood installed in an exterior application.