What thickness upvc

If they are replacing them then that sounds correct.... soffits will be 9mm thick and fascia boards will be 16mm.. you could ask them to slot in a new layer of felt around the bottom of the roof and lap it into the new gutter just incase it’s rotten... shouldn’t be to much more cost... hope this helps

HI....when a tradesman quotes a job stating he will be using 18mm fascia board this would only be used when all timber is to be taken off,you can cap over timber but I would personally only do this with new treated timber.Regarding 9mm soffits there is a choice of vented and general purpose board

The felt / damp should always be changed putting at least 300 mm under the old and into the gutter as for the soffit it is best to use 9mm hollow board this allows this roof space to ventilate better as for the fascias we always use 18mm then you aren’t far off what you are taking off with most old timbers being between 18-22mm Never cover the old timber/wood

Ask if they are removing the bottom row of roof tiles. And are they installing a continuous sheet of 5u felt or dpc turned over the new fascia into the gutter. By doing this it should help to keep the new fascia clean. Are they installing vented soffits to allow for air flow. Highly recommend to be done. Slightly more expensive than plain flat soffit. As stated before 16mm fascia and 9mm soffit.

Take off wooden facia and replace with 16 mm pvc facia and replace soffit with 10mm with vented or non vented depends on if roof breathable