If half of the material ending up as "wood" in a building is epoxy or some other treatment, though, the efficacy of using buildings for carbon capture seems quite decreased.
Not if there is more than a doubling in use of wood. The epoxy, or whatever, makes wood a more compelling construction material, and if it results in far more wood construction, it is a net win.
The raw materials to manufacture it are mostly hydrocarbons. Maybe we should be focusing on making "green epoxy" instead.