Yes, and plenty of people are doing exactly that. What decides your answer is which street you bought on. The historic core is thick with listed buildings and sits inside conservation areas, where the paint colour is somebody else's decision. Most of the city went up after the war and carries none of that. Truro is two planning regimes sharing one postcode, and the estate agent rarely mentions which one you are standing in.
The heritage load is real. Historic England lists 331 buildings in the area: one at grade I, nine at grade II*, and 321 at grade II. Listing applies to the whole building, inside and out, so it is not only the front elevation that needs consent. Replacing windows, opening up an internal wall, adding a rear extension or fitting solar panels all become applications for listed building consent rather than decisions you make with a builder over a cup of tea, and doing the work without consent is a criminal offence rather than a fine and a shrug.
Three conservation areas sit within the area, covering Truro itself, St Clement and Kenwyn Road. Conservation area status does not freeze a house, but it narrows what you can do without asking: demolition, most tree work and alterations affecting the street scene come under control, and councils can further restrict ordinary permitted development rights within these boundaries. The boundary itself is the thing to check, because it often runs down the middle of a street rather than around a neighbourhood.
There are also four scheduled monuments in the area, which is the strictest tier of protection in the system. This matters less for a typical house purchase and more for anyone buying land or a property adjacent to one, where works need separate consent from the national heritage body rather than the council.
For live evidence that alteration happens here anyway, the planning register records 2,763 applications across the area between April 2024 and June 2026, of which 1,181 fall in the last twelve months. That is a steady flow of householders, developers and owners of protected buildings all putting paperwork in. Extending in Truro is normal. Extending in Truro without permission is the part that goes wrong.
Mining legacy is a minor consideration rather than a defining one. About 1% of postcodes sit near a recorded mine entry, with none directly over a recorded working, and the nearest recorded entry is around 350 metres away. The practical effect is that a conveyancer may order a mining search, and in a small number of cases a specialist report, which can influence what a lender or insurer asks for before they commit. It is a process step, not a structural verdict on the house.
In practice, the question to ask before you offer is not whether the house can be extended but which permissions apply to it. On a post-war semi outside the designated areas, ordinary permitted development rights are likely to cover a rear extension or a loft conversion, subject to the usual limits. On anything listed, or inside a conservation area boundary, assume consent is needed and budget the time as well as the fees. The council's planning register will tell you what has already been approved nearby, which is the cheapest research available.
Freedom to alter a home here is more constrained than most of Cornwall, not because the rules are unusual but because the protected stock is concentrated and the boundaries are tighter than people assume. Check the designation before you draw the extension, not after.