Yes, and with less interference than a town this old has any right to offer. Not one conservation area recorded across the whole place. Forty-seven listed buildings, and almost all of them at the lowest grade. Plenty of neighbours are already doing it. The thing most likely to complicate your extension here is not the planning department, it is the ground underneath it.
There are 47 listed buildings in the area: 3 at grade one, 2 at grade two star, and 42 at grade two. If you buy one of those, listed building consent governs almost anything that affects its character, inside as well as out, and that includes the things people assume are cosmetic. Windows, internal walls, roof coverings, the lot. If you buy one of the other several thousand homes in the town, none of that applies to you, and the register of listed buildings is a thing you drive past rather than a thing you negotiate with.
People here alter their houses constantly. Planning applications across the area ran to 126 between April 2024 and June 2026, with 60 of those in the last twelve months. That is a steady flow of extensions, loft conversions, dormers and garden rooms going through the system in a town of this size, which tells you more about how straightforward the process is than any policy document would.
The real constraint is geological. The British Geological Survey puts the shrink-swell hazard at class 3 here, and the whole area reaches that class, meaning the ground beneath every postcode is the kind that swells and contracts with moisture. In practice this is a foundation question, not a permission question. Deeper foundations, a structural engineer's view before you finalise the design, and a proper conversation about any mature tree within striking distance of the new footings. Builders on this island have been dealing with it for generations and price it in. It is not a reason to abandon the extension, but it is a reason not to accept the cheapest quote from someone who has never dug here.
Four listed buildings in the area sit on Historic England's Heritage at Risk register. That register records buildings in poor condition, and an entry can open the door to grant support for repair while guaranteeing that any work attracts close attention. It is a live consideration if you are buying one of those buildings and essentially irrelevant if you are not.
For an ordinary house, the practical position is the national one and nothing worse. Work inside permitted development limits proceeds without an application. Anything beyond them, and anything to a listed building, needs consent from Isle of Wight Council, who decide these on their published policies rather than on a local layer of heritage restriction that simply does not exist here. Nobody buying a post-war semi in East Cowes needs to worry about matching mortar or sourcing reclaimed slate.
Freedom to alter a home is one of the stronger things this town has going for it. The heritage sits in a handful of grand buildings on the edge of the picture rather than draped across every terrace, and the only thing likely to hold up your side return is the survey, not the council.