Yes, for most houses in Sheerness, as long as you check the map first. Very few homes are listed. Three conservation areas cover the older parts of town. The clay underneath moves. Your neighbours put in planning applications all the time, so extending here is routine, provided you get the paperwork right.
Sheerness has 52 listed buildings. One is grade I, 8 are grade II* and 43 are grade II. Listing covers the whole building, inside and out, so almost any change to a listed home needs listed building consent on top of any planning permission. Carrying out work without it is a criminal offence, not a planning technicality. In a town of several thousand homes, 52 is a small number, so the chance that your house is one of them is low. Check the national register before assuming it isn't.
The three conservation areas are Mile Town, Marine Town and the Dockyard. Inside them, the council cares about how a street looks as a whole. That means tighter control on demolition and closer scrutiny of changes to front elevations, roofs and anything visible from the road. Some conservation areas also have local orders that remove permitted development rights, so ask the council directly before you design a new front porch.
There are 3 scheduled monuments in the area, including the Sheerness defences. That's the strictest level of protection there is. It mainly affects land next to or on top of one, and very few domestic back gardens are affected.
Across the 27 months from April 2024 to June 2026, the council received 573 planning applications from the area. 228 of them came in the most recent twelve months. That shows people here do extend, convert and alter their homes regularly. The numbers show how many applications were made. They say nothing about how many were approved.
The ground needs more thought than the heritage does. The British Geological Survey puts every postcode in Sheerness at shrink-swell class 3, the class for clay that expands when wet and shrinks when dry. It's a published hazard classification, and what it means for an extension is practical. Foundations may need to go deeper than the builder's first quote assumes, especially near trees. A structural engineer should look at the ground before the architect starts designing. That's cheaper than finding out from a crack in the new wall.
Two listed buildings in the area are on Historic England's Heritage at Risk register. It's a list of buildings in poor condition. Their repair may qualify for grant support and will be watched closely. That matters if you're buying one of those two. It makes no difference to an ordinary terrace a few streets away.
In practice, most houses outside the conservation areas can use permitted development rights for modest rear extensions and loft conversions without full planning permission, subject to the national limits. Anything inside a conservation area, anything listed, and anything large enough to go beyond permitted development needs an application. A lawful development certificate confirms your plans are within the rules before the builder starts.
Freedom to extend in Sheerness is middling. Most homes can grow without drama, but a conservation-area address or a listed building changes that, and the ground under every house needs an engineer's view first.