Extending in Felpham is mostly fine, sometimes not. Twenty-one buildings sit on the national listing register. Two are Grade II star, nineteen Grade II. One conservation area covers the historic core around the church. Heritage planning inside that core, ordinary planning outside it.
On the listing register, Felpham has twenty-one buildings recorded, none at the highest Grade I, two at Grade II star, and nineteen at Grade II. The Grade II star pair includes Blake's Cottage, where William Blake wrote between 1800 and 1803, and the Church of St Mary. Listing means the building is legally protected against alteration that would change its character of historic or architectural interest. If you own one, what you can do to it is decided by the local authority's conservation officer applying national listing law, not by your own preference for new windows. Replacing original windows with plastic units needs consent. Stripping out internal period features needs consent. Any extension has to be assessed against the building's listed character. Listed-building consent is a separate planning track and runs slower than ordinary planning.
On the conservation area, there is one designated area in the village, covering the historic centre around the church. A conservation area does not protect individual buildings in the listed-building sense, but it does restrict what can be done to their external appearance. Inside the conservation area, you typically need consent for things that would be permitted development elsewhere: changing the roof material, putting up a rear extension over a certain size, replacing original windows on a front elevation, and cutting down trees of a certain trunk diameter. The reasonable buyer inside the conservation area checks with the planning department before assuming any external change is automatic.
For most addresses in Felpham, which are neither listed nor inside the conservation area, the standard permitted-development rules apply: rear extensions within size limits, loft conversions within limits, garden buildings within limits, all without a planning application provided they meet the criteria. Anything outside the permitted-development boundary needs a planning application like anywhere else. The village's post-war housing stock makes up the bulk of the sites that are neither listed nor inside the conservation area, and is the practical context for most extension projects here. Talk to the planning department before you talk to the builder, not the other way round.
On freedom to extend or alter your home, Felpham scores middling, around three out of five. The heritage layer is real but localised. Most homes sit under ordinary planning. A few have the conservation officer in the loop, and a handful have listed-building consent in their future.