Yes, you can extend a house in Forest Row, but the planners and the landscape both get a say first. There are a few dozen listed buildings and a conservation area. The whole village sits inside a protected landscape. The neighbours put in planning applications all the time. Most homes can be extended, provided you follow the process properly.
There are 33 listed buildings in the area. None is grade I, 3 are grade II* and 30 are grade II. Listing covers the whole building, inside and out, so almost any change that affects its character needs listed building consent, from an extension down to new windows. Grade II* buildings get closer scrutiny again. If you're buying one of the 33, you're also taking on responsibility for its upkeep, and the planners will expect lime and timber rather than a quick trip to a builders' merchant.
The area has 1 conservation area, the Forest Row conservation area. Inside it, changes that would pass without comment on an ordinary street can need planning permission. That can include demolition, some changes to the front of a house and work to trees. Check whether the house is inside the boundary before you draw up plans, not after the builder has booked in. The whole village also sits inside the High Weald Area of Outstanding Natural Beauty, where some of the building rights that apply elsewhere are narrower.
There are also 2 scheduled monuments, the strictest tier of heritage protection. They're relevant mainly to anyone whose land borders one, and anything that disturbs the ground near one needs separate consent.
Plenty of residents alter their homes regardless. There were 378 planning applications between April 2024 and June 2026, and 185 in the last twelve months. That's a lot of paperwork for a village this size, and it shows owners here extend, convert and rebuild as a matter of routine. They just get permission first.
In practice, an ordinary house outside the conservation area and not listed may be able to do some work under permitted development rights, though the protected landscape narrows what those rights cover. Anything listed, inside the conservation area or near a monument should assume it needs consent. Ask the council, or pay a planning consultant for an hour before paying an architect for a month. An hour of advice costs far less than an application that gets refused.
Your freedom to extend in Forest Row is middling. Most homes can grow, but expect heritage rules and the protected landscape to shape what gets built.