Yes, most houses in Tring can be extended through the normal planning process, and a smaller group of older buildings come with tighter rules. The town has a few dozen listed buildings. It has one conservation area. Its residents put in hundreds of planning applications a year. For most owners an extension means an application and a wait, and for the owner of a listed building it means a much longer wait.
Historic England lists 68 buildings in Tring. One is grade I, two are grade II* and the other 65 are grade II. Listing covers the whole building, inside and out, so changing a staircase or replacing windows can need listed building consent as well as planning permission, and doing the work without it is a criminal offence. Tring got its market charter in 1315, and the buildings that council officers watch most closely are mostly from the centuries since.
Tring has one conservation area, named after the town. Inside it, ordinary unlisted houses lose some of the freedom they would have elsewhere. Knocking down a building, cutting back a tree, or changing the street-facing side of a house can all need consent that would not be needed a few streets away. About 3% of the area is within the Chilterns Area of Outstanding Natural Beauty, where the rules on what can be built without permission are tighter again.
Dacorum's planning register records 793 applications in Tring between April 2024 and June 2026, and 361 of those came in the most recent twelve months. That is plenty of residents adding rooms, converting lofts and asking to change their houses, and the register is the best evidence there is that alterations are routine here. When Pendley Manor burned down in 1835, its owner rebuilt it in Jacobean Revival style, so Tring has a long record of replacing old buildings with bigger ones.
For a house outside the conservation area and off the listed register, many rear extensions and loft conversions can go ahead as permitted development, without a full planning application, within national limits on size and height. For a listed building, permitted development does not cover the work, and every change goes through the council. For a house inside the conservation area, some changes that would be allowed elsewhere need an application. Historic England's online list and Dacorum's conservation area map show which category a particular house falls into, and checking both settles the question before any plans are drawn.
Your freedom to extend in Tring is middling, easy for most of the post-war houses and slow going for the minority of older buildings the planners guard closely.