Conservation areas often contain Nationally Listed buildings (buildings which have been listed by national government as being of architectural and/or historic interest).
If you live in such a building, further restrictions apply to the type of works that can be undertaken without planning permission or Listed Building Consent. It is therefore always advisable to discuss your proposals with the Planning and Development department prior to carrying out any external or internal alterations, demolition or development within the boundaries of your property.
Some other buildings, although not protected by having been listed at the national level, are never the less "locally listed", meaning that they have been designated by Watford Borough Council as buildings of local historical significance. The council will pay particular attention to proposals affecting such buildings; and demolition is unlikely to be supported.