Take a good look around most suburban areas in the southeast and you can find at least one example of an ugly Loft Conversion or Extension spoiling the appearance of the street. As you might expect the planning system has adapted over a number of years to prevent the proliferation of such eyesores whilst at the same time continuing to encourage homeowners to spend money developing their homes. The system we have today is, on the whole, quite successful in balancing the competing interests of homeowners wanting to extend and develop their properties, neighbours who don't want to be adversely affected by such developments and local people who want to preserve the appearance of the locality. The system in place therefore requires that all Extensions to properties (including building Dormers for Loft Conversions) must have Planning Permission. That Planning Permission can be achieved in one of two ways:
Option 1 - Permitted Development
Loft Conversions are usually carried out using a general Planning Permission granted by Parliament (not the local authority) for the development of houses, known as "Permitted Development Rights". These rights allow you to extend your house in a number of ways without the need to apply for Planning Permission to the local authority. It is important to say here that although most houses have these Permitted Development Rights not all do. Houses within Conservation Areas, Areas of Outstanding Natural Beauty or in National Parks do not have Permitted Development Rights, nor do flats or maisonettes. Also some houses have had their Permitted Development Rights withdrawn by the Local Authority (although this is rare). You can easily check with the local authority to determine if this is the case for your home.
Permitted Development Rights are usually enough to meet the needs of most homeowners wanting to do a Loft Conversion because they allow you to extend the roof space by adding Rear Dormers or Side Dormers and by building up the Gable Ends of the roof. They do not allow you to build Dormers on the front of the roof nor do they allow you to extend the height of the roof beyond the existing highest part. There is also a limit as to how much cubic volume you can add to the building using your Permitted Development Rights (40 cubic metres for terraced houses and 50 cubic metres for detached and semi detached houses). You will also have to use materials which are similar in appearance to those already used and any windows which face to the side will have to be obscured.
There are of course many other specific technical points relating to Permitted Development Rights which must be complied with in order for a development to be considered lawful so it is a very good idea to submit a Planning Drawing of your proposed Loft Conversion to the local authority before work starts so that they can either issue you with a Lawful Development Certificate to certify that the proposed works are covered by your Permitted Development Rights or start to process a Planning Application if not. The have been disputes in the past between local authorities and national government over the technical details of Permitted Development Rights so we always advise clients to obtain a Lawful Development Certificate before work starts where possible although the work can be completed without one if you so choose.
Option 2 - Apply for Planning Permission
Applying for Planning Permission is essentially the process of asking the planning department of your local authority for permission to carry out your proposed development. The local authority will usually have in place a development plan which they will use to decide whether or not to grant Planning Permission. A Planning Officer will look over the Loft Conversion Plans and assess the likely effect or impact of the development on neighbouring properties and the neighbourhood in general. They will consider the outside appearance of the development, how big it is, how it sits within its surroundings, what effect it might have on access, landscaping etc. Unfortunately they will not tell you in advance what you can and cannot build but will instead insist upon seeing a written proposal including Planning Drawings which they will then assess. Since you need to spend some money drawing up and submitting these Planning Drawings without knowing for sure what the outcome will be this route is one which tends to be avoided by most homeowners where possible.