An extension to your house is usually considered to be permitted development and does not require an application for planning permission. While you may not need planning permission, most extensions of properties will require approval under the Building Regulations. This is subject to set limits and conditions.
Building regulations are designed to protect you and to make sure that any work done you have done is structurally sound and safe. It ensures the new room is fire safe and that sound is reasonably insulated between the loft and the spaces below.
Building Regulations (Building Warrant in Scotland) are primarily objective and restrict themselves to the structural aspects of your project’s build.
An application you make for Building Regulations will either conform to the regulations and will be approved, or it will fail to conform and be rejected. However, there is room for pragmatism, and inspectors do have the power to negotiate a relaxation in certain circumstances.
The individual regulations that will apply always depend on the type of conversion you are having built.
As a guide to help we have provide link below to the Planning Portal website, typical elements that are covered by building regulation include:
If in doubt you should always consult your local planning authority.