Outbuildings can serve various different purposes for homeowners, whether it be an annex or an entertainment room, we will use our vast experience to design the outbuilding to your requirements.

The majority of outbuildings can be applied for under a Lawful Development Certificate (Permitted Development). Permitted Development sets out guidelines, that if abided by, the project will be deemed lawful and then a certificate will be issued. Some of the key guidelines noted are as follows;

  • The outbuilding must not cover more than 50% of the land surrounding the original house.

  • The outbuilding must not exceed the principal elevation of the original house.

  • The outbuilding must not be self-contained for example, a separate living accommodation.

  • The outbuilding must have a maximum eaves height of 2.5 metres.


All of the guidelines are best further described on the Planning Portal website. Lastly, a Permitted Development applications takes 8 weeks before your local authority makes a decision and will cost £86. 

The other option for outbuildings is Full Planning Permission. This application type is used when your requirements do not fall under Permitted Development. Planning Permission is an 8-week process and currently has a fee of £385.

Additionally, an Energy Performance Certificate (EPC) will be required. This certificate simply gives the building an energy rating and can give a rough indication as to how much will need to be spent to “run” the building.

When applying for these applications, there are a list of other additional works that may need to be carried out.


Building Control is a service that inspects building works and ensures that the build complies with current (UK) Building Regulations. This service can be completed privately or with the local authority. For outbuildings, Building Control will not be required if is under 15m², may be required if between 15m² – 30m² and will be mandatory if over 30m².


Construction drawings will be obligatory if the outbuilding requires Building Control. These are drawings that state how the building should be built in accordance with current UK regulations.


It may be necessary to calculate the structural elements for Building Control’s Approval. Once the extent of this part of the works is quantified, we can provide a quotation from our in-house engineer or you can appoint your own.


The proposed works may require drainage services from the waste water provider. There are two separate waste water providers that the project may fall under, these are Anglian Water and Thames Water. Each water provider has their own criteria and a simple site visit from A9 Architecture will determine if their services are required and what their fee may be.  For more information, please see their individual websites.


As new builds require foundations, a soil test may have to be carried out in order to determine how deep the foundations will need to be and what method to use. This is often seen in projects where there are large trees in close proximity or where the soil is malleable. Additionally, the soil may also require testing for any contamination. These tests will be carried out by soil specialists and the fee will differ from company to company.


Tree surveys are required when there are trees within close distance of the proposed works. This could range from neighbouring trees to trees that are on public areas. The tree survey will locate each tree that they deem will affect the proposed works. Additionally, the tree survey will also locate Tree Preservation Orders (TPOs). TPOs are put in place to prevent the harm of important species of trees. If a tree does have a TPO there are a list of guidelines that must be abided by when in the construction stage. The fee for a tree survey is once again determined by the company appointed.