The Institution of Structural Engineers
David Ryland
I.Eng. A.M.I.Struct.E.
Structural Engineer
TRADA member

Limited Guidance Notes on Extensions

Section B - Full Planning Permission

1. For developments that are outside the scope of 'Permitted Development' it is usual to apply to the Local Authority planning department for full planning approval.
2. This is normally always required for two storey extensions.

3. In some areas, two storey extensions may only be allowed at the side of a property but this depends on local conditions and the Unitary Plan for the area concerned.

4. Rear extensions should preferably be single storey, to avoid overlooking and privacy issues and usually they may have either a flat or pitched roof or both in combination.

5. Two storey extensions should normally have a pitched roof with slates or tiles to match the existing house.

6. Restrictions apply on the size of an extension and its projections from the line of the original building but these are flexible within 'High Quality Design' parameters.

7. Usually, the side ground floor extension should be set back 225mm (9 inches) from the front of the house. If a porch exists the proposed extension may line through with the porch. If a bay window exists the extension may line through to form a new porch level with the bay.

8. On homes in close proximity to adjacent properties, the first floor front should be set back from the front of the house to provide a visual break. This also results in the roofline at the ridge being lower than the original house so the extension does not dominate. This requirement varies depending on the Local Authority and siting.

9. Some Local Authorities require a gap between the side boundary and the first floor extension of between one and three metres, especially on corner plots. In some cases this may make the upper storey extension too narrow to be practical.

10. A two-storey side and single storey rear extension can be combined in one development.

11. Drawings must accompany the application. It is usual to provide floor plans at each level to be extended and elevations of the front, side and rear. These should be drawn for both the original 'as built' situation and the 'as proposed'. A site location plan is required and also a block plan showing the relationship of the proposals to the surrounding properties.

12. Planning applications usually takes from six to eight weeks to be approved.

13. Most Local Authority planning departments now require the site location plan to be marked on an up to date Ordinance Survey map extract.

14. It should be stated that each Local Authority has its own preferences and approval of a proposal usually depends on good design, which takes into account the general street scene, privacy rights of neighbours, lighting and other additional rules which may apply to Green Belt, Conservation Areas or Areas of Outstanding Natural Beauty. For larger or unusual projects it is best to involve the planning department at an early stage to agree basic principals before getting too far into the design.

Contact details:
Tel: 01953 853040
Mobile: 07802 183823

 Guidance Notes on Extensions 

 Permitted Development 
 Planning Permission 
 Building Control 
 Foundation Engineering 
 The Builder 

Sample drawings
Planning:   Drawing1   Drawing2 
   Drawing3   Drawing4 
Building Control:   Drawing1   Drawing2