Loft Conversion
A loft conversion (or roof extension) is a great way to improve and refresh your home, add bedrooms, bathrooms or storage space without having to move to a new house, and as a result - add significant value to your home.
Planning
The rules for domestic loft conversions are generally universal for all councils with slight variations when it comes to appearance:
Ridge Height
In many cases councils would require that the ridge height be maintained when converting a loft, and that nothing would extend above its level, e.g. dormer windows, extension ridges, etc. At the same time, in order to create habitable space, there would be a minimum clear ceiling height requirement, mostly varying from 2.1m to 2.5m. This could mean that there is not much benefit in considering a loft conversion if the ridge is low and restricts the ceiling height below the minimum requirement. A workaround could be to bring the loft floor at a lower level, however, the resulting head height at the top floor will also need to be compliant with minimum standards.
Appearance
It is common practice for loft conversion items to match the appearance of the original roof, even more so if going through the Permitted Development route. This usually applies to the finish materials, types of windows and the roof shape. Most councils would be mainly concerned with the appearance of the front roof slope, slightly less with the sides, and the least with the rear slope, e.g. front facing dormer windows are a rarity, with most dormer windows being constructed to the rear of a roof, and only skylights allowed to the front and sides. This varies from council to council and depends on the street scene, so it is best to check for each case individually.
Overlooking
Side-facing windows, in most cases, are only allowed to be frosted and non-openable if there is potential for overlooking into your neighbours’ property. Habitable rooms, like a bedroom or a living room, should ideally make use of front and rear facing windows only, which could result in limitations on things like the number of bedrooms, the living area size etc. In lofts, it is common practice to only have skylights to the sides that are entirely above 1.7m from the floor level, or if any dormer windows are constructed to the sides, those would only serve bathrooms, hallways or storage areas.
Further Considerations
Staircases require a clear 2 meters head height (1.9m in some cases) – if the space on the top floor is restricted, it might be challenging to construct a staircase. Furthermore, a staircase takes up space which might be utilised in some other way in the existing house.
Building Regulations
Air tightness and thermal insulation of the loft are great ways of achieving energy efficiency in your home and are also required by the Building Regulations. As warm air tends to find its way to the top of your house, it is crucial that your loft does not leak and is well insulated.
An important thing to consider when converting a loft, is that from a Building Regulations perspective, you are adding a storey to your house. This will have serious fire safety implications if your house has two storeys and the loft becomes its third. A three-storey house must have a safe vertical fire escape route, usually meaning that the hallways and staircases must be fire separated from the rest of the house, requiring that all the walls are rated at least 30 minutes fire resistant.
Structural Considerations
If the original roof is to be retained, the main challenge would be to reinstate its structural stability – many times a loft would have existing structural members, like timber columns and struts, supporting the existing ridge, purlins and rafters, which will need to be removed in order to allow for creating habitable space. This is true even for the least obtrusive loft conversions – while simply adding a skylight seems like a minor alteration from the outside, having a clear space inside might prove challenging and will generate the bulk of the cost.
Furthermore, lofts are usually designed for light storage loads – converting a loft to habitable space would require the floor structure to be able to withstand loads from people and furniture which are significantly higher. Therefore, it is often the case that the ceiling would have to be replaced entirely with a more robust structure, or a new floor must be constructed above it, the latter resulting in reduced head height in the loft.
Permitted development
The householder permitted development rights allow for constructing a loft conversion for a single-family dwelling house, provided that certain limits and conditions are met:
To be permitted development any additional roof space added to the original house must not exceed 40 cubic metres for terraced houses, or 50 cubic metres for detached and semi-detached houses.
All extension items should be behind the plane of the existing roof slope of the principal elevation that fronts a highway.
The finish materials must be similar in appearance to the existing house.
No part of the extension is to be higher than the highest part of the existing roof.
Verandas, balconies or raised platforms are not allowed under permitted development. The only exception, in some cases, would be a Juliet balcony.
Roof extensions, apart from hip to gable ones, are to be set back at least 20cm from the original eaves, measured along the roof plane.
Your existing loft may provide a home to protected species of bats or birds - A survey may be needed, and a licence may be required, if that turns out to be the case.
Constructing any item allowed under permitted development, does not limit your future permitted development rights, with a small exception when it comes to multi-storey rear extensions.
Recent Loft Conversion Projects
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