More About Loft Conversions

Planning Regulations

Lets start with fairly good news, A loft conversion or loft extension for your home is in most cases classed and built as "Permitted Development" therefore you will not need to submit an application for planning permission. To build your new loft conversion under PD rights any additional roof space created must not exceed the volume allowances, 40 cubic meters for terraced houses.

50 cubic meters for detached and semi-detached houses. (This is measured externally)

Loft Conversions and The Laws and Regulations Around Them

Provided the loft conversion falls within certain limits and considerations, a number of factors must be taken into consideration when deciding whether or not your property needs planning permission. You would not normally need to obtain planning permission for your loft conversion providing that:

The property is a domestic dwelling and not a flat or maisonette; the proposed extension or dormer window should not be raised above the highest part of the roof or the slope, which faces a public highway.

Also bear in mind that any previous loft extensions must be included within this volume allowance.

Although you personally may not have created additional space, a previous owner may have already done so.

The permitted development rights of your property are restricted by some conditions.

i.e. side-facing windows (hip to gable) must be obscure-glazed and non opening unless the parts that can be opened are more that 1.7 meters above the floor of the room in which the loft conversion is installed. Importantly materials should be in similar appearance to the existing house.

Planning permission will be required for a loft conversion beyond the existing roof slope of the principal elevation that fronts a highway, also if the existing roof line to your property needs to be raised. (roof lift loft conversions)

The slope or any part of the roof, which faces a public highway, is to be altered.

The building is listed as being of special architectural or historic interest.

The building is situated in a conservation area.


Thermal insulation must be provided to all new walls and ceilings, if you are installing loft insulation as part of a loft conversion project. Insulation has to comply with the relevant building regulations; the insulation in your loft must meet the minimum energy efficiency values.

Care should be taken not to block any ventilation at the edges (eaves) to reduce the possibility of interstitial condensation. This is a critical part of the regulations often misunderstood and overlooked by the less experienced.


Part P of the Building Regulations requires that: Installation of new electrics have to conform to BS 7671:2008 17th Edition IEE Wiring Regulations, installation should have provisions made in the design, inspection and testing in order to protect persons from fire or injury. All wiring within the loft conversion or extension to be protected by an RCD (residual current device)


The existing ceiling joists are unlikely to have the capacity to carry the additional loads of the new floor.

To overcome this problem new floor joists will need to be installed to take these new loads. These can normally be placed between the existing ceiling joists and will probably be larger than the existing joists. If the existing walls are adequate then the new floor joists may be supported on them. Otherwise additional support, such as steel/flitch beams or timber beams should be introduced. The new loft floor in a dwelling or over a garage (Bungalow) will have to resist the effects of fire and smoke penetration for half an hour.

The new floor in the loft conversion or extension must be supported at the ends on load bearing walls or from strap hangers, from beams calculated to accept the floor loads. Joists sizes are dependent on the spans involved.


The ideal type of stair for a loft conversion is a traditional type with landings top and bottom with equally sized steps, in all cases suitable guarding and handrails must be provided and headroom of not less than 2m must be achieved. The headroom requirement is a vertical measurement, however relaxation down to 1.8m will in certain circumstances be acceptable.

Loft ladders are not permitted to any habitable rooms.

Wherever possible the new staircase should rise over the existing staircase and enclosure.

A staircase fitted or located incorrectly can de value a property.

Smoke Alarms

When converting an existing roof space into a room or rooms the provisions for escape needs to be considered throughout the full extent of the escape route. Therefore a hard wired and battery back up interconnected smoke alarm system will be fitted to all habitable rooms off the escape route, with interconnected heat alarm in the kitchen.

For more information or to arrange a design visit please contact us or call free on: 0800 014 2407.

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