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Loft Conversion and Extension Ideas and Costs

Planning Consent for Loft Conversions

Planning permission for most loft conversions is not required.

However, permission is required where you extend or alter the roof space and it exceeds specified limits and conditions.

A loft conversion for your house is considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions:

Any previous roof space additions must be included within the volume allowances listed above.

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

Designated areas include national parks and the Broads, Areas of Outstanding Natural Beauty, conservation areas and World Heritage Sites.


Building Regulations

Building regulations approval is required to convert a loft or attic into a liveable space.

The regulations for an existing house which is no more than two storeys high are different from the requirements for alterations to buildings that are three storeys or more.

The regulations will be applied to ensure that:-

Boarding-out for storage

In most propertiers, the existing timber joists that form the "floor" of the loft space will not have been designed to support much weight.

The joists also tie the pitched members of the roof together to prevent them spreading and support the ceiling lining of the rooms below.

An excessive additional load, for example from storage may mean that the joists are loaded beyond their design capacity. So If you decide to lay flooring boards over the existing joists in the loft space, then this may require a Building Regulations Application to Building Control.



Creating a liveable space

If you decide to create a liveable space in an existing loft space of a home it is likely to require a range of alterations.

Many of these could have an adverse impact on the building and its occupants if they are not properly thought out, planned and undertaken in accordance with the requirements of the Building Regulations.

The value of such conversions will also be discounted entirely if you sell the property and do not the Building Regulation paperwork that shows that the Works were approved by the Local Council.


The Structural Elements of a Loft Conversion

Loft Conversions in Bungalows

In many bungalows there is a central spine wall that will take a great deal of the additional loading from a loft built in the roof space.

This wall may need to be underpinned as many such walls do not have proper foundations like the perimeter walls.



A dormer is generally constructed from timber.  The main parts that form a dormer are the roof, side walls (cheeks) and front wall which faces the garden.  The cheeks can be supported in one of two ways:


Dormer Walls

The front wall of the dormer can be supported off the external wall, or if it is to be set back from the external line of the house, it can be supported off the new floor joists, which should be designed to cater for the extra load of this wall (see also external walls).

The dormer may well need to be constructed so as to give resistance to a fire spreading to or from a neighbouring property – the nature and extent of the construction to give this fire resistance will be dependant on the size of the dormer cheek and its proximity to the boundary.


Removal of rafters

To enable a window, rooflight or dormer to be installed when creating new room(s), it is normally necessary to cut an opening in the existing rafters.

The remaining sections of the cut rafter(s) can be supported by the new dormer  or, in the case of a new window/rooflight, will need to be supported by installing new timbers (known as trimmers) across the head (top) or sill of the new opening.

Depending on the size of the new opening, these may need to be two timbers fixed together (double trimmer) so that they can adequately transfer the load to the existing rafters on either side of the new opening.

It generally good practice to strengthen the rafters on both sides of the opening as they are now taking more load. This can be achieved by bolting another rafter of the same size and length to the existing.


Floor & beams

It is unlikely that the existing ceiling joists will be adequate to support the weight (loads) that arise from the construction, contents and use of a typical habitable room developed in a loft. 

To overcome this problem new floor joists would 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 or timber beams – should be introduced which in turn will be required to be adequately supported and provided with fire resistance.


New walls will contribute to the perimeter of the new room(s) and will help support the existing and new roofs where existing roof supports have been removed.  Such new support for the roof will normally take the form of low level walls towards the eaves of the premises, helping to reduce the span (unsupported length) of the existing rafters.  Other walls, typically loadbearing, will separate the new room(s) from other areas of the home.  These walls may need to be fire resisting.

Sound Insulation

Sound insulation is required between habitable rooms.  With a terraced or semi-detached house, the building control body may also ask for sound insulation between the converted loft and the neighbours loft to be improved.  If they think it is necessary the building control body also ask for a test to be carried out, but this will depend on the neighbours allowing access for the testers.  The existing party wall will need to be upgraded to provided sound insulation between the properties.


Fire Safety in Loft Conversions

When converting an existing roof space into a room or rooms the provisions for escape need to be considered throughout the full extent of the escape route. This often means that additional fire protection will be necessary in the existing parts of the house.

For example, a typical loft conversion to a two-storey house will result in the need to provide new fire-resisting doors and sometimes partitions to protect the stairway it is too dangerous to escape via windows from floors above first floor level.

Mains powered, interlinked smoke alarms will also need to be provided within the stairway at each level.

It may also be necessary to upgrade the fire protection to some parts of the structure of the house such as the floors.


Staircase Access to New Loft

Fire & general safety

To ensure adequate fire safety for the dwelling a new stair serving the new room(s) will be needed.  Where there is not enough room for a full traditional stair, it may be possible to use a "space saving" stair.  Retractable ladders or stairs are not normally acceptable.

For general safety reasons, there are specific criteria that a stair should be designed to.

Opening for new stairs

This would normally be formed by cutting away some of the existing ceiling joists between the existing habitable areas of the home and the loft-space.  As these joists support the existing ceiling and restrain the pitched roof from spreading, replacement support should be provided.  This would normally take the form of timber "trimmers" around the opening, most likely to be at least two timbers fixed together (double trimmer) to ensure the load is transferred to remaining timbers.


Contact Pentacon

Pentacon would be pleased to help with the Structural Design of your Loft Conversiion - So give me a call and email me a copy of any Notices, photos of the building and any other relevant information.

I will provide free advice in an Email on how to deal with your Problem.

Just text or call me on 07557 966 459.

I look forward to hearing from You



Best Regards


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