Loft conversions

Introduction: most houses have a large space under their roofs normally known as the loft or attic, this space is often under utilised and in some instances can offer an ideal opportunity for expanding your home. This guide has been written to provide you with useful information about how the building regulations will affect your loft conversion project.


Not all lofts are suitable for conversion and as a first step it is wise to go into your loft and carry out a brief survey before you get too far into the planning of your project. When carrying out your survey check:

  • That there is enough height within your loft to stand comfortably, bearing in mind that your new floor is likely to be around 200mm higher than your existing ceiling joists.
  • That the loft space is large enough to provide a usable room.
  • That there aren’t any chimneys or services passing through the loft space that will need moving.
  • That your roof has felt under the tiles or is fully weathertight.

If the answer to all of these questions is ‘Yes’ then your loft may well be suitable for conversion.

How to proceed - technical issues

Loft conversions are complex projects and unless you are experienced in construction you will need to get some professional advice.

The roof structure

The roof of your home is currently designed to keep out the rain and snow and to cope with some light loft storage loading. After a loft conversion your roof will have to cope with significantly different loadings, a new floor structure will be required and it is likely that a number of the structural elements will need to be altered to allow for circulation within the room, roof windows etc. Roofs can generally be divided into two types.

Trussed rafter roofs: these have been common since the 1970s, and roofs of this type are difficult to convert. Roof trusses are complex pieces of engineering and they should not be altered without the advice of a structural engineer. When converting this type of roof it is common for a series of beams to be installed to provide support to the new floor and to strengthen the rafters, this allows the bracing sections of the trusses to be cut out to create a clear floor area.

Traditional roofs: these are generally made up from a series of rafters and purlins spanning between load bearing walls. These roofs are less complicated to convert than trussed rafter roofs, however, beams are often required to provide support to the new floor structure and the existing purlins and a structural engineer’s design will be required for all but the simplest conversions. When considering a loft conversion don’t be tempted to simply board over your existing ceiling joists and rafters, this can adversely affect the value of your property and in some circumstances can cause overloading and endanger the structural stability of your home.

Accessing your loft conversion

If you want to convert your loft for habitable use you will need to install a staircase and careful design of this can be critical to the success of your conversion. If there is enough headroom it is often best to continue the stair in the existing stairwell as this saves space and gives a feeling of continuity within the home, alternatively part of a room will have to be partitioned off to accommodate the new staircase. Wherever the stair is installed it should be designed in accordance with the following guidance.

Pitch: the maximum pitch for the stair should not exceed 42 degrees.

Rise and going: the maximum rise of each tread of a domestic stair should not exceed 220mm and the going should be at least 220mm.

Headroom: the clear headroom over the stair should be at least 2m, for some loft conversions the building regulations allow a reduced headroom of 1.9m over the centre of the stair and 1.8m on the outside edge.

Handrails and balustrades: the stair should be provided with a handrail at least 900mm high and any exposed edges of stairs or landings should be provided with balustrading at least 900mm high. For loft conversions where space is very limited and only one room is created, a specialist alternating tread staircase can be used, these are steeper than standard stairs and can provide valuable space in some circumstances.

Fire precautions: house fires can kill and fire precautions are a major concern for the building regulations. The most dangerous fires generally occur at night when everyone is asleep and to give you awareness of a fire it is important that you install smoke detection. When converting your loft you will need to ensure that you have mains powered, interlinked smoke detectors in the hall/landing areas on every floor of your house.

Two storey houses: the building regulations requirements for fire precautions in two storey housing are quite simple as it is generally felt that if you couldn’t get out down the stairs you could jump or be rescued from a first floor window. If you are converting the loft of a bungalow you will need to ensure that you have mains powered interlinked smoke detection at ground and first floor level and that all habitable rooms at first floor level have an ‘escape window’.

Escape windows: as their name suggests, are windows that are large enough to allow people to escape or be rescued through them. They need to have a clear opening area of at least 0.33m2 and a clear width of at least 450mm. The bottom of the opening light should be no more than 1100mm above floor level and they should allow people to escape to a place free from danger. Escape windows need to be fitted with escape hinges that allow the window to fully open. Some of the standard hinges fitted to Upvc windows do not achieve this so it is wise to check this with your glazing supplier when you order your windows.

Three storey houses: when you convert the loft of a house and create a third floor the building regulations require you to look at the fire precautions within the house a lot more seriously. Mains operated smoke detection needs to be fitted to give you awareness of a fire and as, due to the height of your new floor, you can no longer rely on escaping through the windows the only safe way out of the house is down the stairs. It is therefore vital that the stair is protected from fire. To protect the stair all of the doors that open onto the stair need to be half hour fire doors and the stair should end up in a hall with a door direct to the outside. Generally, unless a sprinkler system or alternative escape stair is provided, stairs cannot discharge into other rooms in three storey properties.

Four storey houses: if your house already has three storeys, loft conversions become more complicated. You are likely to need to install a sprinkler system or a second escape stair and the project will need specialist design. Please contact us and we will be happy to provide you with more detailed advice if you are considering one of these projects. Fire is very dangerous and careful design and planning is required to ensure that the risks it poses are minimised.


It is often a nice idea to include a bath or shower room in your loft conversion, the best place for this is generally directly above your existing bathroom as this should ensure that you can connect into the existing drainage and water supplies without the need for excessive pipework. Any bath or shower rooms will also need to be fitted with an extract fan to improve ventilation. It is a good idea to decide on the location of any bathrooms at an early stage in your space planning process.

Thermal insulation

CO2 emissions are a major concern in today’s environment and you will need to provide a high level of insulation to your roof as part of your loft conversion. The most common way of achieving this is to place a high performance insulation board in between and below the rafters. Unless your roof has a breathable felt you will need to leave a void above the insulation and ensure that you have effective roof ventilation to prevent the build up of condensation.

Sound insulation 

To reduce unwanted noise the walls and floor around bedrooms will need to be insulated to reduce sound transmission, this is generally achieved by placing 100mm of sound deadening quilt in the floor void and in the partitions around the bedrooms. If you are converting the loft of a semi-detached or terraced property you will need to ensure that the sound resistance of the Party Wall is upgraded so that sound transmission to your neighbours is reduced.


To maximise the usability of the room you will probably want to install heating, in most instances the most effective way of doing this is to extend the existing central heating system. You will need to check with your plumber or heating engineer to ensure that your existing boiler has sufficient capacity to serve any additional radiators and any new radiators should be fitted with thermostatic valves to control the room temperature. If it is not possible to extend the existing system or if you prefer an alternative method of heating, e.g. electric panel heaters, careful consideration should be given as to how these can be switched and controlled to ensure that they function efficiently.


You are likely to require some electrical alterations as part of your conversion. Depending on the age and condition of your existing electrical system it is sometimes possible to extend existing circuits but sometimes new circuits and even a new distribution board will be required. It is a good idea to get advice from a competent electrician at an early stage. When appointing an electrician please ensure that they are able to issue you with BS7671 test certificates when they have completed their installation as these will be required before your building regulations Completion Certificate can be issued and you will incur additional costs if the test certificates have not been provided.

Windows and ventilation

Any new habitable rooms will need to be ventilated. Generally this is achieved by providing an opening window or roof light equivalent to 1/20th of the floor area of the room with a trickle vent at high level. All new windows must be fitted with highly efficient double glazed units. In bath or shower rooms an extract fan should be fitted and in rooms without opening windows extract fans should be fitted that are triggered by the light switch with overrun timers that allow the fan to remain on after the light is turned out.