Loft conversions

Loft conversions can be a useful way of adding an extra room to your house. The notes below are for domestic properties only. This guide assumes a two storey house, with a new second floor loft room. If your property differs from this example, you should seek further advice.

Note: Certain requirements will not be imposed on bungalows with a loft room. More onerous requirements will be applied to three storey buildings with loft rooms.

Building Regulations

You will need to obtain Building Regulation consent for all work that involves creating a room in an existing roofspace.

You can apply for consent by using the Full Plans or Building Notice procedures. Please note that the Building Notice procedure is not recommended, as work is complex. Agreed plans and other information can be valuable when carrying out a loft conversion.

Building Regulations do not apply if you are only boarding the ceiling and access is by a loft ladder. Walls and linings should not be provided and the space should be used for the storage of goods and materials, etc. and not as a room. You should not overload the ceiling with excessive weight. Limited services such as a light are acceptable.

What work is involved when carrying out a loft conversion?

The existing roof structure needs to be carefully examined and the following considered:

a new floor will be required. Existing ceiling joists and binders are not designed to carry floor loads. This will involve inserting floor joists and supporting beams. Support to the existing ceiling will need maintaining

how the new floor will be supported. Do you have loadbearing walls that can carry the new floor joists and supporting beams? Will you be putting extra weight onto existing supporting beams at a lower level? Can they carry this extra weight?

you may need to increase the strength of the existing rafters and purlins. They need to carry extra weight from plasterboard linings, etc.

if you are installing a dormer window or rooflight you will need to consider how you support the existing roof where rafters and purlins are cut

does the roofspace provide enough headroom for the room and staircase? The new floor will reduce available height

do you have enough room to install a staircase up to the new room? Loft ladders are not suitable

can you make the room safe in the event of a fire? You will need to:
a)   provide, either: an enclosed staircase, containing no rooms, from the new room to the outside of the building, or an enclosed staircase, containing no rooms, from the new room to the ground floor. Once the ground floor is reached you should then have a choice of two fire separated routes to the outside of the building
b)   provide a fire escape window, from the new room, that is accessible by an external ladder. Window size when open to be not less than 0.33m² with no dimension less than 450mm and sited so that the bottom of the opening is between 600mm and 11,00mm above floor level
c)   separate the new room from the rest of the building with fire resisting construction. This will involve the existing ceiling, new staircase enclosure and any new doors
d)   provide self-closing devices to all existing doors that form part of the escape route. Any glazing in fanlights will need to be made fire resisting and
e)   provide mains operated smoke alarms at all levels within the building.

is the existing roof weathertight? Repairs may be needed

can you insulate the structure, including party walls to prevent heat loss?

can you ventilate the rooms and roof voids?

can you insulate the structure, including floor, party walls and ashlar walls against sound transmission?

does the existing party wall require any work? You may have to build it full height for structural, fire, sound and heat loss reasons. You may need to give notice to your neighbour under the Party Wall Act 1996.

Planning permission

You do not normally need to apply for planning permission to convert your loft or to insert roof lights or skylights. However, there are some special rules, which govern extensions to the roof.

You will need to apply for planning permission if you live in a conservation area or a listed building and you want to build an extension to the roof of your house or any kind of addition which would materially alter the shape of the roof.

Outside those areas, you need to apply for planning permission if any of the following is true:

the work would make some part of the house higher than the highest part of the existing roof
the dormer or other addition you want to build would extend beyond the plane of any existing roof slope facing a highway or
a roof extension would add more than 40m³ to the volume of a terraced house or more than 50m³ to any other kind of house.

Additional volume created by an extension, and that includes roof extensions, will count against the total volume limit for your house. So you will also need to apply for planning permission before building a roof extension if:

for a terraced house the volume of the "original house" would be increased by more than 10% or 50m³ (whichever is greater)
for any other kind of house, the volume of the "original house" would be increased by more than 15% or 70m³ (whichever is greater) or
the volume of the "original house" would be increased by more than 115m³.

General

Smoke detection

Detectors should be interlinked, mains powered with battery backup, wired to the lighting subcircuit and be installed on all three levels. Generally, detectors should be positioned over the head of the stair, on each landing.

Fire break walls and sound insulation

In the loft there should be walls separating a property from any adjacent property. This wall both prevents fire spreading between properties and also gives sound insulation. Even if an existing wall separates properties, it may need to be upgraded to give adequate sound insulation. Two possible methods are:

two independent stud walls, with 100mm mineral fibre between and two layers of 12.5mm plasterboard each side and
dense concrete blocks laid as a cavity or solid wall.

Even if the existing wall is solid masonry, it may need to be upgraded. Usually the heavier and denser the wall the better sound insulation provided. Sound insulation can be undermined if joints around bricks or blocks are not completely filled with mortar. Also, holes cut for electrical boxes, etc. reduce the thickness of the masonry and so reduce sound insulation.

Air gap insulation

A minimum of a 50mm air gap is needed over any insulation. This is to prevent a build up of condensation. Condensation encourages rot and reduces the effectiveness of insulation. A 50mm air gap and a through flow of air should prevent this.

A through flow of air must be provided by eaves ventilation the equivalent of a continuous 25mm strip, and ridge ventilation the equivalent of a continuous 5mm strip. The ventilation strip must also have a screen to stop insects from entering the roof. Care should be taken with the type of ventilation strip used. Strips usually are slotted to hold the fly screen in place. This means that a 50mm wide slotted strip will need to be used to be equivalent of a continuous 25mm wide strip. When insulation is installed, care must be taken to make sure the free flow of air is not blocked. The eaves of the existing roof may already have some ventilation. This must be checked, as it may need to be increased to achieve the requirement.

If 100mm of insulation is to be used in the skeiling (the sloping part of the roof) and the existing rafters are also 100mm, to maintain the required 50mm air gap it may be necessary to fix 50 x 50mm battens to the back (underside) of each rafter. Alternatively, a more efficient (thinner) insulation could be used.

To help reduce potential for condensation forming in the roof space, a 500 micron-vapour barrier should be used behind the plasterboard, especially over bathrooms.

Room ventilation

Room ventilation is required to all habitable rooms. This is to prevent and remove unpleasant living conditions. To this end, the following must be provided:

an openable window area equal to 1/20th of the floor area be provided as rapid ventilation
background ventilation equal to 8,000mm² and
bathrooms require mechanical extraction at least equal to 15 litres/second.

Headroom

There is no requirement regarding headroom in loft rooms (except to stairs and landings). However, headroom should be carefully considered. Floor joist sizes, allowances for deflection, decking thickness, battening of rafters, plasterboard thickness all have an effect on the overall headroom within the loft room. This may make the new loft room unusable when complete.

Stairs

Stairs must have the rise (r) and going (g) relationship (2r + g) which must be between 550mm and 700mm. The maximum pitch for a stair is 42 degrees.

Headroom on a stair and landings must be at least 2m, this can be reduced on stairs to 1.9m at the centre and 1.8m at the outside edge (but not landings) where the roof slope crosses the stair.

There is no minimum stair width, but a stair less than 600mm wide will be difficult to negotiate, particularly with furniture. Handrails on the stair should be between 900mm and 1,100mm above the pitch line. Balusters should not allow a 100mm sphere to pass through and must not be readily climbable by children.

Glass and glazing

Any glazing on the escape route (generally, not external windows, WC's or bathrooms) must be half-hour fire resisting (normally Georgian wired glass is suitable) and must be installed with a beading system compatible with the glass used.

Any glazing (both internally and externally) including doors and windows in certain critical locations (typically low level, adjacent or in doors), must be toughened and/or be of safety glazing.

Safety glazing

Safety glazing must be provided in doors, windows adjacent to doors and windows at low level.

Completion Certificates

At the end of a satisfactory job, you will receive a Building Regulations Completion Certificate. Usually this is issued directly to the homeowner, or to the builder to present to the homeowner along with the final account. With either method, it is very important the completion certificate is issued. This Certificate not only demonstrates that the work complies with all current Building Regulations, but also will be required in a future property sale.

Fire design

Means of escape in the event of fire

Means of escape in the event of fire is very important. There are many ways to achieve compliance, below are possible methods:

Fire resisting cell

This method creates a half-hour fire resisting cell in the roof. This is in the event of fire, someone in the loft room can wait for rescue. This method requires:

the first floor ceiling/loft room floor be half hour fire resisting
the door to the loft room be self-closing and half hour fire resisting
all doors off the new or existing stair be fitted with self-closing devices
the new storey is not greater than 50m²
the new storey has not more than two rooms.

The door to the loft room can be at either the top or foot of the stair. If at the foot of the stair, then the underside and enclosure of the stair will need to be half hour fire protected. Two layers of 12.5mm plasterboard with staggered joins can achieve this.

Alternative means of escape must be provided to each new loft room to aid rescue.

A window is an acceptable alternative only if it is provided with an unobstructed openable area of not less than 0.33m², and has a minimum dimension of 450mm in either height or width.

The dimension of 1.7m from sill to eaves is to allow a person climbing from the window, to hang by their fingers across the slope of the roof and find the top of a rescue ladder with their feet.

The maximum sill height above floor is to ensure that a person can climb out of the window without too much difficulty.

The minimum sill height is to ensure young children do not easily get on to the roof slope. To meet this requirement suitable permanent child proof guarding could be erected. The loft window also allows the fire brigade to see into the loft room and determine if anyone needs to be rescued.

The position of the escape window is critical. Structures like sheds, conservatories, porches etc. can all make it difficult or impossible to allow the fire brigade to pitch an escape ladder up to the window. These factors must all be considered before the window can be installed. Even after the work is complete these factors must be considered, particularly if an extension or other structure is erected that may compromise escape from the loft room. Building Control Services will be able to advise.

Protected shaft

This method does not require any special fire provisions to the loft room. However, all doors off the new and existing stair must be half hour fire resisting and be fitted with self-closing devices. Existing doors can be upgraded but often this is not possible and new fire doors are used.

Route to open air

With both of the above methods, the escape route from the new loft room must have a half-hour's fire resistance to its floor. Also, the route must not pass through any room or have any room not protected by a door opening on to it.

At ground floor level it is acceptable for the escape route to pass through a room, provided there are at least two alternative fire resisting routes from the enclosure, and all doors on to the escape route are self-closing 20 minute fire resisting doors.

There will be problems if there are large landings to a stair, or if the stair opens directly into a room not separated by a door, etc. If this is the case, you should contact your Building Control Surveyor to discuss this before starting work.

Also, any glazing to walls or doors (generally not external windows, WC's or bathrooms) on the stair must be replaced with fire resisting glass in a suitable beading system.

Final exit

A final exit is one which leads to open air and not into an enclosed area. It is not acceptable to escape into a fully enclosed courtyard or garden.

Fire resistance to the loft room floor

This can be achieved in many ways. Regardless of the method selected, each must be applied to the whole of the first floor ceiling including any beams and not just the area under the loft room The fire resistance can be achieved in many ways, two of which are:

upgrade from below: two layers of 12.5mm plasterboard can be fixed from underneath. The existing first floor ceiling may already be plaster boarded, so only one additional layer may need to be fixed. If the existing ceiling is plaster on timber lathes, then any plasterboard under will actually fail faster due to the weight of poorly bonded plaster pressing on the back of the new plasterboard. If this is the case, a composite floor method could be better
composite floor: a metal wire basket (chicken wire) must be securely fixed between the floor joists as close to the existing ceiling as possible. This basket is lined with at least 60mm of mineral wool. This insulates the room above from the heat of the fire and non-combustible wire prevents the mineral wool falling out should the ceiling give way. Gaps between the existing ceiling joists must be well packed with mineral wool to stop smoke or flame.

External fire spread - dormer windows

If a dormer window is used, the sides of the dormer will need to be made fire resistant to prevent fire spread between properties. This must be done both internally and externally. Usually two layers 12.5mm plasterboard is sufficient internally. Externally it may be necessary to use a fire resistant board under the waterproof covering e.g. tiles/render.

Fire precautions and home insurance

Some of the requirements laid down by the Building Regulations may seem onerous, but they are designed to protect the occupants in case of a fire. If fire precautions are removed after a Building Regulation Completion Certificate is issued, this may void insurance held on the property in the event of a fire.

Structural design

What is a loft conversion?

A loft conversion is any roof space used for any purpose other than light storage on loose boarding (light storage being household items e.g. suitcases). That is to say any loft space to be used as:

bedroom
bathroom
study or office
playroom or
fixed floored storage with fixed staircase.

Also, a loft is considered to be a conversion if plastered and provided with heating and/or power. If an altered loft could be used as a room it must be treated as being converted into a habitable room.

Is my loft suitable to be converted?

Loft conversions can be an effective way of providing additional space, but most cases will require the existing roof structure to be stiffened and upgraded. The extent of the structural work required will depend on:

Existing walls, foundations and lintels

The existing foundations will need to be exposed so it can be determined if they are suitable to accept the additional loading of the new loft room. If not suitable, they may require underpinning.

Generally underpinning is expensive and the feasibility of the project may depend on this. There is likely to be additional loading on existing lintels and beams, so these also will need to be exposed.

Loft room floor construction

Typically, the existing ceiling below a roof is constructed of 100 x 50mm joists. Normally this is not suitable for the loft room floor. Usually, deeper joists will need to be laid alongside but independent of the existing ceiling joists.

The new floor joists must be laid from load bearing wall to load bearing wall (or beam). Joists need a minimum 50mm bearing each end, and should be lifted clear of the existing ceiling by 25mm. This allows for deflection in the new joists, and means the new timbers will not damage the existing ceiling when loaded.

Existing roof structure

To make the roof space usable, a trussed rafter may require more extensive alterations than a traditional cut and pitch roof.

What is required to convert a roof structure?

Generally, ceiling joists are not designed to take the weight of a floor. New larger joists need to be positioned alongside the existing joists, to support the increased loading. Traditional cut and pitch roofs usually include diagonal struts to provide useable space these will need to be removed. The new floor joists need to be designed to support this load previously carried by purlins and struts, together with the new floor. Openings around stairwells need to be trimmed and ply sheathing used to brace dormer constructions. If a dormer is constructed then a new ridge beam to support the roof may be needed. The architect, designer or structural engineer will be able to help with this.

Are there any internal load bearing walls?

Any internal wall, which is going to take additional load, must have its foundations checked. If the internal walls don't have adequate foundations, it may be necessary to underpin or install beams to support the new joists and roof structure.

Structural calculations

The roof structure should be designed and calculated by a designer or structural engineer. These calculations and details must also be enclosed with your Building Regulations applications.