Loft Conversions

Design Guide to Roof/Loft Conversions

Room on top of the House

If your family is outgrowing your home or simply want more room. A loft conversion allows you to add space without having to move. When considering converting the loft of your dwelling into useful living space such as, a bedroom, playroom or an office/study a number of critical questions need to be answered.

1. Is there enough headroom?

2. Is the area big enough?

3. Will the existing dwelling support the extra loading?

4. Can I get a staircase up to the loft?

Assessing your lofts full potential

Some lofts are more easily converted than others. A full assessment requires professional help, but you can often work out the basics yourself. Make sure you have a torch and a tape measure. Access the loft space and have a look around. Standing under the ridge check the clear height of the roof. You will need 8ft clearance.

timber rafter roof
timber truss roof

Rafters leave attics open.

Most roof trusses don't.

Check the structure of the roof to determine if the roof was constructed using purlins or truss (see above). Purlin roofs can generally be adopted for roof conversions. Trusses cannot, if you find that the roof space has small size timbers coming into the roof void then there is not much that can be done apart from replacing the complete roof. But consult with a professional advisor to determine if the width of the roof would allow purlins to be inserted.

Check the existing ceiling joists, these are generally 4"x2" and are not designed to carry much loading such as required by a living space. New floor joists ranging in size from 6"x2" to 8"x2"can be fitted between the existing ones to form a separate floor above the ceiling joists. This new floor has to be supported on structural walls in the dwelling below. Alternatively, if headroom permits, a new floor can be laid across the existing ceiling joists if the structural walls below form a central hallway and generally require smaller timber sizes.


Access to the loft conversion must be provided, so as you come out of the loft look down to the hall to see if a staircase can be fitted and up to loft to see where the head of the staircase would enter the loft conversion. The head of the stair must have a minimum of 6'- 6" head clearance therefore a stair entering the loft under the ridge line would be ideal. Space saving staircases and loft latter's are not allowed in roof conversions. The use of spiral staircases can be used but are not practical when considering carrying furniture up and down them.

The Building Regulations require that the staircase is build to certain requirements. The clear width of the stair must be a minimum of 2ft if access is to one room only or 2'- 6" if access is to more than one room. So check the width of your hallway, allow an extra 3" onto the width of the staircase for handrails. If the width of the hallway is too narrow then an alternative stairway position may be found by using part of an existing room, or removing a cloakroom or closet.

Staircases must be constructed to a maximum pitch of 42 degree's which translates roughly in to a step of 8" and tread of 10", each step and tread in a staircase must be the same throughout its length.

Don't despair if it's not immediately obvious to you just where the stairs should go, experience designers are often able to work out acceptable solutions in the tightest of places.

inside view of dormer

A room with a View

Natural light is the essential element in transforming a loft into bright, airy living space in addition to providing ventilation and a means of escape in case of fire. The size and location of an escape window is determined by the Building Regulations. The size of the opening must be a minimum of 1'- 8" wide and 2'-10" high and if the window is part of a dormer or on the slope of the roof the window must not be more than 5'- 6" from the eaves.

The amount of light and ventilation the windows provide is also an important factor, the size of the windows must be at least 1/10 of the floor area and the amount of ventilation equal to 1/20 of the floor area. Consider providing more window space than the bare minimum a dramatically improved effect can be achieved by increasing the ratio to 1/5 of the floor area.

Windows are usually installed in the gable ends of the loft or by forming a dormer.

Dormers not only provide a suitable position for windows but also increase the usable floor area. Forming a dormer requires the cutting of the existing roof joists and forming the sides and roof to the opening. This means that you cannot simply cut the joists open in order to install a window without supporting this weight. Again, consult a professional if you're not sure.

velux windows

Alternatively the use of skylights or Velux windows can be used. They come in a number of sizes and are designed to fit between the existing roof rafters. These types of windows can be coupled together side-by-side and or one above the other to provide additional light and to create an attractive design effect.


An area must be set aside for the placing of the existing water tanks. Depending on their location they may require to be moved to a corner of the roof to allow greater floor utilization. If the loft headroom is high, then they may be placed above the new ceiling level.

Additional lighting and power points will be required. Normally these can be easily added to your existing circuits without disrupting the rest of the home. Many central heating systems can be easily extended into the loft and failing that, small electric wall heaters are usually all that are needed.

A warm blanket

All new loft conversions will require insulation; the amount of insulation is determined by the Building Regulations. Depending on their size the existing rafters may need to be battened out to accommodate the insulation. Insulation will also be needed above any new ceiling, behind any walls to roof voids and above existing ceilings exposed to the roof void (see below). The idea is to wrap the new living area in an insulation blanket to maintain a warm room during the winter and to stop the sun turning the new room into a sauna in the summer months.

Additional requirements

A number of additional improvements may be required to your dwelling to meet the Building Regulations if they have not already been incorporated. A self-contained smoke alarm system connected to the mains electricity with battery backup will be required. The existing staircase will need to be upgraded to provide a fire-protected staircase leading to a final exit. Doors in existing two story dwellings will need to be fitted with self-closures and if they are being replaced during a larger refurbishment scheme will need to be provide 1/2 hour fire protection. Also consider that the ceiling below the new attic room may require re-plastering to stop cracks appearing at a later date.