Loft Conversion: Seven Steps To Success
There’s a lot you need to consider when it comes to converting your loft or attic…
1. Is it suitable for conversion?
The features that will decide the suitability of your roof space for conversion are the available head height, the pitch and the type of structure, as well as any obstacles such as water tanks or chimney stacks. For head height, measure from the bottom of the ridge timber to the top of the ceiling joist. The useable part of the roof should be greater than 2.2m. if it’s less than 2.2m you can either raise the roof or lower the ceiling in the room below: both of which are costly operations.
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2. Type of structure
There are two main structures used for roof construction – traditional framed type and truss section type. The traditional framed type is commonly found in pre-Sixties houses where the rafters and ceiling joists are cut to size on site and assembled. This tends to be the most suitable type for conversion. Post-Sixties houses were given structural integrity through the use of braced diagonal timbers. These, however, work on the basis that there are no load bearing structures beneath, and so opening up the space requires a greater added structural input, including the insertion of steel beams between load bearing walls for the new floor joists to hang on and the rafter section to be supported on. Needless to say, this type of structure requires a greater financial outlay.
3. New Joists
Your existing ceiling joists are unlikely to be adequate to take a conversion floor, so additional new joists will be required to comply with Building Regulations. The size and grade of these joists – which run alongside the existing joists – have to be specified by a structural engineer, who will have taken into account the span and the separation distance for a given loading. Thicker timbers are used to bridge the opening above window and door openings to ensure that pressure is not put on the existing opening lintel. You’ll also need RSJs to distribute the load.
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4. Cold or warm roof?
When it comes to insulation, you have two main options. The ‘cold roof’ method, which is the most straightforward option – involves filling the space between the rafters with 70mm-thick slab foam insulation, ensuring that there is 50mm spacing between the roofing felt and the insulation. If you’re good at DIY, you can do this yourself. The other method – the ‘warm roof’ – uses 100mm insulation or similar over the rafters, and a covering capping, followed by tile battens and tiles. The dormer walls are insulated between the studwork, while the internal partition walls use a 100mm quilt that provides sound insulation. Plasterboard is then attached to one side of the wall and the quilt is inserted, followed by plasterboard on the other side. This tends to be one for the professionals!
5. The staircase
In order to make best use of the available height above the staircase, the ideal location for a staircase to land is in line with the roof ridge, but, in practice, the actual position depends very much on the layout of the floor below. Regulations specify that the maximum number of steps in a straight line is 16, but this isn’t usually a problem, as a typical installation usually only requires thirteen steps. The width of steps is unregulated, but, in practice, the winders are likely to limit the reduction in width.
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6. Windows and dormers
You’ll want to get as much natural light and ventilation into your loft conversion. The best way to achieve this is by using rooflights that follow the pitch line of the roof. Dormers are particularly popular with conversions since they’ll not only give natural light, but will add also space to a loft conversion. In fact, they’re particularly effective where the pitch angle is high, as the useful floor area can be increased. Some loft conversion companies will make the dormers off site and then lift them into place, which allows for quick installation.
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7. Fire safety
In a house which hasn’t undergone a conversion, the plasterboard ceiling in the upper rooms will delay the spread of fire to the roof space. When, however, an opening is introduced for the staircase, the risk is shared with the conversion so you must put safeguards in place to reduce the risk. All habitable rooms in the upper storeys served by a single staircase should have an escape window that’s not more than 1.1m above the floor level and you’ll have to install at least one mains-operated smoke alarm with battery backup in the circulation space of each storey.
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