The increased need for extra living space in existing dwellings has also resulted in the dramatic growth in the level of loft conversions being carried out on existing properties. Loft conversions are a relatively simple and inexpensive way of creating new living space from what is often an under utilised area in a dwelling.
Well designed loft conversions can create substantial new living areas, enhancing the value of an existing dwelling. To meet Building Regulations, conversions are required to be adequately insulated against heat loss and where dwellings are attached, such as in semi detached dwellings, acoustic considerations should also be taken into account.
Although it is an accepted fact that a good loft conversion is a highly efficient way of enhancing a property, it is recommended that the conversion is professionally designed from the onset and that it will also meet building control and local authority regulations.
- Multi Roll 44 & Multi Roll 40 are made from glass mineral wool and formed into unfaced rolls which are multi cut, lightweight, flexible, resilient and noncombustible.
- Timber & Rafter Batt 32 is semi-rigid unfaced glass mineral wool batts, easy to friction fit and non-combustible.
When a conversion is taking place in a roof void above an insulated ceiling, measures to minimise and avoid condensation must be put in place. This is a prerequisite of obtaining building control approvals.
Every roof void requires to be ventilated at both low and high level. At the eaves, ventilation openings should be equivalent to a 25mm continuous gap. At the ridge the ventilation opening should be the equivalent of a 5mm continuous gap each side of the ridge.
A ventilated airspace of 50 mm must be provided to each and every space between the top of the insulation and the tiling underlay. In instances where rafter depth is insufficient to accommodate both the required thickness of insulation and the 50mm ventilated airspace, an insulated dry lining may be used, providing the added benefit of minimising thermal bridging.
It is important that a continuous vapour control layer is provided on the warm side of the insulation to ensure that the amount of vapour that passes through the ceiling and dwarf wall is kept to a minimum.
A Room-in-the-Roof conversion requires a combination of insulation at ceiling level, between the rafters and in dormer walls. The horizontal areas of ceiling are dealt with using rolls of insulation quilt in a similar way as described before in ‘Cold Pitched Roofs’.
When installing insulation between rafters, the rafter depth is crucial, as it must accommodate the thickness of insulation required plus a 50mm ventilated airspace. If necessary, timber battens can be applied to the inner face of the rafters over the appropriate area to effectively increase the space to the required depth.
The dormer walls are treated as conventional timber framed walls and must meet Building Regulation requirements for exposed walls. Dormer walls can also be insulated using the same materials as employed in the sloping part of the roof. When insulating all of these areas, it is essential that a continuous layer of insulation is formed. This is facilitated by butting all insulation layers so that habitable rooms have an unbroken envelope of insulation throughout.