Meeting requirements of the new Parts L1 and L2 of the Building Regulations means not only specifying products that can meet the thermal performance requirements in theory, but also that can be applied effectively. Workmanship and design errors lead to gaps and discontinuities in insulation that can represent up to 6 per cent of the overall envelope area, resulting in more than 33 per cent additional heat loss. The new regulations require that air leakage be limited, and that all buildings over 1,000m 3/hr/m 2can show compliance with the maximum acceptable leakage rate of 10m 2at 50Pa.
There are a number of different insulation solutions. For roofs, there is traditional joistlevel insulation which requires 100 + 125mm rock-fibre insulation or 100 + 140mm glassfibre insulation to reach a U-value of 0.16 W/m 2K for the loft. Downsides are that the attic space is no longer easily usable and that, without ventilation of the roof void, there can be problems with interstitial condensation.
Rafter level insulation can typically achieve a U value of 0.2 W/m 2K, with insulation varying from 70mm of phenolic foam (PF) to 210mm of glass mineral fibre. This method keeps the roof space usable and there is no need for ventilation.
Other options at rafter level include the use of closed-cell insulants to provide an 'air barrier' line within the roof assembly, and 'new' concepts such as 1400mm sprayapplied polyurethane (PUR).
Both these systems should achieve a Uvalue of 0.2 W/m 2K and have important advantages: continuity of insulation can be guaranteed and air leakage is inherently low.
Another option is to use profiled metal cladding with a system thickness typically 80mm for polyisocyanurate (PIR) insulated panel, 150mm for a site-assembled system with a rock mineral fibre insulant, or 160mm for a site-assembled system with a glass mineral-fibre insulant.
In addition to their low thermal conductivity, another advantage of PUR/PIR insulated panels is that they have inherently low air leakage and, as with other panel systems, continuity of insulation can be guaranteed. In contrast, site-assembled panels can be subject to defects of workman-