74 INSULATION; INTERIORS


require compromises. Housebuilders may find they need to adopt wider cavities (and therefore plot footprints). In essence, following the notional


dwelling to the letter could lead to unnecessary expense when compliance can be achieved in a smarter, more cost-effective way.


GO BESPOKE Using the SAP methodology allows housebuilders to determine the right whole-house recipe for their requirements. A recipe that finds an optimal balance between building design, high-performance insulation, and low-carbon services. In many cases, the fabric performance


required for compliance can be delivered cost-effectively by adding insulation to the roofs and floors. This means that existing wall insulation preferences and build-ups can be retained. The good news is that compliance


can be achieved more cost-effectively by


taking a bespoke approach instead of using the notional dwelling. So how can it be done? Consider, a three-bedroom semi-detached house with two wet rooms and a gas combi


boiler. Instead of the 0.18W/m2 K wall


U-value, compliance can be achieved by increasing floor and roof insulation, and improving the air tightness of the building, alongside low-cost wastewater heat recovery (WWHR). Coupling this with a simple ventilation system means some rooftop solar PV will be required, but even this can be avoided using upgraded mechanical ventilation with heat recovery. In both cases, it’s possible to


retain a 100 mm non-combustible fully filled cavity. Ultimately, you need to comply with


Part L, but don’t feel forced into following the notional dwelling route. There are better options available by going bespoke. If you don’t want to work with an external SAP assessor, then the right insulation supplier will have whole house recipes available to share.


James Hulbert is head of housing at Knauf Insulation.


UNDER THE NEW REGULATIONS, CO2 EMISSIONS FROM NEW BUILD HOMES MUST BE 31% LOWER THAN CURRENT STANDARDS, WHICH WILL BE DELIVERED BY FABRIC


IMPROVEMENTS AS WELL AS LOW AND ZERO CARBON TECHNOLOGIES


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