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Status of energy efficiency/CO2 improvements in residential buildings

Deep retrofit, typically involves the delivery of whole house interventions; where all elements of a building’s fabric are addressed in a concerted and comprehensive way. This approach may be necessary to deliver the level of CO2 reductions expected from the sector in meeting the ambitious climate change act and CCC carbon budget targets

It can be seen that thus far policy drivers for whole house retrofitting are likely to be limited, given the lack of demand drivers for comprehensive interventions that may not be cost effective. Several demonstration studies have been undertaken to develop knowledge and learning for deep whole house retrofits, with a range of definitions and voluntary standards in operation.

The following section will explore the definition of deep retrofit and zero carbon homes, and include discussion of the industry benchmarking standards and how these standards relate to the existing regime of EPC certificates and SAP score levels.

Framing deep retrofit and low/zero carbon

As identified by there are semantic issues associated with the terms surrounding zero energy, zero carbon and deep retrofit of the domestic building stock. A range of different voluntary standards exists, with some reflecting alternative methodologies for assessing a buildings energy performance. These standards do not all focus on the same metrics and use differing points of comparison for CO2 emissions reduction. Other standards take a purely energy use focus, and include concepts such as primary energy and overheating limits. These varying standards can be seen to create commensurability issues but also infer alternative emphasis in terms of energy conservation against grid level emissions reduction. It will be further demonstrated how these alternate framings have informed the design approaches and technological solutions employed in Section.


Figure  House as a series of energy subsystems by

As shown by  we can frame a house or building as a series of interrelated energy subsystems; the characteristics of the building or fabric, the mechanical systems employed to provide services to the occupants, the occupants themselves, their behaviour and the interaction with the external environment. We can consider interventions or modifications to the subsystems, to be informed by non-energy objectives, that may be mutually exclusive and even have the potential to be antagonistic to the goal of reducing energy consumption. We can consider the example of improving internal daylight via increased glazing to have negative impacts upon overall conductive heat loss.

UK Standardised Method for Benchmarking Energy Performance

There are also many examples of where specific energy interventions are mutually exclusive; introduction of a new efficient condensing boiler may reduce the energy and carbon intensity of heating and hot water, but will have no impact on a buildings heat loss. This is why environmental assessment methodologies such as the CfSH, BREEAM, BREEAM Domestic Refurbishment and LEED have aimed to take a systems level approach to environmental benchmarking. The UK standardised method for benchmarking energy performance in buildings; SAP adopts a simplified metric to provide a simplified picture of the overall energy performance of a building