Top 5 performance gap issues
#1. Junction details. Junctions are where different building elements come together, such as where the roof and walls connect. Failure to consider buildability, provide detailed designs, can lead to reduced insulation, or increased air flow in these areas, creating a so-called “cold bridge”, or air leakage path.  These will increase energy use, and a cold bridge can result in condensation on fabric elements, with potential adverse impacts on building and human health.
Top 5 performance gap issues
#2. Ventilation. There are generally 3 types of ventilation systems in new homes. Passive – which rely on natural air flow, through, for instance, trickle ventilators.  Mechanical extract systems – where air is extracted through a series of fans, which in turn “pulls” fresh air into the house. Mechanically ventilated heat recovery systems, which recovers heat extracted from a building and uses this to provide heat to air entering the building.  All three systems have respective benefits and disadvantages, and monitoring work has shown that many systems work poorly in practice (www.bdx.org.uk).



Top 5 performance gap issues
#3. Construction quality. On some developments there are insufficient quality checks which means that for instance missing insulation, or product substition is not identified. In such instances the finish can hide the absence, or incorrect application of, insulation material. 



Top 5 performance gap issues
#4. Handover. Though is not always given as to either how occupants will use the systems installed in new homes, nor how any particular requirements such as the need to clean filters in ventilation systems will be handed over to first and subsequent occupiers. Experience suggests that how occupants use a building has a major impact on energy use, indoor air quality, and overheating risk.
Top 5 performance gap issues
#5. Experience & complexity. A key risk factor is new homes is when the construction team has little experience of some of the technologies they are installing, or they are doing things in new ways. Additionally in some homes, demanding energy and carbon targets can lead to complex solutions – for instance the use of a combined thermal store, solar hot water system, heat pump, and has boiler. Complex solutions can be made to work, but in practice they are unlikely to operate optimally.

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