Airtightness goes hand-in hand with a well-insulated building envelope and is the basis for a ’fabric first’ approach to designing low-energy buildings. Airtight buildings are comfortable environments free from unwanted draughts from gaps and cracks in the building fabric that cause heat loss and discomfort. Airtightness is achieved by good detailing and construction quality through the creation of a continuous air barrier with monolithic construction of airtight materials or with airtightness membranes and by taping all joints and by overlapping and taping membranes at junctions. To ensure good indoor air quality (IAQ), continuous, controlled background ventilaton is needed (e.g. MVHR) and careful specification of materials that do not offgas and cause health issues.

Building overheating is an increased risk in a changing climate, and is influenced by outdoor environmental conditions, the design of the building, internal production of heat and occupant behaviour. Overheating affects the health and well-being of people, especially older and vulnerable people and can lead to increased injustices and can cause increased mortality. Key strategies to prevent overheating that you should include in your project is to first and foremost ensure all sources of overheating are tackled first and risks minimised. Then provide green, blue and social infrastructure at macro, meso, and micro-scale (building-scale). The design of the building should also include: light coloured surfaces, careful building form, orientation and design of windows, efficient fabric with summer solar shading and appropriate (night) ventilation strategies.

Passive heating is crucial and desirable in many cold climates and in mild climates in winter time to ensure that thermal comfort is provided with minimal energy use, energy costs and CO2 emissions. This can be provided by capturing the sun’s warmth by good passive solar design (i.e. optimising orientation and window locations) and ensuring that the heat is stored in a well-insulated envelope with good use of thermal mass and passive summer-time cooling strategies to avoid building overheating. Passive heating strategies need to be ‘locked in’ at early stages because it is irreversible over the building’s lifespan.

‘Fabric first’ principles are the foundation of zero energy / zero carbon and other low energy / low carbon building designs.