Perplexed by all this talk of u-values and blower door tests? Our sustainable building glossary will help you get to grips with the key terminology.

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Term Definition
Seasonal performance factor

The ratio of useful heat energy output from a heat pump to the electrical energy input (including compressor, circulation pumps and electrical immersion, if present) averaged over an entire heating season

single leaf

A single leaf wall consists of just one layer of a building material. Single-leaf walls of hollow concrete blocks were the most common form of construction in the greater Dublin area for decades. They are different to the cavity wall construction common throughout the rest of the country, which consist of two layers of masonry with a cavity in between.

solar gain

This refers to the heat and light energy that a building receives passively from the sun. Designing a building so that the rooms that are used most during the day face south means they will get light and heat from the sun, reducing the need for mechanical heating systems and electrical lighting

Space heating demand

The amount of active heating input required to heat a building usually expressed in kWh/m2/yr. It is often calculated using building energy software applications such as PHPP, Deap or Sap

Stack effect

The movement of air in and out of buildings due to differences in the temperature or moisture content of air. For example, the opening of high-level windows can allow warm air to rise out of a building, creating a ‘stack’ or ‘chimney’ effect that pulls cooler outdoor air in through open windows down below, helping to provide ventilation.

Strip foundation

A strip of concrete running under all of a building's load bearing walls. This will normally include the external walls, and possibly some of the internal walls.

Structural insulated panels

Structural insulated panels (SIPs) are prefabricated, structural building panels comprising insulation – typically polyurethane – sandwiched between two layers of OSB.

Synonyms - SIPs
Surface to volume ratio

Surface area to volume ratio is a measure of how compact a building is. In passive house design, it is often expressed as the ‘heat loss form factor’, which is the ratio for the external surface area of the building to the treated floor area.

The higher the figure, the less compact the building, meaning there is more surface area from which heat can escape, making it more difficult to meet the passive house standard.

Synonyms - surface area to volume ratios