Energy Glossary

The unintentional movement of air through gaps, cracks and openings in the building fabric.
An airtight building is one where there is little unintentional air movement through the building fabric.
The elements that seperate the interior of a building, i.e. the roof, external walls, lowest floor, windows and doors.
Mechanical systems installed in your home, for example heating systems and ventilation.
This is the cost per tonne of carbon saved by a measure, calculated over its minimum useful lifetime.
The lower the figure, the more cost-effective the measure is in terms of it’s environmental impact.
The carbon dioxide (or equivalent greenhouse gas) released into the atmosphere as a result of a given activity or process.
The removal and long term storage of carbon dioxide from the atmosphere in natural materials such as timber and agricultural products.

Also known as a Thermal bridge, this is an area of a building which is less well insulated than its surroundings, meaning that the internal surface will be colder, causing condensation and potentially leading to damp and mould.
Indicates how much energy you benefit from per unit of energy supplied e.g. an ‘inefficient’ property would require far more energy to be used to provide the same level of comfort as an ‘energy efficient’ property.
A home’s energy efficiency score (or SAP rating) is a rating of a home’s energy efficiency used for Energy Performance Certificates, based on the estimated fuel cost per unit floor area.
An environmental impact rating (EIR) is a measure of a home’s impact on the environment in terms of carbon dioxide (CO2) emissions. The higher the rating the less impact it has on the environment. This rating is based on the performance of the building and its fixed services (such as heating and lighting).
The amount of heat energy needed to maintain your home at a comfortable temperature throughout the year.
Insulation ‘batts’ or ‘slabs’ are insulation materials supplied in standard sizes, designed to fit between timber studs, joists or partitions.
An electrical device which converts ‘Direct Current’ (DC) generated by solar PV to ‘Alternating Current’ (AC) for use in your home.

A horizontal structural beam, usually arranged in parallel at regular intervals. In most homes, joists are the lengths of timber which form floors and ceilings.
The cost of a measure over its predicted (minimum) lifespan, taking into account the initial installation cost and subsequent annual savings.
A heating system which operates at a temperature less than 55°C.
A diagonal beam forming part of the internal structure of a roof.
A government-backed initiative compelling large energy suppliers to pay homeowners for the renewable energy that they don’t use themselves and send back to the National Grid.
You need to own a renewable energy source and you need to sign up with an energy supplier to an approved SEG tariff.
Air movement through or around the insulation, reducing its effectiveness.
The ability of a material to store heat. Thermally massive materials regulate the temperature of their surroundings by absorbing and releasing heat.

A measure of how well a building retains heat.
The ability of a material to resist the transfer of heat.
A small, operable opening in a window to provide background ventilation when the window is closed.
Door undercuts are the space between the bottom of the door and the floor finish. They are required to allow air flow through the home.
A ‘breathable’ or ‘vapour permeable’ material is one which water vapour can pass through.
A layer within the building structure which prevents the movement of water vapour, e.g. a waterproof membrane.