In order to produce an asset rating required for Energy Performance Certificates (EPCs) the properties of construction elements, the infiltration rate of the building and the details of thermal bridges are required by your assessor to enable the calculation of the thermal properties (insulation levels) of the building.
This information may be readily available for a recently constructed building through the design data or building log-book. For a building that has been sold it may have been gathered to produce a condition report survey. If not readily available your assessor will be able to gather standard element values through publications or manufacturers' data but will need to know the category of construction and the year of build.
The category of construction is a reference to the type of build, for example for a wall this could be internal partition, cavity wall or solid masonry, amongst others. For a window this could be the glazing type (i.e Double, Single, Triple) and the frame type (i.e. Wooden, Aluminium, uPVC, etc). When defining the category of construction the more information available to the assessor the more accurate the default allocation of the thermal properties (i.e the U-Value) is likely to be.
The fabric of a building is critical when determining the amount of energy a building will consume during its operation. The building fabric interacts with the external and internal environments controlling the flow of energy.
The building fabric is made up of walls, roof and floor slabs (thermal elements); and windows and doors (controlled fittings). The selection, orientation, layout and construction properties all contribute to the overall energy efficiency of the building and the subsequent asset ratings. The greater the actual or potential heat loss from a building the lower its energy ratings will be.
The building infiltration rate is a measure of the air tightness of the building. Air should leave and enter a building through controlled ventilation, through windows and dedicated air vents. A 'leaky' building will allow heat to escape through cracks and gaps, whilst allowing cold drafts to enter a space, reducing occupant comfort and increasing energy costs. Air tightness is measured as an average volume of air in cubic meters to pass through an area of the building at a given pressure. In a similar vein the characteristics of thermal bridges are required to perform an energy performance calculation.
This refers to a part of the building fabric where thermal properties are changed by either; penetration of the building fabric by materials with a higher thermal conductivity; a change in fabric thickness; a difference between internal and external areas, such as where walls meet floors or ceilings. Poor thermal bridging can lead to increased heat loss, condensation and an array of cosmetic problems.