Find out what a Building Energy Rating (BER) Certificate means for a property's energy efficiency and how it is calculated.

The rating scale

The Building Energy Rating (BER) allows prospective buyers or tenants to objectively compare the energy performance of different dwellings on a like-for-like basis. It helps you to understand the energy efficiency of a home and can be used as an indicator of the running costs and carbon emissions associated with heating the home to a comfortable level.

The rating scale looks similar to the energy rating labels for household appliances. It rates the home on a scale from A-G.

A-rated homes are the most energy-efficient and comfortable. They tend to have the lowest energy bills.
G-rated homes are the least energy-efficient. They typically require a lot of energy to heat the home and have the highest energy bills.


Download a Sample BER Certificate

Calculated vs. Measured Energy Consumption

BER Allows prospective buyers or tenants to objectively compare the energy performance of different dwellings on a like-for-like basis, BER is an asset (calculated) energy rating rather than an operational (measured consumption) rating.

The key difference between calculated energy consumption and the measured energy consumption is as follows.

Calculated Energy Consumption

Key features:

  • The calculated energy usage based on the dwelling NOT the number of occupants – like MPG rating for cars the actual driving style, terrain and conditions not accounted for.
  • There are consistent assumptions made for all dwellings such as:
    • The same level of lighting is required in all dwellings
    • The number of occupants and hot water demand based on the total floor area
    • The fixed length heating season and fixed heating periods per day
    • The dwelling heated to set temperatures
    • Climate

Some pros:

  • Allows all dwellings to be compared on like-for- like basis
  • The prospective buyer or tenant is not dependant on the current occupier behaviour
  • Ideal for dwellings being sold or rented
  • Ideal for evaluating the building for regulatory purposes

Some cons:

  • If the occupant is frugal or wasteful in their energy usage, their energy bills could be much smaller or larger than the asset rating would indicate
  • Requires detailed survey of dwelling fabric and heating system Measured Energy Consumption

Measured Energy Consumption

Key features:

  • Measures the actual energy usage
  • Can be based on bills and/or monitored data
  • No need to identify building components
  • Standardised assumptions not relevant

Some pros:

  • Reflects actual energy usage
  • Does not require a detailed survey of dwelling fabric and heating system

Some cons:

  • Difficult for prospective buyers or tenantenants to compare on like for like basis
  • Highly dependent on the behaviour of occupants
  • Not suitable for demonstrating compliance with regulatory requirements as the home must be occupied to enable measurement of energy consumption

How a BER is calculated

A BER is calculated based on the amount of energy the home requires for:

  • space and hot water heating
  • ventilation
  • lighting

The calculation uses the Dwelling Energy Assessment Procedure (DEAP). This is Ireland's official method for calculating a dwelling's BER. The DEAP calculation framework is based on IS EN 13790 and draws heavily on the calculation and data used for the energy rating of dwellings in the UK.

What the calculation is based on

The calculation is not based on a dwelling's actual number of occupants, the levels and durations of heating or hot water demand. It is independent of how the individual occupants actually use energy in the dwelling. For example:

  • the number of occupants is assumed based on floor area
  • the dwelling's heating patterns and temperatures are assumed to be the same across all dwellings
  • individual ownership and efficiency of particular domestic electrical appliances are not assessed

The BER energy rating is based on the building itself, its fabric and installed systems, and is not an operational rating based on the energy consumption of the occupants. This allows prospective buyers or tenants to objectively compare the energy performance of different dwellings on a like for like basis.

Calculation process

A BER assessor gathers all the information required to complete a BER during an assessment of your home. Your BER assessor will survey each room in the house, including the attic and garage, if present. They will record the survey data in a survey form. The information they collect includes:

  • the building's construction type
  • year of construction of original dwelling and any extensions
  • floor dimensions, room height, window and door sizes
  • the building's orientation
  • insulation levels within the walls, roof and floor
  • details of the space heating systems and heating controls
  • hot water systems and water cylinders
  • ventilation characteristics such as vents, fans and draft lobbies
  • baths and showers
  • lighting
  • any renewable systems

Your assessor will need to take photos of certain elements of your home to support the data inputs in the BER. Your BER assessor will also ask about the age of the dwelling and any extensions. Your BER assessor will also need to know if any retrofit works have been carried out and will request any documentation to support the works. It is worthwhile discussing this with your assessor ahead of the survey to ensure you have all the required information available for your BER assessor.

Following the survey, your BER assessor will complete various calculations and input the information they gathered into the DEAP software. This software was developed for Ireland and takes into account the Irish climate, construction types, heating systems and occupancy patterns. The software then calculates the annual energy use for heating, lighting and ventilating the property.

What affects a BER

The rating a property receives can be affected by a number of things.

Age of construction

The year of construction of the dwelling (and any extensions) is an essential data point for your BER - particularly for existing dwellings. This is because, where there is limited information available, assumptions in relation to the amount of insulation present or the efficiency of a heating system, for example, may be made based on the year of construction /installation. These assumed values (default values) are conservative so as not to overstate the energy performance. They are generally based on the standards in place at the time of construction.

For this reason, it is important that the correct construction age is used in the BER for both the original dwelling and any extensions.

You can find out more information on how to prepare for your BER here.

Floor area

The floor area for the BER is based on internal dimensions and is calculated in accordance with the DEAP methodology. In general, rooms and other spaces, such as built-in cupboards, are included in the calculation of the floor area for the BER, where these are directly accessible from within the dwelling. However, unheated spaces clearly divided from the dwelling are generally not included in the floor area calculation.

Defaults values

In accordance with the DEAP methodology, default values may be used when assessing existing dwellings. So, for example, where there is insufficient documentation available to the BER assessor, insulation levels may be determined based on the age of construction and construction type. These are conservative estimates of the energy performance of certain areas of your home. This may result in your home receiving a lower BER rating than expected.

If you cannot provide your BER Assessor with sufficient documentation of any upgrade works on your home, they will need to use default values.

Please note, however, BER Assessors are encouraged to choose non-default values provided adequate evidence for these values is available. Your BER assessor can advise you on documentary evidence requirements for the BER. Your BER Assessor is required to upload to DEAP, any documentation/photos to support the use of non-default values in your BER assessment. These will form part of your BER data file.

Find out what documentation you need to provide to your BER assessor before the survey.

Thermal insulation

This is the wall, attic and floor insulation of the building. On average, a home loses between 20-30% of its heat through the walls. Up to a further 30% can be lost through a poorly insulated attic.

A property with low insulation levels will generally have more heat loss making it less energy efficient, less comfortable, more expensive to heat and result in a lower BER rating.

Windows and doors

You can lose about 10% of your homes heat through your windows and doors depending on the glazing and frame types.

A property with single-glazed windows and unsealed doors generally will have additional heat loss, making your home less energy efficient. This also reduces the effectiveness of your home's insulation as heat is lost through windows and doors.

Default thermal performance values take account of the age of the windows/doors, frame types (eg. metal, wood, pvc) and glazing types (single, double, triple glazing). These characteristics can generally be determined during the site survey. As with all default values, the assumed default thermal performance is conservative.

Non-default thermal performance values must be supported by certificates stating U-value & solar transmittance values for the installed windows/doors.

Heating systems and controls

Older gas or oil boilers with no controls are less energy efficient than newer solutions such as a heat pump.

A new condensing boiler or heat pump and heating controls can increase the energy efficiency of your home.

DEAP rules apply when determining heating system efficiencies. Your BER assessor will take photographs of the heating system (e.g. boiler, heat pump, etc.) to support data inputs in the BER. Photographs of nameplates with make and model number can also be taken to support non-default efficiencies. Heating system manuals or installation certificates can also be copied and used as supporting data.

In the absence of supporting data, default efficiencies in DEAP manual must be used.

Light fittings

The calculation of lighting use is based on the installed fixed lighting in the home. The type and quantity of fixed lamps within a dwelling are recorded during the site survey. The more energy efficient light bulbs installed in the fixed lighting in your home, the lower the calculated energy usage will be, improving your BER.

It is important to note that your BER assessor does not take account of portable lighting in your home. Instead, certain assumptions are made within the calculation regarding the energy use due to portable lighting.


Renewables installed in your home will have a positive impact on your BER rating. Renewables include, for example, photovoltaics (PV), heat pumps, solar water heating, biomass, wind energy, solar space heating.

It is important to provide your BER assessor with any documentation and certification to support the renewables entry in the BER. Where there is insufficient documentation available, your assessor can take account of the installed renewables by applying more conservative default values.


Talk to your BER assessor

BER helpdesk

Contact us with any questions about your BER.

Call: 01 808 2054