Cold homes loophole: the nuts and bolts
The calculations were based on Energy Performance of Buildings Data. This is published by the Department For Communities and Local Government and contains the Energy Performance Certificates (EPC) for properties constructed, sold or let since 2008.
EPCs are ranked A-G where A is the most energy efficient.
The tool combines the EPC ranking with the floor area of a property to estimate how much money a tenant could save per year if their landlord made energy efficiency improvements, and how much carbon that would save over a year.
If you love sums and want some more details on how the numbers were made, scroll down to the bit at the bottom.
What we did with it
If the property is rated F or G, the tool calculates savings you would make if it went up to an E. This is in line with the legislation about to come into force that requires landlords to raise their properties to an E standard before renting them out.
If the property is rated E or D, the tool will calculate savings up to a C. There’s no legislation forcing people to do this, but it is in line with government plans to bring all fuel poor homes up to C by 2035.
As heating and hot water make up 20% of our carbon emissions, if we want to meet our climate change targets, the government needs to be more ambitious.
Research just published by Frontier Economics argues all homes should be brought up to a C rating by 2035, and all newly built homes to be constructed to a zero-carbon standard by 2020.
The calculations are done following the Government’s Standard Assessment Procedure (SAP) for assessing the energy performance of dwellings. For full details of the procedure, click here (PDF).
The formulas used are defined in that document under sections 13 and 14 on page 35 and copied here.
13 Energy cost rating
The SAP rating is related to the total energy cost by the equations:
ECF (Energy cost factor) = deflator × total cost / (TFA + 45)
if ECF ³ 3.5, SAP 2012 = 117 – 121 ¥ log10(ECF)
if ECF < 3.5, SAP 2012 = 100 – 13.95 ¥ ECF
where the total cost is calculated at (255) or (355) and TFA is the total floor area of the dwelling at (4).
The SAP rating takes into account energy for lighting, and also energy generated in the dwelling using technologies like micro-CHP or photovoltaics.
The SAP rating scale has been set so that SAP 100 is achieved at zero-ECF. It can rise above 100 if the dwelling is a net exporter of energy. The SAP rating is essentially independent of floor area.
The SAP rating is rounded to the nearest integer. If the result of the calculation is less than 1 the rating should be quoted as 1.
Energy efficiency rating bands are defined by the SAP rating according to Table 14.
14 Carbon dioxide emissions and primary energy
CO2 emissions attributable to a dwelling are those for space and water heating, ventilation and lighting, less the emissions saved by energy generation technologies.
The calculation should proceed by following the appropriate section of the SAP worksheet, designed for calculating carbon dioxide emissions for:
a) individual heating systems and community heating without combined heat and power (CHP); or
b) community heating with CHP or utilising waste heat from power stations.
The Environmental Impact Rating (EI rating) is related to the annual CO2 emissions by:
CF = (CO2 emissions) / (TFA + 45)
if CF >= 28.3 EI rating = 200 – 95 ¥ log10(CF)
if CF < 28.3 EI rating = 100 – 1.34 ¥ CF
where the CO2 emissions are calculated at (272) or (383) and TFA is the total floor area of the dwelling at (4).
The EI rating scale has been set so that EI 100 is achieved at zero net emissions. It can rise above 100 if the dwelling is a net exporter of energy. The EI rating is essentially independent of floor area.
The EI rating is rounded to the nearest integer. If the result of the calculation is less than 1 the rating should be quoted as 1.
Environmental impact rating bands are defined by the EI rating according to Table 14.
Primary energy is calculated in the same way as CO2 emission using the primary energy factors in Table 12 in place of the CO2 emission factors.