EPC Certificates Explained. What exactly is an EPC certificate??

Updated: Jan 23, 2019

Quite simply, an EPC Certificate if the energy efficiency rating on your property. Sound easy? Well there is a bit more to it than that . First, a surveyor attends your property, they take measurements, look at the heating systems, hot water systems, how the property is constructed and insulated. And they look at your lighting and glazing. They look at how many rooms it has and if there is a conservatory or any extensions.


Once this data has been collected, the surveyor uses a software called RdSAP (reduced data standard assessment procedure). This is where the surveyor will enter all the details. The software works on assumptions such as building regulations and weather maps etc. For example if your property was built in 1900 there were no building regulations so the software will assume the walls, floor and loft are not insulated. If the surveyor is able to determine any levels of insulation they will input this and will over ride the assumption. If your property was built in 2008 the software will assume it was well insulated at time of construction. Well insulated properties rate better! Weather it was insulated at time of construction, or Insulated after, like the 1900's property.


The software will apply U-Values to the walls, floor, and roof which will determine how quickly these elements lose heat. Then the software will look at the size of the property, heat loss walls (exposed walls) and apply this. When the surveyor measures the property they measure the cubic meters of space. This will account for the height of the walls and the length as well as the thickness of the wall. Myth buster- thicker walls do not retain heat better. It is based on the U-Value of the wall. Stone and solid brick have poor U-Values.


The heating system is entered, if you have a boiler it is reference by the PCDB (product characteristics data base) This will determine the efficiency of the boiler for example 86% efficient.

The software will look at the heating controls such as a thermostat, TRV valves, programmer. This is then calculated in RdSAP. Note: Electric heating is expensive to run and a property will always have a lower rating when electric heating is preset. We then need to tell the software how your hot water is created and stored if you have a hot water cylinder. And if there is any insulation on the hot water cylinder and if it has a thermostat.


The surveyor will have to enter how many rooms there are, how many lights and if the bulbs are the energy efficient type. We only assess fixed lights not table lamps. The glazing type has to be entered, is it double glazed, single glazed, triple glazed?


Once all this information has been entered we can calculate the EPC. The EPC will then tell us how much it will cost over three years for your heating, lighting, hot water. This is based on the property only not how you use it. And it will give us a band rating A,B,C,D,E,F,G and on the last page you will get the carbon rating. You can take two identical properties side by side and they will both have a different rating based on all the elements described.


RdSAP does not care that you hardly ever put the heating on or that you keep the lights off all the time. This is a general rating of how the property performs. This is for whomever is purchasing or letting the property so can have an understanding of what it will cost them to run it.


RdSAP uses current utility rates (updated every 6 months) and applies them so the gas and electric consumption based on the systems in place will be calculated. This is what give us our running costs. Additionally it used default heating patterns and room temperatures. For example the software will assume you heat the property for 11 hours a day and keep your lounge at 21 degrees and bedroom at 18 degrees. This is then applied to your heating system and how much gas/electric it will need to effectively heat the cubic meters of space within your property. The EPC certificate will describe how your property is constructed, insulated, etc. it will make recommendations that are relevant to your property.


Well that is the basics of what an EPC certificate is. I hope you find this article helpful?

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