I’ve noticed a few suggestions that the EPC is nothing more than a bit of fluff and nonsense. So I thought’ I’d post some calcs that I’ve been using the EPC software for on my own house. This is a table of different “what if’s” I’ve entered into the version of the software I have. After completing the calc I change the input to set up a different scenario.



Key things to note.
These calcs are done with an older version of the RDSAP software Dating from Mid 2007. Upgrades have been made since, but they're still close enough to show what it can do.

Energy Use doesn't reflect appliances or home electronics etc.

RDSAP Assumes heating is 21 degrees in the lounge 19 deg elsewhere. 9 hours week days and 16 at weekends.

Saving's possible don't take into account lifestyle effects - using showers, lower room temperatures. These are “standard occupancy” figures established by BRE using research in different households. This isn’t a personal energy prediction but what the ”average family” would get if they lived in your house.

Basic EPC is set to low expectations - it only thinks 63(E)/57(D) are possible. 82(B)/79(C) is possible if the cash is available! This is due to the EPC only highlighting cost effective measures. It wont list fuel source switching, or external wall insulation on cavity built properties.

SAP doesn't model large thermal stores fed from an ASHP run only on E7. Regardless of that - ASHP Has a sizeable drop in running costs & CO2 compared to original gas boiler.

Wood Burner is listed as more expensive than a gas fire - despite my wood being free. SAP Assumes market rates and therefore the rating drops from 56 to 55. Yet kWh/m2/yr & £/yr for heating goes down!? I guess they assume you don't use it as much as a gas fire as it's more hassle! It does add 3 point to the environmental rating.

Despite building a bigger house - it's possible to make it use less energy.

The CO2 is based on grid electric. If you switch to 100% green you effectively have none - apart from a few gallons of [bio]diesel to collect your logs. That's a 100% reduction.
Some of the assumed U values (below) for new build/extensions are lower than I intend to build. So a proper SAP instead of RDSAP assessment would be more accurate.

It appears that having 30% of you roof covered in PV doesn’t lower the cost of running the ASHP. That don’t look right guv’na ! Hope that’s been updated by now!

Appendix of Inputs. U Values have been looked up from SAP 2005 documentation - Appendix S.

As bought House has:
Total Internal Area 104 m2
Heat Loss Perimeter: 33m
Pre-1998 Fan assisted boiler (61% Efficient)
Timer and Room Stat.
130-170L Spray foam tank with thermostat
Pre 1998 Open Flue gas fire. (51% Efficient)
Cavities unfilled (U1.6)
75 mm Loft insulation in main section (U 0.50)
"As built" insulation in flat roof extension (U 2.3) *1
Post 2002 Double Glazing in 85% of the windows.
100% Tungsten lighting

Basics Add:
95% CFLs
Cavity in sections that can take it
Increase to 300mm loft insulation in main house (U 0.13)
Add TRVs
Insulate under suspended floors (N/A in my version but you can now specify additional floor insulation if there is evidence.

Wood Burner:
Replace Gas Fire with Open Flue Enclosed room Heater Log Fuel

External Alternative Wall :
Replace 35m2 of current cavity as built(20mm cavity = unfillable) (U 1.6)
This involves cutting out the external face of bricks - leaving single inner skin,
Add insulation and then timber clad or render.
Enter as solid brick external insulated 2007 or later. (U 0.21)

ASHP + Big Tank :
Specified ASHP as main heating (250% Seasonal Efficiency)
Added Large tank 160mm insulation (although large is only listed as 170L+ )
Add time & temperature Zone Control

Solar HW:
Get to tick a box - will assume size based on floor area :-(
Not the 10+ m2 I plan to install.

New Extension + Full External Insulation.
Adds 32m2 over 2 storeys, timber frame 2006 building regs insulation assumed (U 0.30) :-(
New Flat sedum roof with assumed insulation (250mm). (U 0.25) :-(
Convert old flat roof to pitched and upgrade insulation to 300mm (U 0.13)
Add 150+ mm brings whole house up to 2007 regs.

Is that of any use to anyone?

And Pounds...

The EPC software should allow you to specify Solid Wall with Internal Insulation. Drops the U value from 2.1 to 0.35!