It is interesting that a system based on assumptions that are so easily proven to be wrong is so difficult to correct .- in fact there is little obligation to correct or acknowledge mistakes!
You said it all there Lloyd…
I think I say the same in many more words 
The EPC rating is based on rdSAP (rd = reduced data = guesswork). Every release of SAP moves the goal posts as the criteria become more stringent. With so much time passing even hypothetical prefect tests on the same unaltered property would change. The latest version of SAP was released a few months ago.
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So this basically means that as materials and technology improve to be more carbon efficient etc our homes EPCs can up as well as down . And I know you don’t have the answer to this question, but I’m wondering why they don’t assess double glazing on the green grant scheme to replace if failing.
Just one example of the many I guess… 
As the criteria become stricter houses will get worse results over time, never better.
No government pays householders grants for maintenance tasks, so failed window units or flattened loft insulation are not covered.
The government is again (still) assessing the EPC system. The aim is to make it reflect the real life energy usage of a building! Deja vu or what?
Has anything changed since this thread was last used? I doubt it.
What would members of this forum like to see changed?
The main factor against meaningful change, as far as I can tell, is that the EPC is supposed to be cheap. A proper analysis on a property by property basis will take hours, including the off site element. Time is money, as they say, and if the price rockets there will be an outcry.
I came across this thought provoking table on another site.
My guess is that people living in EPC G rated homes don’t heat the whole property, which skews the result at the bottom on the table but the rest is interesting too.
Edit:
See also
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After reading a lot of criticism of both the EPC system and EPC assessors I thought I would pass on my experience from yesterday.
I and my house have never had an EPC, as I have lived here since 1984. I have, however, found and accepted a quote for a heat pump and needed an EPC to claim my £5000 BUS grant.
Enter Adrian Bunting. He gave a full and proper survey and assessment and I was prepared with evidence of work done where it wasn’t accessible or visible.
I live in a pre-war 4 bedroom house with “solid” masonry walls. Having warned me that a MVHR reduced the EPC score he emailed me the draft certificate this morning with a comment in the email of what the house would have achieved without it’s A+ & Passivhaus certified MVHR.
I was very pleased to see that my planning, hard work and expense would have scored B 86, but unfortunately all I got was C 77 with potential to achieve B 81 if the council ever accept my desire for EWI. There were no other recommendations.
My neighbours have EPCs ranging from G to E for similar houses.
I am chuffed but at the same time disappointed about the MVHR. Revisions of the process need to take the “HR” of MVHR into account.
My IWI was not allowed on the EPC because i did not take photos of its instalion and the assessor could not see it. (It was mostly done in the past and the last outside wall was done this year)
I had a gas fire in the lounge but when I removed it it added 3 points to my EPC ending with a low C.
Cavity wall insulation would help but i do want to keep them clear.
Sealed cavitys top and botton when windows went in but this had no effect on EPC, it was better for the air sealing.
Do you have historical figures for energy use pre and post retrofit measures? And how is your energy consumption comparison now as I think you get a rating by post code on the energy bill? Ultimate comparison to level the playing field is the EPC rating / energy use- kWh/m2 and average temperature of the habitable space. It would be useful for this group to collate this data and see the variation to rate EPC consistency
It is hardly necessary to rate EPC consistency when previous research has shown that there isn’t any!
In my case retrofit has been a long process with an extension being built as well, so before and after figures are not comparable. I live on an inter-war housing estate where most properties are low D or worse. My house has a good C, but it is that low because I use MVHR to recover my waste heat and loose 9 points in the process.
Over the last few days my EPC rating will have dropped further from my theoretical B as I have had a heat pump installed. The EPC system treats that as electric heating, which gets a far lower score than gas. Gas boiler efficiency ~70%, heat pump efficiency ~350%. 
. The heat pump will largely run off my solar panels, so relatively little energy input to the house compared with 100% of my gas being bought in.
Incidentally, you are not allowed to claim your main source of heating water is solar thermal, even if you use no other heat source for 7 months a year and just top up at other times.
I don’t think that any kind of draught proofing or airtightness measures are used for EPCs. If you live in a giant sieve with loft insulation and double glazing you should get an ok result.
I decided to re-read this thread to see what was covered and what might need further investigation.
When I came to this post I reviewed your EPCs and noticed that you have had another one done.
The property descriptions of all of them are more or less identical. Somehow I doubt that for the last one you removed all your low energy lights but apparently they are only worth a maximum of 2 points.
So, 3 practically identical descriptions, 3 very different EPCs. I’m hoping that the people doing the surveys saw more detail as your work progressed but for someone reading the whole document and not just looking at the headline figure there is a marked lack of information.
Just going back through this thread and came across the graph illustrating difference between EPC and metered energy use.
Checked my EPC, which was done in a vain attempt to get some grant-funded retrofit work in 2021.
Detached, inter-war, 155 m2, EPC rating of 59 (D).
Stated primary energy use of 255 kWh/m2 i.e. 39535 kWh/pa.
Stated energy used for heating 24966 kWh/pa
Stated energy used for hot water 2181 kWh/pa
Metered gas use for 2022 15368 kWh
Metered elec use for 2022 1105 kWh
I make my metered energy use 106 kWh/pa v 244 kWh/pa in the table above!
An online ASHP estimate based on EPC suggests I could save c £300/pa on energy bills, (next step is to get full heat loss calcs plus another survey to see how it compares with the British Gas one I’ve already had).
My bills will undoubtedly go up from current levels, but finding it hard to guesstimate by how much!
Oh, and my bills are low because, yes, the house is kept on the cool side!
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By keeping your house cool you are doing your bit against global warming, however unwillingly. For cultural/racial reasons my family won’t do the same.
Your house is fractionally larger than mine but presumably with a significantly larger outside wall area, as mine is a “solid” masonry semi.
This summer I have had a 6kW ASHP fitted. I am looking forward to winter with a little trepidation. As I already had my flow temperature set to 40°C I was able to have a simple slot in solution with no need to change any plumbing. That potentially saved a lot of money but was really payback for earlier investment in high gain radiators and retrofit measures. My neighbours have F-D EPCs depending on what, if any, measures they have taken. I have mid C and without my MVHR would have had low B. That is the result of many years investment in my home, with the aim of a bill free retirement.
You will have a problem getting a company to size and fit a heat pump based on your actual house temperature and heat loss calculations. I had 2 quotes and 4 “not interesteds” before finding a company to do the work.
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How windows and airtightness isn’t assessed.
Currently my understanding of EPC assessment is, if you have double glazed windows you get a tick in the box. Warped UPV frames with openers which no longer close , have failed glazed units and seals are considered worthy of a boost to the EPC calculation.
… we currently cannot afford to have all new windows and our focus remains on draught proofing and trying to repair what we have.
The problem on some of the our windows is the warping - it’s so bad they won’t close properly and leak cold air in and lose heated air out.
We’re currently focused on replacing the two worst of these.
Have you considered double sided adhesive tape and plastic sheeting. Not pretty, wouldn’t pass a real airtightness test but cuts down on draughts on a budget.
Same here Sian - we try and heat the person not the whole house! Which I don’t mind to be honest.
Although when certain room’s aren’t heated , damp rears it’s ugly head - so there is a health balance consideration in certain rooms like the one I’m talking about which is Erykah’s room.
Lovely to hear off you Sian
Thankyou x
I’ll certainly be going down that route if we don’t get windows fitted before winter!!