The older EPC does not make sense at all

[mattman]

Hi everyone

 

I have just received the EPC for two almost complete self-build buildings - a semi-detached barn conversion we have completed.  Next door is owned by my brother-in-law's family and one half is my family's - we each inherited one half of an old steel barn which we each financed and each did up so we could live in them.  I project managed and designed and specced the insulation etc for both houses and I also did the full planning applications for both houses after they received class Q.  I am not an architect by any means but long story short I took on the role and we have ended up with two very nice houses - now in final stages of completion. Now my reason for my thread is a very strange result happened with the EPC results on both houses.  Both houses are absolutely identical area/footprint, same windows and identical in every way (my brother-in-law's family wanted to do the same as us) with the exceptions of the following: my house scored 2.5 on its air tightness score, whereas next door (with it being a semi-detached) decided not to do an air tightness test and instead share our result but due to this had to officially take 4.6 as there air tightness score (they were happy with this as they didn't do any air tightness work whereas our house did a significant amount), my house had a slightly smaller ASHP, 8.5kW, and next door had an 11.2kW ASHP, my house had 50mm more wall insulation, behind the cladding, my house also has a whole house MVHR, where as next door doesn't.  The SAP report results showed my house as having a space heating requirement of just over 3000kWH a year less than next door, and the DER carbon dioxide emissions per year was significantly less too. However the EPC results gave next door one point more than my house.. I questioned the SAP assessor about this and he said our house was significantly better specced and and he couldn't answer why next door scored higher on the final EPC result - he put it down to the older SAP/EPC software. We were on the 2010/2012 (not sure which year exactly but it's the one before the current 2022 one) building regs - as our planning process started in 2019.  Now I am assuming, possibly that the newer building regs and SAP assessment would be a lot more accurate (I would hope so).  Can anyone explain why my EPC score would be one point less than next door when we scored much better in terms of space heating requirement and DER (and virtually everything else)?   This is a like for like test with some, what I had hoped good design choices, but actually caused us to score less in the EPC.. it just doesn't make sense all.

 

Thank you for any help.

Edited April 4, 2023 by mattman

[Alan Ambrose]

The SAP evaluation is a bit ... dodgy. Was this the same assessor? You should be able to see from the detailed report where the properties differ. You'll need to compare line by line. Are any of your values 'assumed'?

 

The SAP objectives seem to be a bit confused on whether they're trying to optimise fabric energy efficiency or energy running cost or environmental carbon impact. For instance, electric heating gets marked down as 'Very Poor' even though it is the only green fuel. I have a property (a barn conversion) marked as EPC E which was completed in 2017 with the wall and floor insulation as 'assumed' for EPC purposes. Yeah, the EPC man could have asked the builder and/or the builder could have told him, but neither could be bothered.

 

Essentially the EPC people put values into a bit of software. Quickly because they don't charge much. If they don't know something they guess - usually a 'conservative guess' i.e. they end up with a worse result. Whatever comes out is whatever comes out, they (usually) don't care, they've already started on the next one.

 

From Wikipedia: "A number of comparisons have indicated that SAP does not provide an accurate model for low-energy buildings.[1][2][3]"

1.  "Archived copy". Archived from the original on 2016-02-08. Retrieved 2016-02-02.
2. ^ Passivhaus project reveals flaws in Code
3. ^ Raising the bar

 

[mattman]

Thank you for your reply Alan. Yes it was the same assessor. And all values are actual.. None are assumed. We used the same builder for both houses and the EPC score in question is the final As Built result. I can only "assume" we got marked down for having a slightly smaller ASHP (we used the same ASHP installer and brand for both houses) but then our air tightness and slightly better insulation meant we didn't need the bigger size. Going through line for line in the detailed SAP report we score slightly better on all accounts. The SAP report is accurate. It's just the actual EPC which is not. Even the EPC certificate second page says our space heating requirement per year is a lot less than next door yet we still got marked down and oddly said our fuel bill would be £20 more a year than next door when we will be using 3000kwH less a year.. Doesn't quite make sense. Don't get me wrong both houses scored extremely well in the SAP and EPC it was just more my own scientific curiosity that is wondering why a house which is more thermally efficient with better air tightness, insulation, and better DER etc, should get a marginally lower score.

 

This was the closest to as good an experiment as you can get really testing how good the old style EPC certificates are, because both houses are identical in all ways apart from a very small but important number of differences. I am just putting it down to the old style EPC being quite inaccurate and not properly linked to the SAP report data. 

[saveasteading]

It takes hours to input properly, so costs a lot.

Thereafter, any tweaks and corrections are easy though.

If ever buyers start to care about epc , then proper assessments might become more valuable.

[Mr Punter]

I thought that if you did not have an airtightness test, the default was something like 15.  May be different for conversions though.

[saveasteading]

As a business we hardly ever had a client who cared. So we just had to pass regs.

We knew the decent figure we would get ( about 3), and used standard details so always to that standard.

Saved the cost of an air test (many hundreds, even thousands,  for a big building) and the time in stopping the trades,  and still passed every time with the default leakage. That required detailed understanding of the building.

Lots of our buildings are out there with C certificates that are really performing as B+.

[ProDave]

8 minutes ago, saveasteading said:

As a business we hardly ever had a client who cared. So we just had to pass regs.

The difference between most people and a self builder.

 

When I gave all the as built details, including the air test result to my EPC assessor (full SAP) my instructions were, if it does not achieve an EPC A, then do not register the EPC, instead discuss with me what improvements I need to make it achieve an A before the EPC is registered.

 

Building inspector at completion remarked this is the first house he has seen with an EPC A

[mattman]

23 minutes ago, Mr Punter said:

I thought that if you did not have an airtightness test, the default was something like 15.  May be different for conversions though.

Hi, that is correct with detached properties. We are semi-detached, and used the same builder so next door had the option of "using" our air tightness score, but they would have to take a lower score than our house, which they did.  We got an actual test result of 2.5 and they used a result of 4.6 (given to them automatically by our SAP assessor).

Edited April 4, 2023 by mattman

[mattman]

Yes it is just my scientific curiosity and as you say, being a self-builder, and someone who spent many hours/days/weeks researching and speccing insulation/all the air tightness methods etc for both houses, I was just really surprised that one house which has a better spec would get a marginally worse EPC result - in quite a controlled test (at least as close to controlled as you could get) - same builder, same footprint, same SAP assessor, same brand insulation, same everything apart from just a few crucial details which "should" make a house more thermally efficient and according to the detailed SAP report does - but the EPC result says not.  Both houses achieved a very good score and EPC A result so are both very highly efficient and I am more than happy with the result - the only differences between the two was our house had the extra details:

- MVHR (other house is naturally ventilated)

- 2.51 air tightness (other house given 4.6) - both houses are standard block brick with cavity wall construction and warm roof.

- 8.5kW Ecodan ASHP (other house 11.5kW Ecodan)

- 50mm more wall insulation 

 

But we scored one point less on the EPC than the other house despite the extra details above.  I can only put it down to some kind of built in formula in the EPC and it possibly not looking at all the variables.. I'm not sure.  The EPC score is just a number at the end of the day and I know during the cold minus -6c winter spell recently ours used very little ASHP energy to heat the house - and all hot water, around 20 to 24kWH per day, so it appears to be performing very well and costing relatively little to run.  It was our first winter in the house.  Thanks for all your replies so far.

Edited April 4, 2023 by mattman

[Alan Ambrose]

Errr, what does the assessor say?

 

>>> When I gave all the as built details, including the air test result to my EPC assessor (full SAP) my instructions were, if it does not achieve an EPC A, then do not register the EPC, instead discuss with me what improvements I need to make it achieve an A before the EPC is registered.

 

I had something similar for my mum's place when the EPC ran out. I said I would need a thorough explanation unless the result turned out the same as the original B. That is, I didn't want any dodgy 'assumptions' knocking down the EPC rating. The situation was a bunch of similar flats with no changes since built (actually converted from an office building 14 years ago). They had all started off with the same B rating but ended up with different ratings over the last few years - with no changes to the fabric, heating methods etc - just depending on how diligent the EPC guys were.

 

I learned a lot talking to my EPC guy who was very thorough. He said the original EPC person will have had access to the builder's docs but he, of course, didn't have access to them - so the rating would likely be lower. In actual fact, he contacted the person who did the original EPC and got the original details from them and therefore generated the same B result. It took him a bunch of time and he didn't charge me extra - I think a professional pride thing.

 

Another reason why builders and sellers should be required to pass a full set of docs down the line.

[ProDave]

56 minutes ago, Alan Ambrose said:

I learned a lot talking to my EPC guy who was very thorough. He said the original EPC person will have had access to the builder's docs but he, of course, didn't have access to them - so the rating would likely be lower.

In the event I need a new EPC in 10 years, I would give the new assessor EVERY single page of the full SAP calculations so there is no doubt he has the full information.

[mattman]

This is what my SAP assessor said in response to me asking why my house scored one point less than next door (please note the assessor did the SAP and EPC and no assumptions were made in the SAP report).. Here's what he said:

 

"I believe it is because of the slightly larger heat pump.

 

To be honest this is not reflective as yours is the better specified house but unfortunately the old SAP software is skewed towards zero carbon tech, for example a lot of developers either go for solar or ASHP because as long as one of the systems is fitted it brings the house into compliance. The software doesn’t allow for the fact that two systems complement each other. However your smaller ASHP should be giving you a higher score as it is consuming less energy."

 

 

So in other words my SAP assessor doesn't know for sure and is blaming the EPC software. Not really that helpful but there's not much can be done. Just highlights how inaccurate EPCs are.. The SAP report is accurate just not the EPC linked to it. I hope the newer EPC software is a lot better.

 

I assume in 10 years time when my house needs a new EPC will it use newer EPC software looking at my current SAP report created last week..so I will hopefully get a more accurate reflective EPC score? Or will it have to use the old inaccurate EPC calculation software again? If the SAP requirements change in 10 years time will I need a completely new SAP report done or can I continue to use my current report? What I'm trying to find out is if everything gets stricter on zero carbon etc in 10 years will older houses potentially need new SAP reports along with the EPCs and may get re-classified in lower EPC bands because they might fail to meet the newer requirements? 

[saveasteading]

I wouldn't count on the software ever being accurate. 

As i have said here before, i have met  some of the people who built and support it, and wasn't impressed.

They have been told since the scheme started that it had these massive logic flaws, as well as glitches.

 

For a better rating, solar panels may take some time to fit after completion, but it doesn't delay the signing off.

 

[Mike]

1 hour ago, mattman said:

So in other words my SAP assessor doesn't know for sure

But could easily find out by selecting the slightly smaller heat pump in the software and looking at the result?

[SteamyTea]

What a fantastic opportunity to monitor two identical (almost) houses.

Get the data monitoring gear in.

[mattman]

2 hours ago, SteamyTea said:

What a fantastic opportunity to monitor two identical (almost) houses.

Get the data monitoring gear in.

 

I thought so too. 

[mattman]

12 hours ago, Mike said:

But could easily find out by selecting the slightly smaller heat pump in the software and looking at the result?

I agree.  I think by that point he had already generated the As Built EPC certificate and it was too late to rectify or check it - I assume not without a bit of hassle on this part.  It was only me who realised the weird EPC score result - he didn't notice it until I pointed it out to him and he then agreed with me it was unexpected. 

UPDATE: I have gone through line by line of the SAP report and I believe it is the MVHR that we have which is causing us to have a slightly lower score (next door don't have an MVHR).  Here is a line in the SAP report which I can only assume is actually an assumption (as I have no idea how much energy an MVHR requires - he may have retrieved this from the make/model of MVHR we have which is a Beam C90):

"mechanical ventilation - balanced, extract or positive input from outside 1034.56 kWh/year"

 

It does seem odd though that even though our house space heating requirement per year is  3000 kWh less per year than next door, it doesn't more than cancel out the energy usage of an MVHR.

[Mr Punter]

I guess that if both houses are equally leaky and yours is also running MVHR, yours will use more energy.

[mattman]

15 minutes ago, Mr Punter said:

I guess that if both houses are equally leaky and yours is also running MVHR, yours will use more energy.

Ours had an air tightness score of 2.5. Next door didn't do any air tightness work on their house so opted not to test their house and instead use our test result, but had to take a lower result of 4.6 due to opting to not test their house. 

[markocosic]

Energy price assumptions.

 

EPC score is based on energy cost only.

 

Newer EPC win have different cost assumptions.

 

Get another if you care; updated with the more current yet out of date assumptions. 🙂

[saveasteading]

If you want a thorough assessment try Energist.

It will cost a lot. But then if you have the input data already that should help. 

[Jilly]

Are you sure he didn't just get his paperwork the wrong way round...?