Double glazing issue under the latest RdSAP10 EPC standards?

Reply to the comment left by Peter Rowley at 04/06/2026 – 10:14
so by that analysis it should come up with the same rating for the same windows as the EPC before as nothing has changed.

Reply to the comment left by Reluctant Landlord at 04/06/2026 – 12:25
For the windows the numerical aspect of the EPC rating will be the same contained within the overall EPC rating, but the descriptor of poor will have changed as previously your double glazing would have been compared to good quality double glazing, rather than what it is now comparing with, which is triple glazing.
As technology moves on the things that existing aspects are compared with get better, so it shows that in general your asset (in this case the windows) have remained static but the “thermal qualities” of windows is generally getting better.
A similar analogy can be found with TVs. About 2 or 3 years ago TVs that were at that time rated say a B rating for energy efficiency are probably rated an E or F rating now, as TVs have been improving in efficiency, so the goalpost measure has moved to accommodate this general trend in improvement in efficiency.
Coming back to your reduced EPC rating, it is as I mentioned earlier probably due to other elements of data that now have to be included in the EPC calculation that previously were not required to be collected and input.
In general the aim of the EPC methodology improvements is to get towards a more “accurate” picture of a property’s energy rating , which has been driven in part by landlords asking for the EPC ratings to more accurately reflect their properties. This is still ongoing and the next iteration of the EPC software (due sometime second half of next year) will go even further to reflect a more accurate picture.

Reply to the comment left by Peter Rowley at 04/06/2026 – 13:36
thanks for the clarity. Wish I hadn’t bothered at all with them now. Whatever the new methodology is it seems unless anything is the best of its kind when the EPC is done, its always going to get marked down later on.

Again absolutely no compulsion to do anything to increase any rating now, until as late as possible because the whole thing is being built on shifting sands…

If they carry on like this, no one will be able to get to a min C (if that is still the plan by then by the time 2030 comes along and there is anyone left renting in the PRS!)

If there is a major shift of sales previously rental going into FTB hands/downsizers etc then that will automatically move a lot of properties out of being counted in for needing to be C rated.

Maybe this IS the plan overall – then Red Ed can say there are more properties achieving a C and NZ targets will be met (the reality being is just a shift of D’s and below not actually being counted because they are privately owned)

Reply to the comment left by Reluctant Landlord at 04/06/2026 – 14:18
It happened to me, I was selling flat so had to get new ePC, the previous one was a D but said on it if I got new windows it will get points bringing it to a C. In 2020, I put in new windows . The surveyor put it in as a D again. he also said it needed underfloor insulation , in a top floor flat. I contacted the EPC complaints people and his boss. The EPC said that they would deal with it if his boss didn’t change it. They did , it is now a C. The surveyor spoke to me like I was an idiot. Connells surveyors… Sold it to another landlord so at least his flat is a C now and needs no work.

I have several flats built to a very high standard in terms on energy, insulation etc, the tenants all report very low energy bill running costs, but the software assumes the worse and the EPC ratings are very poor.. I wonder if I could get a surveyor’s report, thermal camera and or as build designs to show the insulation levels?
I have a ground floor flat the EPC recommends solar panels on the roof I do not own , and a 1st floor flat recommends cavity insulation, but not loft insulation?.. madness !!

I’ll not be bothering with another EPC, it is obvious they are not fit for purpose and do not represent the properties that tenants are perfectly happy with. My place will be up for sale about 12 months before the EPC expiry.

Reply to the comment left by Chris H at 04/06/2026 – 19:13
Chris
If the properties are as you describe, the ground floor flat (when entered as such with another dwelling above) should not recommend PV at all. The top floor floor flat may not recommend loft insulation if the Assessor could not either (1) access the loft as there was no loft hatch; (2) could not access the loft safely either because over stairs, too high; or in a small cupboard area which was full of items – i.e. restricted access; (3) loft hatch was locked or screwed shut; (4) accessed the loft but either fully boarded over loft space or was full of items obscuring view, (5) Assessor was lazy and did not even bother to access loft.
If any of the above reasons for loft access, the Assessor will have selected “Unknown” within the EPC software and the recommendation for loft insulation is automatically repressed i.e. it does not show it.
If you let me have the two addresses I am happy to have a quick desktop look for you at the EPCs and can then possibly let you know what to do next.

Reply to the comment left by Peter Rowley at 05/06/2026 – 08:29
Hi Peter, Thank you for your reply and knowledge

They are at separate addresses,
The ground floor flat is in a block of four and has its own purpose built entrance.

The 1st floor flat is adapted extension to two flats, it did not at the time have a loft access, I have now installed a loft hatch, Is there a guide for the thickness of the insulation required for the best increase in rating? Or is it just to current regs?

Reply to the comment left by Chris H at 05/06/2026 – 11:30
Chris, For the first floor flat if the heating is electric I would suggest 400mm of loft insulation, if it is gas a minimum of 270mm of insulation. Electric costs more than gas hence the difference in suggested loft insulation thickness.

as for the ground floor flat, if there is another flat above, the EPC should state on the front page (right hand side near the top) “Ground floor-flat”. If t states this then PV should not be recommended as there is no roof. If you look at the roof description it should state “Another dwelling above”. If this is not the case on your EPC, contact the original Assessor in writing and ask him/her to explain how they arrived at the apparent disparity of description. The Assessor should respond in 7 days and either accept they did it wrong and correct it Free of Charge, or explain with reasons why your property is not a flat. If you do not like the answer, you can then escalate it to the Accreditation Scheme but include copies of correspondence with assessor to show you have given the Assessor the opportunity to correct the EPC first.
Hope this helps.

Reply to the comment left by Peter Rowley at 05/06/2026 – 11:51
Thank you Peter,
I did not even think to check that part, I just skim that part, you are correct, after checking “Property type Semi-detached house” but in the features it states Roof (another dwelling above), so pure error by the accessor

The ground floor flat is electric, the upper flat is gas, I wonder if there is any benefit to installing 400mm rather than the 270mm, would that improve the EPC rating our would it be a wasted?

I am thinking of trying to obtain the built plans, if not maybe a full survey to prove that the property is much higher in insulation than the low minimum regs of the day (1981)

Thank you again, for your quick replies and knowledge