Double glazing issue under the latest RdSAP10 EPC standards?

Hello, I’ve just been just been shafted as I’ve had a couple of new EPCs done to ground floor flats, both fully D/G windows throughout.

Got a worse rating within the EPC for the window rating than the previous even though they are exactly the same windows!

Now rates the windows as ‘poor’.

Windows are fully functional and no issues, not blown or anything, all uPVC in place no deterioration etc. It all boils down to the fact that I cannot confirm the date when they were originally fitted. This is getting to be a joke now.

RdSAP 10 window categories explained (current rules):
Under RdSAP 10, double-glazed windows are recorded using specific evidence-based categories.

These are the options assessors must use:

Double glazing – unknown install date
Used when the property has double glazing but no proof of age or specification is available.
Default conservative assumptions apply, often resulting in a “poor” rating.

Double glazing installed before 2002
Reflects pre-Building Regulations standards.
Assumed higher heat loss and higher U-values.
Frequently rated “poor”.

Double glazing installed between 2002 and 2022
Improved regulatory standards and better assumed performance.
Requires evidence to be recorded.
Often rated “average” or “good”.

Double glazing installed during or after 2022
Modern glazing standards and lowest assumed U-values.
Typically rated “good”.

Double glazing – known data
Used when installation date and specification can be proven with documentation.
Allows more accurate EPC inputs and usually improves the window rating.

If no evidence is provided, the assessor must default to the least efficient reasonable category.

3. No supporting evidence was available
Without evidence, assessors cannot guess.

Acceptable evidence includes:

FENSA certificate
Building Control sign-off
Installer invoice
Manufacturer specification
Documentation showing installation year

No paperwork = default values.

Thank you,

Reluctant Landlord