All Things Windows: How Glazing Affects Your EPC and Compliance
Window type, frame material, and glazing all affect your EPC rating. Learn how they are assessed and when upgrading makes sense.
By First Certify · 2025-07-30 · 5 min read
First Certify is a UK property compliance platform staffed by accredited assessors and qualified engineers. This article has been reviewed for accuracy against current UK regulations, including MEES, the Electrical Safety Standards 2020, and the Gas Safety (Installation and Use) Regulations 1998.
Windows are one of the most visible elements of a property and they play a significant role in the EPC rating. The assessor looks at the glazing type, the frame material, and the age of the windows to determine how much heat they retain.
Single glazing scores poorly because it allows significant heat loss. Double glazing scores better, and triple glazing best of all. If your property has single glazing, upgrading to double is one of the most impactful improvements you can make, though it is also one of the most expensive.
The frame material is also assessed. U PVC and timber frames generally score better than metal frames, because metal conducts heat more readily. If you have metal framed single glazed windows, the impact on your rating is significant.
The age of the windows matters too. Windows installed before 2002 are assumed to be less efficient than those installed after, when building regulations improved glazing standards. If you have older double glazing, the assessor may record it as a lower specification than modern units.
It is worth noting that the assessor can only record what is visually evident. If you have secondary glazing installed behind single glazed windows, point it out to the assessor, as it may not be immediately obvious. The same applies to any Low E coatings or argon filled units, which are not visible but improve performance.
If you are planning to upgrade your windows, the EPC recommendations report will show the potential improvement in your rating. For properties with single glazing, the upgrade to double can move the rating up by one or two bands. For properties with older double glazing, the improvement from upgrading to modern units is smaller.
FAQs
Do I need double glazing to pass an EPC?
No, but single glazing significantly lowers your rating. Most properties with single glazing score D or below. Upgrading to double glazing can move your rating up by one or two bands.
Does the window frame material affect the EPC?
Yes. U PVC and timber frames generally score better than metal frames, because metal conducts heat more readily. The assessor records the frame material as part of the assessment.
Should I tell the assessor about secondary glazing?
Yes. Secondary glazing behind single glazed windows may not be immediately obvious. Point it out so the assessor can record it, as it improves your rating.