Double Glazing & EPC Ratings: How Much Does It Improve Your Score?

Does Double Glazing Improve Your EPC?

Yes, but less than most people expect. Replacing single glazing with double glazing typically adds 2–5 SAP points — useful but not transformative. If you already have older double glazing (pre-2002), upgrading to modern A-rated double glazing adds only 1–2 points.

Double glazing is one of the more expensive improvements relative to its SAP impact. For most landlords, it should not be the first priority unless the property still has single glazing.

How Much Does It Cost?

UPVC frames are the cheapest option. Timber and aluminium cost 30–50% more. Triple glazing adds roughly 20–30% over double glazing for a marginal additional SAP benefit.

When Is It Worth It?

Do it when:

• The property has single glazing — this gives the biggest EPC gain
• Windows are damaged, draughty, or at end of life anyway — combine maintenance with improvement
• You have done the cheaper measures (loft insulation, heating controls, LED) and still need more SAP points
• The cost cap headroom allows it within your MEES budget

Skip it when:

• The property already has double glazing (even old double glazing)
• You need a large SAP improvement — the cost per SAP point is poor compared to insulation or boiler upgrades
• Budget is limited — loft insulation gives 3–5 points for £300–£600 versus £4,000+ for glazing

What About Secondary Glazing?

Secondary glazing (fitting an additional pane inside existing windows) costs £100–£300 per window and can improve thermal performance without replacing the windows. However, it has minimal impact on EPC ratings because the SAP calculation does not credit secondary glazing as highly as replacement double glazing.

For listed buildings or conservation areas where window replacement is restricted, secondary glazing may be the only option — but don't expect a significant SAP improvement.

Grant Eligibility

Standard double glazing is generally not covered by GBIS, ECO4, or the Boiler Upgrade Scheme. Some local authority schemes may include glazing as part of a whole-house retrofit package, but it is rarely funded as a standalone measure.

This means glazing is typically a full out-of-pocket cost for landlords.

The Bottom Line

Double glazing improves comfort and reduces noise significantly, but it is one of the weaker EPC improvements in terms of cost per SAP point. Do the cheaper, higher-impact measures first and only consider glazing if you still need extra points to reach Band C.

Check your property on EPCFix to see where double glazing sits in your improvement priority list and whether cheaper options get you to Band C first.