EPC Rating and Windows: What Landlords Need to Know for 2026

If you're a landlord with period properties in London, the clock is ticking. New energy efficiency regulations coming into force in 2026 will require rental properties to meet minimum EPC (Energy Performance Certificate) standards—and windows are often the biggest obstacle to compliance.

For owners of listed buildings and properties in conservation areas, the challenge is particularly acute. You can't simply rip out your Georgian sash windows and install UPVC double glazing. So what are your options?

The 2026 EPC Requirements

From 2026, all rental properties in England and Wales will need to achieve a minimum EPC rating of C for new tenancies, with existing tenancies following by 2028. Properties that don't meet this standard cannot legally be let.

Currently, around 60% of English homes have an EPC rating of D or below. Period properties with single-glazed windows are particularly affected—many sit at E, F, or even G ratings.

The penalties for non-compliance are significant: fines of up to £30,000 for letting a property below the minimum standard.

Why Windows Matter for EPC Ratings

Windows are one of the largest contributors to heat loss in any building. In a typical period property:

• Single-glazed windows lose 2-3 times more heat than insulated walls
• Windows can account for 20-30% of total heat loss
• Draughty windows add to this with uncontrolled ventilation

An EPC assessor will specifically examine your glazing type, frame material, and window area. Single glazing with timber frames scores poorly; double glazing scores well. But what if you can't install double glazing?

Secondary Glazing and EPC Improvements

Here's the good news: secondary glazing is recognised by EPC assessors as an energy efficiency improvement. When properly installed, it can:

• Improve your EPC rating by 5-15 points
• Reduce window heat loss by up to 65%
• Eliminate draughts (uncontrolled ventilation)
• Be recorded as "secondary glazing" in the EPC methodology

For a property currently rated D (score 55-68), good-quality secondary glazing combined with other improvements can often push it into the C band (score 69-80).

The Listed Building Advantage

There's an important exemption that many landlords don't know about. Properties where energy efficiency improvements would "unacceptably alter the character or appearance" of a listed building or building in a conservation area may qualify for an exemption.

However, this exemption requires you to demonstrate that you've explored all reasonable alternatives. Installing secondary glazing shows you've taken action to improve efficiency while respecting heritage constraints—strengthening any exemption application.

In practice, secondary glazing often negates the need for an exemption entirely by achieving sufficient EPC improvement.

What EPC Assessors Look For

When an EPC assessor visits your property, they'll examine:

1. Glazing type: Single, double, triple, or secondary
2. Frame material: Timber, UPVC, aluminium, or composite
3. Window area: Percentage of wall area that is glazed
4. Draught-proofing: Evidence of sealed frames and openings

Secondary glazing ticks multiple boxes: it counts as an additional glazing layer, and properly installed units eliminate draughts completely.

Specification Matters

Not all secondary glazing will deliver the same EPC improvement. For maximum benefit:

• Use low-E glass: Low-emissivity coatings reflect heat back into the room
• Ensure airtight seals: Brushes and seals must be properly fitted
• Maximise air gap: Larger gaps (100mm+) improve thermal performance
• Cover the full window: Gaps around frames compromise performance

Cheap magnetic or removable secondary glazing may not deliver the same benefits as professionally installed units with proper sealing.

Cost vs. Penalty Analysis

Let's be practical about the numbers:

Secondary Glazing Investment

For a typical London flat with 6-8 windows:

• Standard secondary glazing: £2,500-£4,000
• Premium specification: £4,000-£6,500

Non-Compliance Penalties

• Fine for letting below minimum standard: Up to £30,000
• Lost rental income during void periods: Variable
• Reduced property value if unlettable: Significant

The investment in secondary glazing pays for itself many times over compared to the cost of non-compliance.

Additional Benefits for Landlords

Beyond EPC compliance, secondary glazing offers landlords several advantages:

• Reduced tenant complaints: Warmer, quieter properties retain tenants longer
• Lower maintenance: Original windows are protected from condensation damage
• Premium rents: Well-insulated period properties command higher rents
• Preserved character: Original features maintained for property value

Getting Started

If you're a landlord with period properties, now is the time to act. The 2026 deadline is approaching fast, and installation schedules fill up quickly as demand increases.

We recommend:

1. Get a current EPC assessment to understand your baseline
2. Identify which improvements will have the greatest impact
3. Request a survey for secondary glazing quotation
4. Plan installation during void periods if possible
5. Get a new EPC assessment after improvements

Our team has extensive experience helping landlords achieve EPC compliance while preserving heritage features. Call 020 7060 1572 to discuss your portfolio.