Why Your EPC Rating Dropped After Renovation: Hidden Factors Explained?

You’ve just completed a renovation — new kitchen, upgraded interiors, maybe even a loft conversion — and expected your Energy Performance Certificate (EPC) rating to improve. But instead, it dropped. How is that possible?

This scenario is more common than you might think, and the reasons often come down to overlooked energy performance factors. Let’s unpack why EPC scores can fall after renovations — and what you can do to fix it.

⚠️ First, EPCs Measure Energy Performance — Not Aesthetics

EPCs don’t account for your new granite countertops or stylish open-plan layout. The EPC is focused solely on energy efficiency, including:

• Insulation levels

• Heating system efficiency

• Glazing performance

• Ventilation and airtightness

• Lighting and controls

So unless your renovation directly addressed these, your EPC may not improve — and could even drop.

🕵️‍♂️ Top Reasons Your EPC Rating Dropped After Renovation

❌ 1. Loft or Extension Without Proper Insulation

New loft conversions or rear extensions can significantly increase heat loss if:

• The roof, walls, or floors weren’t properly insulated

• Cold bridges (like steel beams) weren’t thermally broken

• No insulation documentation was provided

📉 SAP assumes poor performance if no verifiable data is supplied.

❌ 2. Glazing Downgrades or Changes

• Removing a solid wall to add large glass doors or skylights increases heat loss.

• New windows without proper U-value certification may be assumed to perform worse than they actually do.

Even modern-looking glazing can hurt your EPC if it’s unverified.

❌ 3. Increased Floor Area

EPCs consider energy use per square metre. Adding floor area (e.g., with an extension or loft conversion) increases heating demand. If this space isn’t highly efficient, it can lower your rating.

🔍 More space to heat + average insulation = lower energy performance per m².

❌ 4. Lighting Changes

If you replaced ceiling lights with decorative fittings that use standard bulbs (instead of LEDs), your EPC will reflect a higher energy usage for lighting.

❌ 5. Upgrades Without Documentation

Assessors rely heavily on documented evidence. If you’ve:

• Installed insulation but didn’t keep invoices or photos

• Upgraded your boiler but didn’t show the make/model

• Added underfloor heating without performance specs

…they’ll default to worst-case assumptions, which drags your rating down.

❌ 6. Old Heating System Still in Place

Many renovations skip the boiler or central heating system. If your shiny new home still runs on a 20-year-old non-condensing boiler, your EPC will reflect low efficiency.

❌ 7. Room-in-Roof Conversions Without Proper Detailing

Converted lofts need insulation in:

• Sloped ceilings

• Dormer walls

• Gable ends

Missed any of these? Your EPC will penalise the entire space — even if it looks great.

📉 Case Study: How EPC Ratings Drop After Renovation

✅ How to Prevent or Fix a Post-Renovation EPC Drop

✔️ 1. Insist on Proper Insulation During Works

Include insulation specs in architectural plans and ensure contractors follow them. Use Building Control certificates for proof.

✔️ 2. Keep All Documentation

Collect:

• Invoices

• Photographs of insulation installation

• Manufacturer datasheets (boilers, windows, etc.)

• Completion certificates

✔️ 3. Install LED Lighting Throughout

At least 75% of fixed lighting should be low-energy to avoid EPC penalties.

✔️ 4. Upgrade Heating Systems

If you’re renovating, this is the perfect time to replace outdated systems. A modern condensing boiler or heat pump can raise your rating significantly.

✔️ 5. Ensure Window and Glazing Performance Is Verified

Ask for U-value certificates from window suppliers, especially for large glass elements.

🧠 Key Takeaway: EPCs Are About What’s Behind the Finish

Renovations can be energy-positive or energy-negative — depending on how they’re done. EPC scores are data-driven, not design-driven. If energy upgrades aren’t part of the plan (or aren’t documented), your post-renovation rating might disappoint.

🏡 Renovated Your Property in London? Get the Right EPC.

At EPCrate.co.uk, we understand the hidden EPC pitfalls that follow modern refurbishments.
🛠️ We ask the right questions
📸 We help you present proper evidence
📊 We issue landlord- and MEES-compliant reports

📋 Quick Recap: Why Your EPC Dropped After Renovation