EPC Case Study: How a Luton Semi Scored 101, an A

What does an EPC assessor check?

Everything that affects how much energy the house uses. Here's what we checked and found at this house.

• Solar panels. 19 panels on the back roofs, 6.32 kWp in total. We read the installer's label and the generation meter to confirm the size.
• Walls. The main house is solid brick with external wall insulation under the render. The rear extension has insulated cavity walls.
• Loft. We measured 200 mm of insulation. The extension's flat roof is insulated too.
• Windows. Double glazed throughout.
• Heating. A Worcester Greenstar condensing gas boiler heats the radiators and the hot water, run by Hive controls.
• Lighting. All low-energy bulbs.
• Floors. No insulation under the floors.

Can an EPC score go over 100?

Yes. This house scored 101.

The score is based on running costs. Solar panels earn credit for the electricity they make. When a house makes more than it needs, the score can pass 100. Band A starts at 92.

Do solar panels improve an EPC rating?

Yes, more than anything else we see. A 6.32 kWp system is large for a house this size, and it's the main reason this house is an A. Without the panels, we estimate it would be around a C.

We see the same on other jobs. On a D-rated terrace we assessed in Luton, a 2.5 kWp system was worth 13 points on its own, taking it from a C (71) to a B (84).

Does an EPC count the electricity you sell back to the grid?

Yes. The EPC gives credit for all the electricity the panels make. That includes what the house uses and what it sends back to the grid.

Does insulation improve an EPC rating?

Yes. Walls and lofts make the biggest difference after solar panels.

This house has external wall insulation, rated Good. The D-rated terrace had bare solid brick walls, rated Very poor. Insulating them was its biggest single step: 63 to 69, and about £248 a year off the bills.

The loft here has 200 mm of insulation. The terrace had 100 mm.

How does an A-rated house compare to a D?

Here's this house next to a D-rated terrace we assessed in Luton the same month. The A-rated house is 43% bigger, but it needs 17% less energy to heat.

Will an A rating lower my energy bills?

Yes, but the EPC bill figure doesn't show the full picture. Both houses have almost the same estimated bill: £1,272 for the A and £1,275 for the D.

That figure only covers heating, hot water and lighting. It doesn't take off what the solar panels save. So the A-rated house heats a bigger home for the same money, and the panels cut its electricity bill on top.

Is floor insulation worth it for an EPC?

Not usually, if the rating is all you need. This house's only recommendation was floor insulation: £5,000 to £10,000, to save about £59 a year and go from 101 to 103.

The D-rated terrace got the same advice. It added 2 points (69 to 71) and about £76 a year.

How long does an EPC take, and how long does it last?

This visit took under 40 minutes for a 93 m² semi. The certificate was ready the next day. An EPC is valid for 10 years.

Can you rent out a house with a D rating?

Yes. Today you can let a property rated A to E. A property rated F or G can't be let unless an exemption has been registered.