Rated F or G? What It Means and How to Fix It

An F or G-rated commercial building cannot lawfully be let, or continue to be let, unless you register a valid exemption on the PRS Exemptions Register, so in practice it is unlettable until improved. That sounds alarming, and for a landlord relying on the rent it is a real problem. The reassuring part is that the fix is usually straightforward, because the EPC report itself hands you the roadmap, and for most F and G commercial buildings the quickest, cheapest measures are enough to move you comfortably back over the E line.

This guide sets out exactly what an F or G means for you, what it does not mean, and the practical, costed route to a lettable rating. It is written for owners who have just had a fail come back, or who fear one is coming.

What an F or G actually means

The current minimum energy efficiency standard for non-domestic property is EPC E. An F or G is below that line, which has two concrete consequences.

First, you cannot lawfully let the building, or continue to let it, while it is F or G, unless you register a valid exemption. Since 1 April 2023 this applies to existing tenancies, not just new lettings, so an F or G on a currently-tenanted building is a live breach, not a future one. Second, breaching MEES by letting sub-standard space without a registered exemption carries penalties tiered on the building’s rateable value and the length of the breach, up to a maximum of £150,000, per the non-domestic MEES landlord guidance{rel=“noopener”}, and non-compliant landlords can be publicly named.

In plain terms: an unimproved F or G is an asset you cannot rent out lawfully, and continuing regardless is expensive. That is the bad news, and it is worth taking seriously.

What an F or G does not mean

It does not mean the building is stranded for good, and it does not usually mean a huge spend. The EPC is a modelled rating with a built-in remedy: every certificate comes with a ranked list of recommended improvements. For the large majority of F and G commercial buildings, the measures near the top of that list are modest works with an outsized effect on the rating.

It also does not mean you have to guess at the fix. The report tells you which measures move the needle most, so you are not spending blind.

The usual quick wins from F/G to E

The measures that most often lift a commercial building over the E line are, happily, among the cheapest. The exact package depends on the building, but for a typical F or G unit the levers below do most of the work.

Measure	Why it helps	Typical difficulty
LED lighting with occupancy and daylight controls	Lighting is a large, easily-modelled load in shops, offices and warehouses	Low, often the single biggest quick win
Heating upgrade or better heating controls	Old electric heating and uncontrolled systems score poorly	Low to moderate
Insulation where practical (roof, pipework, cavity)	Reduces modelled heat loss	Moderate
Improved building management / controls	Better control of what is already installed	Low to moderate
Draught-proofing and glazing improvements	Cuts fabric losses on older, leaky buildings	Moderate

For an open-fronted shop with single glazing, old lighting and electric heating, a common F-rating profile, replacing lighting and upgrading the heating is frequently enough on its own. A warm-shell warehouse or an older office may need a slightly broader package. Either way, you work down the EPC’s ranked list, cheapest and highest-impact first, until you clear E.

Step by step: from a failed EPC to a lettable rating

The route is methodical, and it starts with a rating you can trust.

1. Get an accredited assessment (or check the one you have). If your fail came from a cheap remote assessment, be cautious, a wrong rating can under-state your building. A proper on-site survey by an accredited Non-Domestic Energy Assessor gives you a rating you can act on and defend. You can look up an existing certificate on the find an energy certificate service{rel=“noopener”}.
2. Read the recommendations as a priority list. The report ranks measures by impact. That ranking is your plan.
3. Cost the top measures. Start with lighting and heating, the usual highest-impact, lowest-cost lifts. Some improvements attract support: the Boiler Upgrade Scheme{rel=“noopener”} can help fund low-carbon heating where recommended, though never the EPC itself. Our grants and funding routes page sets out what applies.
4. Do the works, then reassess. The rating only updates when a fresh assessment is lodged. Once the measures are in, a reassessment produces a new certificate at the improved band, valid for ten years.
5. Consider your headroom. Clearing E is the minimum. If you plan a long lease, or the building is over 1,000 sqm and privately let (and so in scope of the proposed EPC B by 2031 standard), it can be worth pushing higher while the works are open. See our guide on what EPC B by 2031 means.

When improvement is not viable: the exemption backstop

Occasionally a building genuinely cannot be improved to E cost-effectively, all relevant measures have been done and it remains sub-standard, required third-party consent has been refused, or the improvements would devalue the property. In those cases the law provides a backstop: you can register a valid exemption on the PRS Exemptions Register and let the building lawfully while it remains sub-standard.

Treat this as a genuine last resort, not a first move. An exemption is a legal shield, not funding, it must be properly evidenced, and it is time-limited, typically five years, before you have to try again. For most buildings, a modest improvement package is cheaper and lower-risk than relying on repeated exemptions. We cover the register and the qualifying grounds in detail in our guide to MEES exemptions.

Common questions

My building came back G. Is it worthless now?

No. A G means it cannot be let as-is without an exemption, but it is not stranded. The EPC lists the improvements that will lift it, and for most G-rated commercial buildings the combination of LED lighting, heating upgrades and better controls moves it up several bands. A G is a to-do list with a deadline, not a write-off, and the works are usually far cheaper than the rent you are losing while it sits empty.

Can I just register an exemption instead of doing the works?

Only if the building genuinely qualifies, and for most buildings it will not. Exemptions exist for buildings that cannot be improved cost-effectively, where consent is refused, or where works would devalue the property, each of which must be evidenced. You cannot register an exemption simply because you would rather not spend the money. For a normal F or G that responds to standard measures, the improvement route is both the lawful expectation and the cheaper one.

Turn a failed rating into a lettable asset

An F or G is fixable, and the sooner you have an accurate rating and a costed plan, the sooner the building earns again. An accredited Non-Domestic Energy Assessor can confirm your true rating and hand you the ranked improvements that give the biggest lift for the least spend. To get a firm quote for an assessment, or a reassessment after works, request a free commercial EPC quote and we will show you the cheapest route back over the E line.