MEES and EPC: how solar affects a commercial building's rating

An Energy Performance Certificate (EPC) rates a building's energy efficiency on an A to G scale, based on a modelled assessment of the fabric, services and on-site energy. It is produced by an accredited non-domestic energy assessor, and a lodged commercial certificate runs for ten years from the date it is registered unless a newer one supersedes it.

The Minimum Energy Efficiency Standards (MEES) sit on top of that. MEES makes it unlawful, subject to exemptions, to let a commercial property whose EPC rating falls below a set minimum band. The standard already in force is band E: since April 2023 all let non-domestic property in England and Wales must hold at least an EPC E unless a valid exemption is registered, extending a rule that had applied to new lettings and renewals since April 2018. It sits under the Energy Efficiency (Private Rented Property) (England and Wales) Regulations 2015, and it bites on letting rather than on owner-occupation. Scotland and Northern Ireland run separate regimes.

Above that floor sits the EPC B ambition, and its date has moved. A June 2026 government interim response reset the target year to 2031, narrowed it to let non-domestic buildings over 1,000 square metres where reaching the band is cost-effective, and dropped the EPC C step that had been proposed for 2027. That is policy direction rather than enacted law, so confirm the band and the timetable that apply to your building with your property and legal advisers before you rely on either.

An EPC is a model of the building rather than a meter reading. On-site renewable generation is one of the inputs the assessment recognises, so a roof-mounted PV array that supplies part of the building's demand can lift the modelled rating.

How much it moves the band depends on the building. A large array on an energy-intensive site with a poor starting rating can have a meaningful effect; a small system on an already-efficient building may move the number very little. The honest position is that solar contributes to the rating rather than guaranteeing a particular band, and the gain has to be assessed against your specific assessment inputs. The accredited EPC assessor confirms how a given array size translates to band movement for your building before you rely on it.

For that reason, solar is usually one part of a wider efficiency plan that may also cover lighting, controls, heating and building fabric. We can model the generation a roof can support; the EPC band outcome is confirmed by the accredited EPC assessor working from the building's full inputs.

For a landlord the EPC rating is a leasing constraint. A property that drops below the MEES minimum can become harder to let or to keep let, which affects rental income, void risk and asset value. Improving the rating protects the ability to transact.

• Lettability: a compliant EPC keeps the building available to let under MEES.
• Asset value: a stronger rating supports valuation and reduces the risk of a building becoming a stranded asset as the standard tightens.
• Enforcement: letting below the minimum without a valid exemption can expose the landlord to penalties, so the rating is a compliance item as well as a marketing one.

Solar that both lowers running costs and contributes to the EPC rating can therefore serve two parts of the business case at once. The size of each effect is specific to the building and the lease structure.

Solar reduces the energy a building draws from the grid and feeds into the EPC model as on-site generation, so it helps on both the cost side and the rating side. It does not fix a building whose fabric or services are the real problem, and it cannot be assumed to move the band by a fixed amount.

Our role is the engineering: assessing the roof, the structural capacity and the connection, then specifying a system to recognised component and installation standards for systems above the MCS domestic scale. The EPC band itself is determined by an accredited EPC assessor, and MEES compliance is a legal question for your advisers. We size and build the array; we do not issue the certificate.

It helps to know what the assessment is doing under the bonnet, because that explains why the band movement is hard to promise in advance. A non-domestic EPC is produced using the government's Simplified Building Energy Model (SBEM) methodology, run through accredited software by a qualified non-domestic energy assessor. SBEM models the building's notional energy use for heating, cooling, ventilation, lighting and hot water, then expresses it as an asset rating on the A to G scale. On-site renewable generation is fed in as a deduction against that modelled energy demand, so a roof-mounted array reduces the net figure the rating is calculated from.

The mechanics matter because the array is credited against modelled demand rather than against your actual metered import. That is why a system sized closely to your real daytime load, the approach we set out in half-hourly metering, can read differently in the SBEM model than it does on your bill. The assessor enters the installed capacity and the system's expected contribution, and the software does the rest. Two buildings with the same array can land on different bands because their fabric, services and baseline demand differ. The single reliable way to know your number is to have the accredited assessor model the proposed system against the building's full SBEM inputs before you commit. The methodology and assessor accreditation rules sit with the Department for Energy Security and Net Zero and the approved accreditation schemes, so confirm the current SBEM version and conventions with your assessor rather than assuming a figure here.

MEES is not an absolute bar. The Energy Efficiency (Private Rented Property) (England and Wales) Regulations 2015, which underpin the commercial standard, allow a landlord to register an exemption on the government's PRS Exemptions Register in defined circumstances rather than carry out works. The detail and validity periods are policy that changes, so treat the following as orientation and confirm the live position with your property advisers and the register itself.

• All relevant improvements made: where the cost-effective measures available have been installed and the property still falls short, an exemption can apply.
• Seven-year payback test: a measure can be excluded from the required works if its expected payback exceeds a set threshold, assessed on the energy saving rather than on the wider commercial case.
• Third-party consent or devaluation: where a tenant, lender or planning authority withholds consent, or a measure would devalue the property beyond a set level, an exemption may be available.

Solar interacts with this in a practical way. Because an array contributes to the modelled rating, installing it can be part of demonstrating that relevant improvements have been made, or it can lift a building clear of the minimum so no exemption is needed. The payback test is assessed on the measure's own terms, which is a different question from your overall investment case. We keep these separate: we model the engineering and generation, your advisers handle the register entries and the legal tests. The broader return on the system is a finance question and stays gated to commercial finance, never asserted on a regulatory page like this one.

Solar rarely carries a band on its own, so it works best sequenced inside a fuller efficiency programme. The order usually matters: reducing demand first, through the building fabric and services, then sizing generation against the demand that remains, tends to give a cleaner SBEM result than bolting an array onto an inefficient building. A coordinated plan also avoids paying for a larger array than the load can justify.

• Lighting and controls: moving to LED with occupancy and daylight controls cuts a load the SBEM model weights heavily, often for a short payback.
• Heating and cooling: upgrading plant or moving away from electric resistance and older fossil systems changes the modelled energy mix the rating is built on.
• Fabric: insulation, glazing and air-tightness reduce the underlying demand before any generation is added.
• On-site generation: a PV array sized to the residual daytime load, confirmed against your roof through a structural roof survey and the usable area set out in how much roof space you need.

Where the daytime match is weak, storage can shift surplus generation into the demand rather than exporting it cheaply, though battery storage is treated separately in the SBEM model from the array itself. The same data that supports the EPC case also feeds your wider energy and carbon reporting, which we cover in social value and carbon reporting and in the ESOS and SECR context. Our part stays fixed: we assess the roof, structure and connection and specify the array to recognised component and installation standards above the MCS domestic scale, as set out in quality without MCS. The band itself is always the accredited assessor's determination.

An EPC-driven solar project pulls in several parties, and confusion over who owns which step is a common cause of delay. Setting the roles out plainly helps a finance or facilities director keep the project moving.

• Alectrona, a trading name of RVTC Installations Ltd: we carry out the roof, structural and connection assessment, model the generation against your demand, and specify and install the system. We provide the installed capacity and expected contribution figures the assessor needs.
• The non-domestic energy assessor: an independent accredited professional who runs the SBEM model, enters the array data and issues the EPC. They confirm the band, and we do not.
• Your property and legal advisers: they interpret MEES, advise on the minimum band that applies, and handle any PRS Exemptions Register entries.
• Your distribution network operator: the network operator who governs the grid connection the array depends on, separate from the EPC question entirely.

Sequencing these well is what keeps the EPC outcome on track. A useful pattern is to involve the assessor early, so the proposed array can be modelled before installation rather than after, then book the formal EPC once the system is commissioned and its real configuration is fixed. We are happy to work alongside your assessor and advisers from the feasibility stage, sharing the system specification they need; the feasibility study guide explains how that early modelling fits into a project. None of this is legal or compliance advice, and the statutory thresholds, dates and methodology versions move, so confirm the current position with your own advisers before you rely on it.

The original plan, set out in the 2019 and 2021 consultations, proposed two steps for the let non-domestic private rented sector: EPC C by 2027, then EPC B by 2030. The June 2026 interim response confirmed the long-term ambition and reset the implementation. The EPC B target year is now stated as 2031, it applies only to let non-domestic buildings over 1,000 square metres, and only where reaching the band is cost-effective. The interim EPC C step will not be taken forward, and buildings at or below the threshold stay on the current minimum with no committed deadline to go beyond it. Commentators have flagged that the threshold could be tightened later to capture smaller buildings, which is observation rather than a government commitment.

An interim response is a statement of intended direction, not enacted law. The changes take effect only once secondary legislation passes Parliament, and no timetable for the full response has been confirmed, so the 2031 date, the 1,000 square metre threshold and the dropping of the 2027 step are all still open to change in the final regulations. The sensible planning posture is to treat EPC B as a near-certain direction and an uncertain set of specifics, and to plan against the earliest credible date rather than the latest.

Underneath the future target the existing flexibilities matter more than they are given credit for. The relevant cost test for non-domestic property is a seven-year payback test applied measure by measure: a landlord is required to install a given improvement only where seven years of its expected energy-bill savings would meet or exceed the install cost, and where the qualifying measures together still fall short of the band an exemption can be registered on the PRS exemptions register. The cost cap of a few thousand pounds that is sometimes quoted is the domestic test and does not apply to commercial property. Enforcement sits with local authorities, in practice trading standards, who can serve a compliance notice and issue a penalty where a sub-standard property is let without a valid registered exemption. In practice the letting market usually bites first: a building that can only be let with a registered exemption carries a discount in valuation, lender appetite and lettability long before an officer is involved.

A date several years out reads like breathing room, and the working horizon is shorter than it looks once you count backwards through the steps a commercial array actually needs. The binding constraint is rarely the roof; it is the grid connection. Any system over 50 kWp connects under the full G99 route to the Distribution Network Operator, and that assessment window, plus any network reinforcement the operator identifies, sits outside an installer's control. Add the survey, the design, procurement lead times and the install itself, and a straightforward project commonly runs several months from contract to commissioning, longer where planning or reinforcement is involved. Our guide on how long a commercial installation takes walks those phases in order, and the G99 application guide covers the connection step that dominates the variance.

There is a second timing reason to start early that is specific to the EPC route. A band uplift only counts once a new EPC is lodged on the register after the measures are in place, and the assessment has to be commissioned, modelled and lodged before the building can demonstrate compliance. The certificate cannot be backdated to beat a deadline. A building can also hold a valid but stale certificate that understates what a current assessment would show, so checking the lodgement date of the existing one is worth doing before assuming a band at all. A feasibility study front-loads the connection route, the export position and any planning trigger, so the programme is set before the clock matters rather than after.