From 1 October 2030, privately rented homes in England must hold an Energy Performance Certificate rating of C or better. It is one of those regulations that everyone in property has heard of and very few have planned for. Landlords do not know which of their homes are exposed. Installers do not know who to call. And the data that could answer both questions is public, but scattered across datasets that nobody had joined.
So we joined them. EPC Path, a product my team at B4Mind built this year, ingests every energy certificate in London, de-duplicates them to unique properties, flags signals that a home is privately rented, and matches corporate owners through Land Registry's commercial ownership data. This essay is about what that data says, and why one number in it changed the whole business.
The size of the problem
We started with 4.6 million EPC certificates across London's 33 boroughs. Certificates are issued every time a home is sold, let or assessed, so many properties have several. Once you reduce them to the most recent certificate per property, a clear picture appears: around 1.37 million London homes sit below C.
Not all of those are rentals, and not all rentals will be caught by the rule in the same way. But the scale is the point. This is not a niche compliance issue for a few landlords. It is a large share of London's housing stock, with a fixed deadline, and a regulator that will expect evidence.
When I look at a market like this, I look for three things: a deadline, a duty and a buyer who already knows they have a problem. EPC C 2030 has all three. That is why I believe regulation is often the best go-to-market there is. Demand is not created by marketing; it is created by the law, and it arrives on a date everyone can see.
The number that changed the business
The obvious business is to find every landlord with a sub-C property and offer to help. That was our first assumption. The data disagreed.
Only about 6.2% of sub-C rental homes have a traceable corporate owner. The other homes belong to individuals, and the public data deliberately does not name them. That is correct: privacy rules protect private landlords, and they should. But it means there is no list of names for most of the problem. Anyone who tells you they can email every London landlord with a C-rating problem is either guessing or doing something they should not.
That one number changed our go-to-market. Instead of trying to reach everyone, we split the market in two. The roughly 1,400 mid-sized portfolio companies that hold a meaningful number of exposed homes can be reached directly, with a specific, ranked view of their own portfolio. Individual landlords are reached indirectly, through the letting agents and accountants they already trust, rather than through a list of names we should not have.
When the data says your obvious channel is closed, believe it the first time.
Most of the work is closer than it looks
The second finding was more encouraging. Of the sub-C rental homes with a corporate owner, about 62% are within 10 SAP points of a C. SAP is the scoring system behind the EPC rating, and 10 points is often the difference between a few measured improvements and a deep retrofit.
This matters for how the problem is talked about. Much of the public conversation about 2030 assumes landlords face enormous works on every property. For a large share of the exposed homes, that is not what the data suggests. The work is real, but for many properties it is closer to a sequence of sensible upgrades than to a rebuild.
The third finding points the other way. About 15% of these homes cannot realistically reach C at all, given their construction and the improvements listed on their certificates. For those, the right conversation is not retrofit but exemption: what the rules allow, what evidence is needed, and how to register it properly. A landlord who spends money trying to lift a home that will never reach C has been badly advised.
Sell the ranking, not the report
Put those findings together and the product becomes clear. A portfolio owner does not need another PDF telling them their properties are below C. They usually know. What they need is an order of work: which property to start with, which ones are close, which ones are candidates for exemption, and where their money moves the rating furthest.
That is what EPC Path sells. Everyone can produce a report. The value is in the ranking, and in telling an owner which door to knock on first. Cost figures shown to customers are indicative ranges derived from the recommendations on the certificates, not quotes, and they are labelled as such. The 2030 date and the rules around it are tracked against current regulation, because a compliance product that is out of date is worse than none.
What this means for landlords, installers and policy
For landlords, the message is that the problem is more manageable than the headlines suggest, but only if you start with the right properties. Ranking your portfolio by distance from C, and separating the near misses from the exemption candidates, turns a vague obligation into a plan.
For installers, the message is about channels. The corporate segment is small in number of owners and large in number of homes. It rewards a direct, specific approach. The individual segment is vast and unnamed, and it will be reached through the professionals landlords already use. Installers who partner with letting agents and accountants will reach far more of the market than those who buy lists.
For policy, the data raises a practical question. A rule that applies to well over a million London homes, most of which belong to individuals who cannot be identified from public records, will only work if those individuals hear about it from someone they trust, in good time. The data exists to show where the exposure sits. Using it well, while respecting the privacy that rightly protects private owners, is the work of the next few years.
For me, the lesson is broader than property. The best markets are often hiding in public data, waiting for someone to join two datasets and ask a plain question. And the best businesses are built by people willing to let the answer change their plan.