Like many landlords the King is facing a hefty bill

But If the King can't afford to insulate his cottages, what chance for the rest of us?

There's something almost comforting about discovering that the biggest landowner in the country is wrestling with the same headache as many of the rest of us. A recent Guardian investigation this month has highlighted the issue and found that more than 100 rented homes on the inherited estates of King Charles and Prince William fail to meet the minimum legal energy efficiency standard for rented property. 

The Guardian's own estimate for bringing the royal portfolio up to scratch is around £10 million. This reflects the fact that these properties are in the main rural cottages with traditional stone construction (single stone walls with no cavity), single glazing and often traditional heating with coal fires and wood burners.

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The average cost to upgrade a rental property across England to an Energy Performance Certificate (EPC) level C is estimated by the government to be between £6,100 and £6,800, but surveys show these costs can vary widely, from as low as £500 to over £15,000.

With Cavity-walls in modern homes costs can be as low as under £3,000 whereas solid-walls in cottages and Victorian homes can be significantly higher and more expensive due to the high cost of internal or external wall insulation, ranging from £8,000 to £20,000 plus.

According to the latest iteration of the rules recently settled by the current government, all private rental properties in England and Wales must meet a minimum EPC rating of C by 1 October 2030. 

The government's Warm Homes Plan recently consolidated the rules into a single compliance deadline, eliminating the previous two-stage plan that separated new and existing tenancies. 

Timeline and key dates

The road to the 2030 deadline involves several important milestones:  The 1^st of October 2025 involves a retroactive credit where any money you spend on qualifying energy efficiency upgrades from this date forward will count toward the £10,000 cost cap. 

The cap is the absolute maximum a landlord can legally be forced to invest in energy efficiency upgrades to bring a rental property up to an EPC level C by 2030. It includes VAT and the cost of materials and installation labour, as well as the cost of the EPC assessment itself.

The cap serves as a "financial shield" under the Minimum Energy Efficiency Standards (MEES) regulations. If you spend up to this cap and your property still fails to achieve a C rating, you are not legally obliged to spend more money. Instead, you can register for a "cost cap exemption" and continue letting your property legally. 

The Second Half of 2027 will see a new EPC assessment regime launched when the government will roll out the new Home Energy Model (HEM), a system to replace the older SAP assessment method. This will update how energy efficiency is calculated. 

Any property that achieves an EPC level C under the current or older rating system before 1 October 2029 is given “grandfather” rights and will be deemed compliant until that specific certificate expires (EPCs remain valid for 10 years). 

From 1 October 2030 a hard enforcement deadline looms when it is illegal to continue letting any private domestic property unless it has achieved an EPC rating of C or holds a legally registered exemption. 

If the property cannot reach EPC C, say for example you hit the £10,000 cost cap and your property still hasn't achieved a level C rating, you can register for a 10-year cost exemption. Once registered, you will legally be allowed to continue renting out the property. 

Ten million is a lot of money

Ten million pounds is a substantial amount even for an estate with the resources of the Crown Estate and with the Duchy of Cornwall behind it, that’s a great deal of money to them as well, though they can easily afford it.

The Duchy of Cornwall estate alone generated a profit of £21.6 million for the financial year ending 31 March 2026. This was down slightly from the £22.9 million profit reported for the previous financial year ending 31 March 2025. The total asset value of the estate, which spans roughly 130,000 to 140,000 acres of land, is around £1.2 billion

If £10million is what it costs them, it's worth a pause to consider what it means for the rest of us . Farmers and smallholders and small-portfolio landlords who own the sort of solid-wall, single-glazed Victorian or rural housing stock that the royals happen to share with those who live in the countryside, are all in the same boat.

Why is rural housing so different?

This is where the countryside genuinely diverges from the town. Most urban and suburban rental stock has cavity walls or is in a terrace row, which can be filled relatively cheaply or has minimal external walls. They have well-understood risks when installing effective insulation material. 

Rural housing on the other hand includes a big slice of what the royal estates let out which are in the main farm and farmworkers’ cottages. These are overwhelmingly of solid stone wall construction or single thick brick. 

These properties were built long before cavity construction existed, and they are often grade II listed or in conservation areas. Main gas supplies are very limited in rural areas, so heating is often provided by oil, LPG, open hearth fires or log burners. 

You cannot fill a solid wall, so insulating them means either internal lining, which takes off space in what are usually small rooms to start with, or external cladding which affects the appearance and may not be possible with a listed building.

Drastic consequences

Unfortunately, both options have a history of going wrong when inexperienced fitters are involved. There's been a steady rise in stories about botched solid and external wall insulation installations under the government’s retrofit scheme. This usually results in homes left with damp, trapped moisture and mould rather than lower bills. 

The government has recognised these issues exist and therefore two new exemptions are being introduced alongside the 2030 deadline. One of these is specifically for solid wall insulation, where it isn't appropriate, and there’s a broader "negative impacts" exemption for cases where a measure would damage the fabric of the building. There's also a lower spending cap for properties valued less than £100,000. 

Exemptions not the answer

Exemptions are temporary and don’t fix the problem. The property remains below standard, and tenants don’t get a warmer home. They don't answer the practical issue of what a landlord with a couple of rural cottages is meant to do about heating systems that were never connected to gas in the first place. 

Replacing an ancient oil boiler or ripping out a coal fire for an air source heat pump in a solid-wall building with no existing wet radiator system is not a £6,000 job. It's often a five-figure one, before you've touched the walls or the windows. What’s more, with poor wall insulation a heat pump is likely to be inadequate.

Getting round to it

The real parallel with the royal estates and us isn't that the King and the rest of us are in the same boat financially, obviously we're not. It's that the same type of building is causing the same type of problem, at wildly different scales of exposure. 

If a large estate with professional asset managers and £10 million to call on is only getting round to sorting this out now, having presumably known about EPC reform for years, it says something about how genuinely difficult and expensive this work is.

It’s not only reluctant small-scale landlords who hesitate to splash out, for anyone holding rural solid-wall property the burden is doubly difficult. For a start, contemplating the extensive work involved with a tenant in situ is a daunting prospect to say the least.

What to do about it?

Waiting until 2029 is not a sensible strategy. You need to get an up-to-date EPC now, and understand exactly what is required and what new metrics your property will be assessed against. 

You should find out early whether you have a genuine case for the solid wall or negative-impacts exemption rather than assuming you'll need to spend your way to B and C. If you do need work done, use PAS 2035-certified installers with real experience of solid-wall and heritage properties.

 PAS 2030 installers operating within the PAS 2035 framework are accredited tradespeople who retrofit homes for better energy efficiency. They follow whole-house rules, use approved materials, and must register with TrustMark for UK government-backed projects. 

The sector's damp and mould scandal shows exactly what happens when you don’t verify trades people. You should register for exemption property in good time, don’t wait until the threat of fines is upon you. 

None of this makes the underlying arithmetic any easier with a typical solid wall property. But if nothing else, it's worth remembering the next time your tenant complains about a draughty cottage, you’re not on your own. Even their landlord's landlord, in a roundabout way, is in exactly the same boat, stuck with exactly the same bill.

Face the facts

‍Start planning, now whether you have solid walls or not, this legislation is not going away. It will be far easier to upgrade if you know you will be having a vacancy coming up, so take full advantage of any opportunity like that. There’s still time.