A property is unmortgageable when mainstream lenders will not lend on it, and the recurring reasons are construction type, condition, tenure and location or use. Specialist lender Together estimated in late July 2026 that around 1.5 million UK homes, roughly 6% of the country’s 28 million residential properties, fall outside mainstream mortgage criteria.
In short
- Unmortgageable describes lender appetite, which differs between lenders and changes over time.
- The commercial question is whether the defect is curable: a missing kitchen can be fixed, a construction type no lender accepts cannot.
- Cladding has no settled national rule, so the position must be checked case by case before exchange.
- A shrunk buyer pool produces the discount, which can be larger than the cost of curing the defect, but an incurable defect caps your exit.
The 1.5 million figure is Together’s own estimate, and Together is a specialist lender whose business is lending on property that mainstream banks decline. Treat it as a directional estimate from an interested party rather than a measured statistic, and build any decision on the underlying criteria instead of on the headline.
What makes a property unmortgageable
Unmortgageable is not really a property attribute at all. It describes lender appetite, and appetite differs between lenders and changes over time. A property three high street banks decline may be financeable by a fourth, or by a specialist, at a different rate and loan to value.
The recurring reasons a valuer or lender says no fall into a few groups.
- Construction type is one, covering concrete and steel framed post war housing, some timber frame, thatch and other non standard methods.
- Condition is another, and it is the most common: a property with no working kitchen or no working bathroom generally fails the habitability test that standard residential lending assumes.
- Tenure is a third. Lenders set minimum unexpired lease terms, and a lease that runs out too soon relative to the mortgage term is a decline regardless of how sound the building is.
- Location and use add a fourth, covering flats above or adjacent to commercial premises, and some high rise blocks.
The distinction that matters commercially is between defects that are curable and defects that are not. A missing kitchen is usually a contained cost and a short programme of works. A structural construction type that no lender will accept is permanent, and it caps your exit to the same cash buyer pool you bought from.
Cladding remains contested
Cladding deserves separate treatment, because it is the one area where there is genuinely no settled national rule, and where confident advice should be treated with suspicion.
In July 2021 the government said EWS1 forms should not be requested for buildings below 18 metres, citing expert advice that found no systemic fire risk in those blocks. In December 2021 the RICS Independent Standards and Regulation Board reviewed the guidance and confirmed it would keep it unchanged, following consultation with lenders and conveyancers who said EWS1 remained, in their view, the only reliable way to keep property lending functioning at the time.
RICS published further guidance in December 2022 on how valuers should account for agreed remediation funding and timelines, and several major lenders updated their policies in response.
In July 2025 the government said it would legislate to require unsafe cladding on buildings of 18 metres or more to be remediated by the end of 2029, and on buildings of 11 to 18 metres by the end of 2031. Check whether those deadlines are in force, and where a block sits against them, before relying on them.
The result is a patchwork. A building under 18 metres with no known external wall concerns should not normally need an EWS1, but whether a specific lender and a specific valuer take that view on a specific block is a question that can only be answered case by case.
For a buyer, that means the cladding position is a due diligence item to be resolved before exchange, not after. RICS has published a second edition of its cladding valuation standard, effective from 1 November 2026, with updated criteria for blocks of four storeys or less, so the position should be re-checked against it.
Who pays for any remediation is a separate check. The Building Safety Act regime limits what qualifying leaseholders in relevant buildings can be charged for historical safety defects, so whether a flat’s lease qualifies changes the risk you are buying.
How cash buyers price the gap
Much of this matters less if you are not borrowing on completion, and that is where the opportunity sits.
When a property cannot be financed conventionally, the buyer pool shrinks to cash and to bridging. Fewer bidders on the same asset is the mechanism that produces the discount, and the discount can be larger than the cost of curing the defect. The standard route is to buy with cash or short term finance, carry out the works that restore habitability, and then refinance onto conventional terms once the property meets standard criteria.
The arithmetic only works if two things are true.
The defect has to be genuinely curable, and the cost of curing it has to be established before you commit rather than estimated afterwards. Buyers who get hurt in this part of the market are often the ones who priced the discount correctly and the remedial works optimistically.
The exit needs the same scrutiny as the entry. If the works do not bring the property within standard lending criteria, the refinance is not available and you are selling to cash buyers again, so the price you pay has to allow for that.
What this means for property investors
Treat the 1.5 million as a signpost rather than a fact. What it points at is real: a substantial slice of UK housing sits outside conventional lending, and that stock often trades at a discount driven by financeability rather than by the quality of the underlying investment.
The practical discipline is to separate the two things that buyers routinely merge, whether the property is a poor investment and whether it is simply hard to finance. They are not the same test, and the gap between them is where the return is.
A sound terraced house with no bathroom is a financing problem. A flat in a block with unresolved external wall issues and no funded remediation plan is a different order of risk entirely.
Before committing, establish why the property fails lender criteria, whether that reason is curable, what curing it costs, and who your buyer is at exit. If the answer to the last question is still only cash buyers after the works, price accordingly.
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BlackBook Investments is a property investment broker, not a mortgage, tax or investment adviser. Nothing here is a recommendation on any product or on your position. Take regulated advice before acting.