Buy to let for non-standard properties

A standard construction property, in mortgage lending terms, is typically one built with brick or block cavity walls, a pitched roof covered with slate or tile, and conventional foundations. Anything that deviates meaningfully from this definition falls into the non-standard category.

Non-standard construction does not automatically mean unmortgageable. The majority of non-standard construction types can be financed — but by a narrower pool of lenders, sometimes at higher rates, and often with more scrutiny applied to the surveyor’s report. 

Understanding exactly where your property sits on the spectrum, and which lenders are comfortable with it, is the critical first step.

The challenge for buy to let investors is that the mainstream mortgage market — including many high street banks and the products that appear prominently in best-buy tables — is largely calibrated for standard construction. 

Policies that work perfectly well for a Victorian terrace or a 1990s new-build can fail entirely when applied to a steel-framed property, a flat roof conversion, or a property with a history of structural movement.

For residential mortgages, a lender’s primary concern is the borrower’s ability to repay. For buy to let, the property itself carries more weight in the underwriting process, because the lender’s security — the asset they can recover against if the loan defaults — is the property.

Non-standard construction affects two things lenders care about: insurability and resaleability. A property that is difficult or expensive to insure, or that would be difficult to sell quickly at a reasonable price in a forced sale scenario, represents greater risk to a buy to let lender than a property without those characteristics.

This is why construction type can be a deal-breaker, even on otherwise straightforward cases. A landlord with a strong portfolio, excellent credit history, and robust rental income can still be declined for a buy to let mortgage if the property’s construction type sits outside a lender’s acceptable criteria.

Timber-framed properties

Timber frame is one of the most common non-standard construction methods and is generally well accepted by buy to let lenders, including a good number of mainstream lenders. Modern timber frame homes are built to high standards and are frequently indistinguishable from brick-built properties from the outside.

The key considerations are age and condition. Older timber-framed properties — particularly pre-war examples — may present concerns around damp, rot, or insulation that a surveyor will flag. For buy to let purposes, most lenders will proceed, subject to a satisfactory structural survey and adequate buildings insurance. The pool of willing lenders is wide enough that rates are generally competitive.

Steel-framed properties

Steel-framed construction is also mortgageable for buy to let, though the lender pool is narrower than for timber frame. Surveyors will typically inspect for corrosion, particularly in properties built in the mid-twentieth century, and lenders will want to be satisfied that the frame is structurally sound and that the property can be appropriately insured.

Some steel-framed properties were built as part of post-war housing programmes and may share characteristics with the system-built and prefabricated construction types covered below. Where this is the case, additional scrutiny applies.

Concrete panel, pre-cast concrete, and PRC homes

This is one of the most significant construction-type barriers in the buy to let mortgage market. Properties built using precast reinforced concrete (PRC) systems — which includes a wide range of post-war system-built housing types — are generally not mortgageable in standard form. 

The structural concerns relate to carbonation of the concrete, corrosion of the internal steel reinforcement, and the potential for progressive structural deterioration that is not always visible externally.

PRC homes that have been repaired under an approved scheme and certified accordingly are in a different position — but only if the certification is in order, current, and acceptable to the specific lender. This is an area where the detail matters enormously. A property that appears to have been repaired may still be unfinanceable if the certification is incomplete, has lapsed, or relates to a repair scheme not recognised by the lender in question.

Wimpey No-Fines concrete properties fall into the same category. These were built in significant numbers in the 1940s to 1960s and are found across the UK, often in former social housing stock. They are not mortgageable through standard buy to let products.

System-built and modular construction

Post-war system-built housing covers a range of construction methods, including concrete frame and panel systems used from the 1940s through the 1970s. The mortgage position varies significantly depending on the specific system used, the condition of the property, and whether any remedial works have been carried out.

Modern modular construction — factory-built homes assembled on site — is a different proposition entirely and is generally mortgageable, though lender appetite varies and the requirement for a recognised structural warranty (such as from the National Housebuilding Council – NHBC – or Local Authority Building Control – LABC) is often a prerequisite. Without a warranty, the property becomes very difficult to finance, regardless of its condition or specification.

Timber cladding as primary external wall

Properties where timber cladding forms the primary external wall finish can be mortgaged, though insurers and lenders will both assess the fire risk associated with the cladding system. 

Modern timber cladding with appropriate fire treatment and cavity barriers is generally acceptable, but older systems or those without documented fire performance data may be more challenging. 

This is an area where the surveyor’s report and the insurer’s position will heavily influence the lender’s decision.

Stone walls

Solid stone construction are mortgageable for buy to let and this is common in many parts of the UK, particularly in rural areas and older urban properties. 

The principal concern is damp. Solid stone walls without modern damp protection can suffer from penetrating damp and internal condensation, and lenders will typically want a surveyor’s confirmation that damp is not a material issue before proceeding.

Pre-1919 solid-walled properties more broadly — whether stone or solid brick — often require some level of remediation, or further investigation, before a lender will be satisfied. A property with active damp penetration related to its construction method will typically need fixing before mortgage finance is available.

Flat roofs

Flat roofs are one of the most common non-standard construction features encountered in buy to let mortgage applications, and they are not the barrier investors may assume them to be. 

Most lenders will consider properties with flat roofs, though the extent to which the flat roof covers the overall roof area matters. A small flat roof extension on an otherwise standard property is treated very differently from a property where the entire roof is flat.

Condition is the primary concern. Flat roofs have a shorter expected lifespan than pitched roofs, and a surveyor who identifies a flat roof at or near the end of its serviceable life will typically recommend either replacement or further investigation. Lenders may retain funds or require remediation before releasing the mortgage in such cases.

Thatched roofs

Thatched roofs are mortgageable for buy to let, but the lender pool is narrower and the insurance position is more complex. Buildings insurance on a thatched property is more expensive and must be specifically arranged for the construction type. 

Lenders will want confirmation that adequate insurance is in place before proceeding, and some mainstream lenders simply exclude thatched properties from their criteria entirely. 

A specialist broker will be able to identify which lenders are comfortable with thatched properties and, importantly, can help you ensure the insurance is in order before you reach the mortgage application stage.

Asbestos roofing materials

Asbestos in any form — but particularly as a primary roofing or cladding material — is a significant financing obstacle. Where asbestos roofing materials are present, remediation is typically required before a lender will proceed. 

This is not only a mortgage issue; the presence of asbestos affects insurability, ongoing maintenance obligations, and the pool of future buyers, all of which make lenders cautious. A professional survey to identify the extent of the issue, followed by a clear remediation plan, is normally the route to financing these properties.

If you need finance to secure the property, this would be possible using a bridging loan, but would require an asbestos report.

Green and living roofs

Green or living roofs are assessed on a case-by-case basis by most lenders and are generally financeable, particularly where the system has been properly installed and is covered by a structural warranty. 

The surveyor’s report will typically comment on the installation quality and the condition of the underlying roof structure. This is an area where lender familiarity with the construction type varies, and some lenders are simply more experienced with these properties than others.

Studio flats

Studio flats are mortgageable for buy to let, though size is a material factor. Most lenders impose minimum square footage requirements — typically in the range of 30–40 square metres, though this varies — and very small studios can fall below the threshold for acceptable security. 

For buy to let specifically, lenders will also want to be satisfied that the property is lettable and meets minimum standards for habitation.

Converted commercial buildings

Lenders will generally consider converted commercial buildings, but the quality of the conversion, the presence of appropriate warranties, compliance with building regulations, and the existence of permitted development rights or full planning consent all matter significantly.

A converted commercial building without building regulations sign-off, or where the conversion has been carried out without appropriate consent, will typically need these issues resolved before financing is possible. This is an area where thorough due diligence at the purchase stage — ideally before exchange of contracts — is essential.

Park homes

Park homes present particular financing challenges. For buy to let/holiday let mortgage purposes, the property must be a permanent structure, and the land it sits on must be held on terms that satisfy the lender’s security requirements. 

Many park home sites operate under licence arrangements that do not meet standard mortgage criteria, and the pool of lenders willing to consider park home mortgages is small. Specialist products are typically the route to market here.

Before you buy a park home, it is vital to investigate finance costs. Specialist park home finance is typically more expensive than a holiday let mortgage, so if you are buying a holiday let as an investment this is a key financial consideration for your business plan.

Flying freehold

A flying freehold arises where part of one property extends over or under a neighbouring property. This is relatively common in older terraced housing and converted buildings. 

It is mortgageable, but lenders will want to see that adequate legal indemnity insurance is in place to cover the shared structure and the obligations of both property owners. Some lenders exclude flying freehold properties entirely, so product selection is important.

Mixed-use buildings

Properties that combine residential and commercial elements — a flat above a shop, for example — are mortgageable but you need a semi-commercial mortgage, not a buy to let mortgage. 

The nature of the commercial use matters: premises with late night licensing, drinking establishments and bookmakers are treated differently from other properties. Some lenders are comfortable with all commercial uses; others apply exclusions. The lease terms and the split between commercial and residential floor area also influence lender appetite.

Structural movement, subsidence, and heave

A history of structural movement does not automatically make a property unmortgageable, but it must be addressed directly and thoroughly before a lender will proceed. 

The key questions are whether movement is historic and stable, whether it has been professionally investigated and remediated, and whether there is appropriate structural warranty or engineer’s sign-off in place.

Lenders will want evidence of resolution — not just an assertion that the issue has been fixed — and many will require a specialist structural engineer’s report in addition to the standard surveyor’s valuation. 

Properties with unresolved or ongoing movement, inadequate foundations, or significant damp issues directly related to their construction method will require remediation before mortgage finance is available.

Unregulated alterations and missing compliance

Buy to let investors frequently encounter properties where previous owners have carried out structural alterations without building regulations approval, converted spaces without appropriate consent, or made changes that are undocumented. These issues are common, and lenders treat them seriously.

The standard route to resolving compliance issues of this type is either retrospective building regulations consent (where available) or indemnity insurance. Indemnity insurance does not fix the underlying issue, but it provides the lender and future buyers with financial protection against enforcement action. 

Not all compliance issues can be indemnified — some require actual remediation — and a specialist broker can help you understand which route applies in a given situation.

Cladding, EWS1, and fire safety

The cladding crisis that followed the Grenfell Tower fire in 2017 has had lasting consequences for the financing of flats in multi-storey buildings. External wall systems that fail EWS1 requirements — the industry standard assessment for external wall fire safety in blocks above a certain height — can significantly restrict mortgage availability, and in some cases eliminate it entirely until remediation is completed.

The position is evolving, and lenders vary in how they apply EWS1 requirements by building height and type. 

For buy to let investors considering flats in medium or high-rise buildings, confirming the EWS1 position before committing to a purchase is essential. A building without a satisfactory EWS1 assessment may be difficult or impossible to mortgage, and the costs of remediation — which may fall on leaseholders — can be substantial.

Short leases

A lease below 70–80 years can restrict lending optionsp. Most buy to let lenders require a minimum lease term at the point of mortgage application, or at the end of the mortgage term, with requirements typically ranging from 50 to 85 years, though criteria vary by lender. 

Properties with short leases can be mortgaged, but the product range is narrower, and lenders will factor the lease length into their assessment of the property’s security value.

For buy to let investors, lease extension should be factored into the investment calculation at the point of purchase. The cost of a lease extension and the timing of the application — you generally need to own the property for two years before invoking the statutory right to extend — both have implications for your financing strategy.

Onerous lease terms and high service charges

Unusual or particularly onerous lease terms can make a property unmortgageable regardless of its physical construction. 

Leases with ground rents that escalate rapidly, excessive restrictions on use or letting, or terms that significantly limit the leaseholder’s rights are viewed unfavourably by lenders. Very high service charges linked to construction risk — for example, ongoing remediation costs on a building with cladding issues — will also impact lender appetite.

Non-standard construction is one of the areas where the difference between a generalist broker and a specialist buy to let broker is most clearly felt — and where the consequences of that difference are most significant.

A generalist broker, or one who primarily serves residential purchasers, may have limited familiarity with the lenders who actively write non-standard construction buy to let business. They may approach a small number of mainstream lenders, receive declines, and conclude that the property is unfinanceable — when in fact a specialist broker with wide market access would know exactly which lenders have an appetite for that specific construction type, at what loan-to-value, and on what terms.

More importantly, a specialist buy to let broker understands how to present a non-standard construction case effectively. Lenders have criteria, but they also have discretion. A case that is presented with a clear surveyor’s report, appropriate indemnity insurance, a documented remediation history, or any other mitigating factors will always fare better than the same case presented without that context.

Beyond access and presentation, a specialist broker adds value in several other ways on non-standard construction cases:

• Pre-purchase due diligence. Identifying potential financing obstacles before you commit to a purchase — not after. For non-standard construction properties, knowing the mortgage position in advance of exchange can save significant time, cost, and frustration.
• Insurance coordination.Non-standard construction often requires specialist buildings insurance. A buy to let focused broker will understand the interaction between insurance and mortgage criteria, and will flag insurance issues that could derail a mortgage application before they become a problem.
• Structuring the deal correctly. On complex cases — mixed-use properties, converted commercial buildings, properties with compliance issues — the way the purchase is structured can affect which lenders are available and on what terms. Getting this right at the outset is considerably easier than trying to restructure once an application is in progress.
• Portfolio context. If you are building a portfolio that includes non-standard construction properties alongside standard ones, a specialist broker can help you think about how this affects your overall financing strategy — including the impact on lender relationships, cross-portfolio assessments, and future refinancing options.

The buy to let mortgage market is large, specialist, and genuinely varied in how different lenders approach different property types. Navigating it effectively — particularly on non-standard construction — requires experience and whole-of-market access that not all brokers have.