How to get a mortgage for a non-standard construction property

When we think about mortgage lending criteria, we often consider the borrower’s risk. But the type of property you want to buy may also impact an underwriter’s decision.

For most UK homeowners, a house is simply a house: brick or stone walls, with a slate or tiled roof. From a mortgage lender’s perspective, this is “standard construction.” It’s predictable, durable, and straightforward to insure.

But what if you have fallen in love with a converted barn, a post-war concrete prefab, or a chocolate-box thatched cottage? You’re then looking at a “non-standard construction” property.

These homes are often full of character or offer excellent value for money. But they can derail a mortgage application if your chosen lender relies solely on automated computer decisioning.

This guide identifies the different types of non-standard properties that make lenders nervous. It also explains why they see them as a risk, and the most common solutions, where applicable.

Why do lenders view non-standard construction as “risky”?

Before diving into specific materials, let’s consider risk from the lender’s viewpoint. They’re not being difficult for the sake of it; they’re protecting their asset. It is, after all, their money buying the property until you pay off your mortgage.

Their primary concerns usually centre around three things:

1. Resaleability

If you default on your mortgage, your lender will repossess the property to recover any outstanding loan amount. As such, they’ll consider how quickly and easily they can sell it during the underwriting process.

Niche properties have a smaller pool of potential buyers. That means it could take them a while to offload the property once they repossess it.

2. Maintenance & Structural Integrity

Non-standard materials often require specialised, expensive upkeep. If a borrower cannot continually afford this maintenance, the property’s value could plummet.

Neglected, these could leave the lender with an asset worth less than the outstanding loan amount. This predicament is unacceptable to mortgage underwriters.

3. Insurability

Specific properties can prove difficult or prohibitively expensive to insure. Should a catastrophe happen to the property, the rebuild cost could eclipse the initial mortgage amount. Anything that severely devalues their asset poses a significant risk to the lender.

Common types of non-standard construction

So, what are the types of properties that put underwriters on guard? Here are the most common construction types that require approaching specialist lenders.

1. Timber Framed Properties

Timber frames have been used for centuries (think Tudor manor houses). They’re also very popular in modern eco-homes. However, lenders can be wary of them depending on their age and the type of cladding.

The Risk:

The primary concerns are damp, rot, and fire. With older timber properties, there’s a risk that the wood has degraded over time. But not all problems leave obvious visual signs.

For modern timber frames, lenders often require specific guarantees. This includes the buyer providing evidence that the exterior cladding (brick, metal, or plastic) is sound.

2. Steel Framed Houses

Steel-framed homes became common after World War II to address housing shortages. While steel is strong, it isn’t invincible.

The Risk:

Corrosion. If the protective coatings on the steel frame fail, the structure can rust—often invisibly behind the walls. Lenders will usually insist on a specialised structural survey to ensure the frame is sound before approving a loan.

3. Concrete (PRC) Homes

Pre-cast Reinforced Concrete (PRC/prefabs) homes were also widely built in the post-war era. Many of these are now classified as “defective” under housing laws.

The Risk

These properties can suffer from “concrete cancer.” This condition occurs when the steel reinforcement inside the concrete rusts and expands. If left untreated, it can cause the concrete to crack and crumble.

The Solution

Mortgages can still be possible on these properties — but in most cases, lenders will require a PRC (Private Repair Certificate).

This certificate confirms that:

• The property was repaired under an approved repair scheme
• Structural remediation has been professionally completed
• The property has been brought up to a standard acceptable for mortgage lending

4. Thatched Roofs

Thatched cottages are perhaps the quintessential symbol of the British countryside. They’re also highly desirable for foreigners and out-of-towners. But, no matter how picture-postcard-perfect they may look, they come with significant upkeep.

The Risk

Fire is the obvious concern with thatched roofs. This alone leads to higher insurance premiums. But lenders are also acutely aware of maintenance costs.

A thatched roof needs replacing every 30 to 40 years. Depending on the roof area, this can cost tens of thousands of pounds each time. Lenders must be able to discern that you can afford this ongoing liability in addition to your mortgage payments.

5. Flat Roofs

Flat roofs are not uncommon; you’ll find them on many extensions and garages. But a property with an entirely flat roof (or a significant portion of it) can be problematic.

The Risk

Flat roofs are notorious for leaking, even with outlet spouts. They have a much shorter lifespan than pitched roofs (typically 10–20 years).

Lenders also consider them a higher security risk because they provide easier access for burglars. Underwriters may require a roof inspection and evidence of a recent replacement. And, for your own peace of mind, install a sound security system.

6. High-Rise Flats and Cladding

Following the Grenfell Tower tragedy, lending on high-rise flats has changed drastically.

The Risk

Fire safety regarding external cladding systems and egress points within the building.

The Solution

If you are buying a flat in a building above a certain height (usually 18 metres/roughly six storeys, though sometimes lower), lenders will require an EWS1 Form. This document certifies that the external wall system has been assessed for fire safety. Without this, many lenders will simply refuse to lend.

7. Alternative wall materials

Lenders also classify properties built with non-standard materials or to old specifications as non-standard. Cob (made from soil and straw) and clay walls raise questions about durability and general upkeep. Finding a specialist to maintain such a niche construction can be challenging.

Even single-skin brick walls can make an underwriter think twice. If your home dates to the early 20th century or earlier, it probably has this type of construction. Without double-wall insulation, the risk of condensation, mould and rot greatly intensifies.

8. Listed buildings

Their historical nature can immediately cause problems with mortgage applications. They’re often constructed using outdated methods and materials.

They also require strict adherence to regulations for any repairs or modifications. Finding tradespeople with such specialisations can be time-consuming and costly.

How to secure a mortgage for these properties

If you are looking to buy a non-standard construction property, don’t be discouraged. You can still get a mortgage. However, you’ll often need to move away from high-street lenders’ automated “computer says no” systems and take a more specialist approach.

Use a Specialist Broker

At Freelancer Financials, we have access to over thirty specialist lenders. Many of these use manual underwriting.

Manual underwriting means a real underwriter assesses:

• The property type
• The construction method
• The surveying evidence
• The structural reports

This human-led approach is far better suited to non-standard construction than automated systems that reject applications purely based on postcode, property type, or database flags.

Prepare to pay a higher deposit

Lenders may request a lower Loan-to-Value (LTV) ratio to mitigate their risk. This may mean you have to find upwards of 20%-30% deposit.

Get the Right Survey

A standard valuation won’t cut it. Be prepared to pay for a full structural survey or a specialist report (such as a timber and damp report). Providing the results are positive, these will reassure the lender that the property is sound.

Buying a non-standard construction home may require more preparation, more documentation, and more specialist advice – but it is absolutely achievable. With the right broker, the right lender, and the right evidence, you can secure funding for a property that’s as unique as you are.

If you’ve found a must-have non-standard property, you can begin your journey to buying it on our Get Started page.