Non-standard construction types: what you should know

Non-standard construction refers to any property built using methods or materials that fall outside the typical brick and tile construction used in most UK homes. While these properties may offer architectural interest or cost-effective solutions at the time of building, they can present serious challenges when it comes to securing a mortgage.

The origins of post war non-standard construction in the UK lie in the urgent need for housing after World War II. The war left around 250,000 homes destroyed and millions more damaged. With materials in short supply, a labour shortage, and the need to rehouse families quickly, the government turned to innovative, rapid-build methods that bypassed traditional brick and mortar construction.

Between the late 1940s and 1970s, local councils and developers used alternative materials like steel, timber, and concrete to mass produce homes. These included:

• PRC (Precast Reinforced Concrete) houses, such as Airey and Cornish units
• Timber framed homes, often built with panel systems
• Steel framed homes, like BISF and Trusteel types

Many of these homes were part of government-backed building programmes, including the Temporary Housing Programme (for example, prefab homes) and Housing Act schemes. They were designed to be fast, cheap, and scalable, with life expectancies of ten to fifty years, but many remain standing today.

While they solved an immediate crisis, some designs later showed defects such as corrosion and structural cracking. This has led to difficulties with mortgages and insurance in the modern housing market. Mainstream lenders are generally cautious with non-standard construction due to concerns over durability, maintenance costs, insurability, and resale value. Here is a closer look at the most common types of non-standard construction and the reasons they raise red flags:

1. Precast Reinforced Concrete (PRC) Houses

PRC houses emerged across post war Britain, constructed from factory made concrete panels bolted to steel frames. Built quickly and cheaply to address housing shortages, many types like Airey, Reema, Wates, Cornish, Orlit, and Hawksley later deteriorated due to rusting steel reinforcement, cracking, and damp infiltration.

These structural issues led to their classification as defective under the Housing Defects Act 1984, prompting lenders to shy away. Mortgages for unrepaired PRC homes are almost universally refused by mainstream banks unless the building has undergone certified remediation.

Remediation involves removing or encasing the original concrete frame and replacing it with traditional brick and block construction, certified via a PRC Certificate post-repair. Some lenders might accept retrospective certificates, though policies vary and higher deposits are common.

How to identify a PCR Building?

External Clues:

• Large panel sections with visible vertical or horizontal joins
• Unusual wall textures or cladding that looks like concrete
• Shallow roof overhangs and flat roofs in some types
• Repetitive design across a housing estate
• Mismatched extensions where brick has replaced original PRC structure

Internal Signs:

• Unusual wall thickness or hollow-sounding walls
• Cold bridging, condensation, or poor insulation
• Cracks at wall panel junctions

Records and Inspection:

• Local authority records and planning documents
• PRC House Identification Guides, such as Airey or Cornish
• Invasive inspection if necessary, including testing for corrosion

2. Timber-Framed Houses

Timber frame construction is not inherently problematic. Modern homes using this method can be mortgaged without issue. However, older timber frame properties, especially those built in the mid twentieth century, may cause lender concern.

These non-standard buildings combine timber structural frames with cladding such as brickwork, render, or boarding, rather than solid masonry walls. While modern timber frame homes are well engineered and widely used, lenders still categorise them as non-standard, meaning they attract increased scrutiny.

Key risks flagged by mortgage providers include:

• Rot, damp, and insect damage: Timber is susceptible to decay, especially in exposed areas like bathrooms or if waterproofing fails potentially compromising the structure over time.

• Fire safety concerns: With combustible materials in the core, insurers and lenders often view timber-frame houses as higher fire-risk, which leads to elevated premiums or reluctance from mainstream lenders.

• Valuation and resale uncertainty: Lenders worry these homes may be harder to sell quickly if repossessed, affecting their comfort with mortgage security.

That said, many modern timber-frame constructions, especially those built post-1970 with brick outer skins and full compliance with building regulations can secure finance from lenders. Specialist lenders and brokers often offer mortgages for these properties, though borrowers should expect:

1. Higher deposits (typically 15–25%)

2. Preferring properties with NHBC or equivalent certification

Buying a timber-framed home?

– Ensure a full structural survey is conducted
– Confirm building regs and insurance compliance
– Use a broker experienced in non-standard homes

With proper documentation and maintenance, modern timber-framed homes can be both mortgageable and durable.

3. Steel-Framed Houses

Steel framed houses, a hallmark of post war non-standard construction in the UK, use a metal skeleton clad with steel sheets or panels. BISF (British Iron and Steel Federation) houses are among the most recognised, with some featuring asbestos roofs and steel cladding.

While conceptually robust, steel frames are prone to hidden corrosion, especially if exposed to moisture. This deterioration can weaken the structure and raises concerns for lenders and insurers, who may demand structural surveys, impose higher premiums, or refuse cover.

Buying a steel-framed home?

Mortgage approval usually requires a comprehensive structural survey by a qualified engineer, demonstrating either sound steel condition or completed reinforcement works such as brick casing. Specialist lenders, including building societies and niche brokers, may offer non‑standard construction mortgages but applicants should expect higher costs and tighter terms, like elevated interest rates and tougher loan-to-value conditions. The key risks and considerations when buying an steel-framed house are: 

1. Structural Deterioration

2. Mortgage and Insurance Difficulties

3. Costly Repairs or Retrofitting

4. Resale and Future Value

In summary, steel-framed homes can still be financed, but buyers must prepare for added scrutiny: full surveys, increased deposit, and potential reinforcement work are essential steps to secure a mortgage and safeguard long-term value.

Other Problematic Property Types

Non-standard construction in the UK is not limited to PRC, timber, or steel framed homes. Additional property types often flagged by lenders include:

• Flat roofed buildings: Prone to water pooling, leaks, and shorter lifespan, making them harder to insure or mortgage
• Thatched roof houses: High fire risk, expensive insurance, and costly maintenance
• Cob and Wattle and Daub homes: Vulnerable to moisture, structural movement, and costly traditional repairs

While these homes may offer charm or character, they come with increased risks around durability, insurability, and financing.

Final Thoughts

Non-standard construction properties often come with a lower upfront price, but potential hidden costs including surveys, repairs, and limited financing options mean they are not always the bargain they appear to be.

If you are interested in one of these property types, approach with caution. Commission specialist surveys, understand the risks, and work with lenders and brokers experienced in non-standard construction. With the right advice and preparation, these homes can still be a viable and rewarding investment.