Everything You Need to Know About Buying Houses of Non-Standard Construction

Your offer’s been accepted on a house you love, but three weeks into the conveyancing, you hear the dreaded words ‘non-standard construction’.

This is the moment when many house purchases can start to unravel, as it can affect mortgage availability, insurance costs, and how easy the property will be to sell, making buying one more complex. However, many happy homes are non-standard in construction, and lenders and insurers will cover them. And the best way to mitigate any concerns or issues is to get a building survey. 

How to Identify a Non-Standard Construction Property

As a guide, a ‘standard’ property typically refers to a home built with brick or stone walls and a pitched roof covered with slate or tile, and properties that don’t meet these criteria are considered ‘non-standard construction.’

This includes walls built from steel frame, timber frame, concrete panel, cob, or anything clad over anything that isn’t brick. It also covers roofs made of thatch, flat-roof construction, or any material other than slate or tile. Lots of non-standard construction homes can look completely ordinary from the pavement, with timber frames sitting behind smart render and steel frames hidden by pebble-dash.

Steel-framed houses. Lightweight and quick to build, steel-framed houses were widely used during the post-war rebuild. The best-known example is the BISF house, built from 1946 onwards by the British Iron and Steel Federation. Steel frames are prone to corrosion where they meet damp areas, and much of their condition is hidden behind cladding until something starts going wrong. Many BISF homes also contain asbestos. Mortgage lenders are cautious about steel-framed houses, and some won’t lend on them at all.

Timber-framed houses. A timber-framed house has an inner structural frame of wood, with an outer skin of brick, stone, render, or timber boarding. Modern timber-framed homes built to current standards are sound and increasingly common. Older ones can have damp problems behind the cladding and a higher fire risk, and not every insurer will cover them on standard terms.

Prefabricated and modular homes. Around 150,000 prefabs were built in the UK after the Second World War to address the housing shortage. Most were designed to last 10 to 15 years, but a significant number are still standing more than 80 years later. Repairs tend to involve replacing whole structural sections rather than patching, which can be expensive.

Concrete houses. Concrete houses were built in large numbers during the 1940s and 1950s using precast panels, because the method was fast, cheap, and didn’t depend on bricklayers. PRC (Precast Reinforced Concrete) homes are the most well-known example. Concrete deteriorates over time, and the steel reinforcement inside corrodes, which is why several PRC designs have been formally designated as defective under the Housing Defects Act 1984. Most lenders won’t lend on one of these without a PRC certificate confirming the property has been repaired to an approved standard.

Cob houses. Cob is one of the oldest building materials in Britain, made from subsoil, straw, water, and lime, mixed by foot and built up in layers. A well-maintained cob house can last for centuries, and many already have. The important thing is that cob has to breathe. Modern cement renders and plastic paints trap moisture within the wall, causing the cob to fail. Cob houses are particularly common in Devon and the wider South West.

Thatched roofs. Thatched roofs are a non-standard roof covering rather than a non-standard wall construction, but they affect the availability of mortgages and insurance in the same way; premiums are higher because of the fire risk. The thatch itself needs re-ridging every 8 to 14 years and full re-thatching at roughly 25 to 40 year intervals, depending on the material.

Flat roof properties. A flat roof on an extension is normal, but a whole house with a flat roof (common in 1960s and 70s architect-designed homes) is classed as non-standard. Flat roofs have a shorter lifespan than pitched roofs, and the membrane beneath them is where most problems start, so lenders often want evidence of recent condition before agreeing to terms.

Why a Building Survey is More Important Here

You need a Level 3 building survey for a non-standard construction property. It goes well beyond what a mortgage valuation or a Level 2 HomeBuyer Report covers, looking in detail at the construction, the condition, and any defects that need attention.

Every non-standard construction type has its own characteristic problems and the places those problems tend to show up. These include corrosion at the base of a steel frame, damp where modern paint has been applied over cob, and deterioration in particular concrete panel designs. Therefore, it’s important to get a RICS surveyor who understands non-construction properties, rather than a general surveyor or a mortgage valuation.

What to Consider When Buying a Non-Standard Construction House

Mortgage lenders. Some lenders won’t lend on certain construction types at all, while others will, but at lower loan-to-value ratios. Designated defective concrete houses without a certified repair are the hardest to mortgage, and some steel-framed homes are nearly as restrictive. A mortgage broker who has placed non-standard cases before will save you a lot of wasted applications.

Insurance. Insuring a non-standard construction house is more difficult and usually more expensive than insuring a standard one. Standard insurers tend to either decline or load the premium heavily. A specialist insurer is often the right answer, and a good survey report helps them price the policy more accurately.

Maintenance and repair costs. Standard construction is cheap to repair because the trades and parts are widely available. Non-standard construction is not. Each construction type has its own upkeep regime, including protective treatment for timber frames, watertight cladding for steel, lime render (never cement) for cob, and scheduled ridging for thatch. None of this is catastrophic, but it does need budgeting for.

Resale value and marketability. The same factors that made the property cheaper to buy will make it harder to sell. Your future buyer will need to get a mortgage and insurance, too. Properties with a clear paper trail of certified repairs tend to sell more easily than those without.

Future-proofing. Some non-standard properties can be brought closer to standard in the eyes of lenders and insurers. A PRC repair that earns a certificate is the most obvious example. Modern insulation and a fresh damp-proof course can transform an older timber-framed home. It’s worth having a conversation with a builder or architect alongside the survey to understand what’s possible.

Frequently Asked Questions

Why is it important to get a Building Survey on a non-standard construction home?

A building survey is a detailed inspection of the property’s condition by a RICS chartered surveyor. On a non-standard construction home, it’s particularly important because the construction materials and methods have specific failure modes, such as corrosion in steel frames, panel deterioration in concrete houses, and damp in cob walls, that a general inspection can easily miss.

Can I get a mortgage for a non-standard construction house?

In most cases, yes, but it depends on the type of construction and the lender. Many non-standard properties are mainstream-mortgageable; others require a specialist lender, and a small number (particularly designated defective-concrete homes without a certified repair) are very difficult to mortgage at all. A broker with non-standard experience is the fastest way to find out where your property sits.

Is it harder to insure a non-standard construction house?

Yes, obtaining insurance for a non-standard construction property can be more difficult and expensive. Insurers often view these properties as higher risk due to potential structural issues and increased maintenance needs. You’ll likely need to find an insurer experienced in covering non-standard homes, and a good survey report will help them price the policy accurately.

What are the maintenance requirements for non-standard homes?

The requirements vary by construction type. Timber needs protective treatment against pests and rot; steel relies on its cladding staying watertight; concrete houses need their panels monitored for cracking and corrosion; cob needs breathable lime-based finishes; and thatched roofs need ridging and re-thatching on a known schedule.

What should I look for in a building survey for a non-standard construction property?

Above all, you want a surveyor who has worked on that specific type of construction before. The report should name the construction method, assess it against known failure modes, and give a clear, plain-English comment on structural integrity, damp, insulation, and the property’s current condition relative to its age.

Is buying a non-standard construction home a good investment?

It can be. Non-standard homes are often cheaper to buy, and many have real character that standard housing doesn’t. The running costs, insurance, and resale dynamics are different, though, and the question is whether the price reflects those differences. The survey is what tells you that.