In short: Non-standard construction means a house built with a concrete, steel or timber system instead of conventional brick and block. Mortgageability depends on the specific system: designated defective PRC types usually need a repair certificate, BISF and no-fines houses are accepted by many lenders, and modern timber frame is mainstream. A Level 3 survey identifies which you have.
Last reviewed: 26 October 2026 by Patrick Oliver BSc (Hons) MRICS, RICS Registered Valuer.
Every year I inspect a steady number of houses that look ordinary from the pavement but turn out to be something quite different once I am in the loft or tapping the external walls. Many are former council houses built in the post-war rush to replace lost and slum housing, now owned privately and coming up for sale on estates across London, the South East and Yorkshire. Buyers usually find out about the construction type in one of two ways: from my survey, or from a lender declining the mortgage a few weeks before exchange. The first is much cheaper.
This guide sets out what "non-standard construction" means in practice, how the main types differ, what I look for on site and how the construction type affects value and mortgageability.
What counts as non-standard construction?
Non-standard construction is the term lenders, insurers and surveyors use for any building whose main structure is not conventional masonry (solid brick or brick-and-block cavity walls) under a pitched tiled or slated roof. The label covers a very wide range of buildings, from post-war precast concrete council houses to steel-framed homes and modern timber-frame estates, and the risks vary enormously between them.
Most non-standard houses in England were built between the mid-1940s and the 1970s, when councils and government needed large numbers of homes quickly and with less skilled labour and fewer bricks. Factory-made concrete panels, steel frames and in-situ poured concrete allowed estates to be built at speed. Many of these "system-built" houses have performed well for 70 years or more; some have not, and a small number of types were formally designated defective.
Which non-standard construction types matter most for buyers?
The non-standard construction types that matter most for buyers are the designated precast reinforced concrete (PRC) houses, followed by steel-framed, in-situ concrete and timber-framed houses, each with a different risk profile. The table below summarises the types I come across most often.
| Construction type | Typical era | Common clues on site | Main concern | Lender attitude (varies by lender) |
|---|---|---|---|---|
| Designated PRC houses (for example Airey, Cornish Unit, Orlit, Reema Hollow Panel, Unity, Wessex) | Mid-1940s to 1950s | Concrete posts or panels, concrete roof structure in some types, distinctive estate layouts | Carbonation and chloride attack causing corrosion of the reinforcement, cracking of structural concrete | Generally only acceptable with a certificate confirming repair under a licensed scheme |
| BISF steel-framed houses | Late 1940s to early 1950s | Rendered ground floor, profiled steel sheeting to the upper storey, steel columns visible in the loft | Corrosion of the steel frame, especially at column bases and where water has penetrated | Many lenders accept, subject to condition; some decline |
| In-situ concrete (for example Wimpey No-Fines) | 1940s to 1970s | Rendered solid walls with no cavity; thick, cold external walls | Cracking, render failure, poor thermal performance, condensation | Widely accepted, sometimes with restrictions |
| Timber frame (post-war and modern) | 1920s onwards; mainstream from the 1980s | Brick or render outer skin, timber studs and sheathing behind, weep holes and cavity barriers | Moisture in the frame, damaged vapour control, poorly executed alterations | Modern timber frame widely accepted; older systems vary |
| Large panel system flats | 1960s to 1970s | Medium and high-rise blocks built from storey-height concrete panels | Joint integrity and structural robustness; building-wide structural appraisals | Often need evidence of a structural appraisal of the block |
Why were some concrete houses designated defective?
Some precast concrete house types were designated defective because their structural concrete deteriorated far sooner than expected, putting the safety and value of the homes in doubt. In the early 1980s, investigations found that carbonation of the concrete and, in some types, chlorides added to speed curing were allowing the steel reinforcement to rust. Rusting steel expands, cracking the concrete around it, and in houses where the concrete columns and beams carry the structure that is a serious problem.
The government's response was the Housing Defects Act 1984, now consolidated as Part XVI of the Housing Act 1985. Under section 528, a class of buildings could be designated as defective by reason of design or construction where that defect had become generally known and substantially reduced values. The legislation gave eligible owners, mainly those who had bought from a public sector landlord such as under Right to Buy, access to financial assistance within the period set by each designation. Those application windows were time-limited, so most current buyers should assume that no assistance is available and that a repair, if not already done, will be at their own cost.
The practical consequence today is the PRC repair certificate. Houses repaired under the licensed schemes of the time had the defective structural concrete replaced, typically with a new masonry outer leaf, and were issued with a certificate. In my experience, lenders that will consider a designated type usually want to see that certificate. A council "partial repair" or a cosmetic re-skin without certification does not normally satisfy them, even if the house looks like a brick semi.
Are BISF and no-fines houses defective too?
BISF steel-framed houses and Wimpey No-Fines concrete houses are not on the designated defective list, so neither type needs a PRC repair certificate. That does not mean they are free of risk; it means the question becomes one of condition, not designation.
With a BISF house, the condition of the steel frame is the key issue. I look closely at the column feet, where the steel meets the ground floor slab and moisture can collect, at any staining or blowing render that suggests water getting behind the finishes, and at the steel visible in the roof void. Where an owner has over-clad the house with insulation or a new render system, I want to understand what has been covered and whether the frame was inspected first.
With no-fines houses, the walls are poured concrete made without fine aggregate, so there is no cavity and the walls behave quite differently from brick. I check for structural cracking, render that has debonded, and condensation and mould caused by the cold solid walls. Retrofitted external wall insulation is common and generally sensible on these houses, but it must be detailed properly around windows and at the base of the wall.
Is a timber-frame house non-standard construction?
A modern timber-frame house is treated by most lenders as standard construction when it was built to current methods with a recognised warranty, whereas some older and system-built timber houses are still classed as non-standard. Timber frame is a mainstream method across much of the UK and many new-build homes use it.
My concerns with timber frame relate to moisture and alterations rather than the method itself. Water getting into the frame from failed seals, leaking windows or plumbing can cause decay that is invisible behind plasterboard. Owners sometimes cut through studs or the vapour control layer when fitting new sockets, windows or extensions. Cavity wall insulation injected into a timber-frame wall can trap moisture against the frame and should not usually be there at all. These issues are why I always confirm the construction before commenting on insulation or damp.
What about RAAC and other concrete problems in homes?
RAAC (reinforced autoclaved aerated concrete) is a lightweight concrete used mainly in flat roofs, and in some floors and walls, from the mid-1950s to the mid-1990s. RICS guidance notes that RAAC is believed to be more common in schools, hospitals and public buildings, with isolated examples identified in homes, notably in some parts of Scotland. In the areas I cover, RAAC is rarely an issue in houses, but I keep it in mind when inspecting flat roofs and blocks from that period, and if I suspect RAAC I recommend a specialist investigation rather than guessing.
The broader point is that concrete defects are often hidden. A survey reports what can be seen and reasonably inferred. Where the visible evidence points to a hidden structural question, the right answer is usually a targeted structural inspection or an engineer's investigation, not a reassuring guess.
How does a surveyor identify non-standard construction?
A surveyor identifies non-standard construction by combining the building's age and setting with physical evidence from the exterior, the interior and, most importantly, the roof void. Sales particulars rarely mention it, and some types were re-faced in brick decades ago, so the street view can be misleading.
On a typical inspection I will:
- note the estate layout and compare the house with its neighbours, because system-built houses were usually built in runs of the same type;
- check the external walls for panel joints, concrete posts, metal sheeting, render on lath, or brickwork that looks newer than the rest of the house;
- tap and measure wall thicknesses at openings to see whether there is a cavity, solid concrete or a frame behind;
- inspect the loft for concrete or steel roof members, column heads and the inner face of the gable and party walls;
- ask the seller, through the agent, for any PRC certificate, structural reports or over-cladding guarantees.
This is a situation where the level of survey matters. A RICS Level 3 Building Survey gives me the scope to explain the construction, its history and the further investigations needed. A Level 2 HomeBuyer Report will still flag non-standard construction, but in less depth. My guide to choosing between a Building Survey and a HomeBuyer Report sets out the differences.
How does non-standard construction affect value and mortgageability?
Non-standard construction affects value mainly through mortgageability: the fewer lenders that will lend on a construction type, the smaller the pool of buyers and the lower the price the market will pay. A mortgage valuer reports the construction to the lender, and the lender's own criteria then decide whether to lend, at what loan-to-value, or not at all.
This is also why a remote or desktop figure is a poor starting point for these houses. As I explain in Desktop vs Inspected Valuations, a desktop valuation assumes the property is typical of its comparables. With non-standard construction, the construction type is the very thing that makes it untypical.
Worked example (illustrative figures only, not a real case): consider a typical pattern on a post-war estate where conventional brick semi-detached houses sell for around £300,000.
| Scenario | Illustrative market value | Reasoning |
|---|---|---|
| Traditional brick semi, same estate | £300,000 | Full mortgage market |
| Designated PRC type, repaired with a valid certificate | £280,000 to £295,000 | Mortgageable with many lenders; modest discount for a narrower buyer pool |
| BISF house in good condition | £270,000 to £290,000 | Accepted by many lenders, but some buyers and lenders are cautious |
| Designated PRC type, unrepaired or partially repaired | £180,000 to £210,000 | Largely cash buyers; price reflects a repair cost of, say, £60,000 to £80,000, plus risk and inconvenience |
The ranges are deliberately wide. Real discounts depend on local evidence, the condition of the specific house and how many comparable sales of the same type exist. The point of the example is the shape of the pattern: certification and condition can move value by tens of thousands of pounds.
What should I do before buying a non-standard construction house?
Before buying a non-standard construction house, confirm the exact construction type, obtain any repair certificate or structural reports, and check that your lender will accept that type before you commit to survey and legal costs. In practice I suggest:
- Ask the agent early whether the house is of non-standard construction and whether a PRC certificate or structural report exists.
- Give your mortgage broker the construction type so they can check lender criteria before the application.
- Commission a Level 3 survey, and let your surveyor know you suspect non-standard construction so the inspection can be planned accordingly.
- Budget for any specialist investigation the surveyor recommends, such as a structural engineer's report on a steel frame.
- Ask your conveyancer to check the certificate is genuine and relates to the property, and to confirm whether any building regulations approvals cover later alterations. My guide to extensions without building regulations sign-off covers that side.
If you already own a non-standard house and are thinking of selling, re-mortgaging or carrying out repairs, a valuation that takes proper account of the construction type helps you set realistic expectations. Our RICS valuation services cover this.
Non-standard construction: frequently asked questions
Is a non-standard construction house a bad buy?
A non-standard construction house is not automatically a bad buy, but the price must reflect the construction type, its repair history and how many lenders will accept it. A well-repaired, certified or never-defective type bought at the right price can be a sound home; the risk lies in paying a traditional-house price for a house that only cash buyers can purchase.
How do I know if a house is non-standard construction?
The quickest clues are the age (most system-built houses date from the mid-1940s to the 1970s), the location on a former council estate, and an exterior that looks different from neighbouring brick houses, such as concrete panels, render on a steel frame or profiled metal sheeting upstairs. The sales particulars rarely say so, and some types were later re-skinned in brick, so a surveyor's inspection, including the loft, is the reliable test.
What is a PRC certificate and why do lenders ask for one?
A PRC certificate confirms that a house of one of the designated precast reinforced concrete types was repaired under a licensed scheme that replaced the defective structural concrete. Lenders ask for it because the designated types are treated as defective unless properly repaired, and a partial or uncertified repair does not usually satisfy them.
Can I get a mortgage on a BISF or Wimpey No-Fines house?
Many buyers do obtain mortgages on BISF and Wimpey No-Fines houses because neither type is on the designated defective list, but lender appetite varies and some lenders decline or lend at a lower loan-to-value. A surveyor's report on the condition of the steel frame or concrete walls often decides whether the application succeeds.
Which survey do I need for a non-standard construction property?
For a non-standard construction property I usually recommend a RICS Level 3 Building Survey, because it reports on the structure in more depth and gives more room to explain repair history, alterations and further investigations. Where the frame or concrete condition is in doubt, a structural inspection or engineer's report may be needed as well.
Buying a house you think may be non-standard construction? Get an instant quote for a RICS Level 3 Building Survey.
Patrick Oliver BSc (Hons) MRICS, Chartered Surveyor and RICS Registered Valuer, Aston James Associates
This article is general guidance only and is not advice on any specific property, mortgage or legal matter; lender criteria change, so always confirm acceptability with your lender or broker.
Recent Comments