Non-Standard Construction House Surveys: PRC, BISF, Trusteel, Wimpey No-Fines & Laing Easiform

If you are buying a non-standard construction house, the first question is not simply whether it is “non-standard”. The important questions are what structural system was used, whether that exact system has a known defect history, what repairs or alterations have already been carried out, and what evidence a mortgage lender may require before it will lend.

AMS SURVEYS has inspected non-traditional and system-built homes across Liverpool, Manchester, Crewe and the wider North West, including PRC houses, Airey, Cornish, Unity and Wates construction, BISF and other steel-framed homes, Trusteel Mk II, Wimpey No-Fines and Laing Easiform. These systems can look surprisingly similar after re-rendering, overcladding or later brickwork, but their structures, likely defects and investigation requirements are not the same.

This guide explains the main construction types, the mortgage and resale questions that commonly arise, what a survey should investigate, and when a Level 3 Building Survey, Structural Survey or more intrusive structural investigation may be appropriate.

What is a non-standard or non-traditional construction house?

In everyday property terminology, a standard house generally means a dwelling constructed using familiar load-bearing masonry, typically brick or stone walls, with a conventional pitched tiled or slated roof. Non-standard or non-traditional construction is a broad label for homes that depart from that model, for example by using a structural steel frame, precast reinforced concrete components, cast in-situ concrete, timber framing or a proprietary system of prefabricated elements.

That broad label is useful for identification, but it is not a diagnosis. BRE’s reference work on non-traditional housing identifies around 450 house types built between 1918 and 1975 and classifies them by construction form, including metal-framed, precast concrete, in-situ concrete and timber-framed systems. This is why a buyer should avoid assuming that all concrete houses, or all prefabricated houses, carry the same structural or mortgage risk.

Non-standard construction and mortgages: why the exact system matters

Mortgageability is not determined by the words “non-standard construction” alone. Lenders make their own risk decisions, and their requirements can differ according to the construction type, condition, repair history, valuation advice and supporting documentation. UK Finance maintains the Mortgage Lenders’ Handbook, including general and lender-specific instructions, which is a useful reminder that lending requirements are not universal.

The most important distinction is often between a property that uses an unusual but serviceable construction system and a dwelling type that was formally designated defective. Following investigations into post-war precast reinforced concrete housing, more than 20 PRC house types were designated defective. Government-backed repair schemes were then developed to restore confidence and, where the required repair standard was met, general mortgageability.

A non-traditional property can therefore be perfectly serviceable and potentially mortgageable, while another visually similar property may require extensive evidence, structural investigation or a recognised repair history. The survey should identify the actual system rather than simply repeat an estate agent, EPC or valuation description.

The main non-standard house types buyers ask us about

Airey houses

Airey houses are a post-war precast reinforced concrete system. Their structural arrangement uses precast concrete elements with reinforcement, and deterioration of the concrete and embedded steel can be critical. The historic concern that helped trigger wider investigation of PRC housing was the discovery of poor structural elements in an Airey house, associated with carbonation and inadequate cover to reinforcement.

Airey dwellings were among the PRC types designated defective. For a buyer, the key questions are whether the house remains substantially in its original PRC form, whether a structural repair scheme has been undertaken, what documentary evidence exists, and whether the present condition and repair history satisfy the proposed lender. Surface render or brick cladding alone does not establish that a structural repair has been completed.

Cornish Unit houses

Cornish Unit houses are another important family of PRC dwellings. Different forms and configurations exist, and Cornish Unit dwellings were included within the statutory defective housing designations. The structural frame and panel arrangement can be obscured by later external finishes, making correct identification and review of repair records especially important.

A survey should consider the condition of the structural system, evidence of cracking or movement, deterioration at vulnerable junctions, alterations, extensions and any evidence that the original PRC structure has been removed, replaced or made structurally redundant as part of a recognised repair.

Unity houses

Unity and Butterley PRC dwellings were also formally designated defective. They use a precast concrete structural system, and assessment needs to distinguish original construction from later repaired or overclad examples. A buyer should not treat a fresh external finish as proof that the underlying structural work meets a lender’s requirements.

Where a Unity house has been repaired, the documentary trail can be just as important as the visible condition. The surveyor may need to review the repair type, accessible structural evidence and any certificates supplied, while the buyer’s conveyancer and lender confirm whether the documentation is acceptable for the transaction.

Wates houses

Wates PRC dwellings are another designated defective system encountered within the wider stock of post-war system-built housing. They should not be confused with cast in-situ concrete systems simply because concrete is visible or because the external appearance has been altered.

The appropriate investigation depends on whether the building is original, repaired, partly altered or reclad. Where structural elements are concealed, opening-up may be needed to establish what remains and what condition it is in.

BISF steel-framed houses

BISF houses, associated with the British Iron and Steel Federation, use a structural steel frame rather than a load-bearing PRC frame. They are therefore a different technical proposition from Airey, Cornish, Unity or Wates housing.

A BISF survey should focus on the steel frame, areas where moisture can reach concealed steelwork, corrosion risk, junctions at the base and roof, cladding or render changes, roof replacement, insulation and ventilation, and any alterations that may have affected load paths or trapped moisture. Much of the critical frame is concealed, so a purely superficial inspection may not answer a lender’s or owner’s structural question.

Trusteel Mk II houses

Trusteel Mk II is another steel-framed system. BRE published a dedicated investigation report on Trusteel Mk II houses, recording their construction and identifying positions where deterioration was found and where particular attention should be directed during future inspections.

For an existing Trusteel house, this makes system-specific inspection important. External cladding can hide the frame, and corrosion is not necessarily uniform. A structural investigation may need targeted access at known vulnerable positions rather than random opening-up.

Wimpey No-Fines houses

Wimpey No-Fines is fundamentally different from PRC panel systems. It uses cast in-situ no-fines concrete, a concrete mix without fine aggregate that creates an open-textured material. The Concrete Society notes that the method was used extensively for Wimpey housing and that more than 300,000 low-rise dwellings were constructed from the mid-1940s onwards.

Because it is in-situ concrete, a Wimpey No-Fines house should not automatically be described as a defective PRC house. Survey considerations can include cracking, previous repairs, external render and coatings, moisture behaviour, thermal upgrades, openings and extensions, fixings into the no-fines material and the effect of later alterations.

Many Wimpey No-Fines houses have been externally insulated or re-rendered. Those improvements can change thermal performance and appearance, but they can also conceal the original wall surface. The survey should therefore consider both the original system and the detailing of later retrofit work.

Laing Easiform houses

Laing Easiform is a cast in-situ concrete system, not a precast reinforced concrete panel system. BRE’s historic investigation described numerous Easiform variants with an in-situ concrete wall arrangement. A 1988 Government response to Parliament reported that BRE’s study found the construction to be robust and substantial, with the stability and integrity of the houses examined not in doubt.

That does not mean every individual Laing Easiform house is defect-free. Age, alterations, cracking, moisture, external finishes, thermal retrofit, openings and local repairs still matter. The important point is that the system should be assessed on its own construction and condition, not grouped automatically with designated defective PRC housing.

Designated defective PRC does not mean every concrete house is defective

This distinction is one of the most important points for buyers. Historic statutory designations included systems such as Airey, Cornish Unit, Unity and Butterley and Wates, among others. Other non-traditional systems, including many steel-framed and in-situ concrete types, are not automatically in the same category.

The practical consequence is that the words “concrete house” or “non-standard construction” are not enough for a purchase decision. Correct system identification can affect the scope of survey, the need for opening-up, the repair strategy, lender requirements, insurance, future alterations and resale.

What should a non-standard construction house survey investigate?

The inspection should be designed around the construction system and the client’s question. A pre-purchase buyer who wants the whole property assessed has a different requirement from a lender or owner asking a narrow question about concealed steel corrosion or the adequacy of a previous PRC repair.

Depending on the system and accessibility, the survey may need to consider:

• Identification of the structural system and whether later finishes conceal the original construction.

• Evidence of structural movement, cracking, distortion or local failure.

• Condition of accessible steelwork, concrete, reinforcement, panels, posts and key junctions.

• Moisture paths and locations where corrosion, carbonation or material deterioration may develop.

• Roof, wall and floor interfaces, particularly where structural members are concealed.

• Previous structural repairs, overcladding, external wall insulation, re-rendering and alterations.

• Extensions, removed walls, enlarged openings and other changes that may affect load paths.

• Whether targeted opening-up or further intrusive investigation is needed.

• The available repair records, certificates, drawings and warranties, and any gaps in that evidence.

• Likely repair options, priorities and the need for specialist design or calculations.

Level 2 Homebuyer Survey, Level 3 Building Survey or Structural Survey?

Level 2 Homebuyer Survey

RICS describes a Level 2 Home Survey as most suitable for conventional properties that are in reasonable condition and simple in form. AMS SURVEYS also provides Level 2 Homebuyer Surveys for appropriate properties, but a known non-traditional structural system may require a more detailed or specifically targeted investigation than a normal Level 2 scope.

Level 3 Building Survey

RICS describes the Level 3 Home Survey as its most comprehensive home survey. It is intended for properties that are older, unusual, altered, complex or in poorer condition, and it considers how the building is constructed, the materials used, visible defects, potential hidden problems, repair options and future maintenance.

For a purchaser of a non-standard house who also wants the roof, dampness, services, joinery, drainage, grounds and the rest of the property considered, a Level 3 Building Survey is often the logical starting point. The survey can then recommend a more focused structural investigation where the construction system or a suspected defect cannot be adequately assessed visually.

Structural Survey and structural investigation

A Structural Survey is more focused. It can be appropriate where the principal question concerns the structural frame, a lender or valuer has requested further investigation, a defect has already been identified, or targeted opening-up is required. For steel-framed and some repaired or altered PRC properties, this narrower but deeper investigation can be more useful than repeating a general condition survey.

AMS SURVEYS can tailor the investigation to the property and the reason for the report, including structural inspection, opening-up where agreed and practicable, repair advice and, where required, structural calculations or further design input.

Why a mortgage valuation is not a building survey

A mortgage valuation is primarily undertaken for the lender’s lending decision. It should not be relied on as a detailed assessment of the property’s construction and condition. If the valuer identifies non-standard construction, uncertainty about the structural system or evidence of a previous repair, the lender may request additional information before making or confirming an offer.

This is why the sequence matters. Identifying the system early, checking the available documentation and commissioning the right survey can reduce the risk of discovering late in the transaction that the lender requires evidence that has not been obtained.

Buying a repaired PRC house: what evidence should you request?

A repaired PRC house can require more than a visual check of its external appearance. The original Government-backed repair approach was intended to make the relevant structural elements removed and replaced, or structurally redundant, rather than simply patch repaired. The exact repair carried out to an individual house therefore matters.

Before exchange, buyers should ask their legal adviser to obtain and verify all available information about the construction and repair history. Depending on the property, this may include the repair scheme details, completion or certification documents, building control information, guarantees, drawings, invoices and records of later alterations.

The surveyor’s role is to assess the building and the evidence available within the agreed scope. The lender and conveyancer remain responsible for their own requirements, and a certificate or historic repair should never be assumed to guarantee acceptance by every lender.

Structural repairs to non-standard construction houses

Repairs should follow the actual defect and construction system. A generic “non-standard house repair” specification is rarely appropriate.

For a steel-framed house, the repair strategy may involve exposing affected steelwork, determining the extent of corrosion, addressing the moisture source, repairing or replacing structural members and reinstating the envelope with appropriate corrosion protection and detailing. For a concrete system, investigation may focus on cracking, deterioration, reinforcement condition where present, moisture and the integrity of panels or cast walls. For a repaired PRC dwelling, the investigation may instead be about confirming the extent and condition of the previous structural replacement.

Where structural work is necessary, the sequence should normally be investigation first, diagnosis second, then repair design. That avoids spending money on cosmetic work that conceals the evidence without addressing the cause.

Why local experience still matters

Non-traditional housing is not spread evenly across the country. Estates were often constructed using particular systems under local authority and post-war housing programmes, which means certain house types can recur within specific towns and neighbourhoods.

AMS SURVEYS has inspected examples across Liverpool, Manchester and Crewe, as well as the wider North West. In practice, the challenge is often not spotting that a house looks unusual. It is working out which system sits behind later render, brick slips, cladding, insulation or extensions, then deciding what evidence is needed to answer the client’s actual question.

Common mistakes when buying a non-standard construction house

• Assuming all concrete houses are PRC, or that all PRC houses have the same defect history.

• Assuming a brick-clad or rendered elevation proves the original structure has been replaced.

• Relying on an estate agent description or mortgage valuation as proof of the construction type.

• Ordering a Level 2 survey for an unusual property without discussing whether the scope is sufficient.

• Waiting until late in the conveyancing process to check the proposed lender’s requirements.

• Accepting a repair certificate without checking exactly what property and repair work it relates to.

• Carrying out cosmetic repairs before the structural cause of cracking, corrosion or moisture has been investigated.

Frequently asked questions

Can you get a mortgage on a non-standard construction house?

Often yes, but it depends on the exact construction, condition, repair history and the lender’s criteria. A non-standard house is not automatically unmortgageable. Some designated defective PRC systems can be particularly sensitive to repair evidence and lender requirements, while other non-traditional systems are assessed differently.

Is BISF the same as a PRC house?

No. BISF houses use a structural steel frame. PRC houses use precast reinforced concrete structural components. The likely defects, investigation methods and repair options are therefore different.

Is Wimpey No-Fines a defective PRC house?

No. Wimpey No-Fines is an in-situ no-fines concrete construction system and should not automatically be grouped with designated defective PRC systems. Its condition and mortgage position still require property-specific assessment.

Is Laing Easiform a PRC house?

No. Laing Easiform is a cast-in-situ concrete system. Historic BRE investigation reported reassuring findings for the houses examined, but every individual property still needs to be assessed for its present condition, alterations and maintenance history.

Can a Level 3 Building Survey identify non-standard construction?

A Level 3 survey is designed to assess how a property is constructed and is usually the most suitable RICS home survey level for an unusual building. However, concealed frames or specific structural questions can still require targeted opening-up or a separate Structural Survey.

What if the house has already been repaired or overclad?

Do not assume the external finish tells you what happened structurally. Ask for the repair and building control records, and make sure the survey scope addresses whether accessible evidence is consistent with the stated repair. Further opening-up may be appropriate if the structure cannot otherwise be verified.

Get the right survey before you commit

If you are buying, selling, mortgaging or planning repairs to an Airey, Cornish, Unity, Wates, BISF, Trusteel Mk II, Wimpey No-Fines, Laing Easiform or other non-standard construction house, the best starting point is to identify the system correctly and define the question the report needs to answer.

AMS SURVEYS can advise whether you need a Level 3 Building Survey, a focused Structural Survey, or a staged investigation with opening-up and repair advice. We work across Liverpool, Manchester, Crewe, Cheshire, Lancashire and the wider North West.

Request a quote for a non-standard construction house survey, or speak to our team on 0151 314 6650 about the property, the construction type and any requirements already raised by your lender, valuer or solicitor.

Technical sources and further reading

For further technical context, useful independent sources include BRE’s Non-traditional houses reference library, RICS guidance on choosing the appropriate Home Survey level, the RICS Level 3 scope of inspection, the UK Finance Mortgage Lenders’ Handbook, Government material on the historic PRC repair programme, The Concrete Society’s technical information on no-fines concrete, and the Parliamentary record concerning BRE’s Laing Easiform investigation.