Non-standard construction

What non-standard construction means

Surveyors and mortgage lenders use "standard construction" to mean a home whose load-bearing walls are brick, block or stone, either solid or with a cavity, under a pitched roof covered with tiles or slates. A home built any other way is usually described as non-standard.

Many non-standard homes date from the years after the Second World War, when councils needed homes quickly and bricks and skilled builders were in short supply. Builders and manufacturers developed systems using precast concrete panels, concrete poured on site, steel frames and timber frames. Later decades brought cross-wall terraces, blocks of flats built from large concrete panels and, from the 1980s, modern timber frame. Some much older homes count too, such as historic timber-framed or earth-walled cottages.

Non-standard does not mean defective. Many of these homes have stood for well over half a century. But some systems have known weak points, and in the 1980s a number of precast reinforced concrete (PRC) house types were officially designated as defective under legislation that is now Part XVI of the Housing Act 1985.

Why it matters when you buy

• Mortgages. Lenders set their own rules. For a given construction type, some lenders will lend, some only with a structural engineer's report, and some not at all. The same house can suit one lender and not another, so check with your lender or broker before you pay for a survey.
• Insurance. Insurers may ask about the construction, and some charge more or decline certain types. Answer their questions accurately.
• Repair history. Some systems need particular repairs, and the paperwork matters as much as the work. A repaired PRC house, for example, should have a certificate.
• Selling later. If fewer lenders will lend on a home, fewer buyers can buy it when you sell, which can affect how long a sale takes.

How to tell from the outside

• Walls that are rendered, painted or clad where neighbouring homes of the same age are brick.
• Concrete columns, panels or horizontal concrete planks forming the walls.
• Profiled metal sheeting on the upper walls, as on some steel-framed houses.
• Front and rear walls that are tile-hung, boarded or panelled between brick side walls, typical of cross-wall terraces.
• Groups of identical houses built at the same time, often by a council.

Appearances can mislead. A repaired or re-clad house can look like a brick house, and a modern timber-framed house usually does. Neighbouring houses of the same design can help show what a house was built as.

How to tell from the documents

• The listing. Words such as "non-standard construction", "PRC", "system built", "timber frame" or "cash buyers only" are worth asking the agent about.
• The energy performance certificate (EPC). The wall description may say "system built", the energy rating method's term for walls that are neither masonry nor timber-framed, or "timber frame". You can find the EPC on GOV.UK. Treat it as a clue rather than proof, because the assessor does not open up the walls.
• The seller's papers. Repair certificates, engineer's reports and guarantees for insulation, re-cladding or wall tie work show what has been done. If the home was once owned by a council, ask what paperwork came with the purchase.

What we do

For most non-standard homes we recommend a Level 3 Building Survey. RICS describes Level 3 as suited to homes that are unusual or altered, as well as larger, older or run-down ones. In a Level 3 survey we:

• identify the construction as far as a visual inspection allows, including from the roof space
• look for signs of past repair, re-cladding or rebuilding, and compare the house with its neighbours
• ask for any repair certificates, engineer's reports and guarantees, and say what your conveyancer should check
• use a drone to look at roofs, chimneys and gutters, where flight is permitted
• recommend a structural engineer where the structure cannot be assessed without opening it up

Our surveys do not include a valuation or a reinstatement cost.

Where we have found non-standard homes

We analysed the text of more than 1,100 of our own survey reports, written between 2022 and 2026 across Hertfordshire, Buckinghamshire, Bedfordshire, Berkshire, Oxfordshire and north-west London. The map shows the construction types recorded in each postcode district. To protect our clients' privacy, it shows no addresses and leaves out any district where we have fewer than three reports.

The map shows only what our reports recorded. A district with no non-standard homes on the map may still have them.

Guides by construction type

• BISF houses

  Named after the British Iron and Steel Federation, BISF houses were built in the late 1940s around a steel frame. Most of their problems start when moisture reaches the steel.

• Buying a non-standard home

  Many non-standard homes are sound and comfortable, but buying one takes more checks than usual. Here is the order to do things in, the questions to ask and a checklist.

• Cross-wall construction

  Common in 1960s and 1970s terraces and town houses, cross-wall construction carries the building on the walls between homes. The lightweight front and rear walls are where most problems start.

• Laing Easiform houses

  Easiform was the building firm John Laing's method of casting concrete walls on site, used over several decades. The main risks come from steel in the walls corroding.

• Large panel system (LPS) flats

  Many council blocks of the 1960s and 1970s were built from large precast concrete panels. If you are buying a flat in one, the structural history of the whole block matters.

• PRC houses (precast reinforced concrete)

  Precast reinforced concrete houses were built in large numbers after the Second World War, and many types were later designated defective. Here is what that means if you are buying one.

• RAAC (reinforced autoclaved aerated concrete)

  RAAC panels were used mainly in the roofs of public and commercial buildings, and occasionally in homes. We have not recorded RAAC in our house surveys, but it helps to know the signs.

• Steel-framed houses

  BISF is not the only steel-framed house. Other systems share the same main weakness: steel that corrodes, out of sight, where water reaches it.

• Timber-framed houses

  Timber frame covers centuries-old box-framed cottages, post-war system houses and many modern homes. The risks differ with age, but most come back to moisture and fire.

• Wimpey No-Fines houses

  No-Fines houses have solid walls of concrete cast on site. Many were built for councils and they were not designated defective, but they have weak points of their own.

Sources

• RICS: House surveys (UK): the costs, types and benefits of an RICS Home Survey
• BRE: SAP 10 and RdSAP 10 specifications, which define the wall types used on EPCs, including "system build"
• GOV.UK: Find an energy certificate
• legislation.gov.uk: Housing Act 1985, Part XVI
• Civil Aviation Authority: Drones