Non-Standard Construction Houses: Airey, PRC and System-Built

It is a house built with a method or material other than the conventional masonry wall. The terms non-standard, non-traditional and system-built overlap. This guide uses non-standard and non-traditional for the wider group, and system-built for the wall type an EPC records.

BRE's reference work on the subject, Non-traditional houses: Identifying non-traditional houses in the UK 1918-75 (publication AP 294, 2012), catalogues 450 house types in four construction classes: metal framed, precast concrete, in-situ concrete and timber framed. It exists to help surveyors and other professionals identify a house from drawings and by local authority area.

The scale was large. In the Commons in 1984, Housing Minister Ian Gow said some 550,000 houses in Great Britain were built to a variety of different designs in the years following each world war, and that some 170,000 of them used PRC load-bearing components. Those are 1984 figures for Great Britain, so they say nothing about how many such houses stand today.

A non-standard house is not automatically a defective one. In the same debate Gow said that some lenders had extended their caution to other non-traditional types, and that it was “unjustified to assume that, because there are defects in PRC houses, there will be defects in, for example, houses made of unreinforced concrete or of concrete blocks”. Lender caution and the legal label “designated defective” attach to particular types, covered below. Our guide to system-built houses from the 1960s and 1970s covers that era in more detail.

An Airey house is a post-war precast concrete house. A frame of concrete columns carries shiplap-style concrete panels that form the outside wall. Leeds Civic Trust says the type was designed and built after the Second World War by Sir Edwin Airey of Leeds.

Leeds Civic Trust puts the number built by local authorities at some 20,000 in total.

The type has a documented history of problems. After a fire in an Airey-type house in Barnsley, BRE reported in May 1981 that the reinforced concrete components in Airey houses were “liable to cracking and eventual disintegration” through carbonation and, in some cases, excessive chloride. Gow told the Commons that a discretionary scheme of assistance for private owners of Airey houses followed in September 1982. Leeds Civic Trust says that on one ex-National Coal Board Airey estate at Oulton, mortgages and insurance were “difficult if not impossible to obtain”.

Many Airey houses have since been repaired, and some re-clad. BRE Global's repair scheme has a registered repair specification for the Airey, so a certified repair is possible: see buying and mortgages.

A PRC house is built from precast reinforced concrete: load-bearing parts such as columns and panels, made of concrete with steel reinforcement inside, cast before they are fixed in place. The Airey is one PRC type. The 1984 debates on the Housing Defects Bill also named the Wates, Woolaway, Orlit and Reema Hollow Panel.

Gow told the Commons that public bodies built PRC houses after both world wars, when labour and conventional materials were short, so new methods and materials were used. The defect BRE described was corrosion of the steel reinforcement inside the concrete.

The assessor records the wall as a type, and the rating method (RdSAP) gives that type a default heat-loss figure based on the age band of the build. The default stands unless there is evidence of added insulation. For a concrete panel or frame wall, “System built” is the nearest wall type in the specification, though the assessor makes that call on site. The page on how an EPC rating is calculated shows how wall heat loss feeds the score.

The specification's default wall U-values show the effect. A U-value is the heat lost through a square metre of wall for each degree of temperature difference, so a lower figure loses less heat. The table below compares an unfilled cavity wall with a system built wall. England (Table 6) and Wales (Table 9) give the same figures for these rows.

So a system built wall from before 1967 defaults to a higher heat loss than an unfilled cavity wall of the same age. With the same loft, windows and heating, the wall alone would pull the modelled rating down. The specification says to assume the “as built” figure if there is no evidence of retro-fitted insulation, and that added insulation can be specified if adequate evidence exists. If the wall is known to be insulated but the thickness is not, it uses the 50 mm row. Keep installation invoices, guarantees and certificates.

If a wall does not match a listed type closely, the specification tells the assessor to select the nearest equivalent and add a note to the certificate. Your own EPC's wall line is the place to check what was recorded.

Often yes, but the method depends on what the wall actually is, so identify the construction first. “System built” covers several constructions and you cannot assume standard cavity fill will suit.

Ofgem's pre-installation survey form for ECO4 and the Great British Insulation Scheme (draft version 0.1, November 2023) makes the point in a footnote: although most system build properties meet the definition of solid wall, some have external walls of a standard cavity construction and require a cavity wall insulation measure. It concludes that the construction of the external walls of a system build property should be assessed before insulating.

Practical order of work:

• Identify the type. BRE's AP 294 catalogue has drawings of 450 house types and can be searched by local authority area.
• Get a survey from someone who knows the type. For a concrete-framed house with a repair history, ask for the repair paperwork first.
• Deal with structural and moisture problems before adding insulation. Anything that touches load-bearing parts of the house needs a structural engineer.
• Keep evidence of whatever is installed, so the next EPC can credit it.

Sometimes. It depends on the construction type, its condition and repair history, and the individual lender. PRC houses are the group lenders have been most cautious about. In 1984 Gow said building societies were “already extremely cautious about lending on the security of PRC houses”, and BRE Global says mortgage lenders show a reluctance to lend on PRC properties or to offer home insurance.

BRE Global's Pre-cast reinforced concrete Homes Repair Scheme exists to give lenders and insurers confidence that a repair was done properly. It issued its first certificate in July 2016. Only Registered Practitioners can survey, cost and carry out repairs under it, and it has registered repair specifications for the Airey, Reema, Underdown/Winget and Wates. It does not currently cover other PRC types.

An older scheme was run by PRC Homes Ltd, which BRE Global describes as a subsidiary of the NHBC. BRE Global does not cover repairs or certificates from that scheme and refers enquiries about them to the NHBC.

Before you commit:

• Ask the seller early which construction type the house is, and for any repair certificate and the scheme it came from.
• Ask your lender or broker, in writing, whether they will lend on that type before you pay for a survey or valuation. Each lender sets its own criteria.
• Instruct a surveyor who has dealt with the type, and read the wall line on the current EPC.
• If you plan to let it, check the rating against the minimum band before you complete.