The Structural Condition of Pre 1960s – PRC House Types

Original BRE Report Publication Date – June 1984

In the early 1980’s, the Building Research Establishment (BRE) carried out a series of structural evaluations on a number of different pre 1960s prefabricated reinforced concrete – PRC house types.

This article summarises the BRE’s findings and suggests some implications for each house type where applicable. A detailed report of each PRC house type investigation, including suggestions for inspection, maintenance and repair can be obtained directly from the BRE Bookshop. (See reference details at the bottom of this page).


BACKGROUND

Following investigations by the BRE into a number of defects found in Airey houses, an initial report was published in May 1981. Further reports involving larger numbers of Airey PRC houses was provided by local authorities and published in a second report in April 1982. Indications of the deterioration of reinforced concrete components in other PRC houses of the same period led to the BRE evaluating the structural condition of 17 common PRC house types.

Reports on the Boot, Cornish Unit, Orlit, Unity, Wates and Woolaway type houses were published in December 1983. Reports on the Ayrshire County Council, Dorran, Parkinson Framed, Reema hollow panel, Stent and Underdown types were published in June 1984. This article provides an overview of the information contained within the report(s) and incorporates the summary of references that were also published in 1983.

The dwelling types examined account for 98% of the PRC housing stock of this period.


THE HOUSE TYPES EXAMINED

The main loadbearing components of each PRC house type were made of reinforced concrete. The chief features of each design is as follows:

Airey House

Airey houses have closely spaced storey-height reinforced concrete columns with concrete cladding panels. There is an internal spine wall constructed with similar columns.

Ayrshire County Council (Lindsay) and Whitson-Fairhurst houses have identical frames of precast reinforced concrete columns and floor beams. A variety of forms of non-loadbearing cavity walls enclose the columns.

Image of Ayrshire county council prc house
Boot Pier Panel House

Boot Pier and Panel cavity houses have precast reinforced concrete columns and ring beams with unreinforced concrete wall panels.

Cornish Unit houses and flats have precast reinforced concrete columns and ring beams with unreinforced concrete wall panels.

Cornish PRC house
dorran prc house

Dorran houses have narrow storey-height precast reinforced concrete wall panels. The differences between Dorran, Myton, Newland and Tarran variants lie in the inter-panel connections, the use of precut reinforced concrete or steel for ring beams and the use of steel or timber for roofs and floors.

Myton houses – see Dorran.

Newland houses – see Dorran.

Orlit houses have precut reinforced concrete columns, main beams and secondary beams. The walls are clad with precast reinforced concrete panels and flat roofs are decked with precut reinforced concrete slabs.

orlit prc house

Parkinson Framed houses have precast reinforced concrete columns bolted to precut reinforced concrete ring and transverse beams at roof and first-floor levels. The panels between the columns are made of breeze blocks.

reema hollow panel prc

Reema hollow panel houses and flats have large storey­ height pre-cut concrete hollow wall panels, lightly reinforced and joined by in-situ reinforced concrete columns and ring beams at first floor and roof levels. The first-floor level is supported on precast reinforced concrete beams.

stent prc house

Stent houses have narrow storey-height precast reinforced concrete wall panels. These are connected to precast reinforced concrete troughs, infilled with in-situ reinforced concrete, to form continuous ring beams at first floor and roof levels.

Tarran houses and bungalows – see Dorran.

underdown prc house

Underdown houses have rendered loadbearing cavity walls made from precast reinforced concrete blocks. They are joined at intervals by in-situ concrete columns which are usually reinforced and at first floor and eves level by ring beams. Winget houses are similar except for the concrete blocks which are not reinforced.

Example of Unity house construction

Unity houses have precast reinforced concrete columns clad with unreinforced concrete panels.

wates prc house

Wates houses and flats have precast reinforced concrete wall panels and ring beams joined by an in-situ reinforced concrete frame.

Whitson-Fairhurst houses– see Ayrshire County Council (Lindsay).

Winget houses– see Underdown.

Woolaway houses have precast reinforced aerated concrete columns, wall panels and ring beams. First floor and roof construction are usually of timber, apart from the use of reinforced concrete and steel trusses noted above.


INVESTIGATIONS

The evaluation is based on investigations on site, comprising visual inspections of more than three thousand houses, and detailed examinations of the structural components by BRE, and consulting engineers engaged by the BRE, of some 450 houses. In addition, available documentation on design and construction was examined and technical data on present condition available from local authorities and others was reviewed. Although the investigations were often limited by the low numbers of houses available for detailed examination, it is believed that they provide an adequate guide to the range of structural conditions in the housing stock of each type. The proportion of houses in any particular condition, found in the course of the investigation, does not necessarily represent the proportion in this condition within the total population of the type.

The investigations concentrated on the condition of the structure, particularly the reinforced concrete loadbearing components, although deterioration of other concrete components such as cladding and window frames and evidence of roof leakage and condensation was noted.

The condition of other components of the houses was not generally examined. The investigations on site consisted of visual inspection of the outside and inside of dwellings as far as access would allow, noting any signs of deterioration or of structural distress. Where owners permitted, detailed examination of concrete components was made by sampling the concrete to determine cover to reinforcement, condition of reinforcement, carbonation depths, chloride contents and cement contents. Examination of components was limited because components were often hidden in cavities behind wall facings and ceilings and in roof spaces, and because only very local damage during the sampling of components was acceptable.

The most important indication of the structural condition of these reinforced concrete components was whether they were uncracked or cracked due to corrosion of their internal reinforcement. (As corrosion proceeds, bursting forces are produced which cause the concrete to crack and spall.

The implication of this cracking is that the component is reaching the point at which it will no longer perform the function intended by the designer. In the case of uncracked components, the important consideration is the length of their future life before any reinforcement corrosion is likely to cause cracking. Where there is carbonation to, or almost to, the reinforcement, or the presence of a high content of chloride in the concrete, cracking is likely to occur within a few years, with the possible exception of those components in dry environments where cracking may be delayed.

The evaluation of the condition of the houses included an assessment of the effects of deterioration on structural stability and safety.


THE FINDINGS

Overall, the investigations revealed that the reinforced concrete components are gradually deteriorating. They are doing so because of carbonation of the concrete and, in some cases, the presence of high levels of chloride, leading to corrosion of the steel reinforcement (15) and the consequent cracking of the concrete.

The great majority of the houses studied were found to be in structurally sound condition, but there was a wide range in the rate of deterioration both between and within types. Some cracking was found in all types and the nature of the process is such that deterioration will continue, albeit very slowly in some cases, and all houses will eventually be affected by cracking.

Cracking in a proportion of houses of all types will not occur for some years, and a few houses may not display any evidence of deterioration for, say, the next 30 years or more.

The most advanced deterioration identified was cracking in main and secondary beams of Orlit houses, in columns of Airey, Boot, Unity and Woolaway houses and in the columns and perimeter beams, and the connections between them, of Parkinson Framed houses:

Some cracking was also seen in columns in Comish Unit, Myton, Newland and Tarran houses, in wall panels in Wates houses and in infill panels in Woolaway houses. Isolated examples were found of cracking, spalling and rust-staining of the wall panels of Dorran, Myton, Newland and Tarran houses and of cracking of ring beams of Myton houses.

Some cracking was observed at edges of wall panels of Reema hollow panel houses, of reinforced concrete blocks in Underdown houses and of in-situ reinforced concrete columns in Winget houses.

Little cracking was seen in the Ayrshire County Council, Whitson-Fairhurst and Stent houses inspected.

No structurally unsafe conditions were found.

The processes of carbonation and attack by chlorides are likely to affect all prefabricated reinforced concrete houses of this period, in the manner described above.


IMPLICATIONS FOR INSPECTION OF INDIVIDUAL HOUSES

Deterioration of structural concrete components in some of these houses may lead eventually to an unsafe condition. They should therefore be inspected regularly and adequately maintained in the future.

Normal survey practice should record the presence of any visible cracking in Comish Unit, Dorran, Myton, Newland, Reema hollow panel, Stent, Tarran and Wates types. If no cracking or signs of movement are visible, it may be reasonable to assume that in these types, the concrete components are in sound condition at the time of the survey.

Where components are hidden, e.g. in Airey, Ayrshire County Council (Lindsay), Boot pier and panel, Orlit, Parkinson Framed, Underdown, Unity, Whitson-Fairhurst, Winget and Woolaway houses, access will be required to cavities or by removal of render in order to assess the condition of the components. However, cracked render on Boot, Parkinson Framed, Underdown, Winget and Woolaway houses may indicate deterioration of the reinforced concrete components.

If cracking is found, its cause and structural significance should be determined. Analysis of the concrete and ex­ amination of the reinforcing steel will have to be made to determine whether components uncracked at the time of the survey, may crack in the near future.


REPAIR AND REMEDIAL WORK

There are no practicable techniques which can halt deterioration altogether. However, the reinforced concrete components in some houses are now crack-free and in some cases cracking may not occur for some years. The emergence of cracking can be deferred by measures such as those described in BRE Digest 265.

The practicability of repair and replacement of components at economic cost, in order to give these houses a life comparable to that of houses of other designs, depends upon the individual characteristics of each type. The detailed reports on the individual types of house refer to the feasibility of repair in each case.

References – Building Research Station

Airey houses: guidance to engineers and surveyors on inspection of structural columns. Building Research Establishment, May 1981.
2.  Airey houses: technical information and guidance. Building Research Establishment, April 1982.
3.  The structural condition of Boot pier and panel cavity houses. BRE Report, 1983.
4.  The structural condition of Cornish Unit houses. BRE Report, 1983
5.  The structural condition of Orlit houses. BRE Report,1983.
6.  The structural condition of Unity houses. BRE Report, 1983.
7.   The structural condition of Wates prefabricated reinforced concrete houses. BRE Report, 1983.
8. The structural condition of Woolaway houses. BRE Report, 1983.
9. The structural condition of Ayrshire County Council (Lindsay) and Whitson-Fairhurst houses. BRE Report, 1984.
10.  The structural condition of Dorran, Myton, Newland and Tarran houses. BRE Report, 1984.
11.  The structural condition of Parkinson Framed houses. BRE Report, 1984.
12.  The structural condition of Reema hollow panel houses. BRE Report, 1984.
13.  The structural condition of Stent houses. BRE Report,1984.
14.  The structural condition of Underdown and Winget houses. BRE Report, 1984.
15.  Building Research Establishment. The durability of steel in concrete: Part 1. Mechanism of protection and corrosion. BRE Digest 263. London, HMSO, 1982.
16.  Building Research Station. The structural condition of some prefabricated reinforced concrete houses of Boot, Cornish Unit, Orlit, Unity, Wates and Woolaway construction. BRE Information Paper IP 16/83. Building Research Establishment, 1983.
17. The Royal Institution of Chartered Surveyors. Structural surveys of residential property: a practice note. London, RICS, 1981.
18.  Building Research Establishment. The durability of steel in concrete: Part 2. Diagnosis and assessment of corrosion-cracked concrete. BRE Digest 264. London, HMSO, 1982.
19. Building Research Establishment. The durability of steel in concrete: Part 3. The repair of reinforced concrete. BRE Digest 265. London, HMSO, 1982.
This Information Paper summarises the BRE Reports numbered 3-14 (inclusive) above

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