Cornish Unit Type 1

The Cornish Unit Type 1 Precast Reinforced Concrete House

Designated defective by the Secretary of State under Part XV1 of the Housing Act 1985 . (England & Wales Only.) Legislation repealed in Scotland.

• Manufacturer: Central Cornwall Concrete & Artificial Stone Co. / Selleck Nicholls & Co.
• Type: Precast Concrete
• Designer: A E Beresford & R Tonkin
• Period Built: 1946-1960’s
• Number Built: 30,000 including types I & II

The Cornish Unit Type I House is undoubtedly one of the most instantly recognisable system built homes in the UK today due to the typical oversized Mansard hipped roof that encapsulates the first floor elevation of this build.

Designed by A E Beresford and R Tonkin and manufactured by the Central Cornwall Concrete & Artificial Stone Company & Selleck Nicholls & Co as a direct response to the Post War Temporary Accommodation Act of 1944 to provide emergency accommodation for the people of the War torn country.

The Cornish Type I & II variations were produced as bungalows, two storey semi-detached and terraced houses with a medium pitched Mansard hipped roof.
The Cornish Unit Type 1 system is of a PRC beam and post construction built in 2 storey semi-detached house and flat formats.
The Cornish Unit Type II PRC house was built from 1954 – 1960’s. The company also built the lesser known and studied Cornish Flush panel.

The lesser known Cornish Flush Panel system shown above, was a Detached Bungalow manufactured by Selleck Nicholls & Williams in the 1960’s, although the exact number produced of this model is not known.

Over 30,000 ‘Cornish’ houses were built from 1946 through to the 1960’s, however there is no precise number given for the number of Cornish Type I houses that were actually built. The 30,000 number stated is a figure which includes all Cornish constructions including the Type II and Flush panel designs.

The Cornish Houses were made using small panel, lightweight Precast Reinforced Concrete structural elements and panels (PRC) fixed over a concrete frame for the first floor, with the second story utilising the mansard roof with near vertically clad tiles over timber trusses leading to a less steep upper pitch. The windows protrude through the tiles to create an instantly recognisable style not dissimilar to Dormer constructions.

Serious concerns are raised.

In the 1980’s, during the investigation of a fire damaged Airey house, serious cracking was found in the buildings structural PRC columns caused by inadequate protection of the embedded steel reinforcements and chemical changes to the surrounding concrete.

Further investigations by BRE showed that a number of other house types built during the postwar rush to build new homes, exhibited similar defects, that would most certainly lead to eventual structural failure.
In 1984 the Government introduced legislation to compensate owners who had bought affected houses from the public sector under right to buy schemes.  It was deemed that the the severe structural defects could not have been identified during surveys at time of purchase due to the nature of the properties.

The Housing Defects Legislation (now Part XVI of the Housing Act 1985) allowed the Secretary of State to designate particular dwelling types as inherently defective, and empowered local authorities to operate a Scheme of Assistance for all eligible owners, either by way of buy back or by way of repair.

An extract from an early House of Commons debate on this issue can be found HERE

Over 28,000 households were aided under the Scheme of Assistance, with only a small number of eligible properties not taking part.
Most ‘repairs’ were carried out using the system of repair which was licensed, inspected and certificated by PRC Homes Ltd, a subsidiary of NHBC, but not all owners chose this route. Some local authorities carried out ‘partial repairs’ to their own stock which unfortunately did not remove all the defective PRC structural elements from the dwelling.

Surveyors notes

Surveyors encountering a house type which has been Designated Defective are therefore advised to check whether any ‘repairs’ carried out were in accordance with a PRC Homes Ltd licensed system, and certificated as such.

PRC Homes LTD closed ceased operating in 1996.  Houses repaired under the licensed scheme were generally considered by some lenders to be acceptable for mortgage lending purposes with a standard NHBC warranty.”
The legislation did not allow for any improvement during repair, but superficially, the appearance of a reinstated houses changed dramatically, despite key identification characteristics such as window and door openings, and roof pitches, remaining constant. It should again be stressed that the presence of a new brick skin alone on a defective house, does not in itself, signify that the house has been repaired under an approved scheme which would make it acceptable for mortgage purposes. Certification was provided to all homes repaired under the scheme and this should always be viewed and verified prior to sale or purchase.

Further investigations by BRE found that a number of other house construction types built in the postwar period showed signs of similar defects, which would also eventually lead to structural failure.
As a result, in 1984 the Government brought forward legislation to compensate owners who had bought, in good faith, houses
from the public sector with serious structural defects which could not have been known about, or discovered during surveys at time of purchase. The Housing Defects Legislation (now Part XVI of the Housing Act 1985) allowed the Secretary of State to designate particular dwelling types as inherently defective, and empowered local authorities to operate a Scheme of Assistance for all eligible owners, either by way of buy back or by way of repair.

Over 28,000 households were aided under the Scheme with only a small number of eligible properties taking no action.
Most ‘repairs’ were carried out using systems of reinstatement licensed, inspected and certificated by PRC Homes Ltd, a wholly owned subsidiary of NHBC, but not all owners used this route, and in addition some local auth –
orities carried out ‘partial repairs’ to their own stock which did not remove all the defective PRC structural elements from the dwelling. Surveyors encountering a house type which has been Designated Defective are therefore advised to check whether any ‘repairs’ carried out were in accordance with a PRC Homes Ltd licensed system, and certificated as such. 

Classified as defective by the Secretary of State under Part XV1 of the Housing Act 1985

Construction

• The ground floor external walls comprise storey height 225 x 100mm concrete columns which are at 1100mm centres. The columns are rebated to receive thin concrete wall panels which are stitch bonded internally and externally to form a cavity wall.
  On some units the internal leaf is replaced with a thin breeze block or plasterboard panel.
• The wall construction sits on a plinth unit and is capped off with a coping unit at first floor.
• The first floor accommodation is located within a timber framed mansard roof with sloping tiled walls externally and plasterboard internally.
• The party wall is of blockwork and the partitions are also generally of blockwork although some walls can be of stud.
• The roof material and wall insulation fabric used during this time contained asbestos, which was frequently used in the building trade of the time, Wooden frame-based construction means that as the concrete decays with age, the two parts tend to separate, resulting in large amounts of internal cracking.
• The design was so successful that over 30,000 Cornish Unit Type I & II houses were eventually constructed.

Major defects found in some of these properties include:

• Horizontal and vertical cracking of PRC columns

• High rates of carbonation and significant levels of chloride in PRC columns

• Cracking of first floor ring beams