Introduction to the Keyhouse Unibuilt House

The Keyhouse Unibuilt house is a unique and intriguing property type that emerged in the post-World War II era. Designed by Richard Sheppard and G Grey Wornum, these houses were constructed in 1946 by Keyhouse Unibuilt Ltd. Only four of these properties were built, making them a rare find in the UK property market. This article aims to provide a detailed overview of the Keyhouse Unibuilt house, including its construction, typical characteristics, potential hazards, and considerations for buyers and investors.

Historical Context and Manufacturing Details

Period and Location

The Keyhouse Unibuilt houses were constructed in 1946, a time when the UK was grappling with a severe housing shortage following World War II. These houses were part of the broader movement towards system-built properties, which aimed to provide quick and affordable housing solutions. Although only four of these houses were built, they are typically found in suburban areas where post-war housing developments were common.

Manufacturers and Designers

Keyhouse Unibuilt Ltd was the manufacturer behind these unique properties. The design was a collaborative effort between Richard Sheppard and G Grey Wornum, both of whom were prominent figures in the architectural world at the time. Their design aimed to balance functionality with the aesthetic needs of the post-war British family.

Identification Characteristics

Structural Features

The Keyhouse Unibuilt house is a two-storey semi-detached property. One of its most distinctive features is the flat roof covered with bituminous felt. The external walls are made of painted asbestos cement trays, which are narrow at the corners and at the separating wall. The windows and doors are trimmed with PS (polystyrene) materials, and a flat canopy on tubular supports is positioned over the front door.

Alternative Names

While the Keyhouse Unibuilt house is the most commonly used name, these properties may also be referred to by their design or construction features. However, due to their rarity, they are generally recognized by their original name.

Construction Details

Substructure

The substructure of the Keyhouse Unibuilt house consists of concrete strip footings and a vented brick underbuilding. A PRC (precast reinforced concrete) edge beam is used, along with honeycomb brick internal sleeper walls. The structure also includes a damp-proof course (DPC) to prevent moisture ingress.

Frame

The frame is constructed from eaves-height cold-rolled steel channel (RSC) panels. Each panel is formed with three double vertical members and horizontal and diagonal bracings welded between the verticals. Corner units have four vertical members at the corner edge. The frame also includes four rolled steel angle (RSA) perimeter ties and cold-rolled steel channel double horizontal member floor and roof joists.

Protective Coating

The frame is protected with a stove-enamelled coating, which provides a durable and long-lasting finish.

External Walls

The external walls are clad with painted asbestos cement trays filled with woodwool slabs. These are lined with plasterboard on timber noggins, and the joints are masked with flat steel cover strips. The corners and separating walls feature narrow trays.

Separating Wall

The separating wall is a woodwool slab cavity wall, backed and lined with laminated plasterboard. This design provides both structural integrity and sound insulation between the semi-detached units.

Partitions

The internal partitions are made from PSC (precast concrete) studs lined with plasterboard, providing a robust and fire-resistant internal structure.

Floors

The ground floor consists of timber boarding on timber joists, with PRC slabs in the hall and kitchen areas. The first floor features PRC slabs on timber bearers, providing a solid and durable flooring solution.

Ceilings

The ceilings are made from plasterboard, which is a common and cost-effective material for residential properties.

Roof

The roof is constructed from PRC slabs, timber boarding, and bituminous felt. A PC (precast concrete) coping is used around the perimeter to provide additional protection and aesthetic appeal.

Typical Hazards and Risks

Corrosion

One of the most significant risks associated with Keyhouse Unibuilt houses is corrosion. Severe corrosion can occur with complete loss of section to RSC stanchions and bracings, particularly at the bases. Corrosion can also affect the cladding panel fixing clips, internal PS trims around windows, and conduit and socket boxes.

Lack of Insulation and Ventilation

These houses typically lack insulation and ventilation in the roof space, which can lead to issues with dampness and energy efficiency. The absence of proper insulation can result in higher heating costs and a less comfortable living environment.

Deterioration of PRC Elements

The PRC floor slabs and edge beams can deteriorate over time, leading to structural issues. Movement in the PC coping around the roof perimeter is also a common problem, which can affect the overall stability of the roof structure.

Asbestos

The use of asbestos cement trays in the external walls poses a significant health risk. Asbestos is a hazardous material that can cause serious respiratory issues if disturbed. It is essential to handle any renovation or repair work involving asbestos with extreme caution.

Defective Premises Act Considerations

The Keyhouse Unibuilt house is not classed as defective under the Defective Premises Act. However, the potential hazards and risks associated with these properties mean that buyers and investors should exercise caution. A thorough building survey is essential to identify any issues and ensure the property is safe and habitable.

Inspection Tips for Surveyors

Corrosion Checks

When inspecting a Keyhouse Unibuilt house, it is crucial to check for signs of corrosion. Pay particular attention to the RSC stanchions and bracings, especially at the bases. Also, inspect the cladding panel fixing clips, internal PS trims around windows, and conduit and socket boxes for any signs of rust or deterioration.

Insulation and Ventilation

Check the roof space for insulation and ventilation. The absence of these elements can lead to dampness and energy inefficiency. If insulation is lacking, consider recommending the installation of modern insulation materials to improve the property’s energy performance.

PRC Elements

Inspect the PRC floor slabs and edge beams for signs of deterioration. Look for cracks, spalling, or other signs of damage that could compromise the structural integrity of the property. Also, check the PC coping around the roof perimeter for any movement or instability.

Asbestos Management

Given the presence of asbestos cement trays in the external walls, it is essential to handle any inspection or repair work involving asbestos with care. If asbestos is found, recommend that the property owner consults a specialist asbestos removal company to safely manage and remove the material.

Typical Defects in Keyhouse Unibuilt Houses

Structural Defects

Structural defects are common in Keyhouse Unibuilt houses due to the materials and construction methods used. Corrosion of the steel frame and deterioration of the PRC elements can lead to significant structural issues. Regular maintenance and timely repairs are essential to prevent these defects from worsening.

Dampness and Condensation

The lack of insulation and ventilation in the roof space can lead to dampness and condensation issues. These problems can cause damage to the internal finishes and create an unhealthy living environment. Installing proper insulation and ventilation can help mitigate these issues.

Asbestos-Related Issues

Asbestos-related issues are a significant concern in Keyhouse Unibuilt houses. The presence of asbestos cement trays in the external walls poses a health risk if disturbed. It is essential to manage and remove asbestos safely to prevent exposure to harmful fibres.

Energy Efficiency

Due to the lack of insulation, Keyhouse Unibuilt houses are often not energy-efficient. This can result in higher heating costs and a less comfortable living environment. Upgrading the insulation and installing energy-efficient windows and doors can help improve the property’s energy performance.

Variants and Modifications

Canopy Variants

Some Keyhouse Unibuilt houses feature a cantilevered canopy over the front door instead of the flat canopy on tubular supports. This variant provides additional protection from the elements and can enhance the property’s aesthetic appeal.

Modern Modifications

Many Keyhouse Unibuilt houses have undergone modern modifications to improve their functionality and energy efficiency. Common modifications include the installation of modern insulation, energy-efficient windows and doors, and updated heating systems. These modifications can enhance the property’s value and make it more appealing to buyers and investors.

Conclusion

The Keyhouse Unibuilt house is a unique and rare property type with a rich history and distinctive characteristics. While these houses offer a glimpse into the post-war housing solutions of the 1940s, they also come with potential hazards and risks that buyers and investors should be aware of. A thorough building survey is essential to identify any issues and ensure the property is safe and habitable. By understanding the construction details, typical defects, and inspection tips, buyers and investors can make informed decisions when considering a Keyhouse Unibuilt house.

At Flettons, we’re committed to safeguarding your investment. When considering a property purchase, trust our seasoned expertise to reveal any hidden threats. For a thorough building survey, get your instant quote through our quote calculator or reach out directly at 0203 691 0451. Your home’s safety is our top priority.

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