Introduction to the Bison Wall Frame House

The Bison Wall Frame house, also known as the Bryant or Bryant Wall Frame house, is a distinctive type of system-built property that emerged in the UK during the 1960s and 1970s. These homes were part of a broader movement towards prefabricated construction methods, aimed at addressing the post-war housing shortage. Designed by Clifford Culpin and Partners and manufactured by Concrete Ltd, these properties are notable for their unique construction techniques and materials.

In this article, we will delve into the history, characteristics, and common issues associated with Bison Wall Frame houses. We will also provide practical advice for inspecting these properties, ensuring that potential buyers and investors are well-informed about what to expect.

Historical Context and Manufacturing Details

Period of Construction

Bison Wall Frame houses were predominantly built between the 1960s and 1970s. This period was marked by a significant demand for affordable housing, leading to the adoption of various system-built methods. The Bison Wall Frame system was one of the solutions developed to meet this demand, offering a quick and cost-effective way to construct homes.

Manufacturers and Designers

The primary manufacturer of Bison Wall Frame houses was Concrete Ltd, a company known for its expertise in precast concrete products. The design of these homes was spearheaded by Clifford Culpin and Partners, a firm that played a crucial role in the development of several system-built housing solutions during this era.

Number Built and Typical Locations

While exact numbers are difficult to ascertain, it is estimated that thousands of Bison Wall Frame houses were constructed across the UK. These homes were typically found in suburban areas, where there was a pressing need for new housing developments. They were often built as part of larger housing estates, providing affordable accommodation for families.

Characteristics of Bison Wall Frame Houses

Identification Characteristics

Bison Wall Frame houses are typically two-storey semi-detached or terraced properties. They can be identified by their medium pitch gable roofs, which are usually covered with concrete tiles, although some variants feature flat roofs. The external walls are constructed from storey-height concrete panels, giving these homes a distinctive appearance.

Construction Details

Substructure

The substructure of Bison Wall Frame houses is made from concrete, with a damp-proof course (DPC) to prevent moisture ingress.

External Walls

The front and rear walls are constructed from large, dense precast concrete (PC) panels, which are storey-height. These panels feature a cavity filled with 3/4″ polystyrene insulation and a polyethylene vapour control layer, finished with plasterboard on the interior. The gable walls are similarly constructed, with leaves bonded by phosphor bronze wall ties and polystyrene insulation in the cavity.

Separating Walls and Partitions

Separating walls between properties are made from 7″ dense precast reinforced concrete (PRC) panels. Internal partitions are constructed from storey-height PRC panels or timber stud walls lined with plasterboard.

Floors

The ground floor is typically made from concrete, while separating floors between storeys are constructed from 8 1/2″ hollow PRC slabs. Ceilings are either finished directly or with Artex.

Roof

The roof structure consists of large hollow core concrete slabs, although some variants feature timber roofs. In some cases, the ground floor may be a suspended timber construction.

Common Hazards and Risks

Carbonation and Chloride Content

One of the primary concerns with Bison Wall Frame houses is the high carbonation and variable chloride content of the precast concrete panels. Carbonation can lead to the corrosion of steel reinforcement within the concrete, compromising the structural integrity of the property. Chlorides, often introduced through de-icing salts or contaminated aggregates, can exacerbate this issue.

Missing Dry-Pack and Low Bearing Areas

Another common issue is the missing dry-pack beneath internal PC sandwich panels. This can result in low bearing areas, particularly at the roof beams, leading to structural weaknesses.

Hardboard Packing and Fine Cracking

Hardboard packing was often used to level units during construction. Over time, this material can deteriorate, leading to fine cracking in the PC panels. These cracks can allow moisture ingress, further compromising the structural integrity of the property.

Rain Penetration and Condensation

Rain penetration at windows is a frequent problem in Bison Wall Frame houses. This can lead to deterioration of window furniture and increased condensation within the property. Condensation can cause mould growth and damage to internal finishes, posing health risks to occupants.

Defective Premises Act and Bison Wall Frame Houses

Under the Defective Premises Act, properties that are deemed to be defective may be subject to specific legal requirements and obligations. Bison Wall Frame houses, due to their construction methods and materials, can sometimes fall under this category. It is essential for potential buyers and investors to be aware of this and to seek professional advice when considering the purchase of such properties.

Inspection Tips for Bison Wall Frame Houses

External Inspection

When inspecting a Bison Wall Frame house, start with a thorough external examination. Look for signs of cracking in the concrete panels, particularly around windows and doors. Check for any evidence of rain penetration or moisture ingress, such as staining or moss growth on the exterior walls.

Roof and Guttering

Inspect the roof for any missing or damaged tiles, and check the condition of the guttering and downpipes. Ensure that water is being effectively directed away from the property to prevent moisture-related issues.

Windows and Doors

Examine the windows and doors for signs of deterioration, such as rotting frames or corroded hardware. Check for any gaps or poor seals that could allow rainwater to penetrate the property.

Internal Inspection

Inside the property, look for signs of condensation or mould growth, particularly around windows and in corners of rooms. Check for any fine cracking in the walls and ceilings, which could indicate underlying structural issues.

Floors and Ceilings

Inspect the floors for any signs of movement or unevenness, which could suggest problems with the substructure. Check the ceilings for any signs of sagging or cracking, particularly if the property has a suspended timber ground floor.

Professional Survey

Given the potential issues associated with Bison Wall Frame houses, it is highly recommended to commission a professional survey before purchasing. A qualified surveyor will be able to identify any structural concerns and provide advice on necessary repairs or maintenance.

Typical Defects in Bison Wall Frame Houses

Structural Defects

Structural defects are a common concern in Bison Wall Frame houses. These can include issues such as cracking in the concrete panels, corrosion of steel reinforcement, and movement in the substructure. Addressing these defects can be costly, so it is essential to be aware of them before purchasing.

Moisture-Related Issues

Moisture-related issues, such as rain penetration and condensation, are also prevalent in these properties. These problems can lead to mould growth, deterioration of internal finishes, and health risks for occupants. Ensuring that the property is adequately ventilated and that any leaks are promptly addressed is crucial.

Window and Door Deterioration

The windows and doors in Bison Wall Frame houses are often prone to deterioration. This can include rotting frames, corroded hardware, and poor seals. Replacing or repairing these elements can improve the property’s energy efficiency and prevent further moisture ingress.

Insulation and Energy Efficiency

The insulation in Bison Wall Frame houses is typically limited to polystyrene within the cavity walls. This may not provide adequate thermal performance by modern standards, leading to higher energy bills and a less comfortable living environment. Upgrading the insulation can improve the property’s energy efficiency and reduce heating costs.

Conclusion

Bison Wall Frame houses represent a unique chapter in the history of UK housing. While they offer a distinctive architectural style and were a practical solution to the post-war housing shortage, they come with their own set of challenges. Understanding the construction methods, common defects, and potential risks associated with these properties is essential for any prospective buyer or investor.

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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