The Evolution of Open System Building Houses

Open System Building houses, often referred to as OSB, Poulson, or Dare houses, represent a unique chapter in the UK’s architectural history. These properties were constructed between 1967 and 1970, a period marked by a surge in innovative building techniques aimed at addressing the post-war housing shortage. Designed by J G L Poulson and manufactured by Open System Building Ltd, approximately 500 of these homes were built. Predominantly found in urban areas, these houses are typically two-storey semi-detached or terraced homes.

Key Characteristics and Construction Details

The Open System Building houses are distinguished by their shallow pitch gable roofs, which are covered with interlocking concrete tiles. The front and rear external walls are constructed using storey-height precast reinforced concrete (PRC) panels. These panels are infilled with asbestos cement sheets up to the ground floor window sill level, with PVC boarding above. The gable walls are either made of brick or PRC panels, which return around the corners of the front and rear walls. The exposed edges of the PRC slabs are coated with bitumen for protection.

Structural Components

• Substructure: These houses are built on a concrete raft foundation, which is thickened around the perimeter. This design provides a stable base for the structure.
• Frame: The frame consists of three precast concrete (PSC) stanchions, five PSC floor support beams, and four PSC perimeter beams. The frame is protected with a galvanised coating to prevent corrosion.
• External Walls: The front and rear walls are timber frame panels clad with PRC panels. These are lined with polystyrene-backed plasterboard and foil-backed plasterboard. The panels incorporate doors and windows, with asbestos cement sheets and PVC boarding used for cladding.
• Gable Walls: These are constructed from brick and block cavity walls, with brick returns around the corners. They are lined with plasterboard for a finished look.
• Separating Walls: Block cavity walls lined with plasterboard are used to separate different sections of the house.
• Partitions: Internal partitions are made from strawboard, a lightweight and cost-effective material.
• Floors: The ground floor is concrete, while the first floor features tongue and groove boarding on timber joists.
• Ceilings: The ground floor ceilings are made from two layers of plasterboard, while the first floor uses polystyrene-backed plasterboard.
• Roof: The roof structure consists of timber trusses, bituminous felt, and interlocking concrete tiles.

Typical Defects and Hazards

While Open System Building houses were innovative for their time, they are not without their challenges. Some common defects include:

• Cracking and Bowing of PRC Panels: The front and rear walls often exhibit severe cracking and bowing, which can compromise structural integrity.
• Missing Concrete Pads: Some gable walls lack the necessary concrete pads to support beams, leading to potential stability issues.
• Uneven Floors: The timber boarding over PSC support beams can result in uneven floors, affecting the overall comfort and usability of the space.

Inspection Tips for Surveyors

When inspecting an Open System Building house, surveyors should pay close attention to the following areas:

• Steelwork Condition: Ensure that the steelwork is in good condition, as corrosion can lead to significant structural problems.
• Concrete Pads: Check for the presence of concrete pads supporting the beams, particularly in gable walls.
• PRC Panels: Look for signs of cracking or bowing in the PRC panels, which may indicate underlying issues.
• Floor Levels: Assess the evenness of the floors, especially where timber boarding passes over PSC support beams.

Legal Considerations: Defective Premises Act

Under the Defective Premises Act, properties must be fit for habitation. Open System Building houses, due to their construction methods and materials, may be classified as defective if they exhibit significant structural issues. It is crucial for potential buyers to conduct thorough surveys and seek expert advice to ensure compliance with legal standards.

Variants and Adaptations

Some Open System Building houses feature variants in their construction. For instance, PRC panels in gable walls may be supported by additional PSC stanchions and beams. Internal partitions might be made from honeycomb plasterboard, offering a different aesthetic and functional quality.

The Role of Open System Building Houses in Modern Housing

Despite their age, Open System Building houses continue to play a role in the UK’s housing landscape. Their unique construction and historical significance make them an intriguing option for buyers and investors. However, it is essential to approach these properties with a clear understanding of their potential risks and necessary maintenance.

Modern Considerations for Open System Building Houses

In today’s housing market, Open System Building houses present both opportunities and challenges. For investors, these properties can offer a unique investment opportunity due to their historical significance and distinctive architectural style. However, it is crucial to consider the potential costs associated with repairs and maintenance.

Renovation and Modernisation

Renovating an Open System Building house can be a rewarding endeavour, allowing homeowners to blend historical charm with modern amenities. Key areas to focus on during renovation include:

• Asbestos Removal: Given the use of asbestos cement sheets in the original construction, it is vital to safely remove and replace these materials with modern alternatives.
• Energy Efficiency: Upgrading insulation and installing energy-efficient windows can significantly improve the property’s energy performance.
• Structural Reinforcement: Addressing any structural issues, such as reinforcing PRC panels or adding missing concrete pads, is essential for long-term stability.

Community and Environmental Impact

Open System Building houses are often located in established communities, offering a sense of history and belonging. When considering purchasing or renovating one of these properties, it is important to engage with the local community and consider the environmental impact of any changes.

Financing and Insurance Considerations

Securing financing and insurance for an Open System Building house can be more complex than for traditional properties. Lenders and insurers may require additional surveys or impose specific conditions due to the unique construction methods and potential defects. It is advisable to work with professionals who have experience with non-standard construction types to navigate these challenges effectively.

Future Prospects for Open System Building Houses

As the UK continues to evolve, the future of Open System Building houses will depend on the balance between preserving their historical value and adapting them for modern living. With careful planning and expert guidance, these properties can continue to serve as functional and cherished homes for years to come.

Conclusion

Open System Building houses offer a fascinating glimpse into a pivotal era of British architecture. While they present certain challenges, they also offer unique opportunities for those willing to invest in their preservation and modernisation. By understanding their construction, potential defects, and legal considerations, buyers and investors can make informed decisions about these distinctive properties.

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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