Historical Context and Manufacturing

The Siporex 6M house, also known as the Costain Siporex, is a notable example of system-built properties that emerged in the UK during the 1960s. These homes were manufactured by R Costain (Construction) Ltd, a company renowned for its innovative approach to construction during that era. The Siporex 6M houses were part of a broader movement to address the post-war housing shortage, leveraging modern construction techniques to expedite the building process and reduce costs.

Approximately 900 Siporex 6M houses were built, primarily in the 1960s. These properties can be found in various locations across the UK, often in suburban areas where there was a significant demand for affordable housing. The design and construction of these homes were documented in publications such as Architect & Building News in March 1964 and September 1967, highlighting their significance in the architectural landscape of the time.

Design and Construction Characteristics

Architectural Features

Siporex 6M houses are typically bungalows or two- and three-storey terraced houses. They are easily identifiable by their shallow pitch gable, monopitch, or flat roofs, which are usually covered with bituminous felt or asphalt. The external walls are constructed from storey-height lightweight precast reinforced concrete (PRC) panels, sometimes featuring a sprayed finish. In some cases, parts of the front and rear walls are infilled with timber boarding, aluminium sheets, or tile hanging, adding to the distinctive appearance of these homes.

Structural Components

Substructure

The substructure of Siporex 6M houses consists of concrete strip footings, reinforced concrete (RC) ground beams, and a concrete slab. A damp-proof course (DPC) is also included to prevent moisture ingress from the ground.

External Walls

The external walls are made from storey-height 2′ x 8″ lightweight PRC panels. These panels are connected using 1/4″ galvanised mild steel (MS) dowel bars and sand/cement grout. Horizontal continuity reinforcement and precast (PC) lintels are used to enhance structural integrity. A 6″ x 3″ PRC flush string course and 1/4″ cranked continuity reinforcement are also typical features.

Separating Walls

Separating walls between properties are constructed from storey-height 4″ lightweight PRC panel cavity walls, providing both structural support and sound insulation.

Partitions

Internal partitions are made from storey-height lightweight concrete panels, ensuring a consistent and robust internal structure.

Floors

The ground floor is typically a concrete slab, while the upper floors are constructed from 6″ lightweight PRC floor planks. These planks provide a solid and durable flooring solution.

Ceilings

Ceilings in Siporex 6M houses are often finished with Artex, a textured coating that was popular during the period of construction.

Roof

The roof structure consists of 6″ lightweight PRC floor planks, covered with a sand/cement screed and asphalt. This combination provides a durable and weather-resistant roofing solution.

Variants

There are several variants of the Siporex 6M house, which include different materials and finishes for the external walls and roof. Some properties feature storey-height timber frame panels clad with timber boarding, aluminium sheets, or tile hanging. Others have external walls made from storey-height 6″ PRC panels with a sprayed finish of Stonite, Marmonite, or Kenitex. Galvanised rolled steel angle (RSA) lintels and bituminous felt roof coverings are also common variants.

Typical Hazards and Risks

Structural Defects

One of the primary concerns with Siporex 6M houses is the potential for structural defects, particularly in the PRC floor and roof planks. Over time, these components can experience excessive deflections, leading to issues such as sagging floors and roofs. This can compromise the structural integrity of the property and may require significant remedial work to address.

Deterioration of PRC Panels

The lightweight PRC panels used in the construction of Siporex 6M houses are susceptible to deterioration over time. Factors such as moisture ingress, freeze-thaw cycles, and chemical reactions can cause the concrete to degrade, leading to cracks and spalling. This can weaken the structural elements of the property and may necessitate repairs or replacement of the affected panels.

Thermal Performance

The thermal performance of Siporex 6M houses can be a concern, particularly in properties with minimal insulation. The lightweight PRC panels and other construction materials used in these homes may not provide adequate thermal resistance, leading to higher energy consumption for heating and cooling. Retrofitting insulation and upgrading windows and doors can help improve the energy efficiency of these properties.

Moisture Ingress

Moisture ingress is another common issue in Siporex 6M houses, particularly in properties with flat roofs or inadequate damp-proofing measures. Water penetration can lead to issues such as dampness, mould growth, and timber decay, which can affect the health and safety of occupants. Regular maintenance and timely repairs are essential to prevent and address moisture-related problems.

Defective Premises Act Considerations

The Defective Premises Act 1972 imposes a duty on builders, developers, and landlords to ensure that properties are constructed and maintained to a reasonable standard. While Siporex 6M houses were built to the standards of their time, some of the construction methods and materials used may not meet modern standards. As a result, these properties may be considered defective under the Act if they pose a risk to the health and safety of occupants.

Homebuyers and investors should be aware of the potential for defects in Siporex 6M houses and consider obtaining a thorough building survey before purchasing. A detailed survey can identify any issues and provide recommendations for remedial work, helping to ensure that the property meets current safety standards.

Inspection Tips for Surveyors

When inspecting a Siporex 6M house, surveyors should pay close attention to the following areas:

External Walls

Inspect the external walls for signs of cracking, spalling, or other forms of deterioration. Pay particular attention to the joints between PRC panels and any areas where different materials meet, as these can be prone to movement and moisture ingress.

Roof

Examine the roof for signs of sagging, deflection, or water penetration. Check the condition of the bituminous felt or asphalt covering and look for any areas where repairs may be needed. Flat roofs should be inspected for ponding water and potential leaks.

Floors

Check the floors for excessive deflection or unevenness, which can indicate issues with the PRC floor planks. Look for signs of cracking or movement in the concrete slab on the ground floor.

Internal Partitions

Inspect internal partitions for signs of movement or cracking, particularly around doorways and other openings. Ensure that the partitions are providing adequate support and sound insulation.

Moisture and Dampness

Look for signs of moisture ingress and dampness, particularly in areas such as basements, ground floors, and around windows and doors. Check for mould growth, peeling paint, or other indicators of moisture problems.

Thermal Performance

Assess the thermal performance of the property by checking for draughts, cold spots, and inadequate insulation. Consider recommending upgrades to improve energy efficiency, such as adding insulation to walls and roofs or replacing single-glazed windows with double glazing.

Typical Defects and Remedial Measures

Excessive Deflections in PRC Floor and Roof Planks

Excessive deflections in PRC floor and roof planks can be addressed by reinforcing the affected areas or replacing the planks with modern materials. Structural engineers should be consulted to determine the best course of action and ensure that any remedial work meets current building standards.

Deterioration of PRC Panels

Deterioration of PRC panels can be addressed by repairing or replacing the affected panels. This may involve removing damaged sections of concrete, treating any exposed reinforcement, and applying a suitable repair mortar. In some cases, it may be necessary to replace entire panels to ensure the structural integrity of the property.

Moisture Ingress and Dampness

Moisture ingress and dampness can be addressed by improving the property’s damp-proofing measures. This may involve repairing or replacing the DPC, installing a damp-proof membrane, or applying a waterproof coating to external walls. Addressing any roof leaks and ensuring proper drainage around the property can also help prevent moisture-related issues.

Thermal Performance Upgrades

Improving the thermal performance of a Siporex 6M house can involve several measures, such as adding insulation to walls, roofs, and floors, upgrading windows and doors, and installing energy-efficient heating and cooling systems. These upgrades can help reduce energy consumption and improve the comfort of the property.

Conclusion

The Siporex 6M house is a unique and historically significant example of system-built housing in the UK. While these properties offer a range of benefits, including affordability and distinctive architectural features, they also come with potential risks and challenges. Homebuyers and investors should be aware of the typical defects associated with Siporex 6M houses and consider obtaining a thorough building survey before making a purchase.

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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