Historical Context and Background

The MOW Demonstration Expanded Clay house, also known as the Expanded Clay house, is a unique and rare property type in the UK. Designed by the Ministry of Works, these houses were constructed in the 1940s as part of a post-war effort to address the housing shortage. Only two of these properties were ever built, making them a rare find in today’s property market.

The Ministry of Works, responsible for the design and construction, aimed to create a durable and cost-effective housing solution using innovative materials and construction techniques. The use of expanded clay aggregate concrete was a significant departure from traditional building materials, offering a lightweight yet strong alternative.

Typical Characteristics and Identification

External Features

The MOW Demonstration Expanded Clay houses are two-storey semi-detached properties with a steep pitch gable roof covered with tiles. The external walls are rendered throughout, giving the houses a distinctive appearance. The use of expanded clay aggregate concrete for the walls is a key identifying feature.

Internal Features

Internally, the houses feature concrete strip footings, dense concrete underbuilding, and a concrete slab with a damp-proof course (DPC). The ground floor is made of concrete, while the first floor consists of timber boarding on timber joists. The roof structure comprises timber rafters and tiles.

Reinforcement and Durability

One of the unique aspects of these houses is the use of continuous bar reinforcement surrounded by cement mortar. This reinforcement is present 2 inches above door head height and above the head of gable wall windows on the first floor. The separating walls and partitions are also made of expanded clay aggregate concrete, providing additional strength and durability.

Construction Details

Substructure

The substructure of the MOW Demonstration Expanded Clay house includes concrete strip footings and dense concrete underbuilding. A concrete slab with a damp-proof course (DPC) ensures protection against rising damp.

External Walls

The external walls are rendered and consist of 8-inch expanded clay aggregate concrete. The continuous bar reinforcement surrounded by cement mortar provides additional structural integrity.

Separating Walls and Partitions

The separating walls are made of 8-inch expanded clay aggregate concrete, while the internal partitions are 4 inches thick. This construction method ensures robust and durable internal walls.

Floors

The ground floor is constructed of concrete, providing a solid and stable base. The first floor features timber boarding on timber joists, offering a traditional yet effective flooring solution.

Roof

The roof structure comprises timber rafters and tiles, with a steep pitch gable design. This design not only adds to the aesthetic appeal but also ensures effective water drainage.

Typical Hazards and Risks

Structural Issues

One of the primary concerns with the MOW Demonstration Expanded Clay houses is the potential for structural issues. The use of expanded clay aggregate concrete, while innovative, may present challenges in terms of long-term durability and stability. Continuous bar reinforcement, if not properly maintained, can lead to corrosion and weakening of the structure.

Damp and Moisture

Despite the presence of a damp-proof course (DPC), these houses may still be susceptible to damp and moisture issues. The concrete slab and dense concrete underbuilding can absorb moisture, leading to potential problems with rising damp.

Insulation and Energy Efficiency

Given the era in which these houses were built, insulation and energy efficiency may not meet modern standards. The use of expanded clay aggregate concrete, while providing some thermal mass, may not offer sufficient insulation, leading to higher energy costs.

Defective Premises Act Considerations

The MOW Demonstration Expanded Clay houses are not classified as defective under the Defective Premises Act. However, given their age and unique construction, it is essential to conduct thorough inspections and assessments to identify any potential issues.

Inspection and Assessment Guide

External Inspection

When inspecting a MOW Demonstration Expanded Clay house, start with a thorough external inspection. Look for signs of cracking or deterioration in the rendered external walls. Pay particular attention to the areas around windows and doors, where continuous bar reinforcement is present.

Roof Inspection

Inspect the roof for any signs of damage or wear. Check the condition of the tiles and timber rafters, and ensure that the steep pitch gable design is effectively draining water.

Internal Inspection

Inside the house, check for signs of damp or moisture, particularly on the ground floor. Inspect the concrete slab and dense concrete underbuilding for any signs of rising damp. Examine the timber boarding on the first floor for any signs of rot or damage.

Structural Assessment

Conduct a thorough structural assessment, focusing on the expanded clay aggregate concrete walls and continuous bar reinforcement. Look for signs of corrosion or weakening in the reinforcement, and assess the overall stability of the structure.

Insulation and Energy Efficiency

Evaluate the insulation and energy efficiency of the house. Given the age and construction materials, it may be necessary to upgrade insulation to meet modern standards.

Typical Defects and Maintenance

Cracking and Deterioration

Cracking and deterioration in the rendered external walls are common issues with MOW Demonstration Expanded Clay houses. Regular maintenance and repairs are essential to prevent further damage and ensure the structural integrity of the property.

Corrosion of Reinforcement

Corrosion of the continuous bar reinforcement can weaken the structure and pose significant risks. Regular inspections and maintenance are crucial to identify and address any signs of corrosion.

Damp and Moisture

Damp and moisture issues, particularly on the ground floor, can lead to significant problems if not addressed promptly. Ensure that the damp-proof course (DPC) is functioning effectively and consider additional measures to prevent rising damp.

Insulation Upgrades

Given the age and construction materials, upgrading insulation is often necessary to improve energy efficiency and reduce heating costs. Consider modern insulation solutions that are compatible with the unique construction of the house.

Conclusion

The MOW Demonstration Expanded Clay house is a unique and rare property type with a rich history and distinctive characteristics. While these houses offer a fascinating glimpse into post-war construction innovation, they also present specific challenges and risks. Thorough inspections and assessments are essential to identify and address any potential issues, ensuring the long-term durability and safety of the property.

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.