The MOW Demonstration Foamed Slag house stands as a unique relic of post-war British architecture. Designed by the Ministry of Works in the 1940s, this property type is a rare find, with only two known examples ever built. For home buyers and investors, understanding the intricacies of this construction can be both fascinating and crucial. This article delves into the history, construction, and potential risks associated with the MOW Demonstration Foamed Slag house, providing a thorough guide for those considering such a property.

Historical Context and Manufacturing

The MOW Demonstration Foamed Slag house emerged in the 1940s, a period marked by a desperate need for housing solutions in post-war Britain. The Ministry of Works, responsible for the design, sought innovative construction methods to address the housing shortage. The use of foamed slag aggregate concrete was a novel approach, aimed at creating durable and cost-effective homes.

Manufacturer and Designer

The Ministry of Works, a government body, was the primary designer and overseer of the construction of these houses. The actual manufacturing process involved the use of foamed slag, a byproduct of steel manufacturing, which was mixed with concrete to create a lightweight yet sturdy building material. This innovative use of materials was part of a broader effort to explore alternative construction methods during a time of resource scarcity.

Typical Locations

Given the limited number of these houses built, their locations are not widespread. The two known examples are likely situated in areas where the Ministry of Works conducted experimental housing projects. These locations would have been chosen for their suitability for testing new construction methods and materials.

Characteristics and Identification

Identifying a MOW Demonstration Foamed Slag house involves recognizing several distinct features. These properties are two-storey semi-detached houses with a steep pitch gable roof covered with tiles. The external walls are rendered throughout, giving them a uniform appearance.

Construction Details

Understanding the construction of these houses is essential for assessing their condition and potential risks. Here is a detailed breakdown of the typical construction elements:

Substructure

• Concrete strip footings: These provide a stable foundation for the house.
• Dense concrete underbuilding: This adds to the structural integrity.
• Concrete slab: Forms the base of the ground floor.
• Damp Proof Course (DPC): Prevents moisture from rising through the structure.

External Walls

• Rendered finish: Provides a protective and aesthetic outer layer.
• 8″ foamed slag aggregate concrete: The primary material used for the walls.
• 3/8″ continuous bar reinforcement: Embedded in cement mortar, this reinforcement is placed 2″ above door head height on the ground floor and above the head of gable wall windows on the first floor.

Internal Walls and Partitions

• Separating wall: Made of foamed slag aggregate concrete.
• Partitions: Also constructed from 4″ foamed slag aggregate concrete.

Floors

• Ground floor: Wood blocks laid on concrete.
• First floor: Timber boarding on timber joists.

Roof

• Timber rafters and purlins: Provide the structural framework.
• Tiles: Cover the roof, offering protection from the elements.

Variants

No known variants of the MOW Demonstration Foamed Slag house exist, making each example a unique piece of architectural history.

Typical Hazards and Risks

While the innovative use of foamed slag aggregate concrete was a significant advancement, it also introduced certain risks and potential defects. Understanding these hazards is crucial for anyone considering purchasing or investing in such a property.

Structural Integrity

One of the primary concerns with foamed slag aggregate concrete is its long-term durability. Over time, the material can suffer from degradation, particularly if exposed to moisture. This can lead to structural weaknesses, which may require extensive repairs.

Corrosion of Reinforcement

The 3/8″ continuous bar reinforcement embedded in the walls is susceptible to corrosion, especially if the concrete’s protective properties are compromised. Corrosion can lead to cracking and spalling of the concrete, further weakening the structure.

Moisture Ingress

Despite the presence of a Damp Proof Course (DPC), moisture ingress can still be a problem, particularly if the DPC has been damaged or compromised. Moisture can lead to a range of issues, including mold growth, wood rot, and further degradation of the concrete.

Thermal Insulation

The thermal insulation properties of foamed slag aggregate concrete are not well-documented. As a result, these houses may suffer from poor energy efficiency, leading to higher heating costs and potential discomfort for occupants.

Classification Under the Defective Premises Act

The Defective Premises Act 1972 imposes a duty on builders, developers, and landlords to ensure that properties are fit for habitation. Given the potential structural issues and risks associated with the MOW Demonstration Foamed Slag house, it is possible that these properties could be classified as defective under the Act. This classification would necessitate remedial action to ensure the property meets modern safety and habitability standards.

Inspection and Assessment Guide

For surveyors and potential buyers, conducting a thorough inspection of a MOW Demonstration Foamed Slag house is essential. Here are some key areas to focus on during an inspection:

External Walls

• Check for cracks and spalling: Look for signs of concrete degradation, particularly around areas with reinforcement.
• Assess the render: Ensure the render is intact and providing adequate protection against moisture ingress.

Roof

• Inspect the tiles: Check for any missing or damaged tiles that could lead to water ingress.
• Examine the timber rafters and purlins: Look for signs of wood rot or structural weakness.

Floors

• Ground floor: Check the condition of the wood blocks and the underlying concrete slab.
• First floor: Inspect the timber boarding and joists for any signs of damage or weakness.

Internal Walls and Partitions

• Look for cracks: Cracks in the foamed slag aggregate concrete could indicate structural issues.
• Check for moisture: Use a moisture meter to detect any signs of dampness within the walls.

Reinforcement

• Assess for corrosion: Look for signs of rust or corrosion on any exposed reinforcement bars.

Thermal Insulation

• Evaluate energy efficiency: Consider conducting a thermal imaging survey to assess the insulation properties of the walls and roof.

Typical Defects and Maintenance

Understanding the common defects associated with the MOW Demonstration Foamed Slag house can help in planning maintenance and repairs. Here are some typical issues and how to address them:

Concrete Degradation

• Repair cracks and spalling: Use appropriate concrete repair techniques to address any areas of degradation.
• Apply protective coatings: Consider applying a protective coating to the external walls to enhance durability and resistance to moisture.

Corrosion of Reinforcement

• Treat and repair corroded bars: Remove any rust and apply corrosion inhibitors to the reinforcement bars. Repair the surrounding concrete as needed.

Moisture Ingress

• Address DPC issues: If the Damp Proof Course is compromised, consider installing a new DPC or using chemical damp-proofing methods.
• Improve drainage: Ensure proper drainage around the property to prevent water from accumulating near the foundations.

Thermal Insulation

• Upgrade insulation: Consider adding external or internal insulation to improve the thermal performance of the property.
• Seal gaps and drafts: Ensure windows, doors, and other openings are properly sealed to prevent heat loss.

Conclusion

The MOW Demonstration Foamed Slag house represents a unique chapter in British architectural history. While these properties offer a fascinating glimpse into post-war construction innovation, they also come with certain risks and challenges. For home buyers and investors, understanding these aspects is crucial for making informed decisions.

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.

---