Historical Context and Manufacturing Details

The Foamed Slag house, also known as the No-Fines house, is a unique type of system-built property that emerged in the post-World War II era. These houses were constructed between 1946 and 1951, a period marked by a significant housing shortage in the UK. The government and private developers sought innovative construction methods to quickly and efficiently provide homes for the growing population. The Foamed Slag house was one such solution, with approximately 200 units built during this time.

Manufacturers and Designers

The primary manufacturers of Foamed Slag houses were local authorities and private developers who adopted the no-fines concrete technique. This method was designed to be cost-effective and quick to implement, making it an attractive option for post-war reconstruction. The designers of these houses aimed to create durable and affordable homes that could be constructed rapidly to meet the urgent housing needs of the time.

Typical Characteristics and Identification

Foamed Slag houses are typically two-storey semi-detached properties. They feature a medium pitch hipped roof covered with concrete tiles, built above a concrete flat roof that extends approximately 8 inches beyond the external walls. The external walls are either brick or rendered throughout, giving the houses a distinctive appearance. Some houses have a recessed front door, while others feature a flat-roofed precast concrete (PC) canopy over the front door.

Key Identification Characteristics

• Two-storey semi-detached houses
• Medium pitch hipped roof with concrete tiles
• Concrete flat roof extending 8 inches beyond external walls
• Brick or rendered external walls
• Recessed front door in some houses
• Flat-roofed PC canopy over front door in some houses

Construction Details

Understanding the construction details of Foamed Slag houses is crucial for potential buyers and investors. These houses were built using specific materials and techniques that have implications for their long-term durability and maintenance.

Substructure

The substructure of Foamed Slag houses consists of concrete strip footings and a concrete slab. The brick underbuilding provides additional support, and a damp-proof course (DPC) is included to prevent moisture ingress.

External Walls

The external walls are a defining feature of Foamed Slag houses. They are constructed using 9-inch foamed slag no-fines concrete, which is rendered for additional protection. The walls are reinforced with four reinforcing bars adjacent to the first-floor timber joists. Reinforced concrete (RC) ring beams are present at the first floor and eaves level, with two reinforcing bars at the base of the first-floor beam and three bars at the base of the eaves beam. A DPC cavity tray is installed over the first-floor joists to prevent moisture from penetrating the structure.

Separating Walls and Partitions

The separating walls between semi-detached units are not well-documented, but internal partitions are typically made of brick and concrete block. These materials provide adequate sound insulation and structural integrity.

Floors

The ground floor of Foamed Slag houses is constructed from concrete, providing a solid and durable base. The first floor consists of timber boarding on timber joists, which is a common construction method for houses of this era.

Ceilings and Roof

The ceilings in Foamed Slag houses are not well-documented, but the roof structure is notable. The original design featured a flat concrete slab, which has often been modified with timber rafters and concrete tiles. This modification helps improve the thermal performance and weather resistance of the roof.

Typical Hazards and Risks

While Foamed Slag houses were innovative for their time, they come with certain hazards and risks that potential buyers and investors should be aware of.

Vertical and Horizontal Cracking

One of the most common issues with Foamed Slag houses is vertical cracking of the render and foamed slag no-fines concrete external walls, particularly at window head level. Horizontal cracking can also occur at ground and first-floor levels. These cracks can compromise the structural integrity of the house and may require significant repairs.

Spalling of Render

Spalling, or the flaking and breaking off of render, is another common issue. This typically occurs at the corners of external walls and at ground floor lintel level. Spalling can expose the underlying concrete to the elements, leading to further deterioration.

Moisture Ingress

Despite the inclusion of a DPC and cavity tray, moisture ingress can still be a problem in Foamed Slag houses. This is particularly true if the DPC has been damaged or if the cavity tray is not functioning correctly. Moisture ingress can lead to damp issues, which can affect the internal environment and the structural integrity of the house.

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. Foamed Slag houses, given their age and the construction methods used, may be considered defective under this act if they exhibit significant structural issues or fail to meet modern building standards.

Inspection and Maintenance

Regular inspections and maintenance are crucial for ensuring the long-term durability of Foamed Slag houses. Potential buyers and investors should be aware of the common defects and take steps to address them promptly.

Inspection Guide for Surveyors

When inspecting a Foamed Slag house, surveyors should pay close attention to the following areas:

External Walls

• Check for vertical and horizontal cracking: Look for cracks in the render and foamed slag no-fines concrete, particularly at window head level and at ground and first-floor levels.
• Inspect for spalling: Examine the corners of external walls and ground floor lintel level for signs of spalling render.
• Assess moisture ingress: Check for signs of dampness, particularly around the DPC and cavity tray areas.

Roof and Ceilings

• Inspect the roof structure: Ensure that any modifications, such as the addition of timber rafters and concrete tiles, have been carried out correctly and are in good condition.
• Check for leaks: Look for signs of water ingress in the roof and ceiling areas.

Floors

• Examine the ground floor: Check for any signs of cracking or movement in the concrete slab.
• Inspect the first floor: Ensure that the timber boarding and joists are in good condition and free from rot or insect damage.

Internal Partitions

• Check for structural integrity: Ensure that brick and concrete block partitions are sound and free from significant cracks or movement.

Variants and Modifications

Foamed Slag houses may exhibit certain variants and modifications that can affect their condition and value.

Render and Reinforcement Variants

• Smooth render string course: Some houses feature a smooth render string course at ground floor and first-floor lintel levels.
• Lack of reinforcement: In some cases, the first-floor ring beam may lack reinforcement, which can affect the structural integrity of the house.

Brick and Concrete Variants

• Brick string course: Some houses have a brick string course overhanging a dense concrete plinth and floor slab.
• PC outstand string course: A precast concrete outstand string course may be present at ground floor lintel level, along with PC window sills.

Conclusion

Foamed Slag houses represent a unique chapter in the history of UK housing. While they were innovative and practical solutions for post-war housing shortages, they come with specific challenges and risks that potential buyers and investors must consider. Understanding the construction details, typical hazards, and maintenance requirements is crucial for making an informed decision.

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.

---