Historical Context and Origins

The Diatomite house, a unique and historically significant property type, emerged in the 1920s as part of the post-World War I housing boom in the UK. These houses were primarily constructed by the Manchester Housing Department, which also designed them. A total of 1,050 Diatomite houses were built, predominantly in the Manchester area. These properties were part of a broader effort to address the acute housing shortage of the time, providing affordable and durable homes for working-class families.

Identification Characteristics

Diatomite houses are typically two-storey semi-detached properties. They feature a medium pitch hipped or gable roof covered with slates. The external walls are rendered up to the first-floor window sill level, with brick or hollow terracotta blocks above. A distinctive brick stretcher course is present at the ground and first-floor window sill levels, as well as at the first-floor level. These characteristics make Diatomite houses relatively easy to identify for those familiar with their design.

Construction Details

Substructure

The substructure of Diatomite houses consists of concrete strip footings and brick under-building. The ground floor is typically a concrete slab, with a damp-proof course (DPC) to prevent moisture ingress.

External Walls

The external walls are a key feature of Diatomite houses. They are rendered and consist of 10-inch monolithically cast walls made from dense aggregate concrete, clinker aggregate concrete, and half-inch diatomite slabs up to the first-floor window sill level. Brick string courses are present at the ground floor window sill and first-floor levels. Above the first-floor window sill level, the walls are constructed from hollow terracotta blocks tied to 2-inch clinker concrete with wall ties, cast-in timber battens, and half-inch diatomite slabs. Reinforced concrete lintels are used over openings.

Internal Walls and Partitions

The internal walls and partitions of Diatomite houses vary between the ground and first floors. The ground floor partitions are made from clinker aggregate concrete with a brick skin and diatomite slabs on timber battens. The first-floor partitions consist of clinker aggregate concrete and diatomite slabs on timber battens.

Floors

The ground floor is typically concrete, while the first floor features timber boarding on timber joists supported by a brick stringer course.

Roof

The roof structure of Diatomite houses comprises timber rafters and purlins, covered with slates. This traditional roofing method provides durability and weather resistance.

Typical Hazards and Risks

Vertical and Horizontal Cracking

One of the most common issues with Diatomite houses is vertical and horizontal cracking of the concrete external walls. Vertical cracks often appear due to settlement or thermal movement, while horizontal cracks are typically found above window openings and are caused by the corrosion of reinforcement.

Corrosion of Reinforcement

The reinforcement within the concrete walls of Diatomite houses is prone to corrosion. This is often due to the high carbonation levels in the dense aggregate concrete and the high sulfate content of the clinker concrete. Corrosion can lead to structural weaknesses and further cracking.

Carbonation and Sulfate Content

The concrete used in Diatomite houses is fully carbonated, which can reduce its alkalinity and lead to the corrosion of embedded steel reinforcement. Additionally, the high sulfate content of the clinker concrete can cause sulfate attack, leading to expansion and cracking of the concrete.

Defective Premises Act

Diatomite houses are not specifically listed as defective under the Defective Premises Act. However, the issues related to cracking, reinforcement corrosion, and carbonation can lead to significant structural problems. It is essential for potential buyers and investors to be aware of these risks and to commission a thorough building survey before purchasing a Diatomite house.

Inspection Guide for Surveyors

External Inspection

1. Walls: Inspect the external walls for vertical and horizontal cracking. Pay particular attention to areas above window openings and at the junctions of different materials (e.g., where brick meets terracotta blocks).
2. Render: Check the condition of the render, looking for signs of detachment, cracking, or bulging.
3. Brick String Courses: Examine the brick string courses for signs of movement or cracking.
4. Roof: Inspect the roof for missing or damaged slates, and check the condition of the timber rafters and purlins.

Internal Inspection

1. Walls and Partitions: Check for signs of cracking or movement in the internal walls and partitions. Look for evidence of moisture ingress or dampness.
2. Floors: Inspect the ground floor concrete slab for signs of cracking or settlement. Check the first-floor timber boarding and joists for signs of rot or insect infestation.
3. Ceilings: Although the ceiling construction is not well-documented, inspect for signs of sagging, cracking, or water damage.

Structural Elements

1. Reinforcement: Use a cover meter to locate and assess the condition of the reinforcement within the concrete walls. Look for signs of corrosion, such as rust staining or spalling concrete.
2. Carbonation: Conduct a carbonation test on the concrete to determine the depth of carbonation and assess the risk of reinforcement corrosion.
3. Sulfate Content: Test the concrete for sulfate content to assess the risk of sulfate attack.

Typical Defects and Maintenance

Vertical Cracking

Vertical cracking is a common defect in Diatomite houses. It is often caused by settlement or thermal movement. To address this issue, it is essential to identify the underlying cause and implement appropriate remedial measures, such as underpinning or installing movement joints.

Horizontal Cracking

Horizontal cracking above window openings is typically caused by the corrosion of reinforcement. To address this issue, it may be necessary to remove the affected concrete, treat or replace the corroded reinforcement, and repair the concrete.

Corrosion of Reinforcement

Corrosion of reinforcement is a significant issue in Diatomite houses. To address this problem, it is essential to identify the extent of corrosion and implement appropriate remedial measures, such as cathodic protection or the application of corrosion inhibitors.

Carbonation and Sulfate Attack

To address the issues of carbonation and sulfate attack, it is essential to conduct regular inspections and testing of the concrete. Remedial measures may include the application of surface treatments to reduce carbonation or the use of sulfate-resistant concrete for repairs.

Conclusion

Diatomite houses are a unique and historically significant property type, offering a glimpse into the post-World War I housing boom in the UK. While these properties have their share of typical hazards and risks, a thorough understanding of their construction and potential defects can help buyers and investors make informed decisions. By commissioning a detailed building survey and addressing any identified issues, it is possible to maintain and preserve these distinctive homes for future generations.

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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