Historical Context and Background

The Corvus house, a unique and intriguing property type, was manufactured by William Cowlin & Son Ltd and designed by N. Rooke. These properties were constructed in 1946, a period marked by a significant housing shortage in the UK following World War II. Only four of these houses were built, making them a rare find in today’s property market. The Corvus house is also known by its alternative name, which remains unspecified in historical records.

These properties are typically found in suburban areas, where post-war housing developments were most prevalent. The Corvus house is a two-storey semi-detached house, characterized by its medium or steep pitch gable roof covered with interlocking or plain concrete tiles. The external walls are rendered throughout, providing a distinctive appearance. A monopitch canopy supported by concrete columns adorns the front door, and a pitched roof single-storey extension is often found on the gable wall.

Construction Details

Substructure

The substructure of the Corvus house consists of concrete strip footings and concrete under-building. The reinforced concrete (RC) cavity wall construction includes a damp-proof course (DPC) to prevent moisture ingress.

External Walls

The external walls are rendered and constructed with 10-inch RC cavity walls. The outer leaf is made of 4-inch dense concrete, while the inner leaf consists of 4-inch foamed slag concrete. A 2-inch cavity separates the two leaves, providing some insulation. Reinforcement is present at the eaves level, with two additional mild steel (MS) bars in the inner leaf below the first floor level. Weep holes and cavity trays above openings are included to manage moisture.

Separating Wall

The separating wall between semi-detached units is also constructed using foamed slag RC cavity walls, ensuring structural integrity and sound insulation.

Partitions

Ground floor partitions are made of 4-inch or 6-inch foamed slag concrete, while the first floor partitions are 2.5 inches thick, also made of foamed slag concrete.

Ground Floor

The ground floor features mastic asphalt on concrete, providing a durable and moisture-resistant surface.

First Floor

The first floor construction includes mastic asphalt on a sand/cement screed, supported by 12-inch by 5-inch hollow pre-stressed reinforced concrete (PRC) beams. These beams are built into the inner leaf of the external wall and reinforced with 0.5-inch steel bars.

Ceilings

Details about the ceiling construction are not well-documented, but they are likely to be consistent with the robust construction methods used throughout the house.

Roof

The roof structure comprises PRC rafters, purlins, and ceiling joists, covered with concrete tiles. This construction ensures durability and resistance to weather conditions.

Chimney

The chimney is constructed from reinforced concrete, adding to the overall robustness of the property.

Typical Characteristics and Hazards

Identification Characteristics

The Corvus house can be identified by its two-storey semi-detached design, medium or steep pitch gable roof, rendered external walls, and distinctive monopitch canopy over the front door. The single-storey extension with a pitched roof on the gable wall is another identifying feature.

Typical Hazards and Risks

While the Corvus house boasts a robust construction, several potential hazards and risks are associated with this property type:

1. Reinforced Concrete Durability: Over time, reinforced concrete can suffer from corrosion, particularly if the concrete cover is insufficient or if the reinforcement is exposed to moisture. This can lead to structural weaknesses.

2. Carbonation: Carbonation of concrete, a process where carbon dioxide from the air reacts with calcium hydroxide in the concrete, can reduce the alkalinity of the concrete and lead to corrosion of the steel reinforcement.

3. Moisture Ingress: Despite the presence of weep holes and cavity trays, moisture ingress can still occur, particularly if these features are blocked or damaged.

4. Thermal Insulation: The 2-inch cavity between the concrete leaves provides limited thermal insulation, which may result in higher heating costs and potential issues with condensation.

5. Asbestos: Given the construction period, there is a possibility that asbestos-containing materials were used in some components, such as insulation or roofing materials. Asbestos poses significant health risks if disturbed.

Defective Premises Act

The Corvus house is not specifically classed as defective under the Defective Premises Act. However, the potential issues with reinforced concrete durability and other hazards mentioned above warrant careful inspection and maintenance to ensure the property remains safe and habitable.

Inspection Guide for Surveyors

When inspecting a Corvus house, surveyors should pay close attention to the following aspects:

Reinforced Concrete Durability

1. Visual Inspection: Look for signs of cracking, spalling, or rust stains on the concrete surfaces, which may indicate corrosion of the steel reinforcement.
2. Carbonation Testing: Use a phenolphthalein solution to test for carbonation depth. This will help determine if the concrete has lost its protective alkalinity.
3. Moisture Levels: Check for dampness or moisture ingress, particularly around weep holes, cavity trays, and the DPC.

Structural Integrity

1. Foundation and Footings: Inspect the concrete strip footings and under-building for signs of settlement or movement.
2. Walls: Examine the RC cavity walls for any signs of structural weakness, such as bowing or bulging.
3. Roof Structure: Assess the condition of the PRC rafters, purlins, and ceiling joists. Look for any signs of sagging or damage to the concrete tiles.

Thermal Insulation and Energy Efficiency

1. Cavity Insulation: Check if any additional insulation has been added to the cavity walls. If not, consider recommending retrofitting insulation to improve energy efficiency.
2. Windows and Doors: Inspect the condition of windows and doors for drafts and heat loss. Recommend upgrading to double or triple glazing if necessary.

Asbestos

1. Asbestos Survey: If there is any suspicion of asbestos-containing materials, recommend a professional asbestos survey to identify and safely manage or remove these materials.

General Maintenance

1. Render Condition: Check the condition of the external render for cracks or damage that could allow moisture ingress.
2. Guttering and Drainage: Ensure that guttering and drainage systems are functioning correctly to prevent water damage.

Typical Defects and Maintenance Tips

Common Defects

1. Concrete Spalling: This occurs when the surface of the concrete flakes off due to corrosion of the steel reinforcement. Regular inspections and timely repairs can prevent further damage.
2. Cracking: Cracks in the concrete walls or floors can indicate structural issues or moisture ingress. These should be investigated and repaired promptly.
3. Dampness: Persistent dampness can lead to mould growth and structural damage. Ensure that weep holes and cavity trays are clear and functioning correctly.
4. Thermal Bridging: The concrete construction can lead to thermal bridging, where heat is conducted through the structure, leading to cold spots and condensation. Insulating the cavity walls can mitigate this issue.

Maintenance Tips

1. Regular Inspections: Conduct regular inspections of the reinforced concrete elements to identify and address any signs of corrosion or damage early.
2. Moisture Management: Keep weep holes and cavity trays clear of debris to ensure proper moisture management. Repair any damaged render or DPC to prevent moisture ingress.
3. Energy Efficiency Improvements: Consider retrofitting cavity wall insulation and upgrading windows and doors to improve the property’s energy efficiency and reduce heating costs.
4. Asbestos Management: If asbestos-containing materials are present, ensure they are managed safely and in accordance with regulations. Professional removal may be necessary if the materials are damaged or disturbed.

Conclusion

The Corvus house, with its unique post-war construction and robust design, offers a fascinating glimpse into the history of UK housing. While these properties are rare, they present both opportunities and challenges for home buyers and investors. Understanding the construction details, typical hazards, and maintenance requirements is crucial for ensuring the longevity and safety of these homes.

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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