Historical Context and Background

The Corvus house, a distinctive property type in the UK, was manufactured by William Cowlin & Son Ltd and designed by N. Rooke. These properties were constructed in 1946, immediately following World War II, during a period when there was a significant demand for housing. Only four of these unique properties were built, making them a rare find in today’s property market. The Corvus house is a two-storey semi-detached house, typically found in suburban areas, and is known for its medium or steep pitch gable roof covered with interlocking or plain concrete tiles.

Identification Characteristics

Identifying a Corvus house is relatively straightforward due to its unique architectural features. These houses are two-storey semi-detached properties with a medium or steep pitch gable roof. The roofs are covered with interlocking or plain concrete tiles, which were a common choice in the post-war era due to their durability and cost-effectiveness. The external walls of Corvus houses are rendered throughout, providing a uniform and somewhat austere appearance.

One of the most distinctive features of the Corvus house is the monopitch canopy over the front door, supported by concrete columns. This canopy not only adds to the aesthetic appeal of the property but also provides practical shelter from the elements. Additionally, these houses often feature a pitched roof single-storey extension to the gable wall, which can serve as additional living space or storage.

Construction Details

Substructure

The substructure of the Corvus house consists of concrete strip footings and concrete under-building. This provides a solid foundation for the property, ensuring stability and durability. The use of reinforced concrete (RC) cavity walls further enhances the structural integrity of the house. A damp-proof course (DPC) is also included to prevent moisture from rising through the walls, which is crucial for maintaining the longevity of the property.

External Walls

The external walls of the Corvus house are rendered and consist of 10-inch RC cavity walls. The outer leaf is made of 4-inch dense concrete, while the inner leaf is constructed from 4-inch foamed slag concrete. A 2-inch cavity separates the two leaves, providing insulation and reducing the risk of dampness. Reinforcement is included at the eaves level, with two additional mild steel (MS) bars to the inner leaf below the first floor level. Weep holes and cavity trays above openings are also incorporated to manage moisture and prevent water ingress.

Separating Wall

The separating wall between the semi-detached properties is made of foamed slag RC cavity wall. This material choice provides both sound insulation and fire resistance, ensuring privacy and safety for the occupants.

Partitions

The ground floor partitions are constructed from 4-inch or 6-inch foamed slag concrete, while the first floor partitions are made from 2.5-inch foamed slag concrete. This lightweight material is easy to work with and provides adequate strength for internal walls.

Ground Floor

The ground floor of the Corvus house features mastic asphalt on concrete, providing a durable and waterproof surface. This is particularly important in areas prone to dampness, as it helps to prevent moisture from penetrating the floor.

First Floor

The first floor consists of mastic asphalt on a sand/cement screed, which is laid on 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 include half-inch reinforcement for added strength.

Roof

The roof structure of the Corvus house includes PRC rafters, purlins, and ceiling joists, all covered with concrete tiles. This combination provides a robust and weather-resistant roof that can withstand the UK’s variable climate.

Chimney

The chimney is constructed from reinforced concrete, ensuring it is both durable and fire-resistant.

Typical Hazards and Risks

While the Corvus house boasts a solid construction, there are several hazards and risks associated with this property type that potential buyers and investors should be aware of.

Reinforced Concrete Durability

One of the primary concerns with Corvus houses is the durability of the reinforced concrete used in their construction. Over time, reinforced concrete can suffer from corrosion, particularly if it is exposed to moisture. This can lead to structural weaknesses and, in severe cases, may require extensive repairs. Guidance on the inspection and assessment of reinforced concrete durability can be found in BRE Digest 444 (Parts 1-3), BR 254, and BR 19.

Carbonation

Carbonation is a process that occurs when carbon dioxide from the air penetrates the concrete and reacts with the calcium hydroxide in the cement to form calcium carbonate. This can reduce the alkalinity of the concrete, leading to the corrosion of the steel reinforcement. Regular inspections are necessary to monitor carbonation depths and address any issues promptly.

Dampness

Despite the inclusion of a damp-proof course, dampness can still be a concern in Corvus houses, particularly if the DPC has been compromised or if there are issues with the external rendering. Dampness can lead to mould growth, which can have serious health implications for the occupants.

Structural Movement

As with any older property, structural movement can be an issue in Corvus houses. This can be caused by a variety of factors, including ground movement, changes in moisture levels, and the natural settling of the building over time. Signs of structural movement include cracks in the walls, uneven floors, and doors or windows that no longer fit properly.

Defective Premises Act

The Corvus house is not classed as defective under the Defective Premises Act. However, this does not mean that the property is free from defects. As with any older property, it is essential to carry out a thorough survey to identify any potential issues and address them promptly.

Inspection Guide for Surveyors

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

External Walls

Check the condition of the external rendering and look for any signs of cracking or damage. Inspect the weep holes and cavity trays to ensure they are functioning correctly and not blocked.

Roof

Inspect the roof for any missing or damaged tiles and check the condition of the PRC rafters, purlins, and ceiling joists. Look for any signs of water ingress or damage to the roof structure.

Damp-Proof Course

Check the condition of the damp-proof course and look for any signs of rising damp. Use a moisture meter to assess the moisture levels in the walls and floors.

Reinforced Concrete

Inspect the reinforced concrete elements of the property, including the cavity walls, chimney, and first-floor beams. Look for any signs of corrosion or carbonation and assess the overall condition of the concrete.

Structural Movement

Look for any signs of structural movement, such as cracks in the walls, uneven floors, or doors and windows that no longer fit properly. Use a spirit level to check for any signs of settlement or movement.

Internal Partitions

Inspect the internal partitions for any signs of damage or deterioration. Check the condition of the foamed slag concrete and look for any signs of cracking or movement.

Typical Defects in Corvus Houses

Concrete Degradation

One of the most common defects in Corvus houses is the degradation of the reinforced concrete. This can be caused by a variety of factors, including carbonation, moisture ingress, and corrosion of the steel reinforcement. Regular inspections and maintenance are essential to address any issues promptly and prevent further deterioration.

Dampness

Dampness is another common issue in Corvus houses, particularly if the damp-proof course has been compromised or if there are issues with the external rendering. Signs of dampness include mould growth, peeling paint, and a musty smell. It is essential to address any dampness issues promptly to prevent further damage and protect the health of the occupants.

Structural Movement

As mentioned earlier, structural movement can be a concern in Corvus houses. This can be caused by a variety of factors, including ground movement, changes in moisture levels, and the natural settling of the building over time. Regular inspections are necessary to monitor any signs of movement and address any issues promptly.

Roof Issues

The roof of a Corvus house can be prone to issues such as missing or damaged tiles, water ingress, and damage to the PRC rafters, purlins, and ceiling joists. Regular inspections and maintenance are essential to ensure the roof remains in good condition and to address any issues promptly.

Maintenance and Repair Tips

Maintaining a Corvus house requires regular inspections and prompt attention to any issues that arise. Here are some tips for maintaining and repairing a Corvus house:

Regular Inspections

Carry out regular inspections of the property, paying close attention to the external walls, roof, damp-proof course, reinforced concrete elements, and internal partitions. Look for any signs of damage or deterioration and address any issues promptly.

Addressing Dampness

If you notice any signs of dampness, such as mould growth, peeling paint, or a musty smell, it is essential to address the issue promptly. This may involve repairing or replacing the damp-proof course, addressing any issues with the external rendering, and improving ventilation in the affected areas.

Concrete Repairs

If you notice any signs of concrete degradation, such as cracking, spalling, or corrosion of the steel reinforcement, it is essential to carry out repairs promptly. This may involve removing the damaged concrete, treating the steel reinforcement, and applying a suitable repair mortar.

Roof Maintenance

Regularly inspect the roof for any missing or damaged tiles and address any issues promptly. Ensure that the PRC rafters, purlins, and ceiling joists are in good condition and carry out any necessary repairs.

Structural Movement

If you notice any signs of structural movement, such as cracks in the walls, uneven floors, or doors and windows that no longer fit properly, it is essential to address the issue promptly. This may involve carrying out structural repairs, such as underpinning or reinforcing the affected areas.

Conclusion

The Corvus house is a unique and distinctive property type in the UK, with a rich history and solid construction. However, like any older property, it is essential to carry out regular inspections and maintenance to ensure it remains in good condition. By understanding the typical characteristics, hazards, and risks associated with Corvus houses, potential buyers and investors can make informed decisions and protect their investment.

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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