Historical Context and Origins

The Conslab house, a unique and rare property type, was a product of post-World War II Britain, a period marked by a significant housing shortage and a pressing need for rapid construction solutions. These houses were manufactured by Leslie’s Ltd and designed by P M Powell and Charles Woodwood. Built in the 1950s, only two of these properties were ever constructed, making them a rare find in the UK property market.

The Conslab house is a two-storey semi-detached house, identifiable by its medium pitch hipped roof covered with concrete tiles and external walls rendered with pebbledash. These houses were designed to be robust and durable, using a combination of reinforced concrete and other materials to ensure longevity.

Manufacturers and Designers

Leslie’s Ltd, the manufacturer of the Conslab house, was a prominent name in the construction industry during the mid-20th century. The company was known for its innovative approach to building, particularly in the use of reinforced concrete. The designers, P M Powell and Charles Woodwood, were influential figures in the architectural world, contributing significantly to the development of system-built properties in the UK.

Typical Characteristics and Hazards

Construction Details

The Conslab house features several distinctive construction elements:

• Substructure: The foundation consists of concrete strip footings and a concrete slab, with a damp-proof course (DPC) to prevent moisture ingress.
• External Walls: The walls are rendered with pebbledash and constructed from 1 1/2″ precast reinforced concrete (PRC) slabs with splayed edges, reinforced over openings with 5″ dense aggregate concrete, and 1 1/2″ clinker aggregate PRC slabs.
• Separating Wall: An 8″ precast slab cavity wall filled with dense concrete separates the two semi-detached houses.
• Partitions: Loadbearing partitions are made of 6″ PRC slab cavity walls filled with dense concrete, bonded to external walls with cast-in hoop ties. Non-loadbearing partitions are constructed from 3″ Hitchins partitions.
• Floors: The ground floor is concrete, while the first floor consists of timber boarding on timber joists supported by galvanised joist hangers.
• Ceilings: Plasterboard ceilings are used throughout the house.
• Roof: The roof structure includes timber joists, rafters, and purlins, covered with concrete tiles.

Variants

There are a few variants of the Conslab house, including:

• External and separating wall cavities filled with cellular lightweight concrete.
• A 9″ separating wall.
• A ground floor made of suspended timber.
• First-floor timber joists built into external walls.
• First-floor concrete slabs.
• Timber or precast concrete surrounds to openings in external walls for metal windows.

Typical Hazards and Risks

While the Conslab house was designed to be durable, there are several hazards and risks associated with this property type:

• Reinforced Concrete Durability: Over time, reinforced concrete can suffer from corrosion, particularly if the concrete cover is insufficient or if the steel reinforcement is exposed to moisture. This can lead to structural weaknesses and potential safety hazards.
• Carbonation: Carbonation is a process where carbon dioxide from the air penetrates the concrete and reacts with calcium hydroxide to form calcium carbonate. This can reduce the alkalinity of the concrete, leading to corrosion of the steel reinforcement.
• Concrete Spalling: Spalling occurs when the surface of the concrete breaks away, often due to corrosion of the steel reinforcement. This can compromise the structural integrity of the building.
• Damp and Moisture Ingress: Despite the presence of a damp-proof course, moisture ingress can still occur, particularly if the DPC is damaged or if there are issues with the external rendering.

Defective Premises Act

The Conslab house is not specifically classed as defective under the Defective Premises Act. However, given the potential issues with reinforced concrete durability and other construction-related risks, it is essential for prospective buyers and investors to conduct thorough inspections and assessments before purchasing such a property.

Inspection and Assessment Guide

When inspecting a Conslab house, it is crucial to pay attention to several key areas to ensure the property is in good condition and free from significant defects. Here is a step-by-step guide for inspecting a Conslab house:

External Inspection

1. Roof: Check the condition of the concrete tiles and the timber structure. Look for any signs of damage, missing tiles, or sagging.
2. External Walls: Inspect the pebbledash rendering for cracks, spalling, or other signs of deterioration. Pay particular attention to areas around openings, as these are more prone to damage.
3. Damp-Proof Course: Ensure the DPC is intact and functioning correctly. Look for any signs of rising damp or moisture ingress at the base of the walls.
4. Windows and Doors: Check the condition of the window and door surrounds, particularly if they are made of timber or precast concrete. Look for signs of rot, corrosion, or other damage.

Internal Inspection

1. Floors: Inspect the ground floor concrete slab for cracks or other signs of damage. For the first floor, check the condition of the timber boarding and joists, ensuring they are free from rot and securely fixed.
2. Partitions: Examine the loadbearing and non-loadbearing partitions for any signs of movement, cracking, or other structural issues.
3. Ceilings: Check the plasterboard ceilings for cracks, sagging, or other signs of damage.
4. Internal Walls: Inspect the internal walls for any signs of damp, cracking, or other issues. Pay particular attention to the separating wall, as this is a critical structural element.

Structural Assessment

1. Reinforced Concrete: Assess the condition of the reinforced concrete elements, including the external walls, separating wall, and loadbearing partitions. Look for signs of corrosion, spalling, or other deterioration.
2. Carbonation: Measure the carbonation depth in the concrete to determine the extent of carbonation and its potential impact on the steel reinforcement.
3. Corrosion: Check for signs of corrosion in the steel reinforcement, particularly in areas where the concrete cover may be insufficient or damaged.

Maintenance and Repair

1. Concrete Repairs: If any issues with the reinforced concrete are identified, consider appropriate repair methods, such as patch repairs, cathodic protection, or other techniques to address corrosion and spalling.
2. Damp-Proofing: Address any issues with the damp-proof course or moisture ingress by repairing or replacing the DPC and improving drainage around the property.
3. Rendering Repairs: Repair any cracks or damage to the external rendering to prevent moisture ingress and further deterioration.

Conclusion

The Conslab house, with its unique construction and historical significance, can be an intriguing investment for home buyers and investors. However, it is essential to be aware of the potential hazards and risks associated with this property type, particularly concerning reinforced concrete durability and other construction-related issues. By conducting thorough inspections and assessments, prospective buyers can ensure they are making a sound investment and safeguarding their property for the future.

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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