Historical Context and Background

The Conslab house, a unique and rare property type, emerged in the 1950s as part of the post-war housing boom in the United Kingdom. Designed by P M Powell and Charles Woodwood, and manufactured by Leslie’s Ltd, only two of these properties were ever built. This scarcity makes them a fascinating subject for home buyers, investors, and surveyors alike.

The Conslab house is also known by its alternative name, which remains largely undocumented. These properties are typically found in semi-detached configurations, featuring two storeys and a medium-pitched hipped roof covered with concrete tiles. The external walls are rendered with pebbledash, giving them a distinctive appearance.

Identification Characteristics

Recognising a Conslab house involves looking for specific architectural features. These properties are two-storey semi-detached houses with a medium-pitched hipped roof covered in concrete tiles. The external walls are rendered with pebbledash throughout, which is a key identifying characteristic.

Typical Locations

Given that only two Conslab houses were built, their locations are not widespread. They are likely to be found in areas where post-war housing developments were prominent. These houses were part of the broader effort to address the housing shortage in the UK following World War II.

Construction Details

Understanding the construction details of a Conslab house is crucial for anyone considering purchasing or investing in one. These properties were built using a combination of traditional and innovative construction methods, which have implications for their durability and maintenance.

Substructure

The substructure of a Conslab house consists of concrete strip footings and a concrete slab. A damp-proof course (DPC) is also present to prevent moisture from rising through the structure.

External Walls

The external walls are rendered with pebbledash and consist of 1 1/2″ pre-cast reinforced concrete (PRC) slabs with splayed edges. These slabs are reinforced over openings with 5″ dense aggregate concrete. Additionally, 1 1/2″ clinker aggregate PRC slabs are used in the construction.

Separating Wall

The separating wall between the semi-detached units is an 8″ pre-cast slab cavity wall filled with dense concrete. This design provides both structural integrity and sound insulation between the units.

Partitions

Loadbearing partitions are constructed using 6″ PRC slab cavity walls filled with dense concrete. These partitions are bonded to the external walls with cast-in hoop ties. Non-loadbearing partitions are made of 3″ Hitchins partitions.

Floors

The ground floor is made of concrete, providing a solid and durable base. The first floor consists of timber boarding on timber joists, which are supported by galvanised joist hangers.

Ceilings

Ceilings in Conslab houses are typically made of plasterboard, which is a common material used in many types of properties.

Roof

The roof structure includes timber joists, timber rafters, and purlins, all covered with concrete tiles. This combination provides a robust and weather-resistant roof.

Variants

While the basic design of the Conslab house is consistent, there are some variants in the construction details. These include:

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

Typical Hazards and Risks

When considering a Conslab house, it is essential to be aware of the typical hazards and risks associated with this property type. These risks can impact the long-term durability and safety of the house.

Reinforced Concrete Durability

One of the primary concerns with Conslab houses is the durability of the reinforced concrete used in their construction. Over time, reinforced concrete can suffer from corrosion, which can compromise the structural integrity of the property. Guidance on inspecting and assessing the durability of reinforced concrete is provided in several BRE publications, including:

• Corrosion of Steel in Concrete (BRE Digest 444, Parts 1–3)
• Repair and Maintenance of Reinforced Concrete (BR 254)
• Carbonation Depths in Structural-Quality Concrete (BR 19)

Carbonation

Carbonation is a chemical process that occurs when carbon dioxide from the air penetrates the concrete and reacts with calcium hydroxide to form calcium carbonate. This process can reduce the alkalinity of the concrete, making it more susceptible to corrosion. Regular inspections are necessary to assess the depth of carbonation and take appropriate remedial actions.

Damp and Moisture

Despite the presence of a damp-proof course, Conslab houses can still be susceptible to damp and moisture issues. This can be due to various factors, including poor maintenance, inadequate ventilation, and water ingress through cracks in the external walls. Addressing damp and moisture issues promptly is crucial to prevent further damage to the property.

Structural Movement

Structural movement can occur in Conslab houses due to various factors, including ground conditions, temperature changes, and the natural settling of the building. Signs of structural movement include cracks in the walls, uneven floors, and doors or windows that do not close properly. It is essential to monitor these signs and seek professional advice if significant movement is detected.

Defective Premises Act

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. While the Conslab house is not specifically listed as a defective property under this Act, the unique construction methods and materials used in its construction may present challenges in meeting modern building standards.

Inspection and Assessment

Conducting a thorough inspection and assessment of a Conslab house is essential for identifying potential issues and ensuring the property is safe and habitable. Here are some key areas to focus on during an inspection:

External Walls

Inspect the external walls for signs of cracking, spalling, and other damage. Pay particular attention to areas around openings, such as windows and doors, where reinforcement may be present. Check for signs of moisture ingress and ensure that the pebbledash rendering is in good condition.

Roof

Examine the roof for any missing or damaged tiles, as well as signs of water ingress. Check the condition of the timber joists, rafters, and purlins, and ensure that they are free from rot and other damage. Inspect the roof space for adequate ventilation and insulation.

Floors

Inspect the ground floor for signs of damp and moisture, particularly around the edges and near external walls. Check the condition of the timber joists and boarding on the first floor, and ensure that they are free from rot and other damage.

Partitions

Examine the loadbearing and non-loadbearing partitions for signs of cracking, movement, and other damage. Pay particular attention to the bonding between the partitions and external walls, and ensure that the cast-in hoop ties are in good condition.

Ceilings

Inspect the plasterboard ceilings for signs of cracking, sagging, and other damage. Check for signs of water ingress, particularly around light fittings and other openings.

Damp-Proof Course

Check the condition of the damp-proof course and ensure that it is effective in preventing moisture from rising through the structure. Look for signs of damp and moisture on the internal walls, particularly at the base.

Typical Defects

Conslab houses are susceptible to several typical defects, which can impact their long-term durability and safety. Here are some common defects to be aware of:

Concrete Spalling

Concrete spalling occurs when the surface of the concrete breaks away, exposing the reinforcement beneath. This can be caused by corrosion of the reinforcement, freeze-thaw cycles, and other factors. Spalling can compromise the structural integrity of the property and should be addressed promptly.

Cracking

Cracking is a common issue in Conslab houses, particularly in the external walls and partitions. Cracks can be caused by structural movement, thermal expansion and contraction, and other factors. It is essential to monitor cracks and seek professional advice if they appear to be widening or if new cracks develop.

Moisture Ingress

Moisture ingress can occur through cracks in the external walls, roof, and other areas. This can lead to damp and mould issues, which can impact the health and safety of the occupants. Addressing moisture ingress promptly is crucial to prevent further damage to the property.

Corrosion of Reinforcement

Corrosion of the reinforcement in the concrete can compromise the structural integrity of the property. Regular inspections are necessary to assess the condition of the reinforcement and take appropriate remedial actions if corrosion is detected.

Timber Decay

Timber decay can occur in the roof structure, first floor joists, and other areas where timber is used. This can be caused by moisture ingress, poor ventilation, and other factors. Regular inspections are necessary to assess the condition of the timber and take appropriate remedial actions if decay is detected.

Maintenance and Repair

Maintaining and repairing a Conslab house requires a thorough understanding of its unique construction methods and materials. Here are some key considerations for maintaining and repairing a Conslab house:

Regular Inspections

Conducting regular inspections is essential for identifying potential issues and addressing them promptly. Focus on key areas such as the external walls, roof, floors, partitions, and ceilings. Look for signs of cracking, spalling, moisture ingress, and other defects.

Addressing Moisture Issues

Addressing moisture issues promptly is crucial to prevent further damage to the property. Ensure that the damp-proof course is effective and that there is adequate ventilation in the roof space and other areas. Repair any cracks in the external walls and roof to prevent water ingress.

Repairing Concrete

Repairing concrete spalling and other defects requires a thorough understanding of the materials and methods used in the construction of the Conslab house. Use appropriate repair materials and techniques to ensure that the repairs are durable and effective.

Treating Timber

Treating timber decay requires a thorough understanding of the causes and appropriate remedial actions. Use appropriate treatments to address decay and ensure that the timber is adequately protected from moisture and other factors.

Professional Advice

Seeking professional advice is essential for addressing complex issues and ensuring that the property is safe and habitable. Engage the services of a qualified surveyor or structural engineer to assess the condition of the property and provide appropriate recommendations for repairs and maintenance.

Conclusion

The Conslab house is a unique and rare property type with a fascinating history and distinctive construction methods. Understanding the key characteristics, typical hazards, and maintenance requirements of these properties is essential for home buyers, investors, and surveyors. By conducting thorough inspections and addressing potential issues promptly, you can ensure that a Conslab house remains a safe and habitable investment for years to come.

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.