Historical Context and Manufacturing Details

The Lamella house, a unique architectural marvel, was manufactured by F Hills & Sons Ltd between 1946 and 1948. This period marked a significant phase in post-war Britain, where the need for rapid housing solutions was paramount. The Lamella house, also known as the Lamella Roofed Cottage, was one of the innovative responses to this demand. A total of 183 units were constructed, primarily located in suburban areas where the need for family housing was most acute.

Design and Construction Characteristics

External Walls

The Lamella house features a distinctive construction style. The external walls are composed of rendered in-situ no-fines concrete up to the ground floor sill level. This type of concrete, known for its lack of fine aggregates, provides excellent thermal insulation and durability. Above the sill level, the walls transition to cavity brickwork, extending to the underside of the projecting eaves. This combination of materials not only enhances the structural integrity but also contributes to the aesthetic appeal of the property.

Roof Structure

One of the most striking features of the Lamella house is its gable roof, characterized by a lamella grid structure. This timber grid, supported by shaped sprockets, is overlaid with sarking felt and plain tiles or metal sheeting. The roof also includes projecting flat-topped dormer windows, adding to the architectural uniqueness of the property. The gable roof apex is either rendered or shingled, providing additional protection against weather elements.

Floors and Ceilings

The ground floor of the Lamella house is constructed from concrete, ensuring a solid and stable foundation. The first floor consists of tongue-and-groove (T&G) timber boarding on stub joists, which are carried on rolled steel joists (RSJ) bearing on brickwork. This combination of materials provides a robust and durable flooring system. The ceilings are made of plasterboard, offering a smooth and clean finish.

Substructure

The substructure of the Lamella house includes concrete footings, which provide a stable base for the entire structure. This is crucial for ensuring the longevity and stability of the property, especially in areas with variable soil conditions.

Typical Hazards and Risks

Corrosion of Steel in Concrete

One of the primary concerns with the Lamella house is the potential for corrosion of steel reinforcements within the concrete. Over time, exposure to moisture and other environmental factors can lead to the deterioration of steel, compromising the structural integrity of the property. It is essential to regularly inspect and assess the condition of the reinforced concrete to mitigate this risk.

Carbonation of Concrete

Another significant risk is the carbonation of concrete, a process where carbon dioxide from the air reacts with calcium hydroxide in the concrete to form calcium carbonate. This reaction reduces the alkalinity of the concrete, making it more susceptible to corrosion. Regular monitoring of carbonation depths is crucial to ensure the long-term durability of the structure.

Maintenance of Timber Elements

The timber elements of the Lamella house, particularly the lamella grid roof structure, require regular maintenance to prevent decay and insect infestation. Proper treatment and sealing of the timber can help extend its lifespan and maintain the structural integrity of the roof.

Defective Premises Act Considerations

The Lamella house is not classified as defective under the Defective Premises Act. However, it is essential to conduct thorough inspections and assessments to ensure that the property meets modern safety and building standards. Regular maintenance and timely repairs can help address any potential issues and maintain the value of the property.

Inspection Guide for Surveyors

External Walls

When inspecting the external walls of a Lamella house, surveyors should look for signs of cracking, spalling, and moisture ingress. The rendered no-fines concrete should be checked for any signs of deterioration, and the cavity brickwork should be inspected for any gaps or weaknesses. Pay particular attention to the junctions between different materials, as these areas are more prone to issues.

Roof Structure

The roof structure requires a detailed inspection to ensure its integrity. Check the condition of the timber lamella grid, looking for signs of decay, insect damage, or warping. Inspect the sarking felt and tiles or metal sheeting for any signs of wear and tear. The dormer windows should also be checked for proper sealing and weatherproofing.

Floors and Ceilings

Inspect the ground floor concrete for any signs of cracking or settlement. The first floor timber boarding and joists should be checked for any signs of rot or structural weakness. The plasterboard ceilings should be inspected for any signs of water damage or cracking.

Substructure

The concrete footings should be inspected for any signs of movement or cracking. Ensure that the footings are providing adequate support to the structure and that there are no signs of subsidence.

Typical Defects and Maintenance Tips

Cracking and Spalling of Concrete

Cracking and spalling of concrete are common issues in Lamella houses. Regular inspections and timely repairs can help prevent these issues from escalating. Use appropriate repair materials and techniques to address any cracks or spalling.

Timber Decay and Insect Infestation

Timber decay and insect infestation can significantly impact the structural integrity of the roof. Regular treatment and sealing of the timber elements can help prevent these issues. If any signs of decay or infestation are detected, take immediate action to address the problem.

Moisture Ingress

Moisture ingress can lead to a range of issues, including mould growth, timber decay, and corrosion of steel reinforcements. Ensure that the property is properly sealed and that any signs of moisture ingress are promptly addressed. Regular maintenance of the roof, walls, and windows can help prevent moisture-related issues.

Conclusion

The Lamella house, with its unique architectural features and historical significance, offers a distinctive living experience. However, it is essential to be aware of the potential hazards and risks associated with this property type. Regular inspections, timely maintenance, and proper repairs can help ensure the long-term durability and safety of the Lamella house.

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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