Overview of the Jespersen 12M House

The Jespersen 12M house, also known as the Laing Crosswall or simply Jespersen, is a distinctive type of system-built property that emerged in the UK during the 1960s. Designed by P.E. Malmstrom and manufactured by John Laing Construction Ltd, approximately 4,700 of these properties were constructed. These homes are typically found in various regions across the UK, often in suburban areas where rapid housing development was necessary to meet post-war demand.

Historical Context and Manufacturing Details

Period of Construction

The Jespersen 12M houses were predominantly built during the 1960s, a period marked by a significant housing shortage in the UK. The government and private developers sought innovative construction methods to quickly and efficiently provide homes for the growing population. System-built properties like the Jespersen 12M were part of this solution, leveraging prefabricated components to expedite the building process.

Manufacturers and Designers

John Laing Construction Ltd, a prominent name in the construction industry, was responsible for the manufacturing of these homes. The design was the brainchild of P.E. Malmstrom, who aimed to create a cost-effective and durable housing solution. The collaboration between Laing and Malmstrom resulted in a unique property type that combined prefabrication with traditional construction elements.

Identification Characteristics

Structural Features

The Jespersen 12M houses are easily identifiable by their structural characteristics:

• Bungalows and Two-Storey Houses: These properties come in both single-storey and two-storey configurations.
• Flat Roofs: The roofs are flat and typically covered with bituminous felt, a common roofing material of the time.
• External Walls: The front and rear external walls are constructed from precast concrete (PC) spandrel panels, often infilled with vertical timber boarding or other claddings. The flank walls are made of storey-height PC panels or brick.

Variants

There are several variants of the Jespersen 12M house, including:

• Gable Wall of Brick: Some properties feature a gable wall constructed from brick, cavity, or precast reinforced concrete (PRC) panels.
• Narrow Storey Height PRC Panels: In some cases, the front and rear walls are made from narrow storey-height PRC panels.

Typical Construction Details

Substructure

The substructure of the Jespersen 12M house includes concrete strip foundations and a concrete slab. A damp-proof course (DPC) is also incorporated to prevent moisture ingress.

External Walls

The external walls are a complex assembly of various materials:

• Front and Rear Walls: These consist of PC spandrel panels, butyl rubber flashing, paper-faced mineral wool insulation, hardboard-faced polystyrene panels, and galvanised rolled steel angles (RSA) boxed in and fixed to the floor and roof slabs. The walls are clad with vertical timber boarding backed with a breather membrane and lined with plasterboard. Mineral wool insulation is placed between the frame studs.
• Flank Walls: These are made from storey-height PC sandwich panels with polystyrene insulation, located on levelled bolts and supported on drypack concrete. Horizontal in-situ joints contain loop reinforcement from the floor and roof slabs and two horizontal lacing bars. PC coping units are also used.

Internal Walls and Partitions

• Separating Walls: Storey-height PC panels are used for separating walls.
• Partitions: Internal partitions are made from asbestos-cement-faced chipboard.

Floors

• Ground Floor: The ground floor is constructed from concrete.
• First Floor: The first floor consists of tongue-and-groove (T&G) boarding on timber battens, which are placed on hollow PC floor slabs.

Roof

The roof is made from hollow PC roof slabs, pre-felted polystyrene slabs, and bituminous felt.

Ceilings

Ceilings are typically lined with plasterboard.

Wind Bracing

Wind bracing is provided by storey-height PC narrow panels located in the centre of the dwelling between the ground and roof slabs.

Typical Hazards and Risks

Chloride Levels

One of the significant concerns with Jespersen 12M houses is the presence of low to significant levels of chloride in the concrete components. Chlorides can accelerate the corrosion of steel reinforcement, leading to structural issues.

Spalling and Carbonation

Spalling, or the breaking away of concrete surfaces, is a common issue in these properties. Carbonation, a process where carbon dioxide penetrates the concrete and reduces its alkalinity, can also compromise the integrity of the concrete and its reinforcement.

Variable Compaction

The compaction of concrete forming joints between components can be variable, leading to weak points in the structure.

Cracking

Cracking of the PC wall panels is another typical defect, which can be exacerbated by the aforementioned issues of chloride presence and carbonation.

Defective Premises Act Considerations

The Jespersen 12M house is not explicitly classed as defective under the Defective Premises Act. However, the various structural issues and potential hazards associated with these properties mean that they require careful inspection and maintenance. Homebuyers and investors should be aware of these risks and consider them when evaluating the property.

Inspection Guide for Surveyors

Pre-Inspection Preparation

Before conducting an inspection, it is essential to gather all relevant information about the property, including any previous reports, maintenance records, and historical data. Familiarise yourself with the typical characteristics and common defects of Jespersen 12M houses.

External Inspection

• Roof: Check the condition of the bituminous felt covering. Look for signs of wear, tear, or water ingress.
• Walls: Inspect the PC spandrel panels and timber cladding for signs of cracking, spalling, or other damage. Pay particular attention to the joints between components.
• Flank Walls: Examine the storey-height PC panels or brickwork for any defects.
• Foundations: Assess the condition of the concrete strip foundations and the concrete slab. Look for signs of settlement or movement.

Internal Inspection

• Walls and Partitions: Check for any signs of cracking or movement in the PC panels and asbestos-cement-faced chipboard partitions.
• Floors: Inspect the ground and first floors for any signs of unevenness, movement, or damage.
• Ceilings: Look for any signs of water damage or cracking in the plasterboard ceilings.
• Wind Bracing: Ensure that the wind bracing panels are intact and free from damage.

Additional Considerations

• Chloride Levels: If possible, conduct tests to determine the chloride levels in the concrete components.
• Carbonation: Assess the extent of carbonation in the concrete and its impact on the reinforcement.
• Compaction: Evaluate the compaction of the concrete forming joints between components.

Maintenance and Repair Recommendations

Addressing Chloride Issues

To mitigate the impact of chlorides, consider applying corrosion inhibitors to the concrete or using cathodic protection systems to prevent further corrosion of the steel reinforcement.

Repairing Spalling and Cracking

Spalled areas should be repaired by removing the damaged concrete and applying a suitable repair mortar. Cracks should be filled with appropriate sealants or repair mortars to prevent further deterioration.

Improving Compaction

Where variable compaction is identified, it may be necessary to strengthen the joints between components. This can be achieved by injecting grout or other suitable materials to improve the integrity of the joints.

Regular Inspections

Regular inspections are crucial to identify and address any emerging issues promptly. Establish a maintenance schedule that includes periodic checks of the roof, walls, floors, and other critical components.

Conclusion

The Jespersen 12M house is a unique and historically significant property type that offers both opportunities and challenges for homebuyers and investors. Understanding the typical characteristics, common defects, and potential hazards associated with these properties is essential for making informed decisions. By conducting thorough inspections and implementing appropriate maintenance and repair strategies, it is possible to safeguard your investment and ensure the long-term durability 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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