Understanding the Calverley Type II House

The Calverley Type II house, a notable example of system-built properties in the UK, represents a unique chapter in the history of British housing. Constructed between 1966 and 1970, these homes were part of a broader movement to address housing shortages through innovative building techniques. With only 200 units built, the Calverley Type II houses are a rare find, often located in suburban areas where rapid development was necessary during the post-war period.

Manufacturers and Designers

Calverley Ltd, the manufacturer behind these homes, collaborated with designer J L Heap to create a modular housing solution that could be quickly assembled on-site. This collaboration resulted in a series of homes known by various names, including Calverley Modular, Calverley Modular Type I, CM, CM Yuill, CMX, and Yuill. These alternative names reflect the variations and adaptations made to the original design to suit different needs and preferences.

Typical Characteristics of Calverley Type II Houses

The Calverley Type II houses are primarily bungalows and two-storey semi-detached or terraced houses. They feature a medium pitch gable roof covered with tiles, which is a distinctive characteristic of this property type. The external walls are constructed with brick up to the first floor, with tile hanging or vertical timber boarding above. Some dwellings also include a single-storey brick extension to the rear elevation, providing additional living space.

Construction Details

The construction of Calverley Type II houses is a testament to the ingenuity of system-built properties. The substructure consists of a concrete slab foundation, providing a stable base for the house. A damp-proof course (DPC) is included to prevent moisture from rising through the structure. The external walls are built using a platform frame construction method, with storey-height timber frame panels sheathed externally with plywood. This is overlaid with bituminous felt and separately clad with brick to the first floor level, with tile hanging on timber battens above.

Internally, the walls are lined with plasterboard backed by a polyethylene vapour control layer, ensuring effective insulation and moisture control. Paper laminated mineral fibre insulation is placed between the frame studs, enhancing the thermal efficiency of the house. The separating walls are constructed as timber frame cavity walls, backed with plywood and lined with two layers of plasterboard to eaves level and one layer in the roof space. Mineral fibre insulation is also used in these walls to improve soundproofing and thermal performance.

The partitions within the house are made of timber stud lined with plasterboard, providing a lightweight yet sturdy structure. The ground floor is constructed with concrete, while the first floor features plywood on timber joists. Ceilings are finished with plasterboard, offering a smooth and clean appearance. The roof is supported by timber trusses, covered with bituminous felt and tiles, ensuring durability and weather resistance.

Typical Hazards and Risks

While the Calverley Type II houses offer many benefits, they also come with certain hazards and risks that potential buyers and investors should be aware of. One of the primary concerns is the inadequate fixings between the brickwork and timber frame panels, which can lead to structural instability over time. Localised decay of sole plates and plywood sheathing is another common issue, often resulting from prolonged exposure to moisture.

Gaps in separating walls in the roof space can compromise the thermal and acoustic insulation of the house, leading to increased energy costs and reduced comfort. Rain penetration at window flashings is another risk, potentially causing water damage to the interior of the house. Additionally, there is a risk of interstitial condensation, which occurs when moisture becomes trapped within the walls, leading to mould growth and structural damage.

Defective Premises Act Considerations

The Calverley Type II houses are not classified as defective under the Defective Premises Act. However, it is essential for buyers and investors to conduct thorough inspections to identify any potential issues that may require attention. Engaging a professional surveyor with experience in system-built properties can provide valuable insights and help ensure that the property is in good condition.

Inspection Tips for Calverley Type II Houses

When inspecting a Calverley Type II house, there are several key areas to focus on to ensure that the property is structurally sound and free from significant defects. Here is a step-by-step guide to conducting a comprehensive inspection:

1. Foundation and Substructure: Begin by examining the concrete slab foundation for any signs of cracking or movement. Check the damp-proof course to ensure it is intact and functioning correctly.

2. External Walls: Inspect the brickwork and tile hanging for any signs of damage or deterioration. Pay particular attention to the fixings between the brickwork and timber frame panels, as inadequate fixings can lead to structural issues.

3. Roof and Flashings: Examine the roof tiles and bituminous felt for any signs of wear or damage. Check the window flashings for signs of rain penetration, which can lead to water damage inside the house.

4. Internal Walls and Partitions: Inspect the plasterboard lining for any signs of cracking or moisture damage. Check the separating walls in the roof space for gaps that could compromise insulation.

5. Sole Plates and Plywood Sheathing: Look for signs of decay in the sole plates and plywood sheathing, particularly in areas exposed to moisture. Address any issues promptly to prevent further deterioration.

6. Insulation and Vapour Control: Ensure that the mineral fibre insulation and polyethylene vapour control layer are intact and functioning effectively. This will help maintain the thermal efficiency of the house and prevent condensation issues.

7. Floors and Ceilings: Check the concrete ground floor and plywood first floor for any signs of damage or instability. Inspect the plasterboard ceilings for cracks or moisture damage.

Typical Defects in Calverley Type II Houses

Despite their innovative design, Calverley Type II houses are prone to certain defects that can affect their performance and longevity. Some of the most common issues include:

• Inadequate Fixings: As mentioned earlier, inadequate fixings between the brickwork and timber frame panels can lead to structural instability. This issue should be addressed promptly to prevent further damage.

• Localised Decay: Decay of sole plates and plywood sheathing is a common problem, often resulting from moisture exposure. Regular inspections and maintenance can help mitigate this risk.

• Gaps in Separating Walls: Gaps in the separating walls in the roof space can compromise insulation and increase energy costs. Sealing these gaps can improve the thermal and acoustic performance of the house.

• Rain Penetration: Rain penetration at window flashings can cause water damage to the interior of the house. Ensuring that flashings are properly installed and maintained can help prevent this issue.

• Interstitial Condensation: Interstitial condensation occurs when moisture becomes trapped within the walls, leading to mould growth and structural damage. Proper ventilation and moisture control measures can help prevent this problem.

Variants and Adaptations

Over the years, some Calverley Type II houses have undergone adaptations and modifications to suit the changing needs of their occupants. One common variant is the use of vertical timber boarding on the upper storey external walls, providing a different aesthetic and potentially improving weather resistance. Additionally, some houses feature partitions made of honeycomb plasterboard, offering a lightweight and cost-effective alternative to traditional plasterboard.

Conclusion

The Calverley Type II house is a fascinating example of system-built properties in the UK, offering a unique blend of innovation and practicality. While these homes come with certain risks and challenges, they also provide an opportunity for buyers and investors to own a piece of architectural history. By conducting thorough inspections and addressing any potential issues, you can ensure that your Calverley Type II house remains a safe and comfortable home 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.

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