Historical Context and Manufacturing Background

The Cornish Unit Type 1 house is a notable example of post-war British architecture, designed to address the acute housing shortage following World War II. These properties were constructed between 1946 and the 1960s, with approximately 30,000 units built, including both Type I and Type II variants. The primary manufacturers were Central Cornwall Concrete & Artificial Stone Co. and Selleck Nicholls & Co., with the designs attributed to A E Beresford and R Tonkin.

These houses were predominantly built in Cornwall and other parts of the UK, often found in suburban and rural settings. They were part of a broader initiative to provide quick, affordable housing solutions using non-traditional construction methods, specifically prefabricated reinforced concrete (PRC).

Design and Construction Characteristics

General Identification

Cornish Unit Type 1 houses are typically bungalows or two-storey semi-detached and terraced houses. They are easily identifiable by their mansard medium pitch hipped roofs, which are covered with concrete tiles, asbestos cement slates, or cedar shingles. The external walls feature storey-height PRC columns and horizontal precast concrete (PC) panels, with distinctive rounded PC corner units.

Substructure

The substructure of these houses consists of concrete strip footings, concrete block underbuilding, and a concrete slab with a damp-proof course (DPC). This robust foundation was designed to provide stability and durability, although it can present challenges in terms of modern building standards and insulation requirements.

External Walls

The external walls are constructed using PC plinth units with splayed joints, joggle jointed together with mortar. The storey-height PRC columns, measuring 9 inches by 4 inches, feature two grooves and are reinforced with steel tie rods. The walls also include 9-inch or 11-inch by 3-foot by 3-inch PC panels, creating a cavity wall system with additional PC panels on the interior. Quadrant-shaped PC corner units and RSA brackets provide additional structural support, while PC lintels and cornice units are laid in bond to complete the wall assembly.

Internal Walls and Partitions

The separating walls between units are typically constructed from 9-inch PC blocks or brick. Loadbearing internal walls are made from 4-inch dense PC blocks, while non-loadbearing partitions use 4-inch clinker PC blocks. In some variants, non-loadbearing partitions may be timber stud lined with plasterboard.

Floors

The ground floor is a concrete slab, providing a solid and durable base. The first floor consists of timber boarding on timber joists, supported by PC cornice units. This combination of materials offers a balance of strength and flexibility, although it can be prone to issues such as sagging or warping over time.

Roof

The roof structure is a timber frame mansard design, covered with bituminous felt and concrete tiles. Variants may include asbestos cement slates or cedar shingles. The roof space may also feature a 4 1/2-inch PC block or brick separating wall.

Typical Hazards and Risks

Structural Issues

One of the primary concerns with Cornish Unit Type 1 houses is the potential for structural issues, particularly related to the PRC columns. These columns are prone to horizontal and vertical cracking, which can compromise the integrity of the building. High rates of carbonation and significant levels of chloride in some PRC columns can accelerate deterioration, leading to further structural problems.

Cracking and Carbonation

Cracking of the first-floor ring beams is another common issue, often resulting from the same factors that affect the PRC columns. Carbonation, a process where carbon dioxide from the air reacts with the calcium hydroxide in concrete to form calcium carbonate, can reduce the alkalinity of the concrete and lead to corrosion of the steel reinforcement.

Asbestos Concerns

Asbestos cement slates used in the roofing materials pose a significant health risk if disturbed. Asbestos fibres can become airborne and inhaled, leading to serious respiratory diseases, including asbestosis, lung cancer, and mesothelioma. Proper handling and removal by licensed professionals are essential when dealing with asbestos-containing materials.

Thermal Efficiency and Insulation

Cornish Unit Type 1 houses were not designed with modern energy efficiency standards in mind. The cavity wall construction, while providing some insulation, is often inadequate by today’s standards. Retrofitting insulation can be challenging due to the construction methods and materials used.

Defective Premises Act and Designation

Cornish Unit Type 1 houses are designated as defective under the Defective Premises Act. This designation means that these properties are recognized as having inherent structural defects that can affect their safety and habitability. As a result, they may be eligible for government grants or assistance for repairs and improvements, although this varies by location and specific circumstances.

Inspection Guide for Surveyors

Pre-Inspection Preparation

Before conducting an inspection of a Cornish Unit Type 1 house, it is essential to gather as much information as possible about the property. This includes reviewing any available documentation, such as previous survey reports, repair records, and building plans. Understanding the typical construction methods and common defects associated with these houses will help you identify potential issues more effectively.

External Inspection

1. Roof: Examine the roof for signs of damage or deterioration, such as missing or broken tiles, sagging, or water ingress. Pay particular attention to the condition of the asbestos cement slates or cedar shingles, if present.

2. Walls: Inspect the external walls for horizontal and vertical cracking, particularly around the PRC columns. Look for signs of carbonation, such as spalling or rust stains, which indicate corrosion of the steel reinforcement.

3. Corners and Joints: Check the quadrant-shaped PC corner units and joggle joints for any signs of movement or separation. These areas are particularly vulnerable to cracking and water ingress.

4. Damp Proof Course (DPC): Ensure that the DPC is intact and functioning correctly. Look for signs of rising damp, such as damp patches or mould growth on the lower parts of the walls.

Internal Inspection

1. Floors: Inspect the ground and first floors for signs of sagging, warping, or cracking. Pay attention to any areas where the timber joists may be compromised or where the concrete slab shows signs of movement.

2. Walls and Partitions: Check the internal walls and partitions for cracking, particularly around loadbearing walls. Look for signs of movement or separation in the non-loadbearing partitions, especially if they are timber stud lined with plasterboard.

3. Ceilings: Examine the ceilings for signs of sagging, cracking, or water damage. Pay particular attention to areas around the roof structure, where leaks or structural issues may be more apparent.

4. Asbestos: Identify any materials that may contain asbestos, such as roofing slates or insulation. Ensure that these materials are not disturbed during the inspection and recommend professional testing and removal if necessary.

Structural Integrity

1. PRC Columns: Conduct a thorough inspection of the PRC columns, looking for signs of cracking, spalling, or rust stains. Use a carbonation test to determine the extent of carbonation and assess the condition of the steel reinforcement.

2. Ring Beams: Inspect the first-floor ring beams for cracking or signs of movement. These beams are critical to the structural integrity of the building, and any defects should be addressed promptly.

3. Steel Reinforcement: Check for signs of corrosion in the steel reinforcement, particularly in areas where carbonation or chloride contamination is present. Corroded steel can significantly weaken the structure and lead to further deterioration.

Common Defects and Remedial Measures

Cracking and Carbonation

Cracking and carbonation are common issues in Cornish Unit Type 1 houses. Remedial measures may include:

• Crack Repair: Use appropriate repair methods, such as epoxy injection or crack stitching, to address cracks in the PRC columns and ring beams.
• Carbonation Treatment: Apply carbonation-resistant coatings or treatments to the affected areas to slow down the carbonation process and protect the steel reinforcement.

Asbestos Removal

Asbestos-containing materials should be handled and removed by licensed professionals. This may involve:

• Encapsulation: Encapsulating asbestos materials to prevent fibres from becoming airborne.
• Removal: Safely removing and disposing of asbestos materials in accordance with regulatory guidelines.

Insulation and Energy Efficiency

Improving the thermal efficiency of Cornish Unit Type 1 houses can be challenging but is essential for modern living standards. Possible measures include:

• Cavity Wall Insulation: Injecting insulation into the cavity walls to improve thermal performance.
• Roof Insulation: Adding insulation to the roof space to reduce heat loss and improve energy efficiency.
• Double Glazing: Installing double-glazed windows to enhance thermal performance and reduce energy consumption.

Structural Reinforcement

In cases where the structural integrity of the building is compromised, more extensive remedial measures may be required:

• Column Replacement: Replacing severely damaged PRC columns with new, structurally sound columns.
• Steel Reinforcement: Adding additional steel reinforcement to strengthen weakened areas and improve overall stability.

Conclusion

The Cornish Unit Type 1 house represents a significant chapter in the history of British housing, offering a unique blend of post-war innovation and practical design. However, these properties come with their own set of challenges, particularly related to structural integrity and modern living standards.

For home buyers and investors, understanding the typical characteristics, hazards, and remedial measures associated with Cornish Unit Type 1 houses is essential. By conducting thorough inspections and addressing any identified issues, you can ensure that these properties remain safe, habitable, and valuable investments.

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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