Historical Context and Manufacturing Background

The Blackburn Orlit house, a notable example of post-war British architecture, was constructed between 1950 and 1952. This period marked a significant phase in the UK’s housing history, as the country grappled with a severe housing shortage following World War II. The Blackburn Orlit house was one of the many system-built properties designed to address this urgent need for affordable and quickly constructed homes.

Manufactured by the Scottish Orlit Co. Ltd and Blackburn Ltd, these houses were part of a broader initiative to employ innovative construction techniques and materials. The designers aimed to create durable, cost-effective housing solutions that could be rapidly assembled. Approximately 360 Blackburn Orlit houses were built during this period, primarily located in various regions across the UK.

Identifying Characteristics of Blackburn Orlit Houses

Blackburn Orlit houses are typically two-storey terraced homes, easily recognizable by their shallow pitch gable roofs. The external walls are constructed entirely of precast concrete (PC) panels, a hallmark of the Orlit design. These houses were also known by the alternative name “Blackburn, Orlit,” reflecting their dual heritage from the two manufacturing companies.

Key Features:

• Structure: Two-storey terraced houses
• Roof: Shallow pitch gable roof
• External Walls: Precast concrete panels throughout

Construction Details

Understanding the construction details of Blackburn Orlit houses is crucial for potential buyers and investors. These homes were built using a combination of precast reinforced concrete (PRC) and other materials designed to expedite the construction process while maintaining structural integrity.

Substructure:

• Concrete Pads: The foundation consists of concrete pads below the columns.
• Underbuilding: Concrete underbuilding supports the structure.
• PRC Stub Columns: These columns are cast into the pad foundations, providing additional stability.

Frame:

• PRC Columns and Beams: The main frame includes 5 1/2″ x 5 1/2″ PRC columns and 5″ x 7 1/2″ PRC perimeter beams, which are not exposed.
• Steel Connectors: RSA cleats and bolted steel flange connectors are used to join the structural elements.
• Reinforcement: A reinforcement bar is embedded in a concrete stitch at the eaves level for added strength.

External Walls:

• PRC Panels: The external walls are made of 36″ x 16″ x 2″ PRC panels, with a cavity and 2 1/2″ lightweight PC panels.
• Internal Finish: Plasterboard on timber battens is used for the internal finish.
• Wall Ties: Galvanised mild steel wall ties are employed to secure the panels.

Separating and Partition Walls:

• Separating Wall: A 2 1/2″ lightweight PC block cavity wall separates the units.
• Partitions: The specific materials for internal partitions are not well-documented.

Floors:

• Ground Floor: Tongue and groove (T&G) boarding on timber joists, supported by PRC beams on sleeper walls.
• First Floor: Similar construction with T&G boarding on timber joists on PRC beams.

Ceilings and Roof:

• Ceilings: Plasterboard ceilings are standard.
• Roof: The roof structure comprises steel trusses, providing a robust framework.

Typical Defects and Hazards

While Blackburn Orlit houses were innovative for their time, they are not without their issues. Over the years, several defects have been identified, some of which pose significant risks to the structural integrity and safety of these homes.

Chloride Contamination:

One of the most critical issues is the significant levels of chlorides found in the PRC columns and beams. Chlorides can accelerate the corrosion of steel reinforcement within the concrete, leading to structural weaknesses.

Carbonation:

Carbonation of PRC columns and beams is another common problem. This chemical reaction reduces the alkalinity of the concrete, making the embedded steel reinforcement more susceptible to corrosion.

Other Defects:

• Cracking: Cracks in the concrete panels and beams can occur due to thermal expansion and contraction, as well as structural movement.
• Spalling: The surface of the concrete can spall, or flake off, exposing the reinforcement to the elements.
• Dampness: Poor insulation and ventilation can lead to dampness and condensation issues within the property.

Defective Premises Act and Designation

Blackburn Orlit houses are designated as defective under the Defective Premises Act. This designation means that these properties are recognized as having inherent structural issues that can affect their safety and habitability. As a result, they may require significant repairs or even demolition and replacement in some cases.

Inspection Guide for Surveyors

When inspecting a Blackburn Orlit house, surveyors should pay close attention to several key areas to identify potential defects and hazards. Here is a step-by-step guide to conducting a thorough inspection:

1. External Inspection:

• Walls: Check for cracks, spalling, and signs of chloride contamination in the PRC panels.
• Roof: Inspect the shallow pitch gable roof for any signs of damage or wear, particularly around the steel trusses.
• Foundation: Examine the concrete pads and underbuilding for any signs of settlement or movement.

2. Internal Inspection:

• Walls: Look for cracks, dampness, and signs of carbonation in the internal walls.
• Floors: Inspect the ground and first floors for any signs of movement, sagging, or damage to the timber joists and PRC beams.
• Ceilings: Check the plasterboard ceilings for cracks, sagging, or water damage.

3. Structural Elements:

• PRC Columns and Beams: Use a cover meter to detect the presence of steel reinforcement and check for signs of corrosion.
• Steel Connectors: Inspect the RSA cleats and bolted steel flange connectors for any signs of rust or deterioration.

4. Moisture and Ventilation:

• Dampness: Use a moisture meter to check for dampness in the walls, floors, and ceilings.
• Ventilation: Ensure that the property has adequate ventilation to prevent condensation and damp issues.

5. Safety and Compliance:

• Electrical and Gas Installations: Check that all electrical and gas installations comply with current safety standards.
• Fire Safety: Ensure that the property has adequate fire safety measures, including smoke alarms and fire exits.

Typical Construction Variants

While the standard construction details of Blackburn Orlit houses are well-documented, there are some variants that potential buyers and investors should be aware of. These variants can affect the overall condition and value of the property.

Concrete Ground Floor:

Some Blackburn Orlit houses may have a concrete ground floor instead of the standard timber joist and PRC beam construction. This variant can provide better durability and resistance to dampness but may also present challenges for repairs and modifications.

Alternative Wall Materials:

In some cases, the external walls may be constructed using alternative materials, such as brick or blockwork, instead of the standard PRC panels. This can affect the thermal performance and maintenance requirements of the property.

Conclusion

The Blackburn Orlit house represents a significant chapter in the UK’s post-war housing history. While these homes were innovative for their time, they are not without their challenges. Potential buyers and investors must be aware of the typical defects and hazards associated with these properties, as well as the implications of their designation as defective under the Defective Premises Act.

Conducting a thorough inspection is crucial to identifying any issues and ensuring the safety and habitability of the property. By understanding the construction details, typical defects, and inspection guidelines, buyers and investors can make informed decisions and safeguard their investment.

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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