Historical Context and Background

The Arrow House, a distinctive property type in the UK, was manufactured by Arrow Unit Slabs Ltd and designed by D Arnot. These properties were constructed in 1945, a period marked by a significant housing shortage post-World War II. Only 20 of these unique homes were built, making them a rare find in today’s property market. Typically, these houses are located in suburban areas, often in regions that experienced rapid development during the mid-20th century.

Manufacturers and Designers

Arrow Unit Slabs Ltd, the manufacturer behind the Arrow House, was a prominent player in the post-war construction industry. The company specialized in system-built properties, which were essential in addressing the urgent need for housing. The designer, D Arnot, was known for innovative approaches to residential architecture, focusing on efficiency and durability.

Typical Characteristics of the Arrow House

Architectural Features

Arrow Houses are available in two main configurations: bungalows and two-storey detached or semi-detached houses. They feature a medium pitch gable roof covered with Ruberoid-topped steel decking, which was a popular roofing material in the mid-20th century due to its durability and weather resistance. The external walls are rendered throughout, providing a uniform and aesthetically pleasing appearance.

One of the distinctive features of the Arrow House is the pressed steel soffit that follows the outline of the rafters, giving the roofline a clean and defined look. Additionally, a flat concrete canopy over the front door adds a touch of modernist design, which was quite forward-thinking for its time.

Construction Details

Substructure

The substructure of the Arrow House consists of concrete foundations and a concrete slab, with a damp-proof course (DPC) to prevent moisture ingress. This robust foundation system ensures the stability and longevity of the property.

External Walls

The external walls are constructed using rendered 18-inch storey height exposed aggregate precast reinforced concrete (PRC) panels. These panels are designed with 3/4-inch weep holes to allow for drainage and prevent water accumulation. Behind these panels, there is a cavity filled with lightweight foamed slag precast concrete (PC) panels, which provide additional insulation. The walls are further reinforced with PRC beams and dovetail sheeting at the gable ends.

Roof

The roof structure comprises braced light steel trusses and ties, supporting the steel decking and Ruberoid topping. This combination of materials ensures a strong and weather-resistant roof, capable of withstanding the UK’s variable climate.

Internal Features

The internal partitions are made of lightweight precast concrete panels, providing a balance between strength and ease of construction. The ground floor is typically concrete, although some variants feature suspended timber boarding or synthetic asphalt.

Typical Hazards and Risks

Structural Concerns

One of the primary concerns with Arrow Houses is the potential for corrosion of the steel reinforcement within the concrete panels. Over time, exposure to moisture and carbon dioxide can lead to carbonation, which reduces the alkalinity of the concrete and allows the steel to rust. This can compromise the structural integrity of the property.

Thermal Insulation

While the lightweight foamed slag panels provide some insulation, they may not meet modern standards for thermal efficiency. Homeowners may need to invest in additional insulation to improve energy efficiency and reduce heating costs.

Damp and Moisture

The presence of weep holes in the external walls is a positive feature for drainage, but it also indicates that moisture management is a critical aspect of maintaining these properties. Regular inspections and maintenance of the damp-proof course and drainage systems are essential to prevent damp issues.

Defective Premises Act Considerations

The Arrow House is not classed as defective under the Defective Premises Act. However, given the age and unique construction methods of these properties, it is crucial for potential buyers to conduct thorough surveys and assessments to identify any potential issues.

Inspection Guide for Surveyors

Pre-Inspection Preparation

Before conducting an inspection, surveyors should familiarize themselves with the specific characteristics and construction details of the Arrow House. Key references include the BRE Archive NTHSc and relevant BRE Digests and Reports on reinforced concrete durability.

External Inspection

1. Roof: Inspect the Ruberoid-topped steel decking for signs of wear, corrosion, or damage. Check the condition of the braced light steel trusses and ties.
2. Walls: Examine the rendered PRC panels for cracks, spalling, or other signs of deterioration. Ensure the weep holes are clear and functioning correctly.
3. Soffit and Canopy: Check the pressed steel soffit and flat concrete canopy for any signs of rust or structural damage.

Internal Inspection

1. Partitions and Floors: Inspect the lightweight PC panels for any signs of movement or cracking. Check the condition of the concrete ground floor or any variants such as suspended timber boarding or synthetic asphalt.
2. Damp and Moisture: Use a moisture meter to check for dampness in walls and floors. Inspect the DPC for any signs of failure.

Structural Integrity

1. Carbonation Depths: Assess the carbonation depths in the concrete panels using appropriate testing methods. Refer to BRE Digest 444 and BR 19 for guidance.
2. Corrosion: Check for signs of corrosion in the steel reinforcement. This may involve taking core samples and conducting laboratory tests.

Typical Defects and Maintenance Tips

Common Defects

1. Corrosion of Steel Reinforcement: As mentioned earlier, corrosion is a significant concern. Regular inspections and maintenance are essential to address this issue promptly.
2. Cracking and Spalling: Cracks in the concrete panels can lead to spalling, where pieces of concrete break away from the surface. This can be caused by freeze-thaw cycles, moisture ingress, or structural movement.
3. Damp Issues: Inadequate drainage or failure of the DPC can lead to damp problems, which can affect the structural integrity and indoor air quality.

Maintenance Tips

1. Regular Inspections: Conduct regular inspections of the roof, walls, and internal partitions to identify and address any issues early.
2. Moisture Management: Ensure that the weep holes and drainage systems are functioning correctly. Maintain the DPC to prevent moisture ingress.
3. Thermal Insulation: Consider upgrading the insulation to improve energy efficiency and reduce heating costs.

Conclusion

The Arrow House, with its unique construction and historical significance, offers a distinctive option for home buyers and investors in the UK. While these properties come with their own set of challenges, understanding their construction details and potential issues can help you make an informed decision. Regular maintenance and thorough inspections are key to preserving the structural integrity and value 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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