Understanding Unit-Built Houses

Unit-built houses, also known as Unit Construction houses, are a unique and fascinating segment of the UK property market. These properties, primarily constructed in the 1940s, offer a distinctive architectural style and construction methodology that sets them apart from other housing types. As an expert surveyor, I will delve into the various aspects of these properties, from their historical context and construction details to the potential hazards and inspection tips. This comprehensive guide aims to equip home buyers and investors with the knowledge they need to make informed decisions when considering a unit-built house.

Historical Context and Manufacturers

Period and Location

Unit-built houses were predominantly constructed in the 1940s, a period marked by significant housing shortages due to the aftermath of World War II. These houses were primarily built in suburban areas, providing affordable and quickly constructed housing solutions for the growing population. The design and construction of these houses were driven by the need for rapid development and cost-effectiveness.

Manufacturers and Designers

The primary designer associated with unit-built houses is S. Burton, who played a crucial role in the architectural and structural design of these properties. The construction was carried out by various manufacturers, with a focus on using innovative materials and techniques to expedite the building process. The use of reinforced concrete and Gypklith panels was a hallmark of these constructions, providing both durability and ease of assembly.

Characteristics of Unit-Built Houses

Architectural Features

Unit-built houses are typically semi-detached bungalows with a flat roof covered in bituminous felt. The external walls are rendered throughout, giving them a uniform and clean appearance. One of the distinctive features is the recessed front door porch, which adds a touch of character to the otherwise utilitarian design.

Construction Details

Substructure

The substructure of unit-built houses consists of concrete pads below corner columns, concrete strip footings, and a brick underbuilding. A rendered concrete kerb and plastic emulsion damp-proof course (DPC) are also integral parts of the substructure, providing stability and moisture protection.

External Walls

The external walls are constructed using reinforced concrete (RC) columns and Gypklith hollow trough beams infilled with RC. These walls are then rendered to provide a smooth finish. The use of 6’6″ x 3’4″ x 8″ hollow core woodwool (Gypklith) panels with a 1″ leaf is a distinctive feature of these walls.

Separating Wall

The separating wall between semi-detached units is constructed using Gypklith hollow trough downstand beams infilled with RC. This construction method provides both structural integrity and sound insulation between the units.

Partitions

Internal partitions are made of 4″ Gypklith hollow core panels, which are lightweight yet sturdy, allowing for easy modification and customization of the interior layout.

Ground Floor

The ground floor consists of 6″ Gypklith hollow tray slabs on sleeper walls. This construction method provides a solid and stable base for the house, ensuring durability and resistance to ground movement.

Ceilings and Roof

The ceilings are constructed using Gypklith panels, while the roof comprises 6’6″ x 1’8″ Gypklith hollow roof trays covered with bituminous felt. A 4″ x 3″ parapet course is also included, providing additional structural support and aesthetic appeal.

Potential Hazards and Risks

Structural Integrity

One of the primary concerns with unit-built houses is the potential for structural issues, particularly related to the reinforced concrete elements. Over time, concrete can deteriorate due to various factors such as carbonation, chloride ingress, and freeze-thaw cycles. This can lead to corrosion of the steel reinforcement, compromising the structural integrity of the house.

Moisture Ingress

The flat roof design, while cost-effective and easy to construct, can be prone to moisture ingress if not properly maintained. Bituminous felt, commonly used for roofing, can degrade over time, leading to leaks and water damage. Regular inspection and maintenance of the roof are essential to prevent such issues.

Thermal Insulation

Unit-built houses, particularly those constructed in the 1940s, may not meet modern thermal insulation standards. The use of Gypklith panels, while innovative at the time, may not provide adequate insulation, leading to higher energy costs and reduced comfort levels. Retrofitting with modern insulation materials can help mitigate this issue.

Asbestos

Given the era of construction, there is a possibility that asbestos-containing materials were used in some unit-built houses. Asbestos was commonly used for its fire-resistant and insulating properties but is now known to pose significant health risks. A thorough survey to identify and safely remove any asbestos-containing materials is crucial.

Defective Premises Act Considerations

The Defective Premises Act 1972 imposes a duty on builders, developers, and landlords to ensure that properties are constructed and maintained to a reasonable standard. While unit-built houses were innovative for their time, some may be classified as defective under this Act due to issues such as structural deterioration, inadequate insulation, or the presence of hazardous materials like asbestos.

Inspection Tips for Unit-Built Houses

Structural Assessment

When inspecting a unit-built house, it is essential to conduct a thorough structural assessment. This includes checking for signs of concrete deterioration, such as cracking, spalling, or rust stains, which may indicate corrosion of the steel reinforcement. Using tools like a cover meter can help detect the presence and condition of the reinforcement.

Roof Inspection

Inspect the flat roof for signs of wear and tear, such as cracks, blisters, or ponding water. Ensure that the bituminous felt is in good condition and that there are no leaks. Pay particular attention to the parapet course and any roof penetrations, as these are common areas for moisture ingress.

Moisture and Dampness

Check for signs of moisture ingress and dampness, particularly around the base of the walls and in the roof space. Use a moisture meter to detect hidden dampness and ensure that the damp-proof course (DPC) is intact and functioning correctly.

Thermal Performance

Assess the thermal performance of the house by checking for drafts, cold spots, and inadequate insulation. Consider using thermal imaging to identify areas of heat loss and recommend appropriate retrofitting measures to improve energy efficiency.

Asbestos Survey

Given the potential presence of asbestos, it is advisable to conduct an asbestos survey. This involves sampling and testing materials suspected of containing asbestos and, if necessary, arranging for their safe removal by a licensed contractor.

Typical Defects in Unit-Built Houses

Concrete Deterioration

As mentioned earlier, concrete deterioration is a common issue in unit-built houses. This can manifest as cracking, spalling, or delamination of the concrete surface. Regular maintenance and repair of affected areas are essential to prevent further deterioration.

Roof Leaks

Flat roofs covered with bituminous felt are prone to leaks, particularly if the felt has degraded over time. Regular inspection and maintenance of the roof, including re-felting if necessary, can help prevent water ingress and associated damage.

Thermal Bridging

The use of Gypklith panels, while innovative, can result in thermal bridging, where heat is conducted through the building envelope, leading to cold spots and increased energy consumption. Retrofitting with modern insulation materials can help mitigate this issue.

Dampness and Mould

Moisture ingress, particularly around the base of the walls and in the roof space, can lead to dampness and mould growth. Ensuring that the DPC is intact and addressing any roof leaks promptly can help prevent these issues.

Conclusion

Unit-built houses, with their unique construction methods and historical significance, offer a fascinating option for home buyers and investors in the UK. However, it is essential to be aware of the potential hazards and risks associated with these properties, from structural issues and moisture ingress to thermal insulation and asbestos. By conducting thorough inspections and addressing any identified issues, you can ensure that your investment in a unit-built house is both safe and rewarding.

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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