Historical Context and Manufacturers

The Unity Type I house is a notable example of post-war British architecture, designed to address the urgent housing needs of the 1950s. Manufactured by Unity Structures Ltd and Unity House Construction, these homes were part of a broader initiative to provide affordable and quickly constructed housing solutions. The Unity Type I, along with its sibling, the Unity Type II, saw the construction of approximately 19,000 units across the UK.

These homes were primarily built in the 1950s, a period marked by a significant housing shortage following World War II. The Unity Type I houses were designed to be both cost-effective and efficient to construct, leveraging the benefits of system-built properties. They were commonly found in suburban areas and new housing estates, providing much-needed accommodation for the growing population.

Design and Characteristics

Architectural Features

The Unity Type I house is easily identifiable by its distinct architectural features. These homes were typically constructed as bungalows or two-storey semi-detached and terraced houses. The roofs were medium-pitched, either hipped or gabled, and covered with concrete tiles. The external walls were made of stack-bonded precast concrete (PC) panels, with some variations featuring partial or total brick cladding. Tile hanging was often used to decorate the gable apex, and the corners of the buildings were characterized by splayed PC blocks.

Construction Details

Substructure

The substructure of Unity Type I houses consisted of concrete strip footings and a concrete slab. This provided a stable and durable foundation for the rest of the structure.

Frame

The main frame of the house was constructed using storey-height precast reinforced concrete (PRC) columns, measuring 6″ x 3 1/2″. These columns were anchored to the foundation with mass concrete bases. Horizontal metal braces were installed between the columns at the first floor and eaves level, providing additional stability. Diagonal bracing was used in the vertical plane between columns at the corners and adjacent columns, as well as in the horizontal plane between columns in the front and rear walls and RSJ floor support beams.

External Walls

The external walls were constructed using PC panels, creating a cavity wall structure. Copper strap retaining clips were used to secure the panels in place.

Separating Walls and Partitions

The separating walls between units were made of lightweight PC block cavity walls. Internal partitions were constructed using storey-height reinforced plaster units.

Floors

The ground floor was typically made of timber boarding laid on a concrete base. The first floor featured tongue-and-groove (T&G) or laminated timber boarding, supported by RSJ floor beams fixed to the columns with twin steel end plates.

Ceilings and Roof

The ceilings of Unity Type I houses are not well-documented, but the roofs were constructed using timber connected to the column heads with steel plates. The roofing materials included asbestos cement sheets and concrete tiles.

Typical Hazards and Risks

Structural Issues

One of the most significant concerns with Unity Type I houses is the potential for structural issues. Longitudinal cracking of the PRC columns is a common problem, which can compromise the integrity of the building. Additionally, cracking and spalling of PRC lintels, as well as corrosion of steelwork at the interface between PRC columns and RSJ first floor beams, are frequent issues.

Corrosion and Chloride Levels

Corrosion of copper fixings to cladding is another prevalent issue. High levels of chloride in the PRC panels can accelerate the corrosion process, leading to further structural degradation.

Asbestos

Asbestos cement roofing sheets were commonly used in the construction of Unity Type I houses. Asbestos is a hazardous material that can pose serious health risks if disturbed. It is essential to handle and manage asbestos-containing materials with care to prevent exposure.

Defective Premises Act

Unity Type I houses are designated as defective under the Defective Premises Act. This designation means that these properties are recognized as having inherent defects that can affect their safety and habitability. As a result, it is crucial for potential buyers and investors to be aware of these issues and take appropriate measures to address them.

Inspection Guide for Surveyors

When inspecting a Unity Type I 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:

Exterior Inspection

1. Roof: Check the condition of the concrete tiles and asbestos cement sheets. Look for signs of damage, wear, or asbestos exposure.
2. Walls: Inspect the external walls for cracks, spalling, and signs of corrosion in the PRC panels and copper fixings. Pay particular attention to the corners and areas around windows and doors.
3. Foundation: Examine the concrete strip footings and slab for any signs of movement, cracking, or deterioration.

Interior Inspection

1. Floors: Assess the condition of the timber boarding on the ground and first floors. Look for signs of rot, warping, or structural weakness.
2. Walls and Partitions: Check the separating walls and internal partitions for cracks, movement, or other signs of structural issues.
3. Ceilings: Although specific details about the ceilings are not well-documented, inspect for any signs of sagging, cracking, or water damage.

Structural Elements

1. PRC Columns: Look for longitudinal cracking, spalling, and signs of corrosion in the PRC columns. Pay close attention to the interface between the columns and RSJ floor beams.
2. Lintels and Beams: Inspect the PRC lintels and RSJ floor beams for cracking, spalling, and corrosion. Ensure that the steel end plates and other connections are secure and free from rust.

Hazardous Materials

1. Asbestos: Identify any asbestos-containing materials, such as roofing sheets, and ensure they are in good condition. If asbestos is present, recommend professional removal or encapsulation to prevent exposure.
2. Chloride Levels: Test the PRC panels for chloride levels to assess the risk of accelerated corrosion. High chloride levels can indicate a need for remedial action to protect the structural integrity of the building.

Typical Defects and Common Issues

Unity Type I houses are known for several common defects and issues that can affect their safety and habitability. Here are some of the most prevalent problems:

Longitudinal Cracking of PRC Columns

Longitudinal cracking of the PRC columns is a significant concern, as it can compromise the structural integrity of the building. These cracks can develop over time due to various factors, including thermal expansion, moisture ingress, and chloride-induced corrosion.

Cracking and Spalling of PRC Lintels

Cracking and spalling of PRC lintels are also common issues. These defects can weaken the lintels and reduce their load-bearing capacity, potentially leading to structural failure.

Corrosion of Steelwork

Corrosion of steelwork at the interface between PRC columns and RSJ first floor beams is another prevalent problem. This corrosion can weaken the connections and reduce the overall stability of the building.

Corrosion of Copper Fixings

Copper fixings used to secure cladding can also corrode over time, particularly in the presence of high chloride levels. This corrosion can lead to the detachment of cladding panels and further structural issues.

Asbestos-Related Hazards

Asbestos cement roofing sheets pose a significant health risk if disturbed. Asbestos fibers can become airborne and inhaled, leading to serious respiratory diseases, including asbestosis, lung cancer, and mesothelioma.

Variants and Alternative Names

The Unity Type I house has several variants and alternative names, including Butterley, Unity, and Unity Brickclad. These variants may feature different construction details, such as:

• Frame with Twin PRC Corner Columns: Some Unity Type I houses have a frame with twin PRC corner columns, providing additional structural support.
• PRC External Wall Panels: The external wall panels may be square or chamfered at the corners, with a concave splay to the PC corner blocks.
• PRC Columns as Mullions: In some variants, the PRC columns act as mullions, providing additional support for the external walls.
• PRC Lintels Bolted to RSAs: PRC lintels may be bolted to rolled steel angles (RSAs) that are bolted to the columns, providing additional stability.
• Cavity Closers Below Window Openings: Some variants feature cavity closers below window openings to improve thermal performance and reduce the risk of moisture ingress.
• PRC Rafters: The roof structure may include PRC rafters, providing additional support for the roofing materials.
• Concave Chamfer to Splayed Corner: Early Unity Type I houses may have a concave chamfer to the splayed corner, adding a distinctive architectural feature.

Conclusion

The Unity Type I house is a significant example of post-war British architecture, designed to address the urgent housing needs of the 1950s. While these homes provided much-needed accommodation, they are also known for several common defects and hazards that can affect their safety and habitability. Potential buyers and investors should be aware of these issues and take appropriate measures to address them.

When inspecting a Unity Type I house, surveyors should pay close attention to key areas, including the roof, walls, foundation, floors, and structural elements. Identifying and addressing common defects, such as longitudinal cracking of PRC columns, cracking and spalling of PRC lintels, and corrosion of steelwork, is essential to ensure the safety and stability of the building.

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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