Historical Context and Manufacturers

The Unity Type II 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 II, along with its predecessor, the Type I, saw the construction of approximately 19,000 units across the UK. These homes were also known by alternative names such as Butterley, Unity, and Unity Brickclad.

Design and Characteristics

Architectural Features

Unity Type II houses are typically found as bungalows or two-storey semi-detached and terraced houses. They are easily identifiable by their medium pitch hipped or gable roofs, which are covered with concrete tiles. The external walls are constructed using stack bonded precast concrete (PC) panels, with some variations featuring partial or total brick cladding. Tile hanging is often present on the gable apex, adding to the distinct appearance of these homes.

Construction Details

Substructure

The substructure of Unity Type II houses consists of concrete strip footings and a concrete slab. This robust foundation was designed to provide stability and support for the prefabricated components of the house.

Frame

The main frame is constructed using 6″ x 3 1/2″ storey height precast reinforced concrete (PRC) columns. These columns are anchored to the foundation with mass concrete bases. Horizontal metal braces are installed between columns at the first floor and eaves level, providing additional structural integrity. Diagonal bracing is used in vertical planes between columns at corners and adjacent columns, as well as in horizontal planes between columns in the front and rear walls. Steel floor support beams further enhance the stability of the structure.

External Walls

The external walls are composed of PC panels, a cavity, and PC blocks. Copper strap retaining clips are used to secure these components together. This construction method provides a durable and weather-resistant exterior.

Separating Walls and Partitions

The separating walls between units are constructed using 2 1/2″ lightweight PC block cavity walls. Internal partitions are made from storey height reinforced plaster units, offering both strength and ease of installation.

Floors

The ground floor typically features timber boarding on a concrete base, while the first floor consists of tongue and groove (T&G) or laminated timber boarding. These boards are supported by RSJ floor support beams, which are fixed to the columns using RSC end plates.

Ceilings and Roof

The ceilings in Unity Type II houses are not well-documented, but the roof structure is known to consist of timber rafters connected to column heads with steel plates. The roof is covered with asbestos cement sheets and concrete tiles, providing a durable and weather-resistant finish.

Typical Hazards and Risks

Structural Issues

One of the most significant concerns with Unity Type II houses is the horizontal cracking of PRC columns. This issue can compromise the structural integrity of the building and may require extensive repairs. Additionally, cracking and spalling of PRC lintels are common problems that can affect the stability of the structure.

Corrosion

Corrosion of steel components is another prevalent issue in Unity Type II houses. The interface between RSJ floor support beams and PRC columns is particularly susceptible to corrosion, which can weaken the overall structure. Corrosion of copper strap retaining clips is also a common problem that can affect the stability of the external walls.

Chloride Contamination

Significant levels of chloride have been found in the PRC external wall panels of Unity Type II houses. This contamination can accelerate the corrosion of steel components and compromise the durability of the structure.

Asbestos

Asbestos cement roofing sheets are a known hazard in Unity Type II houses. Asbestos is a dangerous material that can pose serious health risks if disturbed. Proper handling and removal by qualified professionals are essential to ensure the safety of occupants.

Defective Premises Act

Unity Type II 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. Buyers and investors should be aware of this designation and consider the potential costs and challenges associated with owning and maintaining a Unity Type II house.

Inspection Guide for Surveyors

Identifying Characteristics

When inspecting a Unity Type II house, surveyors should look for the following identifying characteristics:
– Bungalows or two-storey semi-detached and terraced houses
– Medium pitch hipped or gable roof covered with concrete tiles
– External walls of stack bonded PC panels or partial/total brick cladding
– Tile hanging on the gable apex

Common Defects to Look For

Horizontal Cracking of PRC Columns

Surveyors should carefully inspect the PRC columns for any signs of horizontal cracking. This issue can compromise the structural integrity of the building and may require extensive repairs.

Cracking and Spalling of PRC Lintels

Cracking and spalling of PRC lintels are common problems in Unity Type II houses. Surveyors should check these components for any signs of damage that could affect the stability of the structure.

Corrosion of Steel Components

The interface between RSJ floor support beams and PRC columns is particularly susceptible to corrosion. Surveyors should inspect these areas for any signs of rust or deterioration. Additionally, the condition of copper strap retaining clips should be assessed to ensure the stability of the external walls.

Chloride Contamination

Surveyors should be aware of the potential for significant levels of chloride in the PRC external wall panels. This contamination can accelerate the corrosion of steel components and compromise the durability of the structure.

Asbestos

Asbestos cement roofing sheets are a known hazard in Unity Type II houses. Surveyors should identify the presence of asbestos and recommend proper handling and removal by qualified professionals to ensure the safety of occupants.

Construction Variants

Unity Type II houses have several construction variants that surveyors should be aware of:

Frame with Twin PRC Corner Columns

Some Unity Type II houses feature a frame with twin PRC corner columns. This variant provides additional structural support and stability.

Cladding at Corners

The cladding at the corners of Unity Type II houses can be either square or chamfered. Surveyors should note the type of cladding used and assess its condition.

PRC Columns as Mullions

In some Unity Type II houses, PRC columns act as mullions. This design feature can affect the overall appearance and structural integrity of the building.

PRC Lintel Bolted to RSAs

PRC lintels in Unity Type II houses are often bolted to rolled steel angles (RSAs) that are bolted to the columns. Surveyors should inspect these connections for any signs of damage or corrosion.

Cavity Closers Below Window Openings

Cavity closers are used below window openings in Unity Type II houses. Surveyors should check these components for any signs of deterioration or damage.

Linings to External Walls

The external walls of Unity Type II houses are often lined with plasterboard on timber battens. Surveyors should assess the condition of these linings and recommend any necessary repairs or replacements.

PRC Rafters

Some Unity Type II houses feature PRC rafters. Surveyors should inspect these components for any signs of damage or deterioration that could affect the stability of the roof structure.

Maintenance and Repair Considerations

Structural Repairs

Addressing structural issues in Unity Type II houses can be challenging and costly. Horizontal cracking of PRC columns and cracking and spalling of PRC lintels may require extensive repairs to ensure the stability and safety of the building. It is essential to work with qualified professionals who have experience with PRC construction to carry out these repairs.

Corrosion Prevention

Preventing and addressing corrosion in Unity Type II houses is crucial to maintaining the structural integrity of the building. Regular inspections and maintenance of steel components, such as RSJ floor support beams and copper strap retaining clips, can help prevent corrosion and extend the lifespan of the structure.

Chloride Contamination Mitigation

Mitigating the effects of chloride contamination in PRC external wall panels is essential to prevent accelerated corrosion of steel components. This may involve the application of protective coatings or the replacement of affected panels.

Asbestos Management

Proper management of asbestos in Unity Type II houses is essential to ensure the safety of occupants. Asbestos cement roofing sheets should be handled and removed by qualified professionals to prevent exposure to harmful asbestos fibres.

Regular Inspections

Regular inspections by qualified surveyors are essential to identify and address any issues in Unity Type II houses. These inspections can help detect problems early and prevent costly repairs in the future.

Conclusion

The Unity Type II house is a significant example of post-war British architecture, designed to address the urgent housing needs of the 1950s. While these homes offer unique architectural features and historical value, they also come with inherent structural issues and potential hazards. Buyers and investors should be aware of these challenges and consider the potential costs and maintenance requirements associated with owning a Unity Type II house.

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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