Historical Context and Origins

The Permabuilt house, also known by its alternative names such as the WGH Pre-Fab System or Wilkinsons (Runfold), is a unique type of system-built property that emerged in the post-World War II era. Specifically, these houses were constructed in 1948, a period marked by a significant housing shortage in the UK. The government and private sector collaborated to develop quick and efficient housing solutions, leading to the creation of various prefabricated housing systems, including the Permabuilt house.

Manufacturers and Designers

The Permabuilt house was a collaborative effort involving several key players in the construction industry. The primary manufacturer was Wilkinsons (Runfold) Ltd, a company known for its innovative approach to building materials and techniques. The architectural design was handled by Gilbert and Hobson, while the structural engineering was overseen by J H Coombs, a consulting engineer. This collaboration resulted in a robust and efficient housing solution that met the urgent needs of the time.

Number and Location

Interestingly, only two Permabuilt houses were ever constructed, making them a rare find in today’s property market. These houses were typically located in suburban areas, where there was ample space for new housing developments. The limited number of these houses adds to their uniqueness and historical value.

Identification Characteristics

Identifying a Permabuilt house involves looking for several distinctive features. These houses are typically two-storey semi-detached properties with a steep pitch gable roof covered with interlocking concrete tiles. The external walls are rendered throughout, often using a Tyrolean finish, which gives them a textured appearance. The gable apex is also covered with interlocking concrete tiles, adding to the uniformity of the design.

Windows and Doors

The window and door surrounds in a Permabuilt house are made of Precast Reinforced Concrete (PRC), and the windows are usually metal casement types. One of the most distinctive features is the staggered single-storey flat-roofed extension to the gable wall, which often includes a garage made of storey-height PRC panels.

Construction Details

Understanding the construction details of a Permabuilt house is crucial for both buyers and surveyors. These houses were built using a variety of materials and techniques that were innovative for their time but may present certain challenges today.

Substructure

The substructure consists of concrete strip footings and brick under-building. The base units are made of Precast Concrete (PC) with a fillet that engages rebates in the base of the wall panels. A Damp Proof Course (DPC) is also included to prevent moisture ingress.

External Walls

The external walls are rendered and consist of storey-height ribbed PRC panel cavity walls. These panels are tied together using 3/8″ mild steel horizontal screwed tie rods and short mild steel screw fixings. The corners are reinforced with PRC corner units, and the window surrounds are double-leaf PC units with bituminous felt vertical DPC. A timber wall plate and tarred rope jointing are used to secure the structure, and the gable apex is clad with interlocking concrete tiles.

Separating Wall

The separating wall between the semi-detached units is also made of storey-height ribbed PRC panel cavity walls, tied to the external walls with mild steel straps. At the first-floor level, PC units with integral corbels support the first-floor joists, and a felt DPC is installed at the first-floor ceiling level. In the roof space, a 9″ brick wall provides additional separation.

Partitions

The internal partitions are made of load-bearing 4″ clinker PC blocks for structural walls and 3″ clinker PC blocks for non-load-bearing walls. This combination provides both strength and flexibility in the internal layout.

Floors

The ground floor is constructed of concrete, providing a solid and durable base. The first floor consists of timber joists supported by the first-floor PC string course unit. This design allows for some flexibility in the internal layout while maintaining structural integrity.

Ceilings and Roof

The ceilings are made of plasterboard, a common material that provides a smooth finish and can be easily decorated. The roof structure consists of timber rafters and purlins, covered with interlocking concrete tiles. This combination provides both strength and weather resistance.

Typical Hazards and Risks

While the Permabuilt house was an innovative solution for its time, it does come with certain hazards and risks that potential buyers and investors should be aware of.

Reinforced Concrete Durability

One of the primary concerns with Permabuilt houses is the durability of the reinforced concrete used in their construction. Over time, the steel reinforcement within the concrete can corrode, leading to structural weaknesses. This issue is particularly prevalent in properties that have not been well-maintained or have been exposed to harsh weather conditions.

Carbonation and Corrosion

Carbonation is a natural process that occurs when carbon dioxide from the air penetrates the concrete and reacts with the calcium hydroxide to form calcium carbonate. This process lowers the pH of the concrete, making the steel reinforcement more susceptible to corrosion. Corrosion of the steel can lead to cracking and spalling of the concrete, compromising the structural integrity of the building.

Damp and Moisture Ingress

The presence of a DPC in the construction is intended to prevent moisture ingress, but over time, these barriers can deteriorate. Moisture ingress can lead to a range of issues, including damp, mould, and rot, which can affect both the structural integrity and the living conditions within the property.

Defective Premises Act

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 the Permabuilt house was not specifically listed as defective under this Act, the potential issues with reinforced concrete durability and other construction-related risks mean that buyers should exercise caution and seek a thorough survey before purchasing.

Inspection and Assessment Guide

For surveyors and potential buyers, a detailed inspection and assessment of a Permabuilt house are crucial. Here are some key areas to focus on:

External Inspection

• Walls: Check for signs of cracking, spalling, or other damage to the PRC panels. Pay particular attention to the corners and window surrounds, where stress points are likely to occur.
• Roof: Inspect the interlocking concrete tiles for any signs of damage or displacement. Ensure that the timber rafters and purlins are in good condition and free from rot or insect infestation.
• DPC: Look for any signs of damp or moisture ingress at the base of the walls, which could indicate a failure of the DPC.

Internal Inspection

• Partitions: Check the condition of the clinker PC blocks, looking for any signs of cracking or movement. Ensure that load-bearing walls are structurally sound.
• Floors: Inspect the concrete ground floor for any signs of cracking or settlement. Check the timber joists on the first floor for signs of rot or insect damage.
• Ceilings: Look for any signs of water damage or sagging in the plasterboard ceilings, which could indicate issues with the roof or upper floors.

Structural Integrity

• Reinforced Concrete: Use non-destructive testing methods, such as a cover meter or half-cell potential measurement, to assess the condition of the steel reinforcement within the concrete. Look for signs of carbonation and corrosion, which could compromise the structural integrity of the building.
• Carbonation Depth: Measure the depth of carbonation in the concrete to assess the extent of the issue. This can be done using a phenolphthalein solution, which changes colour in the presence of alkaline concrete.

Typical Defects and Maintenance

Understanding the typical defects associated with Permabuilt houses can help in planning maintenance and repairs. Here are some common issues to look out for:

Cracking and Spalling

Cracking and spalling of the PRC panels are common issues, often caused by the corrosion of the steel reinforcement. Regular inspections and timely repairs can help mitigate these issues and extend the lifespan of the property.

Damp and Mould

Damp and mould can be a significant issue, particularly if the DPC has failed or if there are issues with the roof or external walls. Addressing these issues promptly can help prevent further damage and maintain a healthy living environment.

Roof Maintenance

The interlocking concrete tiles on the roof can become damaged or displaced over time, leading to leaks and water ingress. Regular inspections and maintenance of the roof can help prevent these issues and ensure the property remains weather-tight.

Timber Decay

The timber elements of the construction, including the rafters, purlins, and wall plates, can be susceptible to rot and insect damage. Regular inspections and treatment can help protect these elements and maintain the structural integrity of the property.

Conclusion

The Permabuilt house is a unique and historically significant type of system-built property that offers both opportunities and challenges for home buyers and investors. Understanding the construction details, typical hazards, and maintenance requirements is crucial for making an informed decision. By conducting a thorough inspection and assessment, potential buyers can identify any issues and plan for necessary repairs and maintenance.

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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