Understanding the Permacrete House

The Permacrete house, also known by its alternative names Cemacrete and Cemalite, represents a unique chapter in the history of British housing. These properties were primarily constructed in the 1940s, a period marked by a significant demand for rapid and cost-effective housing solutions. The manufacturer behind these homes was Cemacete Ltd, with H.E. Cavell as the designer. This article delves into the intricate details of Permacrete houses, providing valuable insights for home buyers, investors, and surveyors.

Historical Context and Manufacturing

Origins and Purpose

The 1940s were a transformative decade for the UK, particularly in the aftermath of World War II. The need for quick and affordable housing solutions led to the development of various system-built properties, including the Permacrete house. These homes were designed to address the housing shortage and provide durable, long-lasting residences for the growing population.

Manufacturer and Designer

Cemacete Ltd, the company behind the Permacrete house, was a prominent player in the construction industry during this era. The design was spearheaded by H.E. Cavell, who aimed to create a robust and efficient housing solution. The innovative use of reinforced concrete and pre-cast slabs set these homes apart from traditional brick-and-mortar constructions.

Production and Distribution

While the exact number of Permacrete houses built remains unclear, it is evident that these properties were primarily constructed in the 1940s. They were predominantly found in suburban areas, where the demand for affordable housing was particularly high. The medium pitch hipped roofs, rendered external walls, and distinctive string course at the first-floor level are some of the key identification characteristics of these homes.

Construction Details

Substructure

The foundation of a Permacrete house typically consists of concrete strip footings and reinforced concrete (RC) under-building. A concrete slab forms the base, with a damp-proof course (DPC) to prevent moisture ingress. This robust substructure ensures the stability and durability of the property.

External Walls

The external walls of Permacrete houses are rendered throughout, providing a uniform and aesthetically pleasing appearance. The construction involves a combination of pre-cast (PC) slabs and reinforced concrete infill. Specifically, the walls comprise 9-inch RC, with 3-inch by 2-inch by 1-inch PC slabs, 6.5-inch RC infill, and 1.5-inch PC slabs. Mild steel (MS) ties and bars are used to reinforce the structure, ensuring its strength and longevity.

Separating Walls and Partitions

The separating walls between adjoining properties are constructed using 9.5-inch RC, with a similar combination of PC slabs and RC infill. In the roof space, 9-inch brickwork is used to provide additional stability. Internal partitions are made from 6-inch RC, with PC slabs and RC infill up to the first-floor level, and clinker concrete blocks above.

Floors

The ground floor of a Permacrete house typically features tongue-and-groove (T&G) timber blocks laid on a sand/cement screed over a concrete base. The first floor comprises timber boarding on timber battens, cast in a 6-inch RC slab with 1.5-inch PC slab permanent shuttering. This construction method ensures a solid and stable flooring system.

Roof

The roof structure of a Permacrete house includes timber rafters and purlins, covered with concrete tiles. In some variants, clay tiles are used instead. The roof design, with its medium pitch and hipped configuration, provides effective water drainage and enhances the overall aesthetic appeal of the property.

Typical Characteristics and Identification

Visual Identification

Permacrete houses are typically two-storey semi-detached properties. The medium pitch hipped roof, covered with clay or concrete tiles, is a distinctive feature. The external walls are rendered throughout, providing a smooth and uniform appearance. A string course at the first-floor level adds a decorative element to the façade.

Structural Features

The use of reinforced concrete and pre-cast slabs is a hallmark of Permacrete houses. The combination of these materials ensures the structural integrity and durability of the property. The presence of mild steel ties and bars further reinforces the construction, making these homes resilient to various environmental factors.

Potential Hazards and Risks

Structural Issues

Despite their robust construction, Permacrete houses are not without their potential hazards and risks. One of the primary concerns is the durability of the reinforced concrete. 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 adequately maintained or have been exposed to harsh environmental conditions.

Moisture Ingress

Moisture ingress is another common issue in Permacrete houses. The damp-proof course (DPC) is designed to prevent moisture from entering the property, but if it becomes damaged or deteriorates, it can lead to damp problems. This can cause damage to the internal finishes and potentially lead to mould growth, which can have health implications for the occupants.

Thermal Performance

The thermal performance of Permacrete houses can also be a concern. The use of concrete and pre-cast slabs can result in poor insulation, leading to higher energy consumption for heating. Retrofitting insulation can be challenging and costly, but it is essential for improving the energy efficiency and comfort of the property.

Defective Premises Act and Classification

Legal 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 Permacrete houses were innovative for their time, some may be classified as defective under this Act due to issues such as structural weaknesses, moisture ingress, and poor thermal performance.

Implications for Buyers and Investors

For home buyers and investors, it is crucial to be aware of the potential classification of a Permacrete house as defective. This can impact the property’s value, mortgageability, and insurance premiums. A thorough survey and assessment by a qualified professional are essential to identify any defects and determine the necessary remedial works.

Inspection and Assessment Guide

Pre-Inspection Preparation

Before conducting an inspection of a Permacrete house, it is essential to gather relevant information about the property. This includes historical data, previous maintenance records, and any known issues. Familiarising yourself with the typical construction details and potential defects will help you conduct a more thorough and effective inspection.

External Inspection

Start the inspection by examining the external features of the property. Look for any signs of cracking or spalling in the rendered walls, which could indicate underlying structural issues. Check the condition of the roof tiles and ensure that the roof structure is intact. Pay particular attention to the string course at the first-floor level, as this can be a weak point in the construction.

Internal Inspection

Inside the property, inspect the walls, floors, and ceilings for any signs of damp or moisture ingress. Check the condition of the timber flooring and look for any signs of rot or decay. Examine the internal partitions and separating walls for any cracks or structural weaknesses. Pay attention to the condition of the windows and doors, as these can be areas where moisture ingress occurs.

Structural Assessment

A detailed structural assessment is essential to identify any potential issues with the reinforced concrete and steel reinforcement. This may involve taking core samples of the concrete and testing for carbonation and chloride levels. The use of non-destructive testing methods, such as ground-penetrating radar (GPR) and ultrasonic testing, can also help identify any hidden defects.

Thermal Performance Assessment

Assessing the thermal performance of the property is crucial for determining its energy efficiency. This may involve conducting a thermal imaging survey to identify any areas of heat loss. Check the insulation levels in the walls, floors, and roof, and consider the feasibility of retrofitting additional insulation if necessary.

Typical Defects and Remedial Works

Common Defects

Permacrete houses are prone to several common defects, including:

• Corrosion of Steel Reinforcement: Over time, the steel reinforcement within the concrete can corrode, leading to structural weaknesses. This is often caused by carbonation or chloride ingress.
• Cracking and Spalling: Cracks in the rendered walls and spalling of the concrete can occur due to thermal movement, moisture ingress, or structural issues.
• Damp and Moisture Ingress: Damaged or deteriorated damp-proof courses can lead to moisture ingress, causing damp problems and potential mould growth.
• Poor Thermal Performance: The use of concrete and pre-cast slabs can result in poor insulation, leading to higher energy consumption for heating.

Remedial Works

Addressing these defects requires a combination of preventative and remedial measures:

• Corrosion of Steel Reinforcement: Treating the corroded steel reinforcement and applying protective coatings can help prevent further corrosion. In severe cases, it may be necessary to replace the affected sections of concrete.
• Cracking and Spalling: Repairing cracks and spalled areas with suitable concrete repair products can restore the structural integrity of the property. It is also essential to address the underlying cause of the cracking to prevent recurrence.
• Damp and Moisture Ingress: Repairing or replacing the damp-proof course can help prevent moisture ingress. Installing additional drainage systems and improving ventilation can also help manage moisture levels within the property.
• Improving Thermal Performance: Retrofitting insulation to the walls, floors, and roof can significantly improve the thermal performance of the property. This may involve installing external wall insulation, underfloor insulation, and loft insulation.

Conclusion

The Permacrete house represents a unique and innovative approach to post-war housing in the UK. While these properties have several distinctive characteristics and benefits, they are also prone to certain defects and risks. For home buyers and investors, understanding the construction details, potential hazards, and necessary remedial works is crucial for making informed decisions.

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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