Overview of Perma-Erecta Houses

The Perma-Erecta house is a distinctive type of system-built property that emerged in the UK during the 1940s. These homes were primarily constructed by Perma-Erecta Ltd, with design contributions from Braithwaite & Sackman Ltd. The Perma-Erecta house is a notable example of post-war British architecture, designed to address the urgent housing needs of the time. This article will delve into the various aspects of Perma-Erecta houses, including their construction, typical characteristics, potential hazards, and inspection tips for prospective buyers and investors.

Historical Context and Manufacturers

Period Built

Perma-Erecta houses were predominantly built in the 1940s, a period marked by a significant housing shortage in the UK. The aftermath of World War II left many families without adequate housing, prompting the government and private companies to explore innovative construction methods. System-built properties like the Perma-Erecta house were developed to provide quick, cost-effective housing solutions.

Manufacturers and Designers

The primary manufacturer of Perma-Erecta houses was Perma-Erecta Ltd, a company known for its expertise in prefabricated construction. The designs were also influenced by Braithwaite & Sackman Ltd, who contributed to the architectural and structural elements of these homes. Together, these companies aimed to create durable, affordable housing that could be rapidly assembled to meet the pressing demand.

Identification Characteristics

General Appearance

Perma-Erecta houses are typically two-storey semi-detached homes. They feature a medium pitch hipped roof covered with clay tiles, which is a distinctive characteristic. The external walls are rendered throughout, giving the houses a uniform and somewhat modern appearance for their time. Some variations include single or two-storey side extensions with flat roofs.

External Features

• PC Window Sills and Jambs: These houses often have pre-cast (PC) window sills and jambs, which are notable for their durability and ease of installation.
• Render: The external walls are rendered, providing a smooth finish that can be painted or left as is.
• Roof: The medium pitch hipped roof is covered with clay tiles, a common roofing material in the 1940s.

Construction Details

Substructure

The substructure of Perma-Erecta houses consists of a 6-inch concrete slab, which provides a solid foundation. The base units are 6 inches by 12 inches pre-cast reinforced concrete (PRC) units. Air vents are incorporated to ensure proper ventilation, and a damp-proof course (DPC) is included to prevent moisture ingress.

External Walls

The external walls are constructed using storey-height PRC columns. Intermediate columns measure 7 inches by 5 inches, while corner columns are 9 inches by 9 inches. These columns have 2-inch cored holes running through their height. Reinforced steel channel (RSC) perimeter beams are placed at the first floor and eaves level, with mild steel (MS) angle fixing cleats for additional support. The walls are rendered and consist of channel section PRC panels, cavity walls, and clinker aggregate PRC panels.

Partitions and Separating Walls

Internal partitions are made of clinker concrete blocks, providing robust internal walls. The separating wall between semi-detached units is a PRC panel and clinker aggregate PRC panel cavity wall. A central RSC stanchion encased in concrete supports the RSJ floor beam, ensuring structural integrity.

Floors

• Ground Floor: The ground floor consists of 12-inch by 5-inch PRC panels on brick sleeper walls.
• First Floor: The first floor features timber boarding on timber joists, supported by an RSJ floor beam.

Ceilings and Roof

• Ceilings: The ceilings are made of plasterboard, a common material for its ease of installation and finish.
• Roof: The roof structure includes timber rafters and purlins, covered with clay tiles. Some variants may have a roof of steel trusses and tiling grillage.

Typical Hazards and Risks

Structural Issues

One of the primary concerns with Perma-Erecta houses is the potential for structural issues, particularly related to the PRC elements. Over time, the reinforced concrete can deteriorate, leading to cracking and weakening of the structure. Horizontal cracking of PC window sills is a common issue that can indicate underlying problems with the concrete.

Corrosion of Steel Reinforcement

The steel reinforcement within the concrete can corrode, especially if the concrete has not been adequately protected from moisture. Corrosion of steel in concrete is a significant concern, as it can lead to spalling and further weakening of the structure. Guidance on inspection and assessment of reinforced concrete durability is provided in BRE Digest 444 (Parts 1-3) and other related publications.

Carbonation

Carbonation is a process where carbon dioxide from the air penetrates the concrete and reacts with the calcium hydroxide to form calcium carbonate. This can lower the pH of the concrete, leading to corrosion of the steel reinforcement. Carbonation depths in structural-quality concrete can be assessed using BRE Report 19.

Damp and Moisture Ingress

Due to the age of these properties, damp and moisture ingress can be a concern. The damp-proof course (DPC) may have deteriorated over time, allowing moisture to penetrate the structure. This can lead to issues such as mould growth, timber decay, and damage to internal finishes.

Defective Premises Act

Perma-Erecta houses are not specifically listed as defective under the Defective Premises Act. However, due to their age and the potential for structural issues, it is essential to conduct a thorough survey before purchasing. A detailed inspection can identify any defects and provide recommendations for necessary repairs or maintenance.

Inspection Tips for Surveyors

External Inspection

• Check for Cracking: Look for horizontal cracking of PC window sills and other signs of concrete deterioration.
• Examine Render: Inspect the render for any signs of cracking, spalling, or detachment.
• Roof Condition: Assess the condition of the clay tiles and the overall roof structure. Look for any signs of sagging or damage.

Internal Inspection

• Structural Integrity: Check for any signs of structural movement or cracking in internal walls and ceilings.
• Damp and Moisture: Use a moisture meter to check for dampness in walls, floors, and ceilings. Look for signs of mould or mildew.
• Floor Condition: Inspect the condition of the ground and first floors, paying attention to any signs of sagging or unevenness.

Specialist Tests

• Concrete Testing: Consider conducting tests to assess the condition of the reinforced concrete, including carbonation depth and chloride content.
• Steel Corrosion: Use specialist equipment to check for signs of steel reinforcement corrosion.

Typical Defects and Maintenance

Common Defects

• Horizontal Cracking: As mentioned earlier, horizontal cracking of PC window sills is a common defect.
• Concrete Deterioration: Deterioration of the PRC elements, including spalling and cracking, is a significant concern.
• Roof Issues: The clay tiles may become damaged or displaced over time, leading to potential leaks.

Maintenance Tips

• Regular Inspections: Conduct regular inspections to identify and address any issues early.
• Concrete Repairs: Repair any damaged concrete elements promptly to prevent further deterioration.
• Roof Maintenance: Ensure the roof is well-maintained, with any damaged tiles replaced promptly.

Conclusion

Perma-Erecta houses are a unique and historically significant type of system-built property in the UK. While they offer a glimpse into post-war housing solutions, they also come with potential risks and maintenance challenges. Prospective buyers and investors should conduct thorough inspections and consider the potential for structural issues, particularly related to the reinforced concrete elements.

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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