Historical Context and Manufacturing Background

The Orlit Type I house is a notable example of post-war British architecture, specifically designed to address the housing shortage that followed World War II. These properties were constructed primarily during the late 1940s and 1950s, a period marked by a pressing need for rapid and cost-effective housing solutions. The Orlit Type I houses were manufactured by Orlit Ltd, a company that played a significant role in the development of system-built properties during this era.

The Orlit Type I houses were part of a broader initiative to provide affordable housing to the masses. Approximately 17,000 units of Orlit Type I and II houses were built, making them a common sight in various parts of the UK. These houses were typically found in suburban areas and were designed to be both functional and economical.

Design and Construction Characteristics

Architectural Features

Orlit Type I houses are easily identifiable by their distinct architectural features. They were constructed as bungalows, two-storey semi-detached, and terraced houses. The roofs of these houses were either medium-pitched and hipped, covered with tiles, or flat, covered with asphalt or bituminous felt. The external walls were made of Precast Reinforced Concrete (PRC) slabs, a hallmark of Orlit construction.

Structural Components

The construction of Orlit Type I houses involved several key components:

• Substructure: The houses were built on pad foundations with Precast Concrete (PC) stub columns cast into the foundations.
• Frame: The main frame consisted of 5 1/2″ x 5 1/2″ PRC columns with integral beam stubs, bolted steel flange connectors, and 7 1/2″ PRC beams with concrete cover.
• External Walls: The external walls were made of 2″ concrete base bonding units, 1′ 4″ x 2′ or 4′ x 2″ PC facing slabs, a cavity, 2 1/2″ lightweight PC slabs, and plasterboard on timber framing. Galvanised MS wall ties were used to secure the structure.
• Separating Wall: The separating walls were PRC frame cavity walls infilled with foamed slag aggregate concrete blocks.
• Partitions: The internal partitions were made of lightweight concrete slabs.
• Floors: The ground floor was concrete, while the first floor consisted of PRC beams spanning between internal columns, inverted PRC trough-shaped units with concrete fill.
• Ceilings: The ceilings were made of plasterboard.
• Roof: The roof structure included PRC beams spanning between internal columns, inverted PRC trough-shaped units with concrete fill, timber wall plates, timber trusses and purlins, and tiles.

Variants

Some Orlit Type I houses featured a flat roof made of profiled PRC eaves units, screed, and asphalt or bituminous felt. This variant was less common but still notable in the overall design of Orlit houses.

Typical Hazards and Risks

Structural Integrity

One of the primary concerns with Orlit Type I houses is the structural integrity of the PRC components. Over time, these components can deteriorate, leading to significant issues. The main PRC columns and beams have only up to 30 mm cover, with carbonation depths typically ranging from 10 to 20 mm and significant chloride content. This can result in the cracking of Ordinary Portland Cement (OPC) and High Alumina Cement (HAC) stitches, as well as the deterioration of other PRC components.

Carbonation and Chloride Content

The low-quality HAC concrete used in the stitches is particularly susceptible to carbonation and chloride content. Carbonation can lead to the corrosion of the steel reinforcement within the concrete, compromising the structural integrity of the house. Chloride content can exacerbate this issue, accelerating the corrosion process.

Cracking and Deterioration

Cracking of secondary beams is another common issue in Orlit Type I houses. These cracks can be up to 20 mm deep and are often accompanied by significant levels of chloride content. The deterioration of other PRC components, such as the external walls and roof, can also pose a risk to the overall stability of the house.

Defective Premises Act and Orlit Type I Houses

Orlit Type I houses are classified as defective under the Defective Premises Act. This classification is based on the inherent structural issues associated with the PRC components used in their construction. As a result, these houses may not meet modern building standards and could require significant repairs or modifications to ensure their safety and habitability.

Inspection Guide for Orlit Type I Houses

Pre-Inspection Preparation

Before conducting an inspection of an Orlit Type I house, it is essential to gather as much information as possible about the property. This includes reviewing any available documentation, such as previous inspection reports, maintenance records, and building plans. It is also helpful to familiarize yourself with the typical characteristics and common issues associated with Orlit Type I houses.

External Inspection

Roof

Begin the inspection by examining the roof. Check for any signs of damage or deterioration, such as missing or broken tiles, cracks in the asphalt or bituminous felt, and sagging or uneven areas. Pay particular attention to the condition of the PRC beams and timber trusses, as these components are critical to the structural integrity of the roof.

External Walls

Next, inspect the external walls for any signs of cracking, spalling, or other forms of deterioration. Look for areas where the concrete cover may be compromised, exposing the steel reinforcement to the elements. Check the condition of the galvanised MS wall ties, as these can corrode over time and weaken the overall structure.

Internal Inspection

Ground Floor

Inspect the ground floor for any signs of cracking or unevenness. Check the condition of the concrete and look for any areas where the PRC beams may be deteriorating. Pay attention to any signs of moisture or water damage, as this can exacerbate the deterioration of the concrete and steel reinforcement.

First Floor

Examine the first floor for any signs of cracking or sagging. Check the condition of the PRC beams and inverted PRC trough-shaped units, as these components are critical to the structural integrity of the floor. Look for any signs of moisture or water damage, as this can weaken the concrete and steel reinforcement.

Ceilings

Inspect the ceilings for any signs of cracking or sagging. Check the condition of the plasterboard and look for any areas where the PRC beams may be deteriorating. Pay attention to any signs of moisture or water damage, as this can weaken the concrete and steel reinforcement.

Structural Components

PRC Columns and Beams

Examine the PRC columns and beams for any signs of cracking, spalling, or other forms of deterioration. Check the condition of the concrete cover and look for any areas where the steel reinforcement may be exposed. Pay particular attention to the condition of the OPC and HAC stitches, as these are critical to the overall stability of the house.

Secondary Beams

Inspect the secondary beams for any signs of cracking or deterioration. Check the condition of the concrete and look for any areas where the steel reinforcement may be exposed. Pay attention to any signs of moisture or water damage, as this can weaken the concrete and steel reinforcement.

Additional Considerations

Moisture and Water Damage

Moisture and water damage can significantly impact the structural integrity of an Orlit Type I house. During the inspection, pay close attention to any signs of moisture or water damage, such as damp patches, mould, or water stains. Check the condition of the roof, external walls, and internal floors and ceilings for any signs of water ingress.

Carbonation and Chloride Content

Carbonation and chloride content can accelerate the deterioration of the PRC components in an Orlit Type I house. During the inspection, look for any signs of carbonation, such as cracking or spalling of the concrete. Check the condition of the steel reinforcement for any signs of corrosion, as this can weaken the overall structure.

Typical Defects in Orlit Type I Houses

Cracking and Spalling

Cracking and spalling are common defects in Orlit Type I houses. These issues are often caused by the carbonation of the concrete and the corrosion of the steel reinforcement. Cracks can appear in the external walls, roof, and internal floors and ceilings, compromising the structural integrity of the house.

Deterioration of PRC Components

The PRC components in Orlit Type I houses can deteriorate over time, leading to significant structural issues. This deterioration is often caused by the low-quality HAC concrete used in the stitches, as well as the carbonation and chloride content in the concrete. The deterioration of the PRC components can result in cracking, spalling, and the weakening of the overall structure.

Corrosion of Steel Reinforcement

The steel reinforcement in Orlit Type I houses is susceptible to corrosion, particularly in areas where the concrete cover is compromised. This corrosion can weaken the overall structure and lead to significant structural issues. The corrosion of the steel reinforcement is often exacerbated by the carbonation and chloride content in the concrete.

Moisture and Water Damage

Moisture and water damage can significantly impact the structural integrity of an Orlit Type I house. Water ingress can weaken the concrete and steel reinforcement, leading to cracking, spalling, and the deterioration of the PRC components. Moisture and water damage can also lead to the growth of mould and mildew, which can pose health risks to the occupants.

Conclusion

The Orlit Type I house is a significant example of post-war British architecture, designed to address the housing shortage that followed World War II. These houses were constructed using Precast Reinforced Concrete (PRC) components, which have proven to be susceptible to various structural issues over time. As a result, Orlit Type I houses are classified as defective under the Defective Premises Act and may require significant repairs or modifications to ensure their safety and habitability.

When inspecting an Orlit Type I house, it is essential to pay close attention to the condition of the PRC components, as well as any signs of cracking, spalling, or deterioration. Moisture and water damage can also significantly impact the structural integrity of the house, so it is important to check for any signs of water ingress. By conducting a thorough inspection and addressing any issues promptly, you can help ensure the safety and longevity of an Orlit Type I 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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