Historical Context and Origins

The Dorlonco house, a notable example of early 20th-century system-built housing, holds a unique place in the annals of British architectural history. Manufactured by Dorman Long & Co. Ltd, these homes were constructed between the 1920s and 1928. The company, renowned for its steel production and engineering prowess, ventured into the housing market to address the post-World War I housing shortage. Approximately 10,000 Dorlonco houses were built during this period, primarily in urban and suburban areas across the UK.

Design and Construction

Designers and Manufacturers

Dorman Long & Co. Ltd, a prominent steel manufacturer, collaborated with various designers to create the Dorlonco house. The design aimed to provide affordable, durable housing for the working class. The use of steel in the construction was a significant innovation, reflecting the company’s expertise and the era’s industrial advancements.

Typical Locations

Dorlonco houses are predominantly found in urban and suburban areas, particularly in regions with a strong industrial presence. Cities like London, Birmingham, and Manchester have notable concentrations of these homes. Their distribution reflects the post-war housing policies and the need to accommodate a growing urban workforce.

Architectural Characteristics

External Features

Dorlonco houses are typically two-storey semi-detached or terraced homes. They feature medium pitch hipped or gable roofs, covered with concrete tiles, slates, or pantiles. The external walls are either fully rendered or constructed with a combination of brick and render. The front and rear walls often have brick up to the first-floor level, with render above, while the gable walls are entirely brick. Some homes also have a flat canopy above the front door, adding a distinctive touch to their appearance.

Internal Features

Internally, Dorlonco houses exhibit a robust construction with concrete floors and expanded metal lathing. The ground floor is concrete, while the first floor comprises concrete on expanded metal lathing. Ceilings on the ground floor are finished with sand and cement, while the first floor features clinker concrete on expanded metal lathing with a sand and cement finish.

Construction Details

Substructure

The substructure of Dorlonco houses includes a concrete ground beam and slab, with a damp-proof course (DPC) to prevent moisture ingress. This solid foundation ensures the stability and longevity of the structure.

Frame

The frame of a Dorlonco house is a testament to Dorman Long’s steel expertise. It consists of 22 rolled steel angle (RSA) stanchions around the perimeter, a single-storey composite stanchion, a rolled steel channel (RSC) spine beam, and various floor support beams. The frame layout is meticulously designed to provide structural integrity and support.

External Walls

The external walls are constructed with expanded metal lathing rendered on both sides, creating a cavity filled with clinker concrete blocks. This design offers excellent thermal insulation and durability. The separating walls between houses are also made of clinker concrete block cavity walls, ensuring sound insulation and fire resistance.

Roof

The roof structure includes timber sarking and concrete tiles, providing a robust and weather-resistant covering. The use of timber rafters and purlins, along with bituminous felt, ensures the roof’s longevity and resistance to the elements.

Variants and Modifications

Over the years, various modifications and variants of the Dorlonco house have emerged. Some homes lack the setting out jig, intermediate stanchions, or stanchions in the separating wall. Others feature different materials for external walls, such as rendered concrete, cork, or clinker block. Roof coverings also vary, with some houses having slate or pantile roofs instead of concrete tiles.

Typical Hazards and Risks

Corrosion

One of the primary concerns with Dorlonco houses is the corrosion of steel components. The RSA stanchions, particularly at their bases, are prone to minor to severe corrosion. This issue can compromise the structural integrity of the house if not addressed promptly. Additionally, metal lathing in walls, floors, ceilings, and roof coverings can also suffer from corrosion, leading to potential safety hazards.

Carbonation and Cracking

Carbonation of the render and vertical cracking of brickwork and render at stanchion locations are common issues in Dorlonco houses. These defects can result in water ingress and further deterioration of the structure. Regular maintenance and timely repairs are essential to mitigate these risks.

Wall Ties

Corrosion of wall ties is another significant concern. Wall ties are crucial for maintaining the stability of cavity walls, and their failure can lead to structural issues. Inspecting and replacing corroded wall ties is vital to ensure the safety and longevity of the property.

Defective Premises Act

Dorlonco houses are not classified as defective under the Defective Premises Act. However, the potential hazards and risks associated with their construction necessitate thorough inspections and regular maintenance. Homebuyers and investors should be aware of these issues and take appropriate measures to address them.

Inspection Guide for Surveyors

Preliminary Assessment

When inspecting a Dorlonco house, start with a preliminary assessment of the external and internal features. Look for signs of corrosion, cracking, and other visible defects. Pay particular attention to the bases of RSA stanchions and the condition of the render.

Detailed Inspection

Substructure

Examine the concrete ground beam and slab for any signs of cracking or movement. Check the damp-proof course for effectiveness and any signs of moisture ingress.

Frame

Inspect the RSA stanchions, RSC spine beam, and floor support beams for corrosion. Use a moisture meter to detect any hidden moisture that could accelerate corrosion. Check the protective coating for any signs of deterioration.

External Walls

Examine the render and brickwork for carbonation and cracking. Look for signs of water ingress and assess the condition of the expanded metal lathing. Check the cavity walls for any signs of movement or instability.

Roof

Inspect the roof covering for any missing or damaged tiles. Check the condition of the timber sarking, rafters, and purlins. Look for signs of water ingress and assess the effectiveness of the bituminous felt.

Internal Features

Examine the concrete floors and expanded metal lathing for any signs of corrosion or deterioration. Check the condition of the ceilings and look for any cracks or signs of movement.

Common Defects

Corrosion

Corrosion of steel components is a common defect in Dorlonco houses. Regular inspections and maintenance are essential to address this issue and prevent further deterioration.

Cracking

Vertical cracking of brickwork and render at stanchion locations is another common defect. These cracks can allow water ingress and lead to further structural issues if not repaired promptly.

Wall Ties

Corrosion of wall ties is a significant concern. Inspect the wall ties regularly and replace any corroded ties to maintain the stability of the cavity walls.

Maintenance and Repair

Preventive Measures

Regular maintenance is crucial to prevent the common defects associated with Dorlonco houses. Apply protective coatings to steel components to prevent corrosion. Regularly inspect and repair any cracks in the render and brickwork to prevent water ingress.

Repairs

Corrosion

Addressing corrosion involves cleaning and treating the affected areas with rust inhibitors. Replace severely corroded components to ensure the structural integrity of the house.

Cracking

Repair cracks in the render and brickwork using appropriate fillers and sealants. Ensure that the repairs are carried out promptly to prevent further deterioration.

Wall Ties

Replace corroded wall ties with new, corrosion-resistant ties. Ensure that the replacement ties are installed correctly to maintain the stability of the cavity walls.

Conclusion

The Dorlonco house, with its unique construction and historical significance, offers a fascinating glimpse into early 20th-century British housing. While these homes present certain challenges, such as corrosion and cracking, they can be maintained and preserved with regular inspections and timely repairs. For homebuyers and investors, understanding the typical characteristics and potential hazards of Dorlonco houses is essential to make 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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