Historical Context and Origins

The Nissen-Petren house, a unique architectural marvel, emerged in the mid-1920s as a response to the housing needs of the time. Designed by the innovative minds of Petter & Warren and manufactured by Nissen-Petren Houses Ltd, these properties were constructed in 1925. Only 20 of these distinctive homes were built, making them a rare find in today’s property market. These houses are typically located in suburban areas, often in regions that experienced rapid development during the interwar period.

Design and Construction

Identification Characteristics

Nissen-Petren houses are easily identifiable by their unique architectural features. These are two-storey semi-detached houses with a semi-circular or curved roof covered with bituminous-coated corrugated steel sheets. The external walls are rendered with roughcast, giving them a distinctive textured appearance. These characteristics make the Nissen-Petren house stand out among other properties from the same era.

Substructure

The substructure of the Nissen-Petren house consists of a concrete slab that is thickened around the perimeter. This design choice was likely made to provide additional stability and support to the structure. A damp-proof course (DPC) is also included to prevent moisture from rising through the foundation, which is crucial for maintaining the integrity of the building.

Frame

The main frame of the Nissen-Petren house is composed of five semi-circular rolled steel joist (RST) ribs. Each rib is made up of three sections connected by bolted plates. This semi-circular frame is a defining feature of the Nissen-Petren house and contributes to its unique aesthetic. The frame is protected by a grey oxide paint coating, which helps to prevent corrosion and extend the lifespan of the steel.

External Walls

The external walls of the Nissen-Petren house are constructed from rendered concrete block cavity walls. This type of construction provides good thermal insulation and helps to keep the interior of the house warm during the winter months and cool during the summer. The roughcast render adds an additional layer of protection to the walls and gives the house its distinctive appearance.

Separating Wall and Partitions

The separating wall between the two semi-detached houses is made of masonry, providing a solid and durable barrier between the two properties. Internal partitions are constructed from concrete blocks, which offer good sound insulation and structural stability.

Floors

The ground floor of the Nissen-Petren house is made of concrete, providing a solid and durable base for the property. The first floor consists of tongue-and-groove (T&G) boarding on timber joists. This type of flooring is both strong and flexible, making it suitable for residential use.

Ceilings

The ceilings in the Nissen-Petren house are made of lath and plaster, a traditional construction method that provides a smooth and durable finish. This type of ceiling construction is also effective at soundproofing and fire resistance.

Roof

The roof of the Nissen-Petren house is supported by timber purlins and covered with bituminous-coated corrugated steel sheets. This type of roofing material is lightweight, durable, and resistant to weathering, making it an ideal choice for the curved roof design of the Nissen-Petren house.

Typical Hazards and Risks

Corrosion

One of the most common issues with Nissen-Petren houses is the corrosion of the steel components. Superficial corrosion can occur on the steel ribs, particularly at the bases and in the roof. More severe corrosion can affect the corrugated steel sheets, leading to deterioration of the bituminous protective coating. This can result in leaks and structural damage if not addressed promptly.

Wet Rot

Wet rot is another common issue in Nissen-Petren houses, particularly in the timber purlins that support the roof. Wet rot occurs when timber is exposed to moisture for extended periods, leading to decay and weakening of the wood. This can compromise the structural integrity of the roof and requires immediate attention to prevent further damage.

Lack of Separating Wall in Roof Space

Another potential hazard in Nissen-Petren houses is the lack of a separating wall in the roof space. This can pose a fire risk, as a fire in one property can easily spread to the adjoining property through the roof space. It is important to address this issue by installing a fire-resistant barrier in the roof space to enhance the safety of the property.

Defective Premises Act

The Nissen-Petren house is not classed as defective under the Defective Premises Act. However, due to the age and unique construction of these properties, it is essential to conduct a thorough survey before purchasing. This will help to identify any potential issues and ensure that the property is safe and structurally sound.

Inspection Guide for Surveyors

External Inspection

When inspecting a Nissen-Petren house, start with a thorough external inspection. Look for signs of corrosion on the steel ribs and corrugated steel sheets. Check the condition of the bituminous coating on the roof and look for any signs of deterioration or leaks. Inspect the rendered external walls for cracks or damage, and ensure that the damp-proof course is intact and functioning properly.

Internal Inspection

Inside the property, check for signs of wet rot in the timber purlins and other wooden components. Inspect the concrete block partitions and masonry separating wall for any cracks or structural issues. Examine the floors for any signs of damage or wear, and ensure that the tongue-and-groove boarding on the first floor is in good condition. Check the lath and plaster ceilings for any cracks or signs of sagging.

Roof Space Inspection

In the roof space, look for any signs of corrosion on the steel ribs and timber purlins. Check for the presence of a separating wall or fire-resistant barrier between the two properties. If there is no separating wall, recommend the installation of a fire-resistant barrier to enhance the safety of the property.

Typical Defects and Maintenance

Corrosion Prevention

To prevent corrosion, regularly inspect the steel components of the Nissen-Petren house and address any signs of rust or deterioration promptly. Apply a protective coating to the steel ribs and corrugated steel sheets to prevent further corrosion. Ensure that the bituminous coating on the roof is in good condition and reapply it as needed to maintain its protective properties.

Wet Rot Treatment

To address wet rot, identify and eliminate the source of moisture that is causing the timber to decay. Replace any affected timber purlins and apply a wood preservative to prevent further rot. Ensure that the roof is watertight and that there are no leaks that could lead to further moisture damage.

Fire Safety

Enhance the fire safety of the Nissen-Petren house by installing a fire-resistant barrier in the roof space if one is not already present. This will help to prevent the spread of fire between the two properties and improve the overall safety of the house.

Variants of the Nissen-Petren House

While the standard Nissen-Petren house has a concrete slab foundation and rendered concrete block cavity walls, there are some variants of this property type. These variants include:

Concrete Strip Foundation and Brick Underbuilding

Some Nissen-Petren houses have a concrete strip foundation and a brick underbuilding instead of a concrete slab. This type of foundation provides additional stability and support to the structure.

Rendered Brick Cavity External Walls

In some cases, the external walls of the Nissen-Petren house are constructed from rendered brick cavity walls instead of concrete blocks. This type of construction provides similar thermal insulation and protection as the standard concrete block walls.

Suspended Timber Ground Floor

Some Nissen-Petren houses have a suspended timber ground floor instead of a concrete floor. This type of flooring is more flexible and can provide better insulation and comfort underfoot.

Angular Mansard Roof

A variant of the Nissen-Petren house features an angular mansard roof instead of the standard semi-circular roof. This type of roof design provides additional living space in the attic and can enhance the overall aesthetic of the property.

Conclusion

The Nissen-Petren house is a unique and distinctive property type that offers a range of benefits and challenges for home buyers and investors. With its semi-circular roof, rendered external walls, and innovative construction methods, the Nissen-Petren house stands out as a rare and valuable find in the property market. However, it is essential to conduct a thorough survey and address any potential issues, such as corrosion, wet rot, and fire safety, to ensure that the property is safe and structurally sound.

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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