Overview of the SNW House

The SNW house, named after its manufacturers Selleck Nicholls & Williams, is a distinctive property type that emerged in the 1960s. These properties are primarily found in the UK and are known for their unique construction methods and materials. As an expert surveyor, I will delve into the various aspects of the SNW house, including its construction, typical characteristics, potential hazards, and inspection tips. This guide aims to provide home buyers and investors with a thorough understanding of what to expect when considering an SNW house.

Historical Context and Manufacturers

Period Built

The SNW houses were predominantly built during the 1960s, a period marked by a significant demand for housing in the UK. This era saw a surge in the construction of system-built properties, which were designed to be cost-effective and quick to assemble.

Manufacturers and Designers

Selleck Nicholls & Williams were both the manufacturers and designers of the SNW houses. Their innovative approach to construction involved the use of pre-cast (PC) panels and timber infill panels, which allowed for rapid assembly and reduced labour costs.

Number Built

While the exact number of SNW houses built is not well-documented, it is known that these properties were constructed in significant numbers to meet the housing demands of the time. They were primarily built as 2-storey terraced houses, although the system was also used for flats.

Identification Characteristics

External Features

SNW houses are easily identifiable by their shallow monopitch roofs covered with bituminous felt. The front and rear ground floor external walls are made of large, near storey-height PC panels. The first-floor external walls are a combination of approximately half-storey height PC panels and timber infill panels. The flank walls also feature a combination of near storey-height and near half-storey height PC panels. A distinctive chamfered panel is often found over the ground floor windows.

Internal Features

Internally, SNW houses typically have timber frame studs faced with plasterboard for partitions. The ground floor is usually concrete, while the first floor consists of tongue-and-groove (T&G) boarding on timber joists. Ceilings are generally plasterboard.

Construction Details

Substructure

The substructure of SNW houses includes concrete foundations and a damp-proof course (DPC) to prevent moisture ingress.

External Walls

The front and rear ground floor external walls are constructed from large, near storey-height PC panels with pronounced chamfers. The first-floor walls are formed by PC spandrel panels with timber infill panels faced with horizontal boarding. A timber truss beam at the head of the front and rear walls provides bearing for the roof trusses.

Flank Walls

The flank walls are a combination of near storey-height and near half-storey height PC panels, with horizontal timber boarding.

Separating Walls and Partitions

Separating walls are made from large storey-height PC panels, while internal partitions are timber frame studs faced with plasterboard.

Floors

The ground floor is typically concrete, while the first floor consists of T&G boarding on timber joists, with inclined timber noggings bolted to the face of the front and rear PC wall panels.

Roof

The roof is a shallow monopitch design, constructed from timber roof trusses with transverse timber bracing and woodwool slabs, covered with bituminous felt.

Typical Hazards and Risks

Structural Issues

One of the primary concerns with SNW houses is the potential for structural issues, particularly related to the durability of the reinforced concrete. Over time, the steel reinforcement within the concrete can corrode, leading to spalling and weakening of the structure. This is particularly prevalent in properties that have not been well-maintained or have been exposed to harsh environmental conditions.

Moisture Ingress

The use of PC panels and timber infill panels can also pose a risk of moisture ingress, particularly if the damp-proof course (DPC) has failed or if there are gaps in the external cladding. Moisture ingress can lead to a range of issues, including mould growth, timber decay, and deterioration of the internal finishes.

Thermal Performance

SNW houses were built during a time when energy efficiency was not a primary concern. As a result, these properties often have poor thermal performance, leading to higher heating costs and potential issues with condensation.

Asbestos

Given the era in which SNW houses were built, there is also a risk of asbestos-containing materials being present. Asbestos was commonly used in construction during the 1960s, particularly in insulation and fireproofing materials. It is essential to have a thorough asbestos survey carried out before any renovation or demolition work is undertaken.

Defective Premises Act

Classification

The SNW house is not specifically classed as defective under the Defective Premises Act. However, the potential structural issues and other hazards associated with this property type mean that it is essential to carry out a thorough survey and assessment before purchase.

Legal Implications

Under the Defective Premises Act, property owners and builders have a duty to ensure that a dwelling is fit for habitation. If a property is found to be defective and poses a risk to the occupants, legal action can be taken to seek compensation for any damages or necessary repairs.

Inspection Tips for Surveyors

External Inspection

• Roof: Check the condition of the bituminous felt covering and look for any signs of damage or wear. Inspect the timber roof trusses for signs of rot or decay.
• Walls: Examine the PC panels for signs of cracking, spalling, or other damage. Check the timber infill panels for signs of rot or decay. Look for any gaps or defects in the external cladding that could allow moisture ingress.
• Windows and Doors: Inspect the condition of the windows and doors, paying particular attention to the chamfered panels over the ground floor windows.

Internal Inspection

• Floors: Check the condition of the concrete ground floor and the T&G boarding on the first floor. Look for any signs of movement or deflection in the timber joists.
• Walls and Partitions: Inspect the internal partitions for signs of damage or deterioration. Check the separating walls for any signs of cracking or movement.
• Ceilings: Examine the plasterboard ceilings for signs of sagging or damage. Look for any signs of water staining, which could indicate a roof leak.

Structural Assessment

• Reinforced Concrete: Assess the condition of the reinforced concrete elements, paying particular attention to any signs of corrosion or spalling. Use a cover meter to check the depth of the concrete cover over the reinforcement.
• Timber Elements: Inspect all timber elements for signs of rot, decay, or insect infestation. Pay particular attention to areas where timber is in contact with concrete or other potentially damp materials.

Moisture Assessment

• Damp-Proof Course: Check the condition of the DPC and look for any signs of rising damp. Use a moisture meter to assess the moisture levels in the walls and floors.
• Ventilation: Ensure that the property has adequate ventilation to prevent condensation and mould growth. Check for any signs of mould or mildew, particularly in areas with poor ventilation.

Asbestos Survey

• Materials: Identify any materials that may contain asbestos, such as insulation, fireproofing, or floor tiles. If asbestos is suspected, arrange for a professional asbestos survey to be carried out.
• Safety Precautions: Ensure that any asbestos-containing materials are handled and disposed of safely, in accordance with current regulations.

Typical Defects in SNW Houses

Concrete Spalling

Concrete spalling is a common defect in SNW houses, caused by the corrosion of the steel reinforcement within the concrete. This can lead to cracking, flaking, and weakening of the concrete elements. Regular maintenance and repair are essential to prevent further deterioration.

Timber Decay

Timber decay is another common issue, particularly in the timber infill panels and roof trusses. This can be caused by moisture ingress, poor ventilation, or insect infestation. Regular inspections and treatment are necessary to prevent further damage.

Moisture Ingress

Moisture ingress can lead to a range of issues, including mould growth, timber decay, and deterioration of internal finishes. It is essential to ensure that the DPC is in good condition and that there are no gaps or defects in the external cladding.

Poor Thermal Performance

SNW houses often have poor thermal performance, leading to higher heating costs and potential issues with condensation. Upgrading the insulation and improving the ventilation can help to address these issues.

Asbestos

Asbestos-containing materials are a potential hazard in SNW houses, particularly in properties that have not been renovated or updated since the 1960s. It is essential to have a thorough asbestos survey carried out and to handle any asbestos-containing materials safely.

Conclusion

The SNW house, with its unique construction and historical significance, presents both opportunities and challenges for home buyers and investors. Understanding the typical characteristics, potential hazards, and inspection tips for these properties is essential for making an informed decision. While SNW houses are not specifically classed as defective under the Defective Premises Act, the potential structural issues and other hazards associated with this property type mean that a thorough survey and assessment are crucial.

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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