Overview of the Wil-Mac House

The Wil-Mac house, a distinctive property type from the 1960s, stands as a testament to the era’s innovative approach to system-built housing. Designed and manufactured by Dow-Mac (Products) Ltd and Wilson Ltd, these properties are relatively rare, with only three known to have been built. Despite their limited numbers, understanding the intricacies of Wil-Mac houses is crucial for potential buyers and investors, particularly given their unique construction methods and potential risks.

Historical Context and Manufacturing Details

Period and Location

The Wil-Mac houses were constructed during the 1960s, a period marked by a significant push towards prefabricated and system-built housing in the UK. This era saw a surge in the use of pre-cast concrete (PC) panels and other innovative building materials aimed at addressing the post-war housing shortage. These properties are typically found in urban settings, where rapid construction was necessary to meet the growing demand for housing.

Manufacturers and Designers

The Wil-Mac houses were a collaborative effort between Dow-Mac (Products) Ltd and Wilson Ltd. Dow-Mac was known for its expertise in pre-cast concrete products, while Wilson Ltd brought additional design and construction capabilities to the table. Together, they created a property type that was both innovative and functional, albeit with some inherent risks and challenges.

Typical Characteristics of Wil-Mac Houses

Structural Features

Wil-Mac houses are two-storey terraced properties with several distinctive features:

• Flat Roof: Covered with asphalt, these roofs often include acrylic roof lights, providing natural illumination to the upper floors.
• External Walls: The walls are constructed from storey-height PC panels with a unique square dimpled finish. The ground floor lobby is rendered, adding a different texture to the front elevation.
• Windows and Fascia: The properties feature vertical sliding sash anodised aluminium windows and eaves level aluminium fascia, contributing to their modernist aesthetic.

Internal Layout

Internally, Wil-Mac houses are designed with practicality in mind:

• Ground and First Floors: Both floors are constructed from 6″ coffered PC slabs, providing a robust and durable foundation.
• Partitions: Internal partitions are made from storey-height 3″ PC panels, ensuring structural integrity and sound insulation.
• Ceilings: While specific details about the ceilings are not known, they are likely to be consistent with the overall pre-cast concrete construction.

Potential Hazards and Risks

Structural Concerns

One of the primary concerns with Wil-Mac houses is the durability of the reinforced concrete used in their construction. Over time, concrete can suffer from various issues, including:

• Corrosion of Steel Reinforcement: As detailed in BRE Digest 444, parts 1-3, the steel reinforcement within the concrete can corrode, leading to structural weaknesses.
• Carbonation: According to BR 19, carbonation depths in structural-quality concrete can compromise the integrity of the material, making it more susceptible to damage.
• Maintenance and Repair: Guidance on the repair and maintenance of reinforced concrete is provided in BR 254, highlighting the need for regular inspections and timely interventions.

Defective Premises Act

Wil-Mac houses are not specifically classified as defective under the Defective Premises Act. However, given their age and the potential for structural issues, it is essential for buyers and investors to conduct thorough inspections and assessments before making a purchase.

Inspection Guidelines for Surveyors

External Inspection

When inspecting a Wil-Mac house, surveyors should pay close attention to the following external features:

• Roof: Check for signs of wear and tear on the asphalt covering and inspect the acrylic roof lights for any damage or leaks.
• External Walls: Examine the PC panels for cracks, spalling, or other signs of deterioration. The square dimpled finish can sometimes mask underlying issues, so a detailed inspection is necessary.
• Windows and Fascia: Ensure that the aluminium windows and fascia are in good condition, with no signs of corrosion or damage.

Internal Inspection

Internally, surveyors should focus on the following areas:

• Floors and Partitions: Inspect the coffered PC slabs for any signs of structural weakness or damage. Pay particular attention to the joints and connections between panels.
• Ceilings: While specific details about the ceilings are not known, any signs of sagging, cracking, or water damage should be thoroughly investigated.
• Reinforced Concrete: Use non-destructive testing methods to assess the condition of the reinforced concrete, particularly looking for signs of corrosion or carbonation.

Typical Construction Details

Substructure

The specific details of the substructure for Wil-Mac houses are not well-documented. However, given the era and construction methods, it is likely to consist of a concrete foundation designed to support the weight of the pre-cast concrete panels.

External Walls

The external walls of Wil-Mac houses are constructed from storey-height room-width PC panels with a square dimpled finish. These panels are designed to provide both structural support and insulation. The walls typically include:

• Cavity: A cavity between the panels helps to improve thermal insulation and reduce the risk of dampness.
• Polystyrene Insulation: A 1″ layer of polystyrene is often included to enhance the thermal performance of the walls.
• Eaves Beam: An 18″ pre-cast concrete eaves beam provides additional structural support at the roof level.

Separating Walls and Partitions

The separating walls between properties are constructed from storey-height PC slab cavity walls, providing excellent sound insulation and fire resistance. Internal partitions are made from 3″ PC panels, ensuring a robust and durable internal structure.

Floors and Ceilings

Both the ground and first floors are constructed from 6″ coffered PC slabs, providing a solid and stable foundation. The ceilings, while not specifically detailed, are likely to be consistent with the overall pre-cast concrete construction, offering good sound insulation and fire resistance.

Roof

The roof of a Wil-Mac house is constructed from 6″ coffered PC slabs, covered with a 2 1/2″ vermiculite screed and asphalt. Acrylic roof lights are often included to provide natural light to the upper floors.

Common Defects in Wil-Mac Houses

Structural Defects

Given the age and construction methods of Wil-Mac houses, several common defects may be encountered:

• Concrete Deterioration: Over time, the pre-cast concrete panels can suffer from cracking, spalling, and other forms of deterioration. Regular inspections and maintenance are essential to address these issues promptly.
• Corrosion of Steel Reinforcement: As mentioned earlier, the steel reinforcement within the concrete can corrode, leading to structural weaknesses. Non-destructive testing methods can help to identify and address this issue.
• Carbonation: The carbonation of concrete can reduce its strength and durability, making it more susceptible to damage. Regular monitoring and maintenance are necessary to mitigate this risk.

Thermal and Moisture Issues

• Insulation: While the polystyrene insulation within the walls provides some thermal performance, it may not meet modern standards. Upgrading the insulation can help to improve energy efficiency and reduce heating costs.
• Dampness: The cavity within the walls helps to reduce the risk of dampness, but it is still essential to check for any signs of moisture ingress, particularly around windows and doors.

Roof and Windows

• Roof: The asphalt covering on the roof can deteriorate over time, leading to leaks and water damage. Regular inspections and maintenance are necessary to ensure the roof remains in good condition.
• Windows: The aluminium windows, while durable, can suffer from corrosion and other forms of damage. Ensuring that the windows are well-maintained and in good condition is essential for both security and energy efficiency.

Practical Tips for Buyers and Investors

Conduct Thorough Inspections

Given the potential risks and defects associated with Wil-Mac houses, it is essential to conduct thorough inspections before making a purchase. Engaging a qualified surveyor with experience in system-built properties can help to identify any issues and provide guidance on necessary repairs and maintenance.

Budget for Repairs and Maintenance

While Wil-Mac houses can offer excellent value for money, it is important to budget for potential repairs and maintenance. Addressing issues such as concrete deterioration, insulation upgrades, and roof repairs can be costly, but they are essential for ensuring the long-term durability and safety of the property.

Consider Modernisation

Given the age of Wil-Mac houses, modernisation may be necessary to meet current building standards and improve energy efficiency. Upgrading insulation, windows, and heating systems can help to reduce energy costs and enhance the overall comfort of the property.

Legal Considerations

While Wil-Mac houses are not specifically classified as defective under the Defective Premises Act, it is still important to be aware of any legal considerations. Ensuring that the property meets current building regulations and standards is essential for both safety and resale value.

Conclusion

The Wil-Mac house, with its unique construction methods and distinctive features, represents an interesting and potentially rewarding investment opportunity. However, given the potential risks and defects associated with this property type, it is essential for buyers and investors to conduct thorough inspections and budget for necessary repairs and maintenance. By understanding the intricacies of Wil-Mac houses and taking a proactive approach to maintenance, you can ensure that your investment remains safe and valuable for years to come.

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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