Historical Context and Origins

The Wilvan house, a unique and rare property type, stands as a testament to the innovative construction methods of the mid-20th century. Manufactured by W & C French and designed by the renowned engineer Owen Williams, these properties were constructed in the 1940s. Only two of these semi-detached, two-storey houses were ever built, making them a rare find in the UK property market.

Manufacturers and Designers

W & C French, a prominent construction company of the time, collaborated with Owen Williams, a visionary in the field of engineering and architecture. Williams was known for his pioneering use of reinforced concrete, which is a defining feature of the Wilvan house. This collaboration resulted in a property that was not only innovative but also reflective of the post-war era’s need for durable and quickly constructed housing.

Typical Characteristics of the Wilvan House

Architectural Features

The Wilvan house is easily identifiable by its distinct architectural features:
– Two-storey semi-detached structure: This layout was typical of the era, providing ample living space for families.
– Flat roof: A modern design choice at the time, which also simplified construction.
– External walls of eaves height PRC panels: These panels are a hallmark of Owen Williams’ design, providing both structural integrity and aesthetic appeal.
– Splayed corner columns: These columns add to the unique visual appeal of the property while also serving a structural purpose.

Construction Details

The construction of the Wilvan house is a fascinating study in mid-20th-century building techniques. Here’s a detailed breakdown:

Substructure

• Concrete strip footings: These provide a solid foundation for the property.
• Damp Proof Course (DPC): Presumed to be present, this layer prevents moisture from rising through the structure.

External Walls

• Eaves height PRC corner columns: These columns are integral to the structure, providing support and stability.
• Curved expanded clay aggregate PRC panels: These panels are reinforced with mild steel (MS) bars and bolted together, creating a robust external wall system.
• Timber framing lined with plasterboard: This combination offers both structural support and interior finish.
• Bitumen bonded glass fibre insulation: This insulation, along with bituminous paper backing, provides thermal efficiency.

Separating Wall

• PRC panel cavity wall: Lined with plasterboard on timber framing, this wall provides sound insulation and structural separation between the semi-detached units.

First Floor

• PRC flitch beams: These beams, reinforced with MS plates and timbers, support the first floor.
• V-shaped fixing plate: Welded to the MS plates, this component adds to the structural integrity.

Ceilings and Roof

• Plasterboard ceilings: Standard for the era, providing a smooth finish.
• PRC panels with tapered flanges: These panels form the roof, with varying depths to accommodate structural needs.

Variants

Some Wilvan houses may feature:
– Rendered external walls to the first floor level: This adds an extra layer of protection and aesthetic appeal.
– Timber cladding above the first floor: Enhances the visual appeal and provides additional insulation.
– Two-storey side extension with through driveway: This modification offers additional living space and convenience.

Typical Hazards and Risks

Structural Concerns

The use of Precast Reinforced Concrete (PRC) panels, while innovative, comes with its own set of challenges. Over time, PRC can suffer from:
– Corrosion of steel reinforcement: This can lead to structural weaknesses.
– Carbonation: The process where carbon dioxide penetrates the concrete, reducing its alkalinity and leading to corrosion of the steel reinforcement.

Thermal Efficiency

While the bitumen bonded glass fibre insulation was advanced for its time, it may not meet modern standards. Upgrading insulation can be a significant consideration for potential buyers.

Moisture Ingress

The presumed presence of a Damp Proof Course (DPC) is crucial. However, if the DPC is compromised or absent, it can lead to rising damp, which can cause significant damage over time.

Defective Premises Act

The Wilvan house is not classed as defective under the Defective Premises Act. However, due to its age and the materials used, it is essential to conduct a thorough survey to identify any potential issues.

Inspection Guide for Surveyors

When inspecting a Wilvan house, surveyors should pay close attention to the following areas:

External Walls and Columns

• Check for signs of corrosion: Look for rust stains or spalling concrete, which can indicate corrosion of the steel reinforcement.
• Assess the condition of the PRC panels: Look for cracks, bulges, or other signs of distress.
• Inspect the timber framing: Ensure it is free from rot and insect infestation.

Roof and Ceilings

• Examine the PRC roof panels: Check for signs of water ingress or structural weakness.
• Inspect the plasterboard ceilings: Look for cracks or sagging, which can indicate underlying issues.

Insulation and Moisture Control

• Check the condition of the insulation: Ensure it is intact and providing adequate thermal efficiency.
• Assess the effectiveness of the DPC: Look for signs of rising damp, such as damp patches or mould growth.

Structural Integrity

• Examine the PRC flitch beams: Ensure they are free from corrosion and providing adequate support.
• Check the V-shaped fixing plates: Ensure they are securely welded and free from rust.

Typical Defects Common in Wilvan Houses

Corrosion of Steel Reinforcement

As mentioned earlier, the steel reinforcement within the PRC panels can corrode over time. This is often due to carbonation or chloride ingress. Signs of corrosion include rust stains, spalling concrete, and cracks.

Carbonation

Carbonation is a natural process where carbon dioxide from the air penetrates the concrete, reducing its alkalinity. This can lead to corrosion of the steel reinforcement. Surveyors should measure the depth of carbonation and assess its impact on the structural integrity.

Thermal Bridging

The design of the Wilvan house, with its PRC panels and timber framing, can lead to thermal bridging. This occurs when there is a break in the insulation, allowing heat to escape. Upgrading the insulation can mitigate this issue.

Moisture Ingress

Moisture ingress can occur if the DPC is compromised or absent. This can lead to rising damp, which can cause significant damage to the structure and interior finishes. Surveyors should check for signs of damp and assess the effectiveness of the DPC.

Timber Decay

The timber framing within the walls and floors can be susceptible to rot and insect infestation. Surveyors should check for signs of decay and recommend treatment or replacement if necessary.

Maintenance and Repair Recommendations

Addressing Corrosion

To address corrosion of the steel reinforcement, surveyors may recommend:
– Cathodic protection: This technique involves applying a small electrical charge to the steel reinforcement to prevent corrosion.
– Concrete repair: Damaged concrete can be removed and replaced with new concrete, ensuring the steel reinforcement is adequately protected.

Improving Insulation

Upgrading the insulation can improve the thermal efficiency of the Wilvan house. Options include:
– Adding external insulation: This can be applied to the outside of the PRC panels, reducing thermal bridging and improving energy efficiency.
– Upgrading internal insulation: Replacing the existing insulation with modern, high-performance materials can also improve thermal efficiency.

Moisture Control

To address moisture ingress, surveyors may recommend:
– Installing a new DPC: If the existing DPC is compromised or absent, a new DPC can be installed to prevent rising damp.
– Improving drainage: Ensuring that the ground around the property slopes away from the walls can help prevent moisture ingress.

Timber Treatment

To address timber decay, surveyors may recommend:
– Treating the timber: Applying a preservative treatment can protect the timber from rot and insect infestation.
– Replacing damaged timber: Severely damaged timber should be replaced to ensure the structural integrity of the property.

Conclusion

The Wilvan house, with its unique design and construction, offers a fascinating glimpse into mid-20th-century building techniques. While these properties come with their own set of challenges, a thorough survey and appropriate maintenance can ensure they remain a valuable investment.

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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