Understanding the Purpose Built Type I House

The Purpose Built Type I house, a hallmark of mid-20th-century British architecture, represents a significant chapter in the UK’s housing history. Constructed between 1966 and 1979, these homes were designed by A W Penn and manufactured by Purpose Built Ltd. With approximately 1,500 units built, these properties are primarily found in suburban areas across the UK. Known alternatively as Millard or Purpose Built homes, they offer a unique blend of architectural style and practical design.

Key Characteristics and Design Features

Purpose Built Type I houses are typically bungalows or two-storey semi-detached and terraced houses. They feature medium or shallow pitch gable or monopitch roofs covered with concrete tiles. The external walls are often constructed entirely of brick, though some variations include rendered gable walls or upper storeys clad with materials such as tile hanging, horizontal timber boarding, profiled metal sheets, or asbestos cement slates. A distinctive feature of some dwellings is the horizontal timber boarding beside the front door, complemented by a flat or pitched canopy over the entrance.

Construction Details

The construction of Purpose Built Type I houses is a testament to the innovative building techniques of the time. The substructure consists of concrete strip footings with brick under-building and a damp-proof course (DPC). The external walls employ a platform frame construction, utilizing storey-height timber frame panels sheathed externally with plywood, overlaid with bituminous building paper, and separately clad with brick. Internally, these walls are lined with plasterboard backed with a polyethylene vapour control layer, with mineral fibre insulation between the frame studs.

The separating walls are timber frame cavity walls, backed with polyethylene film and lined with plasterboard, with mineral fibre insulation between the frame studs of one leaf and a 4-inch block in the cavity. Partitions are timber stud lined with plasterboard. The ground floor is concrete, while the first floor consists of plywood on timber joists. Ceilings are finished with plasterboard, and the roof structure comprises timber trusses, bituminous felt, and concrete tiles.

Variants and Alternative Cladding

Purpose Built Type I houses exhibit several variants, particularly in the cladding of the front and rear upper storey external walls. These may be clad with tile hanging, asbestos cement sheets, horizontal timber boarding, or profiled metal sheets on timber battens. The gable external wall may be separately clad with rendered brick, and some homes feature a directly clad horizontal timber boarded feature panel beside the front door.

Typical Hazards and Risks

While Purpose Built Type I houses offer many benefits, they also present certain hazards and risks that potential buyers should be aware of. One common issue is the localised sinking of foundations, which can lead to structural instability. Additionally, the timber boarded feature panels are prone to decay, particularly in areas exposed to moisture. External wall cavities may be bridged by mortar, leading to potential damp issues. Gaps in separating walls can also compromise the thermal and acoustic insulation of the property.

Defective Premises Act Considerations

Under the Defective Premises Act, properties must be constructed in a manner that ensures they are fit for habitation. While Purpose Built Type I houses are not inherently classified as defective, the aforementioned hazards and risks can lead to issues that may require remediation to comply with the Act. It is crucial for buyers to conduct thorough inspections and address any defects to ensure the property meets legal standards.

Inspection Tips for Purpose Built Type I Houses

When inspecting a Purpose Built Type I house, it is essential to adopt a systematic approach to identify potential issues. Here are some key areas to focus on:

1. Foundation and Substructure: Check for signs of sinking or movement in the foundation. Look for cracks in the brick under-building and ensure the damp-proof course is intact.

2. External Walls: Inspect the cladding for signs of decay or damage. Pay particular attention to the timber boarding and any areas where mortar may have bridged the cavity.

3. Roof and Ceilings: Examine the roof for missing or damaged tiles and check the condition of the bituminous felt. Inside, look for signs of water ingress or sagging in the plasterboard ceilings.

4. Internal Walls and Partitions: Check for gaps in separating walls and ensure the plasterboard lining is in good condition. Look for signs of moisture or mould, particularly in areas with poor ventilation.

5. Floors: Inspect the concrete ground floor for cracks or unevenness. On the first floor, check the plywood and timber joists for signs of rot or damage.

6. Insulation and Vapour Control: Ensure the mineral fibre insulation is intact and that the polyethylene vapour control layer is not compromised.

Common Defects and Remediation

Purpose Built Type I houses may exhibit several common defects that require attention. These include:

• Foundation Movement: Address any signs of sinking or movement by consulting a structural engineer. Remedial work may involve underpinning or other foundation stabilization techniques.

• Timber Decay: Replace decayed timber boarding and ensure proper sealing to prevent future moisture ingress.

• Damp Issues: Address any bridging of wall cavities by removing excess mortar and ensuring proper ventilation to prevent damp.

• Insulation Gaps: Fill any gaps in insulation to improve thermal efficiency and reduce energy costs.

• Roof Repairs: Replace missing or damaged tiles and repair any leaks in the bituminous felt to protect the property from water damage.

Conclusion

The Purpose Built Type I house remains a popular choice for home buyers and investors in the UK, offering a unique blend of architectural style and practical design. However, it is essential to be aware of the potential hazards and risks associated with these properties and to conduct thorough inspections to ensure they meet legal standards. By understanding the construction details and common defects, buyers can make informed decisions and safeguard their 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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