Overview of the Unitroy House

The Unitroy house, a distinctive property type from the 1950s, stands as a testament to post-war British ingenuity in the construction industry. Designed by M Flatman and manufactured by Unitroy Ltd, these properties were part of a broader movement to address the housing shortage in the UK. With only 200 units built, these homes are relatively rare, making them a unique find for home buyers and investors alike.

Historical Context and Manufacturing Details

Period Built and Typical Locations

The Unitroy houses were constructed during the 1950s, a period marked by a significant demand for affordable and quickly built housing solutions. These homes are typically found in suburban areas, often in regions that experienced rapid post-war development. The design and construction methods reflect the era’s emphasis on efficiency and cost-effectiveness.

Manufacturers and Designers

Unitroy Ltd, the manufacturer behind these homes, collaborated with designer M Flatman to create a property that could be mass-produced while maintaining structural integrity and aesthetic appeal. The collaboration aimed to address the urgent need for housing in the post-war period, resulting in a design that was both innovative and practical.

Identification Characteristics

Structural Features

Unitroy houses are easily identifiable by their 2-storey semi-detached design. They feature a steep pitch gable roof covered with interlocking concrete tiles, which is a distinctive characteristic. The external walls are rendered throughout, providing a uniform and clean appearance.

Alternative Names and References

While commonly known as Unitroy houses, these properties may also be referred to by their reference code, NTHSc. This code is often used in official documents and surveys to identify the specific construction type.

Typical Characteristics and Hazards

Construction Details

Substructure

The substructure of Unitroy houses typically consists of concrete strip footings and a concrete slab. A damp-proof course (DPC) is also included to prevent moisture ingress.

External Walls

The external walls are rendered and constructed using 18″ x 3′ x 2 1/2″ lightweight precast (PC) flanged panels. These panels are supported by a 4 1/2″ cavity and plasterboard on timber framing. Reinforced concrete (RC) columns are formed by semi-circular rebates in the flanged ends of the PC panels. Metal hook bolts are cast into the columns for additional support. U-shaped PC troughs and RC ring beams are used at the first floor and eaves level, while L-shaped foamed clinker PC corner blocks provide additional structural integrity.

Separating Wall

The separating wall between semi-detached units is a brick cavity wall, offering both structural support and sound insulation.

Partitions

Internal partitions are typically made of timber stud lined with plasterboard, providing a lightweight yet sturdy solution for dividing internal spaces.

Floors

The ground floor is constructed of concrete, while the first floor consists of timber boarding on timber joists. These joists are supported by a PC spine beam, which is in turn supported by the separating and gable walls and intermediate columns.

Ceilings

Ceilings are generally made of plasterboard, offering a smooth and easily maintainable surface.

Roof

The roof structure comprises timber trusses, fibreboard sarking, and interlocking concrete tiles. This combination provides both durability and weather resistance.

Variants

Some Unitroy houses feature variations in their construction, such as:

• Substructure of foamed clinker block underbuilding with a 9″ cavity wall up to the DPC.
• Cavity filled with concrete to ground level.
• External wall plasterboard linings backed with bituminous felt.
• Ground floor of timber joists supported on a sleeper wall.
• First floor of timber joists on a steel joist.
• Partition linings made of Norfolk reeds, vermiculite, and cork or expanded clay sandwiched between plasterboard sheets.
• Roof constructed with RST rafters and purlins.

Typical Defects and Risks

Designated Defective

Unitroy houses are designated as defective under the Defective Premises Act. This designation means that these properties have been identified as having inherent structural issues that could pose risks to occupants. It is crucial for potential buyers and investors to be aware of this designation and to conduct thorough inspections before making a purchase.

Common Defects

Corrosion of Steel in Concrete

One of the most common issues with Unitroy houses is the corrosion of steel reinforcement within the concrete. This can lead to structural weaknesses and potential safety hazards. Guidance on inspecting and assessing the durability of reinforced concrete can be found in BRE Digest 444 (Parts 1–3) and other related publications.

Carbonation Depths

Carbonation of concrete is another concern, as it can reduce the alkalinity of the concrete and lead to corrosion of the steel reinforcement. This issue is particularly prevalent in older properties where the concrete has been exposed to the elements for an extended period.

Render Deterioration

The external render on Unitroy houses can deteriorate over time, leading to cracks and potential water ingress. Regular maintenance and repairs are essential to prevent further damage.

Timber Decay

Timber elements within the structure, such as joists and trusses, can be susceptible to decay, particularly if they have been exposed to moisture. Inspecting these elements for signs of rot and taking appropriate remedial action is crucial.

Inspection and Assessment Guide

Pre-Inspection Preparation

Before conducting an inspection of a Unitroy house, it is essential to gather as much information as possible about the property. This includes reviewing any available documentation, such as previous survey reports, maintenance records, and building plans.

External Inspection

Roof

Inspect the roof for any signs of damage or wear, such as missing or broken tiles, sagging, or water ingress. Pay particular attention to the condition of the timber trusses and fibreboard sarking.

Walls

Examine the external walls for cracks, render deterioration, and signs of moisture ingress. Check the condition of the PC flanged panels and RC columns, looking for any signs of corrosion or structural weakness.

Substructure

Inspect the substructure for any signs of movement or settlement. Check the condition of the concrete strip footings and slab, as well as the DPC.

Internal Inspection

Floors

Inspect the ground and first floors for any signs of movement, sagging, or damage. Check the condition of the timber joists and PC spine beam, looking for any signs of decay or structural weakness.

Partitions

Examine internal partitions for any signs of damage or deterioration. Check the condition of the timber stud and plasterboard linings.

Ceilings

Inspect the ceilings for any signs of sagging, cracks, or water damage. Check the condition of the plasterboard and any supporting timber elements.

Specialist Inspections

Reinforced Concrete

Given the potential issues with reinforced concrete in Unitroy houses, it is advisable to conduct a specialist inspection to assess the condition of the steel reinforcement and the extent of any corrosion or carbonation. This may involve taking core samples and conducting laboratory tests.

Timber

A specialist timber inspection can help identify any areas of decay or infestation. This may involve using moisture meters and other diagnostic tools to assess the condition of the timber elements.

Maintenance and Repair Recommendations

Regular Inspections

Conducting regular inspections is essential to identify and address any issues before they become more serious. This should include both visual inspections and specialist assessments as needed.

Roof Maintenance

Regular maintenance of the roof is crucial to prevent water ingress and other issues. This may involve replacing damaged tiles, repairing or replacing timber trusses, and ensuring that the fibreboard sarking is in good condition.

Render Repairs

Addressing any cracks or deterioration in the external render is essential to prevent water ingress and further damage. This may involve patch repairs or, in some cases, re-rendering the entire property.

Concrete Repairs

If issues with the reinforced concrete are identified, it is essential to take appropriate remedial action. This may involve repairing or replacing corroded steel reinforcement, addressing carbonation, and applying protective coatings to prevent further deterioration.

Timber Treatment

Treating any areas of timber decay or infestation is crucial to maintain the structural integrity of the property. This may involve replacing affected timber elements, applying preservative treatments, and addressing any sources of moisture.

Conclusion

The Unitroy house, with its unique design and historical significance, offers both opportunities and challenges for home buyers and investors. Understanding the typical characteristics, potential defects, and maintenance requirements of these properties is essential to make an informed decision. By conducting thorough inspections and taking appropriate remedial action, it is possible to preserve the structural integrity and value of these distinctive homes.

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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