Understanding the MOHLG 5M House

The MOHLG 5M house, also known as the CLASP 5M, is a distinctive type of system-built property that emerged in the UK during the 1960s. Designed by the Ministry of Housing & Local Government Development Group under the leadership of Patricia Tindale, these homes were constructed between 1963 and 1970. With approximately 3,500 units built, the MOHLG 5M houses are a significant part of the UK’s architectural heritage.

These properties are typically found in various configurations, including bungalows, two-storey, and three-storey semi-detached and terraced houses. The design aimed to address the post-war housing shortage by providing affordable and quickly constructed homes. However, like many system-built properties of that era, the MOHLG 5M houses come with their own set of unique characteristics and potential issues.

Identifying Characteristics of MOHLG 5M Houses

Exterior Features

The MOHLG 5M houses are easily identifiable by their flat roofs covered with asphalt. The front and rear external walls often feature vertical tongue-and-groove (T&G) boarding or exposed aggregate precast reinforced concrete (PRC) panels up to the first-floor level. Above this, you may find decorative tile or slate hanging, or roughcast panels between the upper window frames.

The flank walls of these houses can vary, with some featuring brick or decorative tile hanging throughout, while others have exposed aggregate PRC panels up to the first floor and decorative tile hanging above. Plywood or ribbed asbestos cement fascia panels typically encircle the dwelling at the first floor and eaves level, with vertical timber cover strips at the corners.

Interior Features

Internally, the MOHLG 5M houses have a variety of construction elements. The ground floor is usually a concrete slab with a raised perimeter kerb and apron. The frame consists of nine RS hollow box stanchions, composite floor and roof support beams, plywood box perimeter beams, and timber floor joist beams. The external walls are timber frame panels clad with vertical T&G boarding over bituminous building paper, with mineral fibre insulation blankets between the frame studs.

The separating walls are laminated plasterboard panel cavity walls with mineral fibre insulation in the cavity and asbestos cement sheet fire stops. Partitions are timber stud lined with plasterboard, and the ceilings are also plasterboard. The first floor typically features T&G boarding on timber joists, while the roof comprises a mineral fibre insulation blanket, plywood decking, and asphalt.

Typical Hazards and Risks

Structural Issues

One of the primary concerns with MOHLG 5M houses is the potential for structural issues. The RS hollow box stanchions, particularly at the bases, can suffer from superficial corrosion. Excessive steel shim packing pieces and carbonation of the concrete kerb are also common problems. Additionally, the PRC panels can experience carbonation, cracking, and spalling, which can compromise the structural integrity of the property.

Timber Decay

Timber decay is another significant issue in MOHLG 5M houses. The plywood box perimeter beams and lower areas of timber claddings are particularly susceptible to rot. This decay can weaken the structure and lead to costly repairs if not addressed promptly.

Insulation and Asbestos

The insulation in the external walls of MOHLG 5M houses is often ineffective, leading to poor thermal performance and higher energy bills. Furthermore, asbestos cement sheet external sheathing, fascia panels, ceilings in passageways, and strip fire protection are common in these properties. Asbestos poses a serious health risk if disturbed, so it is crucial to handle any asbestos-containing materials with care and seek professional advice for removal or encapsulation.

Roofing Problems

The flat roofs of MOHLG 5M houses can develop cracks and suffer from poor drainage, leading to water ingress and potential damage to the interior of the property. Regular maintenance and inspections are essential to ensure the roof remains in good condition.

Defective Premises Act and MOHLG 5M Houses

The Defective Premises Act 1972 imposes a duty on builders, developers, and landlords to ensure that properties are constructed and maintained to a reasonable standard. While the MOHLG 5M houses were innovative for their time, many of the issues outlined above can render them defective under this Act. It is crucial for potential buyers and investors to be aware of these risks and to conduct thorough surveys before purchasing such properties.

Inspecting a MOHLG 5M House: A Step-by-Step Guide

Exterior Inspection

1. Roof: Check for cracks, poor drainage, and signs of water ingress. Ensure the asphalt covering is intact and free from significant wear.
2. Walls: Inspect the front, rear, and flank walls for signs of cracking, spalling, and carbonation in the PRC panels. Look for rot in the timber claddings and plywood box perimeter beams.
3. Fascia Panels: Examine the plywood or ribbed asbestos cement fascia panels for signs of deterioration or damage.
4. Timber Cover Strips: Check the vertical timber cover strips at the corners for signs of decay or damage.

Interior Inspection

1. Ground Floor: Inspect the concrete slab for cracks or signs of movement. Check the raised perimeter kerb and apron for any damage.
2. Frame: Examine the RS hollow box stanchions for superficial corrosion, particularly at the bases. Look for excessive steel shim packing pieces and signs of carbonation in the concrete kerb.
3. Walls: Check the timber frame panels for signs of rot or decay. Ensure the mineral fibre insulation is intact and effective.
4. Separating Walls: Inspect the laminated plasterboard panel cavity walls for any signs of damage or deterioration. Check the asbestos cement sheet fire stops for any issues.
5. Partitions: Examine the timber stud partitions for signs of damage or decay.
6. Ceilings: Check the plasterboard ceilings for cracks or signs of water damage.
7. First Floor: Inspect the T&G boarding on timber joists for any signs of wear or damage.

Asbestos Inspection

Given the presence of asbestos in many MOHLG 5M houses, it is crucial to conduct a thorough asbestos survey. Look for asbestos cement sheet external sheathing, fascia panels, ceilings in passageways, and strip fire protection. If asbestos is found, seek professional advice for safe removal or encapsulation.

Typical Construction Details

Substructure

The substructure of MOHLG 5M houses typically consists of a concrete ground floor slab with a raised perimeter kerb and apron. A damp-proof course (DPC) is usually present to prevent moisture ingress.

Frame

The frame comprises nine RS hollow box stanchions, two composite floor and roof support beams, six plywood box perimeter beams, and two timber floor joist beams. The frame is protected with red oxide and zinc chromate paint to prevent corrosion.

External Walls

The front and rear walls up to the first floor are storey-height timber frame panels clad with vertical T&G boarding over bituminous building paper. The flank walls to the first floor are also storey-height timber frame panels but are clad with exposed aggregate PRC panels. The upper storey walls are timber frame panels sheathed externally with asbestos cement sheets, building paper, and tile hanging. The walls are lined with foil-backed plasterboard, and mineral fibre insulation blankets are placed between the frame studs. Timber cover strips are used at the corners, and flat plywood fascia panels are present at the first floor and eaves perimeter beams.

Separating Walls

The separating walls are laminated plasterboard panel cavity walls with mineral fibre insulation in the cavity. Asbestos cement sheet fire stops are also present.

Partitions

The partitions are timber stud lined with plasterboard.

Floors

The ground floor is concrete, while the first floor features T&G boarding on timber joists on joist hangers.

Ceilings

The ceilings are plasterboard.

Roof

The roof comprises a mineral fibre insulation blanket, plywood decking, and asphalt.

Variants of MOHLG 5M Houses

There are several variants of MOHLG 5M houses, which may include:

• PRC kerb bedded in concrete slab.
• Concrete strip footings and brick underbuilding.
• Additional stanchions for two-storey (extra bedroom) or single-storey (passageway, garages) extensions.
• Brick outer leaf flank wall.
• Exposed aggregate PRC panels or brick flank wall returned around ground floor corners.
• Flank, front, and rear external walls of timber frame panels sheathed externally with fibreboard and slate or tile hanging.
• Ribbed asbestos cement sheet fascia panels.
• Rendered 3″ block cavity separating wall.
• Chipboard flooring.
• Asbestos cement sheet ceilings to through passageways.
• Single-storey extension of exposed aggregate PRC panels forming enclosed porches, storage areas, or integral garages to some dwellings.

Common Defects in MOHLG 5M Houses

Superficial Corrosion of RS Hollow Box Stanchions

The RS hollow box stanchions, particularly at the bases, are prone to superficial corrosion. This can weaken the structural integrity of the property and may require remedial work to address.

Excessive Steel Shim Packing Pieces

Excessive steel shim packing pieces can be a sign of poor construction practices and may indicate underlying structural issues. It is essential to inspect these areas thoroughly and address any problems found.

Carbonation of Concrete Kerb

Carbonation of the concrete kerb can lead to cracking and spalling, which can compromise the structural integrity of the property. Regular inspections and maintenance are necessary to prevent further deterioration.

Rot in Timber Claddings and Plywood Box Perimeter Beams

Timber claddings and plywood box perimeter beams are susceptible to rot, particularly in lower areas. This decay can weaken the structure and lead to costly repairs if not addressed promptly.

Ineffective Insulation in External Walls

The insulation in the external walls of MOHLG 5M houses is often ineffective, leading to poor thermal performance and higher energy bills. Upgrading the insulation can improve the energy efficiency of the property and reduce heating costs.

Cracks and Poor Drainage in Asphalt Roof Cover

The flat roofs of MOHLG 5M houses can develop cracks and suffer from poor drainage, leading to water ingress and potential damage to the interior of the property. Regular maintenance and inspections are essential to ensure the roof remains in good condition.

Asbestos Cement Sheet External Sheathing and Fascia Panels

Asbestos cement sheet external sheathing, fascia panels, ceilings in passageways, and strip fire protection are common in MOHLG 5M houses. Asbestos poses a serious health risk if disturbed, so it is crucial to handle any asbestos-containing materials with care and seek professional advice for removal or encapsulation.

Conclusion

The MOHLG 5M house, with its unique design and construction, represents an important part of the UK’s architectural heritage. However, potential buyers and investors must be aware of the various hazards and risks associated with these properties. Conducting thorough inspections and addressing any issues promptly can help ensure the longevity and safety of these 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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