Understanding the Mowlem House

The Mowlem house, a distinctive type of system-built property, holds a significant place in the UK’s architectural history. Constructed between 1965 and 1981, these homes were designed by Constructional Services Ltd and manufactured by Mowlem (Buildings) Ltd. With approximately 14,500 units built, Mowlem houses are commonly found in various parts of the UK, particularly in suburban areas. Known alternatively as “No-Fines” houses, these properties come in various forms, including bungalows, and two- and three-storey semi-detached and terraced houses.

Identifying Characteristics

Mowlem houses are easily identifiable by their unique architectural features. They typically have shallow pitch gable or monopitch roofs covered with concrete tiles, or flat roofs covered with asphalt. The external walls are either entirely brick or render, or a combination of brick/render on the ground floor and tile hanging or horizontal timber boarding on the upper floors. Some of these dwellings also feature balconies, porches, and bay windows, adding to their distinctive appearance.

Construction Details

Substructure

The substructure of Mowlem houses consists of concrete strip footings, concrete under-building, and a concrete slab. A damp-proof course (DPC) is also included to prevent moisture from rising through the structure.

External Walls

The external walls are constructed with a 2-inch cavity and 4-5 inches of aerated lightweight concrete. Wall ties are used to connect the inner and outer leaves of the wall, and continuous tie bar reinforcement is present at the first floor and eaves level. Above openings, rolled steel angles (RSA) provide additional support. A timber wall plate is used to secure the roof structure to the walls.

Separating Walls

Separating walls between properties are made of 2-inch aerated lightweight concrete walls cast back-to-back. These walls are keyed and bonded with wire ties to ensure stability and sound insulation.

Partitions

Internal partitions are constructed from lightweight aerated concrete, providing a balance between strength and ease of construction.

Floors

The ground floor is typically a concrete slab, while the upper floors consist of timber boarding on timber joists, supported by a rebated timber wall plate.

Roof

The roof structure varies depending on the design. Some Mowlem houses have trussed rafters with concrete tiles, while others have flat roofs made of timber joists, woodwool slabs, and asphalt. Flush fascia boards are a common feature in these properties.

Variants

There are several variants of Mowlem houses, including those with 9-inch no-fines concrete external walls reinforced with dense reinforced concrete (RC) ring beams at the first floor and eaves level. Additional reinforcement is provided over openings, and two bands of continuous reinforcement are placed below window openings. Rendered external walls and upper storey external walls clad with tile hanging or horizontal timber boarding on timber battens are also common. Partitions may be made of honeycomb plasterboard, and concrete window sills and asbestos cement soffit boards are often present. Upper floors in some variants are constructed with timber boarding on timber joists built into the inner leaf.

Typical Hazards and Risks

Structural Issues

One of the most common issues with Mowlem houses is the cracking of brickwork at separating wall junctions. This can be attributed to the movement of the lightweight concrete walls and the differential movement between the brick and concrete materials. Over time, these cracks can widen and compromise the structural integrity of the property.

Moisture Ingress

Due to the age of these properties, moisture ingress can be a significant concern. The damp-proof course (DPC) may have deteriorated, allowing moisture to rise through the structure. This can lead to dampness and mould growth, which can affect the health of the occupants and the longevity of the building materials.

Asbestos

Asbestos cement soffit boards are commonly found in Mowlem houses. Asbestos was widely used in construction during the period these houses were built due to its fire-resistant properties. However, asbestos poses serious health risks if disturbed, as the fibres can become airborne and inhaled, leading to respiratory diseases.

Insulation and Energy Efficiency

Mowlem houses were built before modern energy efficiency standards were established. As a result, they may have inadequate insulation, leading to higher energy bills and a less comfortable living environment. Retrofitting insulation can be challenging due to the construction methods used.

Defective Premises Act

Mowlem houses are not generally classified as defective under the Defective Premises Act. However, individual properties may have specific issues that could render them defective. It is essential to conduct a thorough survey to identify any potential defects and address them promptly.

Inspecting a Mowlem House

When inspecting a Mowlem house, it is crucial to pay attention to specific areas that are prone to defects. Here is a step-by-step guide to help you conduct a thorough inspection:

Exterior Inspection

1. Roof: Check the condition of the roof tiles or asphalt covering. Look for signs of wear, damage, or missing tiles. Inspect the fascia boards for any signs of rot or damage.

2. Walls: Examine the external walls for cracks, particularly at the junctions of separating walls. Check for signs of moisture ingress, such as damp patches or mould growth. Inspect the render or brickwork for any signs of deterioration.

3. Windows and Doors: Check the condition of the window sills and frames. Look for signs of rot, damage, or gaps that could allow moisture ingress. Ensure that the windows and doors are properly sealed and functional.

4. Balconies, Porches, and Bay Windows: Inspect these features for any signs of structural issues or damage. Check the condition of the materials used and ensure that they are securely attached to the main structure.

Interior Inspection

1. Walls and Partitions: Check for cracks in the internal walls and partitions. Pay particular attention to the junctions between different materials, such as brick and concrete. Look for signs of moisture ingress or mould growth.

2. Floors: Inspect the condition of the ground and upper floors. Look for signs of sagging, unevenness, or damage. Check for any signs of moisture ingress, particularly in the ground floor slab.

3. Ceilings: Examine the ceilings for any signs of damage, sagging, or moisture ingress. Check for any signs of asbestos-containing materials, such as asbestos cement soffit boards.

4. Roof Structure: If possible, inspect the roof structure from the inside. Look for signs of damage, rot, or insect infestation. Check the condition of the trussed rafters or timber joists and ensure that they are securely attached to the wall plate.

Services

1. Electrical: Check the condition of the electrical system. Look for any signs of outdated or unsafe wiring. Ensure that the electrical system meets current safety standards.

2. Plumbing: Inspect the plumbing system for any signs of leaks, corrosion, or damage. Check the condition of the pipes, fixtures, and fittings.

3. Heating: Check the condition of the heating system. Ensure that it is functional and meets current safety standards. Look for any signs of wear or damage to the boiler, radiators, and pipework.

Typical Defects in Mowlem Houses

Cracking of Brickwork

As mentioned earlier, cracking of brickwork at separating wall junctions is a common issue in Mowlem houses. This can be caused by the movement of the lightweight concrete walls and the differential movement between the brick and concrete materials. Over time, these cracks can widen and compromise the structural integrity of the property.

Moisture Ingress

Moisture ingress is a significant concern in Mowlem houses due to the age of the properties and potential deterioration of the damp-proof course (DPC). This can lead to dampness and mould growth, which can affect the health of the occupants and the longevity of the building materials.

Asbestos

Asbestos cement soffit boards are commonly found in Mowlem houses. Asbestos poses serious health risks if disturbed, as the fibres can become airborne and inhaled, leading to respiratory diseases. It is essential to have any asbestos-containing materials inspected and, if necessary, removed by a qualified professional.

Insulation and Energy Efficiency

Mowlem houses were built before modern energy efficiency standards were established. As a result, they may have inadequate insulation, leading to higher energy bills and a less comfortable living environment. Retrofitting insulation can be challenging due to the construction methods used.

Structural Issues

Structural issues, such as sagging floors or roof structures, can be a concern in Mowlem houses. These issues can be caused by the movement of the lightweight concrete walls, deterioration of the timber elements, or inadequate support. It is essential to address any structural issues promptly to prevent further damage and ensure the safety of the occupants.

Addressing Common Defects

Cracking of Brickwork

To address cracking of brickwork, it is essential to identify the cause of the movement and take appropriate measures to stabilize the structure. This may involve reinforcing the walls, repairing or replacing damaged materials, and ensuring that the foundations are stable.

Moisture Ingress

To address moisture ingress, it is essential to identify the source of the moisture and take appropriate measures to prevent it from entering the property. This may involve repairing or replacing the damp-proof course (DPC), sealing any gaps or cracks in the walls, and ensuring that the roof and windows are properly sealed.

Asbestos

If asbestos-containing materials are present, it is essential to have them inspected and, if necessary, removed by a qualified professional. Asbestos removal should be carried out in accordance with current safety regulations to prevent the release of asbestos fibres into the air.

Insulation and Energy Efficiency

To improve the insulation and energy efficiency of a Mowlem house, it may be necessary to retrofit insulation in the walls, roof, and floors. This can be challenging due to the construction methods used, but it is essential to ensure that the property meets current energy efficiency standards. Upgrading the heating system and installing energy-efficient windows and doors can also help to improve the energy efficiency of the property.

Structural Issues

To address structural issues, it is essential to identify the cause of the problem and take appropriate measures to stabilize the structure. This may involve reinforcing the walls, repairing or replacing damaged materials, and ensuring that the foundations are stable. It is essential to address any structural issues promptly to prevent further damage and ensure the safety of the occupants.

Conclusion

Mowlem houses, with their distinctive architectural features and unique construction methods, hold a significant place in the UK’s architectural history. While these properties offer a range of benefits, they also come with specific challenges and potential defects that must be addressed to ensure their longevity and safety. By conducting a thorough inspection and addressing any issues promptly, home buyers and investors can safeguard their investment and enjoy the unique charm of a Mowlem house.

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.