MOHLG 5M Steel Framed House

The 5M steel framed house is constructed from a lightweight composite steel-and-timber-framed system which was designed by the Ministry of Housing and Local Government Research and Development Group, otherwise referred to as M.O.H.L.G.
The 5M was essentially a progression of the earlier CLASP system of construction that had been used in the erection of school buildings during the 1950s.
The first 5M dwelling was constructed in 1961 and general production followed in 1963. The ‘M’ in the title 5M represents the term ‘module’, This form of construction utilized the 1ft 8 inch or five times the module of 4-inch grid system. Imperial measurement still dominated at this time; however, 4 inches was very close to the metric scale of 100 mm. By comparison, a 12M (4’0″) system related to the standard Imperial sheet material size of 8’0″ x 4’0″.

The long-term concept of the Modular House, was to design and build using interchangeable components of standard sizing that would be compatible with other manufacturers systems who deployed the same size modular grid.

The 5M system used a number of standard sized components which were utilized to produce a wide variety of plans and layouts. Unfortunately, the system was not a great success as it was considered to be grossly over designed and susceptible to water penetration by many outspoken critics. The excessive number of joints and cladding fixture points dramatically increased the risk of water ingress.

Some Critics even went so far as to suggest that the internal steel frame was surplus to requirement as the modular steel construction alone, offered sufficient support for the structure.

Identification
The basic design is of single- or two- or three-storey flat-roofed terraced dwellings with a distinctive continuous fascia at first-floor level and at roof level.
The ground-floor elevations are largely storey-height door and window units, with intermediate panels clad with V-jointed vertical tongued and grooved boarding or exposed aggregate precast concrete panels.
The flank-end wall is clad with similar concrete panels or with brickwork.
At first-floor level, a wide flat plywood or asbestos cement fascia panel encircles the terraced block.
The upper-floor elevations are clad with a variety of forms of decorative tile hanging. A matching fascia panel encircles the terraced block at roof level, and distinctive vertical timber cover strips mask the joints at corners.
The roof is flat with an up stand around the perimeter. The rain-water is drained down internally.

The range of possible designs is wide. Some of the terraces are very long, up to twelve dwellings, and a combination of features such as single-storey extensions, link rooms over external passageways and steps and staggers are used to break up the line.
The single­-storey extensions form enclosed porches, entrance hall storage areas or integral garages.
Many of these dwellings have recently undergone refurbishment work where the exterior walls have been Externally insulated with brick slip cladding or render application to the exterior. A brickwork outer leaf and the incorporation of pitched roofs (As seen below) have significantly altered the appearance of some properties, making them difficult to identify in the future.

5M Bungalow Variant

• The 5M Bungalow contains a mixture of steel and timber framing.
• The front and end walls are framed out in timber stud-work, which is lined internally with plasterboard.
• The external cladding is of vertical tongue and groove boarding on timber battens or tile hanging on battens on asbestos fibre-board or plywood boarding.
• The flat roof is of timber joists at regular centres spanning between the steel eaves beams and internal flitch beams.
• The roof is finished with felt.

Reported 5M Issues

• Carbonation of the concrete to the kerb upstand and precast concrete cladding panels
• leading to corrosion of the steel reinforcement and spalling of the concrete faces.
• Horizontal cracks across the concrete cladding panels.
• Damp penetration of the concrete kerb upstand.
• Deterioration of the protective coatings to the steelwork and superficial corrosion at the base of stanchions.
  Excessive numbers of steel shim packing pieces.
• Broken and missing tiles from the tile hanging.
• Wet rot in the plywood box perimeter beams, door and window joinery units and lower areas of timber claddings.
• Ineffective insulation and mould growth.
• Poorly fitting floor joists and large notches cut into the joists.
• Cracks in the asphalt roof covering, allowing water to penetrate through to the structure.
  Poor drainage of the roof creating pooling.

These points listed above do not constitute a comprehensive list of all possible defects.
Not all defects will necessarily be present in one property.
The list serves to highlight possible areas which should be subjected to close examination.

If significant corrosion of the steelwork has occurred, the extent of deterioration may be masked by the corrosion product itself. In such cases it is difficult to determine the condition of the steelwork solely by a visual inspection.

This limits the effective application of visual inspection techniques, including optical probes. If corrosion is observed, the affected component should be exposed in order to establish the full extent of deterioration and subsequent removal or repair.

GENERAL CONDITION

Some of the 5M houses subjected to survey were in their original condition.
Steel stanchions were generally found to be in good condition. Deterioration of protective coatings and superficial corrosion is evident at the stanchion bases. Corrosion is occurring to the reinforcement in the kerb up stand and cladding panels, largely due to carbonation of the concrete.
Rain penetration through cracks in the asphalt roof covering has led to wet rot in the plywood box perimeter beams.

Resources

• Ministry of Housing and Local Government. 5M System Specification Notes and Component Drawings. London, MHLG, 1965.
• 2 Harrison H W. Steel-framed and steel-clad houses: inspection and assessment. Building Research Establishment Report. Garston, BRE, 1987.
• You can purchase the Building Research Establishments Report – 5M steel-framed houses which provides further constructional details from: BRE Bookshop Building Research Establishment Garslon, Watford, WD2 7JR Telephone: 0923 664444