Overview
The XW house is a precast concrete, system-built house from the 1960s onward. It was both designed and manufactured by Selleck Nicholls & Williams Ltd to meet the growing demand for housing in the UK, and approximately 3,700 were built.
The 1960s saw a surge in system-built housing, designed to be assembled quickly and at low cost, and Selleck Nicholls & Williams were among the pioneers of prefabricated construction. Their modular components allowed rapid assembly, and the XW was widely used during the housing boom of the 1960s and 1970s. The houses were built predominantly in suburban areas as affordable housing. They take the form of bungalows and two-storey terraced houses.
Typical characteristics & construction
The substructure is concrete strip footings and a concrete slab, with a damp-proof course. The front and rear walls are eaves-height PC panels lined with foil-backed honeycomb plasterboard on timber battens. Storey-height timber frame panels are fixed to the PC panels with galvanised mild steel brackets, and these are clad with oil-tempered hardboard backed with bituminous felt. The gable wall is brick, a cavity, and storey-height PC panels lined with plasterboard on timber battens.
The separating wall is storey-height 6-inch PC panels lined with plasterboard on timber battens, and partitions are timber studs lined with plasterboard. The ground floor is a concrete slab, and the first floor is timber joists on bitumen-coated joist hangers. Ceilings are plasterboard, and the roof is timber trusses with concrete tiles.
There are variants. Some roofs are formed with a midspan rolled steel joist, timber joists, screeded woodwool slabs and bituminous felt, and some gable walls are clad with stone-effect concrete blocks.
| Element | Typical construction | Inspection focus |
|---|---|---|
| Substructure | Concrete strip footings, concrete slab, DPC | Cracks or settlement in the slab, dampness |
| Front and rear walls | Eaves-height PC panels with honeycomb plasterboard lining; timber frame panels on galvanised MS brackets, clad in oil-tempered hardboard | Corrosion, honeycombing, rust staining, spalling, joints and connections between panels |
| Gable wall | Brick, cavity, storey-height PC panels lined with plasterboard; some clad in stone-effect blocks | Cracks or movement in the brickwork |
| Separating wall and partitions | Storey-height 6-inch PC panels; timber stud partitions with plasterboard | Damp, mould, structural damage, condition of plasterboard and battens |
| Floors | Concrete slab ground floor; timber joists on bitumen-coated hangers above | Cracks or settlement, rot or damage to joists |
| Roof and ceilings | Timber trusses and concrete tiles, or flat roof in bituminous felt; plasterboard ceilings | Missing or broken tiles, felt condition, water damage or sagging ceilings |
Potential hazards & inspection priorities
Primary concern: the precast concrete panels
The structural issues in these houses are specific. Failure to mate the vertical lacing bar with the panel loop bars leads to structural instability. The embedded mesh reinforcement in the PC panels corrodes over time, compromising structural integrity, and this is a common issue identified by rust staining or spalling concrete. Honeycombing, meaning voids within the concrete, weakens the crosswalls and can be detected by tapping the walls and listening for hollow sounds. Variable rates of carbonation and low chloride content in the PC panels affect the durability of the concrete.
The PC panels should be examined for corrosion, honeycombing and other structural issues, with particular attention to the joints and connections between panels. Corroded areas are treated with rust inhibitors and the damaged concrete repaired; voids from honeycombing are filled with a suitable repair mortar.
Secondary concerns: damp, mould and asbestos
Poor insulation and ventilation lead to damp and mould, with health implications for occupants. Walls and partitions should be checked for damp and mould, ceilings for water damage or sagging, and the gable brickwork for cracks or movement. Signs include discolouration, peeling paint and a musty smell. The answer is better ventilation, repairs to leaks and treatment of affected areas with anti-mould solutions.
Given the era of construction, some building materials may contain asbestos. An asbestos survey should be carried out wherever its presence is suspected.
Is this house right for you?
The XW house is a significant example of 1960s system building, and its condition depends on what is happening inside the concrete panels rather than on the surface finishes.
- Commission a full building survey
- Establish the condition of the PC panels, their reinforcement and the panel connections
- Gather construction plans and previous survey reports where they exist
- Commission an asbestos survey if its presence is suspected
Thorough inspection and prompt attention to any issues are what keep an XW house safe over the long term.
Mortgage & resale considerations
The XW house is not designated defective under the Housing Defects Act 1984. A thorough survey is still essential to identify any issues that require remediation, and significant defects must be addressed for the safety and well-being of occupants.
What a survey can — and cannot — tell you
A building survey provides an informed assessment of the visible condition and construction of an XW house. Inspections are non-intrusive and limited to areas that are accessible at the time of inspection.
- Identify visible rust staining, spalling and cracking to the PC panels
- Assess signs of dampness, mould and moisture ingress
- Comment on pitched or flat roof coverings, gable brickwork and the external envelope
- Review the general condition of accessible floors, ceilings and partitions
- Highlight defects that may require repair, monitoring, or further investigation
However, there are limitations to what a survey can determine without intrusive investigation.
- Confirm the condition of mesh reinforcement embedded in the PC panels
- Confirm whether lacing bars and panel loop bars are properly mated
- Measure carbonation depth or chloride content without testing
- Confirm whether materials contain asbestos without specialist sampling
- Inspect areas that are inaccessible or covered at the time of inspection
Where higher-risk indicators are identified, further specialist or intrusive investigation may be recommended.
