Overview
The Edinburgh Foamed Slag house is an in-situ concrete house built in 1944, at a time when demand for affordable, quickly constructed homes was at its height. Only two were ever built. They were constructed by Holland and Hannen and Cubitts, a well-known construction firm of the time, to a design by S Bunton.
The aim was a durable, cost-effective house using new materials and construction techniques. The use of foamed slag aggregate concrete for the walls and partitions is what sets these houses apart from other houses of the period.
Typical characteristics & construction
The house sits on concrete underbuilding and a concrete slab, with a damp-proof course (DPC). The external walls are rendered 7-inch foamed slag aggregate concrete, a material chosen for its light weight and insulating properties, with precast reinforced concrete (PRC) lintels and PRC trims around the windows.
The separating wall between each pair is a 4-inch foamed slag aggregate concrete cavity wall with a 2-inch cavity, which helps with sound insulation and adds some thermal efficiency. Loadbearing partitions are 7-inch foamed slag aggregate concrete, and non-loadbearing partitions are 4-inch foamed slag aggregate PC blocks or, in some variants, 2-inch gypsum plaster planks.
The ground floor is timber boarding on 2 inches of foamed slag aggregate concrete, on 4 inches of concrete, on a half-inch cold asphalt damp-proof membrane (DPM), on 3 inches of ashes and a 6-inch concrete slab. The first floor is timber boarding on timber joists, and ceilings are plasterboard. The roof is timber rafters and timber sarking, covered with bituminous felt and tiles.
| Element | Typical construction | Inspection focus |
|---|---|---|
| Substructure | Concrete underbuilding, concrete slab, DPC | Deterioration of the DPC, moisture ingress |
| External walls | Rendered 7-inch foamed slag aggregate concrete; PRC lintels and window trims | Cracking or deterioration of render, spalling, condition around windows and doors |
| Separating wall | 4-inch foamed slag aggregate concrete cavity wall, 2-inch cavity | Cracking |
| Partitions | 7-inch foamed slag concrete (loadbearing); 4-inch foamed slag PC blocks or 2-inch gypsum plaster planks (non-loadbearing) | Cracks, structural movement |
| Ground floor | Timber boarding on foamed slag concrete, concrete, cold asphalt DPM, ashes and concrete slab | Damp, rot or decay in boarding |
| First floor and ceilings | Timber boarding on timber joists; plasterboard ceilings | Rot, decay, general condition |
| Roof | Timber rafters and sarking, bituminous felt, tiles | Damaged or missing tiles, felt condition, water ingress to rafters and sarking |
Potential hazards & inspection priorities
Primary concern: carbonation and reinforcement corrosion
Structural integrity is the main concern. Foamed slag aggregate concrete is prone to carbonation, which reduces the alkalinity of the concrete and leads to corrosion of the embedded steel reinforcement, compromising the structure. Cracking and spalling of the concrete are common defects in these houses, caused by carbonation and the corrosion that follows.
Externally, cracking or deterioration of the render points to underlying problems in the concrete, and the areas around windows and doors, where the PRC lintels and trims are, deserve particular attention. Where carbonation or corrosion is suspected, specialist testing is the next step: measuring carbonation depth and assessing the condition of the reinforcement. Guidance on these tests is given in BRE Digest 444 and BR 254.
Secondary concerns: damp and the roof
Moisture ingress remains a concern despite the DPC, particularly where it has deteriorated over time, and damp causes further structural damage and an unhealthy living environment. The ground floor needs checking for damp, and the timber boarding for rot or decay. Additional damp-proofing measures are worth considering where the DPC is not intact.
The roof should be inspected inside and out: the condition of the tiles and bituminous felt from outside, and water ingress or damage to the rafters and sarking from the loft. Damaged or missing tiles should be replaced promptly.
Long-term considerations: thermal efficiency and asbestos
Foamed slag aggregate concrete gives some insulation, but these houses do not meet modern thermal efficiency standards, which means higher energy bills and a less comfortable home in colder months. As with many properties of this period, asbestos may be present in the construction materials. Materials that may contain asbestos should not be disturbed, and professional advice should be taken before any work that could disturb them.
Is this house right for you?
The Edinburgh Foamed Slag house has an unusual history and was innovative for its time, but it carries specific risks that come from its materials. Regular inspection and maintenance are what keep these houses safe and durable.
- Commission a full building survey from a professional surveyor
- Look closely at the render and the areas around the PRC lintels and window trims
- Be prepared for specialist carbonation and reinforcement testing
- Check for damp at ground floor level and maintain the roof
Understanding the characteristics, construction and likely hazards of the house is what allows an informed decision.
Mortgage & resale considerations
Edinburgh Foamed Slag houses are not designated defective under the Housing Defects Act 1984. They were innovative for their time but do not meet modern building standards, and significant defects can still be found. A thorough assessment by a professional surveyor before purchase is strongly recommended.
What a survey can — and cannot — tell you
A building survey provides an informed assessment of the visible condition and construction of an Edinburgh Foamed Slag house. Inspections are non-intrusive and limited to areas that are accessible at the time of inspection.
- Identify visible cracking and deterioration of the render and spalling of the concrete
- Check the condition of the PRC lintels and window trims
- Assess signs of dampness and moisture ingress, particularly at ground floor level
- Comment on the roof coverings and, where accessible, the rafters and sarking
- Highlight defects that may require repair, monitoring, or further investigation
However, there are limitations to what a survey can determine without intrusive investigation.
- Measure carbonation depth in the foamed slag concrete
- Confirm the condition of steel reinforcement concealed within the concrete
- 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.
