Building pathology competency

Q: Please explain the how you assessed the movement to the wall of building K.

A: The owner was concerned about cracks to one elevation of a single-storey 1960s commercial building that they had acquired. I carried out a desktop study using the client’s drawings and information. I followed this with a visual inspection, noting the construction, location and cracks to the building. The affected elevation has an external cavity wall leaf made of calcium silicate brick. The external wall had vertical cracks at regular intervals running from the damp-proof course (DPC) through the window openings; the wall also oversailed the DPC at each end. Only the southern elevation, facing the sun, was affected.

I followed BRE guidance including DG251 and DG227-229 and monitored the cracks with gauges, pins and digital callipers to assess the cause. My calculations and findings confirmed it was due to thermal movement, so thermal movement joints were required.

Q: You gave advice on damp affecting an office, X, converted from an 1890s house. Could you explain your reasoning?

A: The client had noticed recent low-level staining to the porch's internal finishes. I inspected the construction and investigated the staining, which was characteristic of damp to the external solid wall. Damp-meter readings of the skirting were in excess of 22 per cent moisture content but nine per cent elsewhere, indicating damp-affected timber with an increased risk of fungal growth. A wall profile gave higher relative readings at a low level.

Moisture meters can provide potentially misleading results in masonry; following guidance including BRE's Understanding dampness and its DG245 as well as isurv, I used a calcium carbide meter that confirmed the higher moisture content in the lower wall area. Thermo-hygrometer readings indicated no condensation risk.

Externally, a new flowerbed breached the slate DPC, and the client said the stain became worse after rain. Protimeter salts analysis tests indicated nitrates and chlorides were present, which supported a groundwater or soil issue rather than condensation. No other damp sources were present. I advised that the likely cause was the high soil level, which should be reduced to at least 150mm below the DPC. I followed guidance including BS 6576 to recommend that, after it is confirmed that there is no further damp and the wall is sufficiently dry, then the finishes should be repaired.

Ewan Craig is an APC assessor, APC coach and consultant

Related competencies include: Building pathology, Inspection

Further information: rics.org/pathways