ABSTRACT: A dielectric probe developed for vertical soil moisture measurement was adapted for horizontal use in solid brick masonry. A calibration test showed that a moderate salt contamination had a large influence on the measurements, so the results were only indicative for the change in water content. The change in water content in the wall of a historic warehouse was monitored over a period of 9 years. The horizontal moisture profiles indicated that the source of water to the wall was rising damp. A chemical damp proof course installed at the base of the wall seemed not to be very effective, as there was only 10% reduction in water content after eight years.