Damp diagnosis case studies

Stages 1-3

Property details A detached 3-bedroom bungalow in a rural position in County Tyrone, Northern Ireland. The original building comprises living room, kitchen and bedroom (once a stable) built around 1800, with more recent additions Site: set in 14 acres of agricultural land approximately 200m from the western shore of Lough Neagh (likely to indicate a high water table); fully exposed to the prevailing weather systems in an area of outstanding natural beauty Construction: original parts constructed of local irregular shaped rounded stones (‘weeping stones’); additions (bathroom/bedroom 3) were of a conventional insulated cavity wall of outer leaf brickwork and inner leaf blockwork External finish: perimeter walls have been covered with a cementitious render and painted Roof: new concrete tile pitched and hipped roof (originally thatched) Floors: all solid construction Windows: replaced PVC-U double-glazed, side- and top-hung, casement sashes Services: gas-fired central heating (floor-mounted boiler) and a mains water supply; waste pipes from the property connected to a main drainage network Survey date: October 1999; weather conditions: cool with drizzle

Aims of the survey

To inspect the property and identify the cause of dampness at low level to the external and internal walls and kitchen floor; to provide a written report of findings and recommendations to resolve the defects.

Research before the investigation

Part of the original building was constructed using local stone taken from the shore of the Lough and transported to site by hand. It was not known precisely why the stones were called ‘weeping stones’. Perhaps there was a religious connection. Perhaps it was because the surface of the stone contained small indentations that created pools as the water from the Lough washed over the stone, or that small deposits of water became trapped into the indentations giving an appearance of weeping.

A local surveyor had diagnosed ‘rising damp’ at the property. The problem had become more severe in the preceding year and was constantly present, even in summer. If anything, it was spreading. The kitchen floor was particularly damp; water was visible. The client wondered whether the weeping stone was so named because it was porous enough to draw ground moisture up the walls from the soil.

The roof, gutters and rainwater pipes had all been replaced some 15–20 years before the survey. Some areas of internal damp did correspond with the locations of rainwater pipes externally, but the client confirmed that the dampness did not become worse during rainfall.

Due to the distance needed to travel, the client invited the surveyor to stay overnight on site. Conversations with the owners ahead of the survey greatly helped the surveyor to plan what equipment would be needed, which was being taken by air. He was unable to take a calcium carbide test kit due to flight restrictions; instead he packed an ample supply of film containers in case he needed to bring samples back for moisture content analysis.

Investigation

1. Walk-over – Stage 1

On arrival, the surveyor quickly walked around the property. Dampness was noted in virtually every room.

The pattern of dampness was similar at each location. Internal and external walls were damp to the touch, with a clear and visible tidemark and blistering of painted surfaces. The extent of the damp fluctuated in height to a maximum of 500mm above floor level.

The kitchen floor, overlaid with cork tiles, was extremely wet. Water oozed out from the joints between tiles as they were walked on.

2. Detailed analysis – stage 2 and 3

The surveyor used the electrical resistance moisture meter to scan the pattern of dampness in each room and added the results to a sketch plan he had prepared (see figure 1). Although the wall plaster in the bedroom had blistered and was visibly stained at testing station E, the electrical moisture meter indicated that the wall contained a very low level of damp (14 R/R). The client explained that the old back boiler located in the fireplace of the living room had leaked some time before the survey, which was why they had decided to install central heating.

Figure 1: Floor plan

The timber skirting boards had soaked up a great deal of moisture and the electrical moisture meter indicated maximum readings along the affected sections of wall near to the radiator positions, decreasing in severity away from the radiator positions. The surveyor removed sections of the skirting and saw that the plaster wall finish was in contact with the floor screed.

Samples of moisture from the walls and kitchen floor were collected and tested. None showed any signs of either chlorides or nitrates.

The surveyor decided not to extract wall samples for later testing using the calcium carbide method because the walls were demonstrably damp, and it was doubtful whether the drill would have much impact on the granite-like weeping stones.

Given the exposed rural location in Northern Ireland, which experiences high rainfall, together with the absence of chlorides and nitrates, the surveyor suspected rainwater as a likely source. There was also a link between moisture penetrating the external walls due to the locations of the damp walls and the external downpipes (as shown on figure 1). However, the owner had indicated that the problem was not altered by external weather conditions.

Turning to his sketch plan, it was clear that the patterns of dampness and locations of the damp walls corresponded to the locations of the central heating radiators throughout the property and, more importantly, to the flow and return heating pipes that had been laid into the cementitious floor screed.

But the salts tests remained a puzzle. Water from the mains would inevitably contain some salts, yet the tests were negative. The surveyor speculated that the water inside the heating system may have become distilled (deionised) due to repeated boiling and cooling.

The surveyor could not find an accessible pipe duct in the solid floor, indicating that the floor had been channelled out to accommodate the pipe runs. The copper pipes may not have been laid with any protective coating or taping to prevent corrosion from the surrounding sand/cement screed mix.

The surveyor sealed a floor hygrometer to the bathroom floor (location G). Within the first hour it recorded a relative humidity of 100% and remained so for over 12 hours.

Diagnosis

Water was leaking from the central heating pipes into the floor screed. Inadequate ventilation was preventing the moisture from leaving the building; condensation was also evident.

Prognosis

The survey was done during the autumn, and cooler external temperatures would further increase the risk of condensation internally. Given the amount of moisture within the property, excessive condensation would cause a significant hydration of the internal envelope coupled with moisture produced during periods of occupation.

The surveyor recommended that the client should engage a qualified heating engineer to carry out a pressure test of the heating system to check for leakage.

The property lacked adequate ventilation. The replacement PVC-U windows did not have any trickle vents and there was no mechanical ventilation.

The surveyor recommended the installation of humidistat-controlled mechanical extraction fans in the kitchen and bathrooms, vented to the outside air to remove water-vapour-laden air during periods of peak moisture production (cooking, washing and bathing).

If the central heating pipes were found to be leaking then it would be advisable to consider cutting the existing pipes flush with the floor, capping them off and installing new pipes above the solid floor. The surveyor suggested that the heating engineer should comment on radiator positions and check that the radiator heat outputs were sufficient to meet the heat requirements of each room. They might also consider installing a combination-condensing boiler run from the mains water supply, because the sealed system would eliminate the need for a feed and expansion tank or a hot water cylinder.

The timber skirting boards would need to be removed and replaced, perhaps replaced with a PVC-U profile skirting. The wall plaster should be removed from the base of the walls to form a gap with the floor screed of approx. 50mm.

Follow-up advice

Following the initial survey inspection, the client said that the heating engineer had tested the system and confirmed a leak.

the surveyor suggested that the client should install a dehumidifier to begin the process of drying out the property. He explained that the dehumidifiers would work more efficiently with the windows closed and that leaving the heating on for long periods (24 hours initially) once it had been repaired would also help.

Twelve months after the heating pipework had been rerouted and the heating system upgraded, the client confirmed that the property had dried out and decorating would be the next consideration.

Lessons learned

• Single-storey structures with solid floors do not lend themselves favourably to rigid pipe runs, given door thresholds. However, use of the loft should be considered with careful planning to minimise the number and locations of any pipe drops from the loft void to the radiator positions.

Additional comments The composition of the weeping stones was never discovered, as an attempt to drill into the stone using a tungsten carbide-tipped drill (hammer action) made little impression on the stone. One can only speculate that the granite-like stone is virtually impervious to moisture penetration due to its density – making it an ideal selection for use as a building material for walls.