Technical Updates

"Excessive condensate formation in false ceilings."

The Problem with Ceilings

Directive No: 2007/Ceiling/001

As a design-build specialist, Meridian Homes® inspects properties at various stages of construction – including on completion. Using special proprietary probes, we have been able to record several interesting findings. One classic, recurring problem we encounter is the ‘excessive sweating’ peculiar to false ceilings.

Issue

Excessive sweating in ceilings accelerates structural deterioration.

Observation

  1. Rusty studs, runners and counter battens, nails in false ceilings.
  2. An existing solution is to use galvanised products and special nails, but this action only serves to delay the onset of the problem by a couple of years (7 years on average) - it does not solve it.

Investigation & Discovery

  1. Very damp air space.
    1. We discovered humidity levels in excess of 90%, which causes widespread condensation, and resultant rust on all surfaces including welding joints and scratched surfaces.
    2. In certain areas, condensation is so bad that water constantly drips onto the false ceiling surfaces. As the droplets accumulate, they will leave water marks, or bubbles, on the underside of the false ceilings. The occupier below could discern these as rust stains/marks if he looks up the ceiling.
    3. Another consequence of water dribbles is the growth of fungi, and the eventual decomposition of organic materials like timber. Wood, for example, will rot or attract termites and other pests
  2. In the ceiling void under a concrete flat roof , the humidity level is much lower than that found under a metal roof.
    1. But the humidity level in the ceiling void under a concrete flat roof is still higher than in the surrounding air outside.
    2. Static humid air tends to condense, particularly when the surrounding temperature drops. This will cause water droplets to form.

Challenges

  1. Why was the humidity level so high, in excess of 90%?
    1. There were no leakages, otherwise we would have detected other symptoms, including surface patchiness. As it occurred in so many properties, we could confidently rule out leakages from the outright failure of waterproofing membranes and/or the roof.
  2. Why is ‘sweating’ so undesirable?
    1. Excessive moisture has long-term structural implications. If rusting continues unabated, metal structures could eventually lose their strength, causing instability.

Postulation

  1. Our first postulation was that since it was not a leak, it might be from capillary action.
    1. We observed a similar occurrence of ‘sweating’ in concrete flat roofs. There was no visible presentation of leaks, so physical water causing the high humidity was ruled out. We saw the same problem on external walls and toilet walls built of concrete, brick, cement or masonry.
    2. We postulated that waterproofing membranes are effective as they stop water molecules from passing through. However, all matter has size and a finite dimension. In our particular postulation, the pores of the waterproofing membrane are small enough to prevent water passage, but is still big enough for molecules to pass through, especially when gravity helps ‘force’ these molecules through.
  2. Gases.
    1. Since physical water was ruled out, we thought that water in its gaseous state was the most probable culprit. Metal roofs in the tropics tend to get very hot, reaching surface temperatures in excess of 60-degree Celsius. Sudden squalls can result in water droplets turning into steam.
    2. A metal roof uses an overlapping medium around its ridges but it is not airtight – the only features stopping physical water from getting under the roof are the ridges. Steam, being a gas, can travel between the overlaps and ridges to a location of lower pressure, bringing with it high humidity air.
      Once the temperature drops, the humid air condenses on the cooler surfaces. Metal parts, by their nature, will provide the perfect places for condensation to take place.
      Condensation occurs during the early hours of morning or after a downfall when surface temperature drops. Thus, water droplets form and ‘sweating’ occurs.
    3. We find this postulation to be the most valid based on our observations and understanding.

Remedy

  1. For all ceilings under a roof or toilet, allow for open ventilation to occur. This prevents static air – which is prone to condensation, and reduces build-up of moist air.
  2. Use appropriate materials. Routinely used/existing products are grossly inadequate to address this issue. We analysed what are currently available, put them against standard industry practices, and realised that a major change in direction was needed.
  3. Preference for concrete flat roof. A membrane-based false ceiling may be costly and difficult to install, but it is one of the better solutions available today. If liquid-based membrane is to be used, it should be made up of several layers so that micro-pores can be overlapped multiple times. This will help minimise molecular migration, but it does not prevent rusting over the long-term.

Long Term Solution

  1. Meridian Homes® has developed new methodologies, system components and detailing to address these challenges, and complement our findings. This includes, but is not limited to, doubly-reinforced systems, as well as new materials never before used in such situations.
  2. To the industry (and workers) unfamiliar with the implementation of these methods and systems, it can prove a troublesome process. As Meridian Homes® has established a dedicated training centre in Northern Thailand to imbue our workers with the know-how, they are well-qualified to apply these systems in our projects.