Mechanical Systems

In a previous article, we discussed ice dams frequently being the suspected cause of building leaks. Further investigation revealed that inadequate detailing and/or construction methods were the cause. This month’s issue deals with an inadequate mechanical systemthat led to condensation and humidity problems.

2172610181_e30b21d7a7_mCondensation Problems

A building containing a pool at a mountain resort was experiencing problems with condensation and excessive humidity. It was relatively easy to determine that the cause was mechanical equipment not providing sufficient air changes. The problems caused by the excessive humidity included:

  1. Saturated insulation and roof deck
  2. Deteriorated exterior wood siding
  3. Rusted doors
  4. Rotted wood trim and structural elements
  5. Humid, foggy windows and disease-carrying stale air

In short, the inadequate mechanical system was threatening the integrity of the entire structure.


Our investigation sought to determine whether the reason for the inadequate system was a result of poor design, construction, or both.

We began with an overall assessment that took inventory of the problems caused by the excessive humidity and also noted problems with the mechanical equipment in place.

A plan review revealed that the system installed differed greatly from the designed system. The system originally designed had called for drier outside air to be brought in as “make-up” air to control the high humidity. Because the building was located in a mountain environment, the make-up air would be cold and would need to be heated. Heat would have been provided by an electric heating coil, as natural gas was not available at the time of the installation.

Cost Savings?

We eventually learned that the originally designed system had been shelved in favor of a more “economical” system. In addition to eliminating the supply of make-up air, the system installed was undersized. Mechanical systems installed at 9,000 feet above sea level operate at about 70 percent efficiency compared to an equivalent system at sea level.

Even though the electrical heating coil for outside air had been eliminated, the existing system was still costly to operate because it was constantly running at full power and was not fueled by natural gas. A system that had been installed because the property owner wanted to save money up front ended up being more expensive in the long run. In addition to high electric bills, the property owner had to rehabilitate the damaged structure at great expense, and still replace the entire mechanical system.


The new system installed is fueled by natural gas, which had subsequently become available in the area. The system incorporated the use of make up air from the outside but utilized a heat exchanger to transfer heat from the outgoing air to the incoming air. The combination of natural gas and an appropriate system has led to decreased operating costs. The room now provides a pleasant environment and is maintained at a reasonable cost.

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