Common Situations

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Condensation in the Attic

It is not uncommon for HVAC equipment to be located in an attic. Generally, the attic is not a conditioned space, so humidity levels may be high. If high humidity is present, there is a great danger of having condensation from the A/C equipment. This can lead to insulation damage, collapse of ceiling drywall below, and mold.

To avoid these problems, it is important to maintain a vapor seal between the cold surfaces and the attic air. Do this by installing a vapor barrier on the outside of the duct and equipment insulation.


It is not uncommon in new buildings to see the formation of mold and mildew. How can this happen?

Over the years I have observed the mold formation phenomenon resulting from a variety of causes, but generally all come down to poor construction technique. In one case, the staged drywall was allowed to get wet. In another, lined ductwork was left out in the rain before installation.

In each case, the construction materials were allowed to get damp or wet. After installation, the air conditioning was turned on, and the materials were exposed to low dewpoint temperature air. The result: dampness became liquid water, and spores grew into mold.


Most know that today's double pane windows save energy. But other factors contribute to the satisfactory performance of the window, including whether the window frame creates condensation.

In cold climates it is important to install a metal frame window that is "thermally broken". This means a frame with physical discontinuation between the exterior and interior. If the frame is not thermally brokem, that is, continuous from cold outside to warm inside, the inside frame will be cold. That cold surface will cause condensation of airborne mositure in the space. Eventually, that "sweating" on the frame interior will cause the formation of mold and mildew.

Thermal broken metal frame windows should be installed in any climate where the winter temperature falls to below 55 F.


In a 6 month old building, metal surfaces were rusting, and mold was everywhere. Vinyl wall coverings were coming unglued. What was the cause?

The air conditioning system in this building employed small (5 tons or less) direct expansion units. The fans units ran continuously, and included fixed outside air intakes. All of the equipment was sized for a peak daytime cooling load with high outdoor temperatures and sun. In many cases two small cooling units served a single space.

We took temperature and humidity measurements, and foudn that the indoor humidity level was well above 60%. I theorized that during moderate weather, the compressors would cycle on temperature, but the high humidity outdoor air would continue to be introduced to the space, as the fans ran all the time. When a compressor would come on, the cold air from the system would cause condensate of the highly humid air.

Our solution was to disable half of the cooling units. This allowed for longer operation of the remaining equipment, allowing for better dehumidification. After about an hour in this operational mode, the indoor humidity dropped from 63% to 51%, solving the problem.

After confirming the solution, we made some duct and temperature controls modificiations, and the humidity and mold problem was solved.

Carbon Monoxide - It is Odorless, but Lethal

Carbon Monoxide is a silent and deadly gas resulting from either incomplete combustion or poor furnace maintenance, generally in older buildings. Issues have involved poorly fitted flue connections and something as simple as a deteriorated screw connection in a flue path. Clues to the problems have been widespread soot or jumpered siring, which indicates a lack of maintenance.

Design / Build Gone Wrong

The design/build method of project delivery is popular because it is seen to save both time and money in the construction process. In many cases, when ethical contractors are employed, results are favorable. There are times, however, due to either cost or schedule pressures, the owner is unsatisfied with the product.

I have been called to consult on some of these. In almost all projects, a professional engineer is hired by the contractor to execute a design, as stamped drawings are required to obtain a building permit. In the best of all worlds, the contractor and engineer, working together, can create a design that provides an excellent, cost effective solution.

Watch out, however, for the design/build solution that responds mostly to cost pressures. Most of my litigation assignments involve in some way a design and implementation that cuts corners to save money. Some that come to mind include a lack of control valves, skimping on insulation, undersizing of pipe and ductwork, and inferior temperature control systems.

When using the design/build method, it is always a good idea to employ an independent engineer to review the proposed design to make sure that it delivers what is required. Poor system performance is no bargain.