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Residential Energy Efficiency Blog
Sunday, November 10 2019
PITFALLS OF NOT FINDING THE RIGHT SOURCE OF A MOISTURE ISSUE IN YOUR HOME
Your home is a complex system. Before you do work to any specific part, you need to know a few key building science principles. There is nothing more frustrating than learning that you should have done this or you should have done that...after you already paid for the wrong solution. This happens all too often in home remodeling and retro fitting because there are so many different trades involved and unfortunately, incorrect or outdated ways of thinking are guiding contractors and homeowners to the wrong solutions.
AN EXAMPLE OF BUILDING SCIENCE PRINCIPALS LEADING THE WAY
I was the second appointment in two days time for a homeowner with a condensation problem in Columbia, MD Howard County. To be clear, condensation was on the pane of glass inside the home and could be wiped away. This was a summer issue during hot, humid days which are plentiful in Maryland. Also, this issue is not to be confused with fogging between the glass panes that cannot be wiped away. That type of issue is a different problem related to the window unit. This issue had to do with indoor air quality.
FINDING THE RIGHT SOLUTION
Next, I wanted to take a look at the new heating & cooling (HVAC). It was "new" according to the homeowner. I checked the size and age of each unit. I took at look at the outside and inside units. The house was zoned with two systems and in my opinion, needlessly. The house was built in the 80's. It is a typical four bedroom house with a basement, first floor and 2nd floor.
Bigger is not always better in HVAC. In summer, a larger machine in a smaller home runs a shorter time and does not effectively pull humidity out of the air. I found that the house's HVAC combined was 5.5 tons for 3000 sq ft of conditioned space with 8' ceilings. The number of square feet of floor space that can be cooled by a ton of AC capacity depends on climate, shade, insulation levels, internal heat gains and air leakage. This home would rank in the range of a home with average air tightness, R-values, shade and reasonably well installed AC systems. The calculation would be 800 square feet cooled per ton. Calculation: 3000/800=3.75 Needed for this size home: 3.5 - 4 ton system would suffice. Again, this home has 5.5 tons, too much. This conclusion would lend to a more humid indoor air quality.
Next, I was curious about the basement. A small utility closet revealed a 4' portion of the rim joist (at the top of the foundation wall) and it revealed that there was no thermal/pressure boundary (insulation). Likely that was to be the case around the entire perimeter at the leaky rim and band joist, but accessing that area would be costly because the ceiling drywall would have to be removed. It might be something that should be done if other possible remedies do not help with the moisture issue. In any case, any accessible portion of the rim joist should be air sealed and insulated to the recommended levels in your area. In Maryland it is R-19. So, another likely source of humidity issues in this home were due to infiltration of warm, humid air at the leaky portions of the rim joist.
The next step in my search for answers to the problem was to locate any source of interior moisture in the basement. Showers, washing machines, sinks and determining how often they were used and what, if any, exhaust fans were in place and how often were they being used. As it turns out the bathroom was used on occasion and the clothes washer was in the basement and used regularly. Testing performed to the bathroom exhaust fan revealed that the fan was not functioning. Therefore, there was no way of getting any moisture created in the basement to move "outdoors".
The living space inside the home is referred to as the envelope. Other moisture sources in the home can also contribute to humidity levels in the basement. I moved along to test other exhaust fans in the kitchen and bathrooms. I discovered that there was not a single working exhaust fan in the home. Showers, cooking, moisture from the inhabitants of the home were all getting trapped. It is also summer so windows are closed in MD if you want to be able to breathe. This finding, along with the others, began to guide my recommendations.
THE LIKELY SOLUTION HAS EMERGEDAn energy audit is comprehensive and looks at the entire home's insulation and pays particular attention to the boundary between the inside and outside of the home. When the boundary is compromised, as it typically is in most homes, HVAC machines have to fight against outside air infiltration (summer) and ex filtration (winter).
In this case, here was my diagnosis based on the information that was discovered:
The windows are least likely to be the source of the condensation/humidity problem in the basement because they are tight