Ask the Builder: Ventilation and the fight against moisture in your home

You may have had the good fortune to live and work inside old homes. I’m talking about houses that were built over 100 years ago. The architects who designed them and the builders who built them were wise.

I started my building career in Cincinnati. My good friend John and I started a small handyman business in college. One day, while hanging out in the student center at the University of Cincinnati, we saw a help-wanted posting and applied for the job. Karl was hiring laborers to help rehabilitate foreclosed houses. Each one of these houses was built in the late 1800s or early 1900s.

Each house we worked in had a window in the bathroom. Some bathrooms had two windows. The house I grew up in had a wretched leaky steel casement window in the sole bathroom in the house. Architects knew that bathrooms needed fresh air for a host of reasons. The windows also provided wonderful natural lighting.

Some young architects decided windows in full and half-bathrooms were old-fashioned. They kicked bathroom windows to the curb. The building codes responded by requiring mechanical ventilation in bathrooms.

A tug-of-war ensued in the late 1990s, in my opinion, as houses and windows became more and more airtight. The building code strove to keep up as less and less air leaked into homes. The houses of old had windows that leaked lots of air. It was rare to come across an up-down sash window that had weatherstripping.

Mold and mildew issues rarely were a problem in old houses, but soon became a major problem in newer homes. The air leakage in old homes helped dry out bathrooms in minutes or hours before mold and mildew could grow.

It’s important to realize the building code is a set of minimum standards. If your house just passes the code, it’s like getting a 70% on a test. You can always build better than the code requirements. This is true with bathroom fan ventilation. You can purchase powerful bathroom vent fans that will exhaust more air than is required by the current code.

I’ve shared in previous columns that I’m helping my son finish his basement. This past weekend we installed three fans in the basement. One was in the full bathroom we’re adding, one was in a bedroom, and the third fan was in an open area that extends throughout the basement.

The current building code requires this much mechanical ventilation when you don’t have windows that can open and provide enough old-fashioned air exchange. Keep in mind the code officials know that even the best windows do leak some air. This means some fresh air will enter the basement when the windows are closed.

Water might leak from your bathroom fan. You may think it’s a roof leak when, in fact, it’s condensation flowing down the vent pipe back into your bathroom. Insulated vent pipes will prevent this condensation.

The condensation happens when uninsulated bathroom vent pipes pass through cold attic spaces. The pipe gets cold in the winter months. The moist, warm air gets sucked from your bathroom as you shower and starts to flow through the cold pipe. Condensation starts to form on the inside of the cold pipe just as it forms on the outside of cold soda or beer cans in the summer months.

You could have a much bigger problem. Your builder or remodeler may have terminated your bathroom vent fan into the attic space. The moist humid air dumps into the attic. If you live where it gets cold in the winter, this moisture will condense on the underside of the roof and on the roof-framing timbers or trusses. Mold and wood rot will cause huge issues over time.

You may not like your noisy bathroom fan. Remote bathroom exhaust fans can be located 10 feet or more away from your bathroom. These fans work similar to your heart. Just as your heart draws blood back from your fingers and toes, these remote fans pull air out of bathrooms. The fans then push the air outdoors via outlets in the sidewalls of gable ends. They can also connect to roof outlets as long as snow doesn’t accumulate on your roof.

I urge you to do lots of research about bathroom fans before you build or remodel. There are remarkable fans available that will do a great job of exhausting moist air. Be sure your builder or remodeler tapes all the seams of the metal vent pipe. Use real metallic duct tape that HVAC professionals use to seal their ducts. This tape is affordable and easy to apply.

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