After spray foam: humidity and fresh air through a Columbus year

A tighter house changes how moisture behaves indoors. That is mostly good news in Central Ohio, where summers are sticky and winters are dry, but it means ventilation and humidity controls matter more than they did when the house leaked. Here is what to watch, season by season, in the first year after a foam project.

Why tightness changes humidity

Leaks do two jobs badly. In summer they let outdoor humidity pour in, and in winter they pull indoor moisture out. Seal them, and indoor humidity starts to depend on what happens inside: showers, cooking, laundry, breathing, houseplants, and any dampness rising from a basement or crawl space. The Residential Code of Ohio treats that as a design question for new homes by making whole-house mechanical ventilation mandatory, and a sealed older house deserves the same thinking.

Buy an inexpensive digital humidity monitor or two and log a reading each morning. EPA guidance is to keep indoor relative humidity below 60 percent, ideally between 30 and 50 percent, and a monitor tells you more about your own house than any rule of thumb can.

Summer: June through September

Sealing the attic floor, the rim joist, and the crawl space cuts the humid air that used to leak in, which lowers the moisture load on the air conditioner. Two things can undercut that benefit.

• An oversized air conditioner. Equipment sized for the old, leaky house runs in short bursts and cools the air before it has pulled much water out. If a Dublin two-story feels cool but clammy after a foam job, that is the likely reason. A lower blower speed, a variable-speed system, or a dedicated dehumidifier fixes it.
• Ventilation at full speed on muggy days. An energy recovery ventilator hands some moisture back to the outgoing air, but it still brings outdoor air in. On the stickiest days, a low continuous setting beats boost mode.

If indoor humidity sits above 60 percent for days at a time, something needs adjusting.

Fall: the easy months

September and October are the gentle stretch between cooling and heating seasons, and the best time for a checkup. Confirm every bath fan and the range hood actually exhaust outdoors. Clean or replace the filters on any ventilator, and wash its core if the manufacturer allows. In a sealed crawl space, look along liner seams and the tops of foundation walls for condensation or musty odor, and make sure the dehumidifier drains properly.

Winter: November through March

Cold outdoor air holds little moisture, so winter flips the problem. A tight house often holds a comfortable indoor humidity on its own, which is one of the quieter benefits of sealing. Watch the windows. Condensation on the glass on the coldest mornings means indoor humidity is too high for that window, and the fix is more ventilation and more use of bath and kitchen fans, not less. If the house has a whole-house humidifier, turn it down after a foam project, because a house that needed one when it leaked may not need it now. Check top-floor closets on outside walls and the area around the attic hatch for signs of condensation.

Spring: basements and crawl spaces wake up

In spring, the clay-rich till soils around Columbus stay wet for weeks, and basements and crawl spaces pick up moisture. Look for musty smells after heavy rain, white mineral deposits on foundation walls, and damp spots along the rim joist. A sealed crawl space should have its humidity control running, and a finished basement may need a dehumidifier through the first wet season after a project. The crawl space service explains how sealed crawls are set up.

Houses heated by boilers

Many older homes in Clintonville, Upper Arlington, Bexley, and German Village are heated by hot-water or steam radiators and cooled, if at all, with window units or a ductless system. Those houses have no central air handler to move and dehumidify air, so after a sealing project two things deserve attention. Fresh air has to come from somewhere on purpose, usually a quiet bath fan set to run continuously or a small ductless ventilator, because there is no duct system to connect a ventilator to. And summer humidity has to be handled room by room or with a standalone dehumidifier in the basement. Neither is a reason to avoid sealing; both are reasons to plan fresh air and dehumidification along with the foam.

What to log in the first year

A simple notebook or a phone note turns the first year into useful data. Record the indoor humidity each morning in a main room and in the basement, the outdoor temperature, and any window condensation. Note the monthly therms and kilowatt-hours from the Columbia Gas and AEP Ohio bills next to the same month a year earlier. After twelve months you will know whether the ventilation settings are right, whether a dehumidifier is earning its keep, and what the project actually saved. That record is useful to a future buyer as well.

Signs the balance is off

• Humidity above 60 percent for days in summer.
• Window condensation most winter mornings.
• Stuffy bedrooms and lingering cooking smells, which point to too little fresh air.
• Very dry air and static shocks, which point to too much ventilation in deep winter.

Each has a simple adjustment, and none requires undoing the foam. For the ventilation math, read ASHRAE 62.2 in plain English; for the moisture side, see will spray foam make my house too humid.