We have a two year-old, two-story town house with:
- fiberglass insulation in the walls;
- a Tyvek vapor barrier under foam board on the exterior walls;
- blown cellulose insulation in the attic;
- stucco outside;
- and a refrigeration cycle air conditioning.
We live in Phoenix, AZ (desert climate) and our indoor humidity levels are consistently 20% to 35% higher than outside. During the summer we consistently have humidity levels in excess of 80% (not 70%), even with the damper fully open. It has been so humid inside that the tile floors had sweat on them.
We have no indoor plants or water features. Our dryer vent is operational, and our exhaust fans from the bathrooms are vented externally through the roof. There are no unusual ceiling vaults and we do have ceiling fans to stir the air. Ours is an end unit, so we have one shared wall with a neighboring town house, which has no vapor barrier.
We have had the builder heavily involved for warranty work to determine the root cause of the humidity sources. We have tried:
- Slowing the AC blower motor down to allow the water in air to condense;
- Looking for water leaks with an infrared camera (FLIR);
- Looking for blockages in the vents in the eaves;
- Calibrating the thermostat (Ecobee);
- Balancing the air flow by adjusting the vents inside with flow meter hood;
- Adjusting the air conditioner refrigerant cycle pressures;
- Fully opening the damper to let in dry air;
- Increasing the exhaust fan to run for 30 min in a 60 min cycle.
The problem hasn't gone away and we're not sure what to do next. Is there anything else we can try before we resort to installing a whole house dehumidifier, or adding additional attic ventilation?
What are your thoughts on the RH trend over time?
Also, I did a rough calculation that the home needs to express ~350 pints of water per day (ASHRAE) psychometric chart corrected for altitude, but the HVAC company measured the AC system is operating properly and measured the AC will remove 77 pints of water per day. I read that whole home dehumidifiers typically remove ~100 pints per day. What are your recommendations on how to best ventilate the attic while controlling cost?