soffit vent question

Yup, you are on the tropical side of WA. As I sit here at 22% RH it is difficult for me to advise people about ventilating their house or attic when they have a rain forest outside. Not quite, but your outside humidity is a problem.

When you say "not installed" in regards to those fans, do you mean not at all or they were being vented into the attic

You should probably become comfortable with relative humidity, temperature, and dew point. And you should be monitoring those numbers inside your home and your attic.

An ideal solution would be 4" of foam on the roof with new sheathing and shingles, converting your attic from a vented space to a sealed conditioned space that would share the heat and air conditioning from inside. That approach eliminates the decision of when outside air is good or bad to be entering that attic. I'm certain this is not on your option list but wanted to state it as the optimal solution.

As a vented attic, you will have to deal with the outside humidity.

For your house, if you are experiencing high moisture levels there are some small steps you can take.
1. Switch to low flow shower heads that have a flow control at the head. That flow control allows the user to further reduce the shower volume at times during the shower. And limit the duration of the showers.
2. Be sure the dryer is venting to the outside.
3. No cloths drying inside.
4. No firewood stored inside.
5. Once you get the bath fan going, install a delayed off switch to allow the fan to run for a pre-selected time after you switch it off, 20 minutes is common.
6. Do you use natural gas for cooking and heating? If so, burning NG produces a lot of moisture so run the kitchen fan any time the stove is in use.
7. Be sure your gas water heater is not backdrafting as that will be dumping moisture into the house.

8. Do not use any ventless gas heaters, lots of reasons, including moisture.

Pick up a couple of RH meters to start getting used to the numbers around the house.

Bud