If people are having a hard time controlling humidity levels in their home I would check the weatherstripping and seals around windows and doors and if that doesn't help consider the crawlspace.
If in the US in the northern states the crawlspace vents would probably be a good idea to remain open throughout the seasons but if you live in the Southeast or any state with high humidity the latest research shows those vents are not a good idea. Theoretically they are there to create good cross ventilation to keep the crawlspace dry but since the advent of central air conditioning in states such as Florida, Georgia, Louisiana for example those vents actually forced hot humid air into the cooler crawlspace environment and allows for condensation and increased humidity. They recommend now encapsulating the crawlspace with active dehumidification.
With a little online research this is a very easy project for anyone to do assuming you have somewhat easy access to your crawlspace and there is room for you move around. For those interested here's a simple outline of what I did to encapsulate my crawlspace. This is a project you can really do by yourself and save yourself thousands of dollars in the process. I did this work a little at a time over the course of one summer. You can do it over a couple of weekends if you work fast and had help.
First you want to seal any cracks or gaps in your crawl space around doors, vents, pipes, electric conduit or anywhere there is penetration into the crawlspace. Seal that with Loctite foam. This stuff: Loctite Foam
I would also seal the area along the perimeter of the subflooring where it meets the walls of your home. Though there should insulation there it is often times not adequate and there is gaps in the subflooring where air from the crawlspace is entering your home. This is not good for your health anyway as mold, allergens, and gases such Radon can potentially enter your living space along with humid air.
There should also may be insulation under your subflooring and in-between the joists. If it's not there you might want to consider hiring a contractor for that or add some yourself if you find areas that are not well insulated. I just purchased batts of roll up insulation and used insulation wire to prop it up against the subflooring.
I then purchased rolls of 6mm polyethylene sheeting for a vapor barrier and placed it on the dirt floor and just taped it all together at the seams with sheathing tape overlapping by about 5 inches.
This stuff: Sheathing tape
and this stuff: vapor barrier
I ran the sheets up the walls and columns of my home about a 2 feet off the ground and attached the sheets to the crawlspace walls with acoustic glue. There are videos online on how to attach the vapor barrier to the columns. It's pretty easy but any method could work.
This stuff: acoustic glue
Before I glued the sheeting to the perimeter walls I poured a line of diamataceous earth for termite and pest control where the groundfloor meets the crawlspace floor. This stuff is nontoxic but it does kill any insect that crawls over it over time.
I then painted the crawlspace walls with Drylok waterproofer. The recommended course is to actually use foam insulation along the walls but since my crawlspace is above grade and I wanted to hang things like shelvings and kayak supports along the walls I kept them bare.
The next step would be to close off the vents leading to the outside of the home but do it in such a way that if I wanted to open them again it would be an easy task. Meaning DON'T SPRAY FOAM SEALER into the crawl space vents like my neighbor did in his garage. He had to remove that stuff when he sold his home so that the next owner could get it insured. I simply used Pink Pather project size pink insulation (This stuff foam board
)and cut them to cover the vents from inside the crawlspace attaching them to the crawlspace walls with this stuff: Loctite foam board adhesive
. You can't use regular sealant as it will melt the foamboard. My vents double up as flood vents and if there was ever a flood in my area the water pressure would easily break through this foam board and allow the vents to operate as they normally would.
The final step was to add a dehumidifier and find a way to drain the excess water from the drip pan. I suspended a Santa Fe compact 70 using a hanging kit from Santa Fe. As long as the dehumidifier is hung higher than the drain line exit points the water will drain. Most crawlspaces should have an entry door or vent. In my case I had a walk through large aluminum vent/hatch that allowed entry into my crawlspace. I had a plastics company fabricate me a thick plastic door the same size as that vent and I attached it with wing nuts to the preexisting bolts. I also weather stripped this door. (I saved the vent if ever I had to replace it again or for insurance inspections) I then drilled a 1/4 hole in the bottom section of the door and stuck the drain line through that. Voila my drainage challenge resolved! I installed clear strip doors to maintain the humidity levels in the crawlspace since I often go down there to retrieve household items like my kayaks. This stuff: strip door
This set up maintains my crawlspace at 44% humidity throughout the entire year whereas in years past it would go as high as 85% especially in the summer. I have an back up indoor dehumidifier in the piano room set at 45% humidity and it has never
gone on in over a year whereas in years past if would turn on and off every few minutes or so. That's how much humidity can enter your home from the crawlspace in the Southeast and my house is relatively new and well constructed. The crawlspace dehumidifier only turns on at certain times of the day when it expected for RH to rise in the crawlspace. Overall though it is pretty air tight and stable.
The added benefit of this encapsulation is that it saves your floor joists and subflooring, (Our subdivisions clubhouse subflooring and joists had to replaced after 20 years due to wood rot). The dry air prevents ants and termites from entering your home as they are attracted to moist environments. It protects your home from radon gases entering the living space. You have extra storage space ( a big plus) and finally your piano is protected.