Humidity question

[johny2050]

If you have a high humidity level in your house during the humid months but no moisture problems and start refinishing rooms by adding insulation and sealing all air leaks are you opening up problems for that room (ex: trapping the humidity because of no air flow)?

I ask because I finished up my basement (no moisture problems) prior to Christmas and it had a nice NEW SMELL . Now that the humid months have started my basement is developing a smell. It doesn't smell musty but there is a smell. I put a hygrometer down there and the humidity was at 74%. So I took it upstairs and the humidity was around 70% and dropped to 68% in the morning. So could I be trapping the humidity in the basement (partial/walk out basement)? Hope that makes sense.

I know its time for a Dehumidifier. I'm waiting on a quote for a central AC unit to be installed.

thanks

John

[chandler]

John, yes, if you have no recirculation of the air in the basement, you will entrap it in the basement. A dehumidifier will be beneficial, but if you are planning on installing CHVAC, you will be far ahead of the game.

[Rugged]

rather than start a new thread I wanted to ask a nearly identical question.

I also just finished out the basement with the exception of the floor. we have lived here 3 years and house was brand new. In the past years I never noticed a smell or moisture before. I did drylok as directed and then insulated and hung drywall & finished the ceiling with acoustical tile.

This year has been very, very wet and around the middle of may i noticed the basement had a smell; not musty though. at first I thought it was the new ceiling tiles but after i got a hygrometer and saw the RH was 80%. i put a dehumidifier down there and the problem instantly improved. I also have the basement ducted for AC and earlier in May the unit wasn't on because it just wasn't hot enough. Now the AC is on majority of the day and the dehumidifier is still working. Our weather hasn't changed much; still wet outside.

my question is---is the smell/high humidity more a function of having a very wet spring/summer or a result of finishing the basement or both? Also, will finishing the floor help improve the humidity problem; right now it's just concrete slab?

thanks

[airman.1994]

Both of you are in a green grass state. A dehumidifier is a good thing to use in basements in your areas. They should be sized to handle your basement and non load times. A minimum of 60 pints is a good place to start. They should run from about April to October. Finishing the floor will not help with the RH. The SantaFe makes very good units.

[Rugged]

okay thanks. I have an LG unit believe it's 45 pints and I empty it every 2 days.

i'm curious as to why it seems like i'm the only guy on the street with a dehumidifier. i've built out mine comparable to theirs but when I ask around I get quizzical looks. seems odd that i have a humidity problem and they don't.

oh well.

[airman.1994]

I bet they do! For good IAQ keep RH below 55%

[Rugged]

thanks for the help.

[johny2050]

Thanks guys. I think this is whats happening so correct me if I'm wrong because I would like to know if my thought process is in the right direction. I have a home that is not insulated and very leaky. In the summer months it gets very hot and humid inside. But since the house is leaky there is a constant circulation of fresh air so you really don't notice it. Now when a room gets insulated and air sealed, you have just cut off the fresh air movement so the same hot humid air hangs in that room which causes the air to become stale and at times musty smelling. So I think I'm fighting a vicious battle until I get every room insulated and sealed and its only going to get worse as more rooms get finished unless I control the humidity, correct? So hopefully when all rooms are insulated and sealed that should cut the humidity throughout the house so hopefully I will not need the humidifier for the basement anymore. Hopefully!!

[airman.1994]

No the RH has always been there. With finishing the basement there is more things for the RH to cling to (so to speak). Air movement will make things seam less humid but they are really not. Again there is not a basement in a green grass state that will not benefit from a dehumidifier. Question do your windows sweat in the winter time?

[johny2050]

I know the humidity has been there but why? Is it because I have a leaky house? If it were tight and sealed would I have this high humidity problem?

No my windows did not sweat this past winter. What would that mean?

I was just talking to my neighbor who has a finished basement with carpet,drywall walls and ceiling. Don't know if its insulated but he has no humid/musty smell and doesn't run a dehumidifier.

John

[airman.1994]

If it was tight your windows would sweat in the winter. Also being tight would make the RH worse in the summer. Your neighbor may have a HVAC system designed to remove more RH but I bet he has moisture problems. Basements in green grass states will have higher RH.

[johny2050]

neighbor has no central air and only a window unit in the basement but hasn't been turned on yet.

I thought insulating and good air sealing would eliminate air infiltration which should help reduce the humidity?

[airman.1994]

Yes air sealing will reduce air movement. But moisture will migrate through the structure. Air sealing will not help this.

[johny2050]

Thanks airman. Its always something right? Fix something and in return you create another problem Oh well!! Guess its time to grab another beer and hope the Phillies win this game over Boston. Boston, just walked in 2 runs. Go Phils!!!!

[luckydriver]

Originally Posted by airman.1994

If it was tight your windows would sweat in the winter. Also being tight would make the RH worse in the summer. .

thats a very interesting statement. 3 years ago i replaced a few of my windows. This included a 13x5 in my living room and one about 8x4 in the dining room. Both were original 1950's aluminum. Not airtight by any stretch of the imagination. Matter of fact, 2 years after they were installed i had a blower test and found out the woodwork underneath was leaking something awful. I always felt a draft at my feet so this was expected. However i was disappointed that the water on the bottom of the windows never disappeared, even with the new 2500 dollar window.

All the aluminum windows sweated a lot in winter so i dont understand how, with my known air leaks, my house could be anything even close to 'tight' With the wind tunnel i had in here i should never have had any condensation lol

I did rip off the wood and put foam under each now so at least now i have justification for my water on my windows in winter

[airman.1994]

The moisture from your crawl most likely was the RH source.

Originally Posted by luckydriver

thats a very interesting statement. 3 years ago i replaced a few of my windows. This included a 13x5 in my living room and one about 8x4 in the dining room. Both were original 1950's aluminum. Not airtight by any stretch of the imagination. Matter of fact, 2 years after they were installed i had a blower test and found out the woodwork underneath was leaking something awful. I always felt a draft at my feet so this was expected. However i was disappointed that the water on the bottom of the windows never disappeared, even with the new 2500 dollar window.

All the aluminum windows sweated a lot in winter so i dont understand how, with my known air leaks, my house could be anything even close to 'tight' With the wind tunnel i had in here i should never have had any condensation lol

I did rip off the wood and put foam under each now so at least now i have justification for my water on my windows in winter

[luckydriver]

Originally Posted by airman.1994

The moisture from your crawl most likely was the RH source.

you must not be following my crawlspace thread

the consensus is the RH isnt coming from my crawl (i especially have a high bathroom reading. Otherwise my 98% crawl would make my house more than the 60-70 it is

i've had an exhaust fan on a bit for the past day and hasnt dropped from 98

[airman.1994]

I don't belive that! The crawl space RH will rase the RH in the home. 60 70 % is way to high.

[luckydriver]

well take a peek over there (dont want to clutter up this thread with my issue) and let me know why the RH is lower over the rooms i have a lake under but higher over the dry part of the crawl - among many other questions about drying this out.

[Perry525]

The average temperature under ground is about 52f
the daytime temperature outside is way above that at this time of year.
This means that the air in your basement is inclined to condense onto and into the walls, furnishings and other contents making them damp and leading to mould and smells.
The solution:
Is either to raise the temperature to slightly above the outside temperature, this will enable the air to hold the humidity.
Add forced air change by way of a extractor fan, this will slowly adjust the basement temperature to match the outside humidity and temperature and over time reduce the damp and smell.
Use a dehumidifier to lower the humidity and extract the damp from the walls, furnishings and other contents, then run the extractor fan whenever the cellar is in use. If you set it around 65% this will do the trick.

Take into account that whenever the cellar is occupied, the occupiers will be breathing and sweating - this added water vapour needs to be got rid of and you will want the atmosphere in the cellar to smell neutral or at least OK and you need fresh air to breath.

[luckydriver]

Originally Posted by Perry525

Is either to raise the temperature to slightly above the outside temperature, this will enable the air to hold the humidity.

thanks for the idea....here i've been trying to vent out the humidity the past few days, when i really should have been sucking in outside air to raise the temp from 65 to the outside 75, thus lowering the RH. Will reverse the fan flow as soon as i get home

[Perry525]

Originally Posted by johny2050

Thanks guys. I think this is whats happening so correct me if I'm wrong because I would like to know if my thought process is in the right direction. I have a home that is not insulated and very leaky. In the summer months it gets very hot and humid inside. But since the house is leaky there is a constant circulation of fresh air so you really don't notice it. Now when a room gets insulated and air sealed, you have just cut off the fresh air movement so the same hot humid air hangs in that room which causes the air to become stale and at times musty smelling. So I think I'm fighting a vicious battle until I get every room insulated and sealed and its only going to get worse as more rooms get finished unless I control the humidity, correct? So hopefully when all rooms are insulated and sealed that should cut the humidity throughout the house so hopefully I will not need the humidifier for the basement anymore. Hopefully!!

High humidity by itself is not a problem.

The sun beats down on the Gulf of Mexico and lifts thousands of tons of water vapour into the air every day. This warm moist air moves northwards as clouds until it meets a cold front, when the cold turns the moist air into ice and then rain.

This is what happens in our homes.
The humidity in the air by itself is not a problem.
But, when it comes into contact with a cold surface, the air cools - it is not cold enough to turn to ice.

But, the air cannot hold the same amount of moisture, so it drops out as condensation.
Some condensation you can see as a running window, a lot you cannot see.

The condensation you cannot see goes into the walls, ceilings, floors, furniture, beds and just sits.

When these things warm up the moisture moves on. If they do not warm up, the damp sets in and starts to turn to mould.

When you seal up a room, to stop the heat loss through the holes in the walls etc;
you need to provide another form of ventilation.

After all, you need air to breath and you need to get rid of the moisture you and your family put into the home by breathing, washing, cooking.

In cold weather by all means use a dehumidifier, this saves on heat loss, but at some time you will need to open the windows to get in some fresh air, or have a ventilation system that will give you a more managed system.

Don't take it for granted that an AC unit will provide fresh air, a lot don't they merely recirculate the same stale air.

[airman.1994]

I'll leave my two cents again. Dehumidifiers are better used in the cooling season and ventilation better used in the heating season to remove RH. That being said I will agree that a home could use at least 60 cfm of fresh air during occupied times. Also blowing air into the crawlspace will put it into a positive pressure and force all of the dirt, mold and RH up into your home.

[luckydriver]

Originally Posted by airman.1994

I'll leave my two cents again. Dehumidifiers are better used in the cooling season and ventilation better used in the heating season to remove RH. That being said I will agree that a home could use at least 60 cfm of fresh air during occupied times. Also blowing air into the crawlspace will put it into a positive pressure and force all of the dirt, mold and RH up into your home.

That seems counterintuitive to me. In the cooling season (summer), i can have my windows open without penalty of paying for more oil to heat the home. (though i realize part of ventilation you are speaking of is exhaust fans). Plus from my education on here ive been told that keeping surfaces at an even 'warm' temperature is what prevents mold and that even 80 RH wont both my cabinets if they are evenly warmed plus i have my windows open. In winter the inside of cabinets are colder so i understand any high RH is bad at that time

in heating season, when you typically would want to keep the heat in the house (ie not suck it out with fans nor have a window open), i dont understand why that wouldnt be the best time to use a dehumidifier vs summer. It would remove moisture plus warm the air inside the house at the same time. Seems like in summer you wouldnt want to use a dehumidifier because it would heat the house.

regarding the blowing of air into my crawl, you cant argue with results and those are with the fan on 12 hours it got my crawl sensor down to 79RH and up to 68 degrees. Of course it shoots right back to the upper 80s and 65 degrees when the fan is off but i dont know how else to get rid of the remaining water and RH under there since it's too low for any sump. (3 days of the fan on exhaust did nothing at all for me either with water level or sensor readings)

[Perry525]

Luckydriver, I would like to come back to your final paragraph regarding the puddle in your crawl space.
I am puzzled as to why you want to get rid of it when it does no harm?
Would you feel the same way about a puddle in your yard?
If you have a puddle in your yard, you either leave it to dry out with the heat of the sun or by the wind blowing over it or it might drain away into a crack in the concrete.
You might use a quick solution and sweep it away.
With it under your home, the sun won't shine on it, the wind won't blow over it and you probably won't sweep it away.
You are not going to step into it, so why worry about it?
As for the humidity again what harm can high external humidity do to your crawl space, or indeed your home?
You live inside what we call your comfort zone, this is limited to the space inside your home, not including the crawl space or roof space, these latter areas have little to no effect on the inside of your home.

[airman.1994]

Well it will cause high RH inside the home. Will cause mold in the crawlspace that could become air bourne and get inside the home. Could cause rot. Moisture in the crawl needs to be reduced to under 55%.

[luckydriver]

Originally Posted by Perry525

.
You are not going to step into it, so why worry about it?
As for the humidity again what harm can high external humidity do to your crawl space, or indeed your home?
You live inside what we call your comfort zone, this is limited to the space inside your home, not including the crawl space or roof space, these latter areas have little to no effect on the inside of your home.

I keep forgetting not everyone knows my history. last year i paid for a mold/home inspection and the guy put on the spacesuit and went under the house and said it's one of the worst he's every seen. And now that i know what i look for i can confirm that most of my joists are covered in white mold. It's definitely not good to be breathing in that but let's forget about the health aspects for now.

This mold (i hope) was caused by all the water going into my crawlspace after every rain. he saw that my rain pipes were emptying into the corner of my house in the back and then somewhere in back water was also coming in and would flow down the slope to the front. I've personally (while installing RG6) waded thru 4-5 inches of water under there and it's not fun at all let me tell you.

as far as harm, i'm hoping all that water down there is the cause of my 95% RH there and once i dry it out that the RH subsides and in turn my house dries out. Per this site Crawlspace Inspections | U.S. Inspect amongst thousands of others, moisture in the crawl IS very harmful and i do believe that. In no case do i think standing water is a good thing, matter of fact outside it's bad as well and they have to spray my township every year for some kind of bugs and they've allbut made it illegal to have standing water around your house. (planters, trash cans etc)

Water control and management in the crawlspace is essential for maintaining a house. The most common problem associated with wet crawlspaces is that moist conditions can lead to wood destroying fungus that deteriorates exposed framing. In addition, excessive moisture is a conducive condition that can lead to infestation of wood destroying insects, such as termites. In exceptional cases, water penetration into a crawlspace can lead to the undermining of the foundation.

So i have to disagree when you say water in the crawl isnt harmful. I think i'm lucky enough that my joists are safe from rot, the last time i tried to screw in a hangar into a joist it was a bit difficult (ie the wood wasnt soft). but I only go in one small section of the crawl and i have probably over 3000 sq ft of it.

I know for a fact that the water from the crawl does seep out somewhere because under my living room window, right where the lowest part of the crawl is, when they excavated, they saw puddles in their ditch. Water was in no other part of the ditch they dug. However it's very slow and i was hoping to dry it out 'fast' so that now that the project is virtually done, we can get some heavy rain and i can 'prove' to myself that spending 12,000 for this work was indeed worth it and they did waterpoof my crawl. Nothing like results to justify that kind of $$$$

also as we have discussed at great length before, i used to believe that the high RH in my house was coming from my crawl. I'm still not 100% convinced it's not coming from the crawl but again, thats why i want to dry it out so i can see if the house dries out too. Even as i sit here now, my living room is 14% higher than my bathroom

So since i believe that the 95% is caused by the lake under my house, yes i want the water out asap

I was seriously thinking of just using an old blanket and half in the crawl half outside but im unsure if it will 'wick up' the 2 feet needed in that manner

[Perry525]

Luckydriver
I accept the things that you write.
May I note that US Inspect are a commercial company and as such have salespeople looking for business.
I am aware of their site and have read their advertising, sales and marketing...... you need to read it again!
As I have written before....... condensation only forms on surfaces that are colder than the surrounding air temperature.
I have also written..... that the joists and floor boards are normally kept warmer by the heat emanating from the rooms above (where the rooms are heated) the heat by conduction and radiation keeps the wood warmer and it is not therefore liable to condensation.
It follows therefore, that where rooms are cold, the floor is cold the joists are cold and condensation will form.
Surely you can see that heating your home on the inside and enjoying the comfort thereof.......is better than throwing money away on removing puddle in a crawl space where the use and cost of a dehumidifier will go on for ever?
Or you could do as recommended, box the joists in with sheet closed cell insulation; polystyrene (which is more or less waterproof) and save yourself a fortune.

[airman.1994]

There is a lot of talk about condensation. Condensation will cause mold growth but so will RH over 60%. It does not matter if there is no condensation. To keep mold from growing you must keep RH under 55% and have no water infiltration.

[luckydriver]

Originally Posted by Perry525

is better than throwing money away on removing puddle in a crawl space where the use and cost of a dehumidifier will go on for ever?
Or you could do as recommended, box the joists in with sheet closed cell insulation; polystyrene (which is more or less waterproof) and save yourself a fortune.

closing joist in without removing the tons of mold seems foolish to me. yes it would be easier but i believe it's better to remove the mold before closing off anything. Plus if i seal stuff up, any maintenance on my cabling or plumbing will be very difficult. Regardless, i do believe it's foolish to do anything until the water is dried up and the RH in the crawl is assuredly water free and i find out it's truly waterproof now. I'm assuming stopping water from coming in will lower RH. If not, ill be quite upset.

Originally Posted by airman.1994

There is a lot of talk about condensation. Condensation will cause mold growth but so will RH over 60%. It does not matter if there is no condensation. To keep mold from growing you must keep RH under 55% and have no water infiltration.

so are you saying even in summer where all surfaces in the house may be 80 degrees that my 65-75%+ RH in the house will cause mold issues? This is opposite what ive been recently told and now my head is spinning

[airman.1994]

Yes mold can and will grow with RH above 60%.

[luckydriver]

well them im screwed as even with windows open and low outside RH, my inside still remains high alot of the time.

[ecman51`]

As the temp goes up, the Rh goes down, in relation to it. Conversely as the temp goes down, the Rh goes up.

With that in mind, you could take your measuring device otside in the shade and see what it says away from your house. It be good perhaps to pick a time when the outside temp is about that of the inside temp, so you could better tell what you are comparing. Then see if you high humidity is really due to what is locked into your house and furnishings and carpeting, etc., as opposed to what the humidity is outside, well away from yor flooded crawl space.

[Perry525]

Luckydriver
Lets take another look at why the puddle in your crawl space is not important.

You have already confirmed that leaving your windows open lowered your internal humidity.
And you have shown that driving outside air into the crawl space, warmed it and lowered the humidity.

Lets look at what happens when you put your hand on a cold mirror – the warmth and damp of your hand leaves a damp hand shape on the mirror, that gradually fades as the damp moves into the air.

When you breath onto a cold mirror, you leave a damp patch, that gradually fades.....

When you have a building with a tin roof you find frost or dew on the roof about 200 mornings a year...... the same roof is running with condensation on the inside, this is due to the temperature difference, between the air outside and the air inside the building. During the day the roof is dry both inside and outside.

On a hot dry summers day you can often see the moisture rising from a wooden fence as the sun beats down and raises its temperature.... and this moisture becomes humidity.

When you take a bottle of beer from the fridge, the humidity in the air settles on the bottle and it runs with water, after a while the bottle reaches air temperature and the condensation moves back into the air and the bottle is dry.

If you then put the bottle in the freezer and leave the lid open, the bottle cools down and if you leave the °freezer lid open the air in the room condenses on the bottle and forms a frost.

The above is what happens in your crawl space.

The crawl space being under the house doesn't get hot from the sun and it stays about 12°C or 59°f it doesn't get very cold overnight either.

During the night the air outside gets cold and if its much colder than the puddle, concrete walls and earth inside the crawl space then water vapour will evaporate from the puddle, concrete walls and earth and be held in the air as water vapour and will move outside where its colder.

During the day the crawl space is still 59°f and the outside air temperature rises upwards above 59°f as the temperature rises outside the crawl space becomes an attractive cold spot and the humidity moves from the outside onto the crawl space surfaces, that include your puddle, the concrete walls and earth. (And possibly your woodwork if its cold?)

So, as I wrote earlier provided the temperature of the house floor is higher than that of the crawl space the water vapour in the air will move to the colder ground and puddle.

And the cold water in the puddle will not evaporate, turn into water vapour and settle on your crawl space ceiling. From reading your blogs so far it would seem that that puddle is not getting smaller,so that the work you had done either isn't working or the water vapour condensing into the puddle during the warm days is greater than that evaporating during the night.

[luckydriver]

but even running the fan all day only gets the crawl RH down to the 80s if i'm lucky. I wont run it while i'm not awake or while i'm away so how do i keep it from shooting back to 95% and further destroying my joists and coating them with more mold? Almost seems like i should have had them dig out another window in back of the house and vent the thing. but too late now.

the only solution i can see is putting the dehumidifier in the crawl (running it for 5 cents an hour) and that's not a fun process carrying something 60lb through the tight window..that sucker is heavy and also id have to have to rig it to drain into a bucket them use my sump (if it even works) to drain out the window. And thats only the left side of the house, i never even measured the center room of the crawl (no window for access) and the right side of the crawl (equal sized room to the left) but at least that has a window and no water really.

[ecman51`]

Originally Posted by luckydriver

but even running the fan all day only gets the crawl RH down to the 80s if i'm lucky. I wont run it while i'm not awake or while i'm away so how do i keep it from shooting back to 95% and further destroying my joists and coating them with more mold?

We have this quote from lucky (should be 'unlucky', it seems to me).

And then we have a rather conflicting quote from Perry525 below:

Luckydriver
Lets take another look at why the puddle in your crawl space is not important.

Then why is his joists being destroyed and coated in mold? Is the theory wrong? Or, correct theory, but temps are falling in the range that DO cause condensation on the underside?

[luckydriver]

just as an aside, i got an infrared thermometer for other purposes so decided to point it in the crawl...unsure if it's helpful or not but it sure is fun seeing what the temp of everything is

water sitting in the crawl is 63

underside of uninsulated floor (ie crawlspace ceiling) is 68

upstairs hardwood floor 72

upstairs carpet 73

[Perry525]

Originally Posted by ecman51`

We have this quote from lucky (should be 'unlucky', it seems to me).

And then we have a rather conflicting quote from Perry525 below:



Then why is his joists being destroyed and coated in mold? Is the theory wrong? Or, correct theory, but temps are falling in the range that DO cause condensation on the underside?

++++++++++++++++++++++
The reason the joists are covered in mould is down to history!
One: The house was flooded at some time, a leaking roof or burst pipe.
Two: The house was left empty for probably a year or more and during this time the joists reached the same low temperature as the rest of the crawl space. Result. Mould.
I would guess the second is most likely.
The solution is: Mould dies when it can no longer feed, eat the cellulose in the wood, or when it is deprived of water, both of these are unlikely to happen. Due to the high humidity in the area and lots of wood to feed on.
The recommended solution is professional cleaning - this will cost a lot.
Trying to dry out all the humidity in the world with one dehumidifier, will never work!
Water vapour has a built in tendency to equalize but, look at the sky all the cloud shapes are different, the same patten is repeated on ground. The moisture is forever moving from one warm place to the next cold one, from one area of high pressure to the next area of low pressure..... trying to equalize and never succeeding.
Unless you have a sealed room, humidity can only be controlled never beaten. Sealing the crawl space and the floor above plus the ground below is too expensive.... I guess.
Probably better to pull the house down and start again.
I do wonder who inspected this house prior to purchase
and if they are liable in law. Certainly, a lot of insurers do not include mould damage in their policy now.

[airman.1994]

An average size crawl space will be under 3000 grand for mold remediation and a vapor barrier.

[Perry525]

Originally Posted by luckydriver

just as an aside, i got an infrared thermometer for other purposes so decided to point it in the crawl...unsure if it's helpful or not but it sure is fun seeing what the temp of everything is

water sitting in the crawl is 63

underside of uninsulated floor (ie crawlspace ceiling) is 68

upstairs hardwood floor 72

upstairs carpet 73

======================
Glad you bought the infrared temperature gauge?
I think that you can see the final part of the puzzle.
We established that humidity doesn't just land on anything, nor does mould just start to grow.
The mirror showed that if the surface is warm enough the condensation from your hand and breath just fades into the air.
The bottle test showed that if a surface is cold enough the humidity in the air will soak it. (And if this happens without a warm patch to dry it out = the mould that is present every where can take root.)
Your measuring the temperatures in the crawl space, shows that the floor is warmer than any thing else in the crawl space and that the floor above would not be cold enough to become damp and the puddle is not warm enough to turn into water vapour.
To prove this point you could collect a bucket of water from the crawl space and dump it in the yard - it will warm in the sun and disappear into the sky. Whereas, it has sat in the crawl space for months - cold and doing no more than collecting water from the air.
Running the dehumidifier in the crawl space, is like opening the freezer lid, all the humidity in the crawl space and in your yard (and every where else for that matter) will make a dive for that freezing space, you can never collect it all.
Water vapour is a very very tiny molecule, so small that it can move inside the surface of most things in a home, wood, fabric, plastic etc; To stop it entering your crawl space is impossible, you can slow it down by lining everything with plastic but not stop it.
The same thing happens in your home, the water vapour comes in through the walls, through holes in the lower walls and goes out through holes in the ceiling and upper walls.
You can't stop it, you can slow it down - you can make life easier on your dehumidifier so it doesn't have to work so hard.