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Old 07-12-2012, 10:31 AM   #1
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space? My crawlspace is about 1300 s.f. and 12-16" high throughout. One contractor told me a dehumidifier would be unnecessary because there would be plenty of ventilation through the floor and the crawl space wasn't large enough (volume). What do you think?

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Old 07-12-2012, 10:34 AM   #2
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


How many vents are down there to the exterior?

By encapsulated, do you mean that there is no ventilation?

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Old 07-12-2012, 10:41 AM   #3
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


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Originally Posted by agradywills View Post
Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space? My crawlspace is about 1300 s.f. and 12-16" high throughout. One contractor told me a dehumidifier would be unnecessary because there would be plenty of ventilation through the floor and the crawl space wasn't large enough (volume). What do you think?
Ventilation through the floor?
Depends, is there a 6 mil. plastic vaper barrier on the ground?
How may and what style vents.
Is the grade lower then the outside grade.
Do you have gutters. a grade outside the runs away from the foundation not toward the house, no mulch piled up again the foundation and no flower beds forming ponds for water to lay in up again the foundation?
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Old 07-12-2012, 10:43 AM   #4
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


Who is the contractor to say whether you need a dehumidifier or not. After all he has done his job and would not reveal any problems that might appear. You better consult but someone who can give you expert and impartial advice.
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Old 07-12-2012, 10:55 AM   #5
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


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How many vents are down there to the exterior?

By encapsulated, do you mean that there is no ventilation?
There are 6 foundation vents (cinder blocks turned sideways). They will be filled with foam and the rest of the crawlspace (floor/inside walls/etc.) will have 10 mill plastic laid down and tacked. It will be 'encapsulated'.
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Old 07-12-2012, 10:59 AM   #6
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


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Ventilation through the floor?
Depends, is there a 6 mil. plastic vaper barrier on the ground?
How may and what style vents.
Is the grade lower then the outside grade.
Do you have gutters. a grade outside the runs away from the foundation not toward the house, no mulch piled up again the foundation and no flower beds forming ponds for water to lay in up again the foundation?
There will be a 10 mil barrier encapsulating the entire crawlspace.
Vents will be closed up with foam.
The grade inside the crawlspace is a little higher than outside.
No gutters.
Soil is extremely porous/permeable. It's sand pretty much. Never any standing water around house. Underneath house is always very dry.
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Old 07-12-2012, 11:04 AM   #7
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


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Originally Posted by agradywills View Post
There are 6 foundation vents (cinder blocks turned sideways). They will be filled with foam and the rest of the crawlspace (floor/inside walls/etc.) will have 10 mill plastic laid down and tacked. It will be 'encapsulated'.
I guess I am unsure why the crawl space is intentionally being encapsulated.

It should be vented.

Is there a reason why you want to close it up?
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Old 07-12-2012, 11:08 AM   #8
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


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I guess I am unsure why the crawl space is intentionally being encapsulated.

It should be vented.

Is there a reason why you want to close it up?
It is pretty popular down here.
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Old 07-12-2012, 11:10 AM   #9
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


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It is pretty popular down here.
Why?

What is to be gained from closing it off?
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Old 07-12-2012, 12:18 PM   #10
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


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Why?

What is to be gained from closing it off?
Energy efficiency, prevention of mold growth.
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Old 07-12-2012, 01:44 PM   #11
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


If it ain't broke...
I'm having a hard time getting my head around doing this preventatively when it sounds as though you already have conditions that would inhibit mold growth.

What's energy efficient about running a compressor 24x7?

I may be missing some critical factor from your OP but I don't get it.
Sorry if that sounds snippy, I just want to understand the process that led you to this point.

Can we start with where are you located?
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Old 07-12-2012, 02:10 PM   #12
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


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If it ain't broke...
I'm having a hard time getting my head around doing this preventatively when it sounds as though you already have conditions that would inhibit mold growth.

What's energy efficient about running a compressor 24x7?

I may be missing some critical factor from your OP but I don't get it.
Sorry if that sounds snippy, I just want to understand the process that led you to this point.

Can we start with where are you located?
From what I've heard/read 'Just as you are introducing ventilation into a crawlspace you are also introducing humidity.' While my soil is very absorptive the climate in GA is still fairly humid at times. Moisture can linger in a crawlspace here even with foundation venting.
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Old 07-12-2012, 11:45 PM   #13
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


for those interested I have a link you might like to check out http://www.buildingscience.com/docum...%20VENTILATION

it is an article by Joseph Lstiburek of Building Science Corporation entitled "The Top 10 Dumb Things To Do In The South." Dr. Lstiburek is a leading scientist that studies building construction and the effects of the environment on them. Just google his name and you'll come up tons of posting, has some really enjoyable YouTube videos. I'm posting this because he discusses exactly what the OP was asking ..... Also because I'm the inverse of #1, I'm a southerner that came north to design homes. Had a lot of new tricks to learn and some to forget.

Enjoy
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Old 07-14-2012, 04:27 PM   #14
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


There is considerable research on the advantages of closed crawl spaces.

See http://www.crawlspaces.org/

What occurs in humid climates is that often air brought in to ventilate the crawl space is at a temp at or near the dew point....the moisture condenses on surfaces inside the crawl space, causing mold and rot.

The first step should be to place a vapor barrier of at least 6 mil (I used a great product, StegoWrap), on the dirt floor, and run it up the foundation wall and attach near sill plate. Often may be desirable to attach below the sill plate, allowing a space for termite inspection.

The website above will reference whether it's better for you to insulate the floor or walls. I did my walls. The vents should be closed and sealed.

Although a dehumidifier nay be necessary, depending on moisture levels, an often adequate solution for dehumidification is to have a 4" vent, with a damper to prevent backflow, to blow either heated or A/C air into the crawl space. The idea is that the air will then exfiltrate back into the home.

There is much instrumented data available on the above website. This research was done with assistance of federal and state grants.

The articles and papers therein made a lot of sense to me, and I did mine myself. It was dirty and hard work in a 12-16" high space....but was worth the effort.
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Old 07-14-2012, 05:20 PM   #15
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Is it absolutely necessary to have a dehumidifier in an encapsulated crawl space?


It would be best to just wait and see if you need a dehumidifier. There is nothing like actual real observation to get the correct information - rather than hunches and guesses from people who don't know the details of your particular circumstances.

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