Help in dehumidifying a basement...

[Vettedrmr]

First off, thanks in advance for any help.

I'm trying to get the humidity in my basement under control. It's unfinished, vapor barriers on the open dirt and typical shuttered vents for airflow (they're closed this time of year). Humidity levels are way too high; to the point of having standing condensation on the vapor barrier. A separate humidistat shows RH around 70%.

So, I bought a 70 cup/day dehumidifier, which has been working almost continuous, even this time of year. Seems to be pulling about 1-1.5 gallons of water out of the air per day, with ambient temps around 60F. When outside dew point drops there's a pretty rapid drop on the humidistat. Now the interior humidity has dropped to around 60-63%, which is good enough to control mildew/fungus.

BUT, what happens when it warms up? Right now the vents are closed, but should I open them in the spring? Seal them up permanently?

Help! And, have a Merry Christmas!
Mike

 

[RivennHewn]

Assuming your floor between living space/ basement is insulated, keep the air moving.

Never completely close the vents.

 

[Jackfre]

Tjernlund makes a crawl space ventilator that has a humidistat controller on it

 

[knobby]

A LGR style dehumidifier would probably be your best bet if the house is in a area with a high humidity,if the ambient humidity is high just venting wont do much good

These santa fe dehumidifiers are decent units

http://www.santa-fe-products.com/

 

[Vettedrmr]

Whether my dehumidifier is an LGR or not I don't know, other than the one I'm running is pulling a lot of water out of the air on a daily basis. So, with that running, what should I do with the vents? Let them continue to open when it warms up, or keep them closed?

 

[finn]

Open vents are no longer recommended per the information I sifted through while researching this.

Vapor barrier on the floor, insulated walls and rim joists, drain tile around the footings, and a dehumidifier as required seems to be the latest thinking.

The open vents let in warm, moist air in the summer. The warm, moist air hits the cooler temps in the crawl space or basement and results in even higher relative humidity.

 

[r_egan]

As indicated above by Finn, it is no longer recommended to vent a crawlspace. I had severe moisture issues in my crawlspace which resulted in costly mold remediation. I now have sealed vents, a substantial vapor barrier and dehumidifier (Santa Fe Max Dry Dual XT) capable of removing 155 pints/day. I monitor humidity levels closely and never let it get above 40%.

I am happy to answer any questions, feel free to PM me.

 

[pattenp]

Assuming your floor between living space/ basement is insulated, keep the air moving.

Never completely close the vents.

ThIs is not correct advise in every situation. The thinking on crawl spaces being open to outside air have change to where they are now being sealed and climate controlled.

 

[yeldogt]

You can only ventilate a craw space when the outside humidity is lower than 50 .. if you live in a place where the grass is green most of the year this will not be the case.

Years ago crawl spaces had some ventilation and open vents from heating ducts -- so in areas where heat and AC was used the Crawl Space was cleared by positive pressure.

It sounds like you make be getting moisture from the ground -- are you sure the plastic is tight? Are you getting moisture from the walls?

The Santa fe's are great units -- they work in cooler areas and will pull the humidity down and keep it down -- the smaller units are costly to run and often can not get the space dry enough.

If it is running all the time and is still above 60 RH -- the unit is not removing enough moisture.

 

[RivennHewn]

Is is not correct advise in every situation. The thinking on crawl spaces being open the outside air have change to where they are now being sealed and climate controlled.

Interesting.

Any ideas on what it cost to seal, insulate, and climate control a basement?

If there are problems with the foundation or drainage, would you still have to fix the problems when you start sealing and controlling the space?

I don't do residential work anymore, so I haven't kept up with codes/practices.

I do know that proper ventilation is free, and works well if there aren't other problems that introduce moisture.

 

[CNGsaves]

OP . . . so tell us . . . you in Houston . . . or Florida ???

If not, why so much humidity . . WHERE you at ??

Now would be good time to Update GJ Profile with City / State.

 

[Platonic Solid]

Sounds like you're treating the symptom rather than the cause.

A bit short on info: Type of foundation and age of house would be useful.
Is the land properly graded?
Do you have gutters?
Are the downspouts draining properly away from the house?

 

[rburke65]

There is a lot of humidity in Panama!

 

[Vettedrmr]

OP . . . so tell us . . . you in Houston . . . or Florida ???

If not, why so much humidity . . WHERE you at ??

Now would be good time to Update GJ Profile with City / State.

Hot Springs, AR. Probably fairly middle of the road from a temperature and humidity POV, except for the nearby (1/2 mile?) lake.

Thanks for confirming what my engineering brain thought about ventilation. I expect the temps in the basement will stay pretty constant year round, and dew points do get into the 70s in the spring and summer.

A bit short on info: Type of foundation and age of house would be useful.
Is the land properly graded?
Do you have gutters?
Are the downspouts draining properly away from the house?

Sorry for the lack of info.
Foundation: Pier & Beam. Semi-underground basement (that's the target of the current task) Built in 1988.
Grade: I'm not sure exactly how to interpret "grade", but the house is built into the side of a hill, probably a 10% grade front to back.
Guttering: Guttered all around the house. All but one downspout is drained well away from the house, and that one is on the side of the 2 car garage slab. All downspouts terminate at least 20 feet from the house.

 

[bgarrett]

being on a slope is ideal for earth tubes to control humidity