How much moisture comes from the soil in a crawlspace with an exposed dirt floor?
Where do you live?
So the answer is related to where you live?
Let’s say TEXAS.
Vented or non-vented. Any problems with the stem wall? Downspouts?
I answered before your second post. Let’s say Ohio Valley. We get rain now and then…
And even more related to the particular lot, drainage etc.
It varies from no problem all the way to major issue around here.
Depends of the type soil, amount of foundation proofing, topographical conditions, number of vents…whether etc.
Jeff
Ya’ll may be missing the point.
The question is “How much moisture comes from the ground?” In gallons or pounds.
I have found an answer of 100 pounds (12.2 gallons) of water can come from the exposed crawlspace ground per day per 1,000 square feet of a house. (averages)
Agree? Or do you have another calculation?
I have no idea, but don’t doubt the figure you quote. Crawl spaces around here are like rain forests this time of year. I often feel like I need one of these…
http://farm3.static.flickr.com/2530/3958673084_6589609c58.jpg
“Can”, which relates to all of the above answers.
What kind of soil?
Gravel
Bedrock
Sand
Clay
Y’all may be missing the point, Ben.
You gave an illustration with the word “can”…
but is arbitrary. It just depends on many different factors and different areas of the USandA.
Really?
Oy.
I thought that water evaporates at a rate that is (on average) constant.
So,
Let’s take where you live… Do you know how much water can evaporate from the ground - in relation to your zip code?
Jae, Ohio, what’s the rate?
Michael, MN, what’s the rate?
Currins, from IL, what’s your rate?
Ben I can take you to at least 5 different soil types with 30 minutes of my location.
What are you going for.
Your number is very high IMHO.
Where is it from?
Doing research for the next InterNACHI course…
Several studies have considered how a crawl space can
contribute to the moisture level in a building. Britton
reported an average evaporation rate of 12.1
gal/1000 ft2/day (490 g/m2/day or 0.10 lb/ft2/day).
But this is old data. (R.R. Britton, Crawlspaces and their effects on dwellings.)
I’m looking for new research.
Moist air from the crawlspace is often the most significant source of moisture entering a home.
I’ve also read - If soil is damp in a 1,400 square foot crawl space, as much as 20 gallons of water a day can evaporate into the air.
Dan Morrision from GreenBuildingAdvisor, “About a gal. per 44 sq. ft.) evaporate from bare soil in a crawl space”
Hey Guys-
Could that be the culprit of these condensation drops on the bottom of the air ducts? No barrier on the ground, a couple of open vents to the exterior, no rain in the last week but hot (90s and 100s) and humid. There were no indications of leaks coming from above and the duct branches came off of the top side of the main trunk. 95% of the crawls I inspect have no vapor barrier.
Kenny
You can not have evaporation without a Delta h.
This changes with location, elevation, air properties, air flow, ventilation rates etc.
Today in Nashville, Tn you won’t get a 1 qt/day of water evaporation.
In the fall it may be as much as 10 gallons.
As everyone is pointing out, soil content prevents a constant.
Where are you going with this?
Maybe I can lay this out better with the psychrometric properties of air if I knew where your headed.
Are we talking evaporation rates or condensation rates. They are not the same.
The question IMO is evaporation rate without considering contributing factors like lot topography, drainage, etc.
That said, evaporation rate comes down to two things, current moisture content in the soil and soil composition. Wet soils release more water vapor into the atmosphere (evapotranspiration) than do dry soils because more of the water is available at the soil surface. In a very wet state, the soil evaporation rate is largely controlled by atmospheric conditions. Is it a humid, dry, or windy day? All of these are examples of factors that may vary the evaporation rate in wet soils.
As the soil drys, the rate of soil evaporation is controlled more by the composition of the soil. Soils with high sand content will dry faster than clay soils, like those we have around here in San Diego.
H. Trethowen says that 13.2 gallons of water per 1000 sq. ft. per 24 hours can evaporate from the ground.
I guess he’s referring to any ground that is wet.
Trethowen, H.A. 1994. Three Surveys of subfloor moisture in New Zealand. ASHRAE Transactions, 1994, V. 100 Pt. 1. ASHRAE, Atlanta GA. Published in Recommended Practices for Controlling Moisture in Crawl Spaces, ASHRAE Technical Data Bulletin volume 10, number 3.
Ralph R. Britton says 12.1 gal/1000 ft2/day (490 g/m2/day or 0.10 lb/ft2/day) can evaporate from a wet exposed ground - say from a crawlspace of a dwelling.
**[FONT=Times New Roman][size=3]
Moisture control in crawl spaces
Moisture Release from Crawl Spaces
**[/size][/FONT][FONT=Times New Roman][size=3]Several studies have considered how a crawl space can
contribute to the moisture level in a building. Britton
(1948) reported an average evaporation rate of 12.1
gal/1000 ft[/size][/FONT][FONT=Times New Roman][size=1]2[/size][/FONT][FONT=Times New Roman][size=3]/day (490 g/m[/size][/FONT][FONT=Times New Roman][size=1]2[/size][/FONT][FONT=Times New Roman][size=3]/day or 0.10 lb/ft[/size][/FONT][FONT=Times New Roman][size=1]2[/size][/FONT][FONT=Times New Roman][size=3]/day). Trethowen
(1994) measured a similar average rate of about
10 gal/1000 ft[/size][/FONT][FONT=Times New Roman][size=1]2[/size][/FONT][FONT=Times New Roman][size=3]/day (400 g/m[/size][/FONT][FONT=Times New Roman][size=1]2[/size][/FONT][FONT=Times New Roman][size=3]/day or 0.082 lb/ft[/size][/FONT][FONT=Times New Roman][size=1]2[/size][/FONT][FONT=Times New Roman][size=3]/day),
but found a large variation in evaporation rates, both by
site and season. Abbott (1983) found that when the soil
reaches a “critical” moisture content, its evaporation rate
equals that of free water. Britton (1948) also found a
maximum rate of 19.1 gal/1000 ft[/size][/FONT][FONT=Times New Roman][size=1]2[/size][/FONT][FONT=Times New Roman][size=3]/day which corresponds
to more than 770 g/m[/size][/FONT][FONT=Times New Roman][size=1]2[/size][/FONT][FONT=Times New Roman][size=3]/day or 0.16 lb/ft[/size][/FONT][FONT=Times New Roman][size=1]2[/size][/FONT][FONT=Times New Roman][size=3]/day but such a
high moisture-release rate is unlikely to occur in practice.
[/size][/FONT]