HA! That’s hilarious! Great catch, Marcel. Box of goodies coming to you.
Roy, I understand where you coming from. There are many factors involved and nothing is simple in building science. However, in relation to water evaporation - I don’t think most of that stuff in your list matters. I believe there has to be a constant formula that is used by scientists - An evaporation rate for water.
It is known that a family can release a few gallons of water in a house every day simply by breathing. Right?
It is known that a clothes dryer can release 20 gallons of water into a house in a day. Right?
Well, what about simple a 5-gallon bucket of water? How much time will it take for that water to evaporate? There’s got to be an answer. The answer has nothing to do with waterproofing the foundation.
What about a flat roll roof? If you see a puddle of water, are you able to comment upon the puddle in relation to the last time it rained? Yes. From what I understand, there shouldn’t be any puddles on a flat roof after 48 hours from a rain event. That has something to do with a formula with water evaporation. Has nothing to do with downspouts.
People dealing with crop spray know about evaporation; people who deal with energy and water conservation know about evaporation of water from soil; people who garden inside a greenhouse know about water evaporation and condensation formation. There’s got to be a simple answer about how much water enters a crawlspace, given the exposed soil is relatively damp/wet.
I believe I’ve gotten some excellent help in answering this question; I just find it odd that out of all of the courses on moisture that I’ve written, and all of the research that I’ve done on building science, I have not come across anything other than the following estimate: 10-20 gallons per day per 1,000 square feet can enter a crawlspace from the exposed soil.
BTW: this is the stuff I do in order to produce the courses for InterNACHI. I just keep asking “dumb” questions in order to produce a GREAT course.
Thanks for the help, ya’ll.
Again, it has nothing to do with the amount of moisture in the soil once it becomes saturated to the point that there is enough moisture to keep up with the air’s relative humidity (or vapor pressure).
Vapor pressure regulates that amount of moisture that changes state from a liquid in the soil to a vapor in the air. Actually, that has nothing to do with anything.
In most cases in our business, when there is high moisture in the CS it causes a 100% rh level in the space and ANY drop in temperature will cause it to rain!
I find many CS’s that have 100% rh and the soil is dry!
That’s because it is moving from the soil to the air. If ventilation is there, the moisture is gone and is constantly being replaced within the CS. The soil dries out.
I still do not see where the gallons/hr condensation has any bearing on our industry!?
Once it gets “wet”, it’s too wet.
I think the old tests results is the same today as it was 10 years ago when it was done.
Review “Relative Humidity” . The amount of water that turns to a vapor is in direct proportion to the Relative Humidity, which is the amount of water the air can hold at that temp and pressure.
As I said previously; location, elevation, and weather conditions…
David, You bring up a good point.
InterNACHI provides benefits that spans several industries, not just residential home inspections.
For example, we’re opening doors to Independent Adjusters next month by offering a free course in insurance and state-exam preparation. InterNACHI members (home inspectors) can become IAs via InterNACHI. And IAs can get free CE courses. That brings great opportunity and crosses thousands of home inspectors with 10s of thousands of independent adjusters. Cool stuff.
Another example, as soon as EPA approves our RRP Lead Paint course, we’ll open the doors to contractors, millions of 'em.
I expect InterNACHI to be truly International, appealing to many industries, throughout many countries. Exciting stuff.
Okay, I must be missing something here. Can somebody explain the no venting of a crawlspaces when a moisture barrier is applied? Humidity will build up in a crawlspace without venting, just like a inside a vacant house, if the air is not condition.
All crawlspaces need to have moisture barriers, right? Regular venting will not eliminate enough moisture, in most circuimstance, in crawlspaces without moisture barriers.
I disagree. I’ve seen many crawlspaces without vapor barriers and no problems. If the house sits on top of a hill, has good functional gutters, good ventilation, has a relatively high crawl space, etc. there may be no moisture problems at all without a vapor barrier. I do not recommend a vapor barrier unless I see an issue. (I do, however, report the presence and amount of a vapor barrier for information purposes.) Who am I to advise someone to spend hundreds of dollars to correct a non-existent problem?
Please notice I did say “in most circumstances”
Now I see that. 
Joe, did you take psychrometric readings of the air to determine this?
As I posted above, the soil may look very dry (thats because all the water is now in the air).
You seem to worry about a lot of other stuff that is not necessary, why stop here? A vapor barrier is an industry standard for several reasons.
Just interesting that you take a stand at this point.
I take moisture readings of the wood floor structure in various places. I look for wet soil or signs of moisture intrusion. I look for signs of fungi. I look for decay. I look for deteriorated insulation. I look for proper ventilation. If I don’t see a concern, why recommend a fix when there isn’t a problem?
My own house has been sitting on top of a hill with dry sandy soil since 1880. There is not a vapor barrier and the framing is in exceptional condition. I’d be pretty PO’d if a future home inspector recommended a vapor barrier just because it is “industry standard”.
What I’m talking about, mainly, is putting such an issue in the Summary section of a report. The Summary highlights “significant” issues, get’s all the attention, and is required in NC. I wouldn’t be opposed to putting a note recommending it in the body of the report, as long as it wasn’t blown into a “significant issue” when no detrimental affects were observed.
So you are testing. Moisture of the wood is relative to moisture in the air.