TOPIC: venting crawlspaces

How many home owners are going to go out and buy then crawl under their house and take a psychrometer reading every day to determine the temperature and humidity of their crawlspace?

Technicals are great for us to know, but try explaining that stuff to a home owner and their eyes will glaze over on you.  Its like your wife talk shoes to you.  It don't happen!!!  lol

Not really.

If you lower the temperature of high humidity air, it RAINS.

Just like it does outdoors.
Warm humid air moves into a cool area and it rains.
What's so hard to understand about that?
You hear about it on the weather channel every day.

The chart is for those that say it dos not happen (not for your client).

This is a law of thermodynamics. It doesn't change.

Okay, just wasn't sure if you were trying to go this in depth with all your clients.  That's all.

I'm sorry. I didn't expect anyone here to use a psychrometric chart. Just using it as a graphic representation of what's happening. All too many people post made-up information without any supporting documentation. This simply represents what I am saying.

It seems like there is constant debate on the subject and local building code requirements actually facilitate extensive water damage to the structure due to inadequate ventilation requirements of the crawlspace.

The spacing and number of crawlspace ventilators in the foundation wall are based upon the number of ventilators required per square footage of the space. This is the building code and you're not going to move in unless you comply.

However, from my point of view the proper number of ventilators and the adequate ventilation can be determined by the effects the ventilation on the air temperature of the crawlspace. Adequate ventilation will raise the temperature in the crawl space above the dew point and prevent condensation from occurring across 100% of the space. In reality the number of ventilators required to accomplish this may actually affect the structural capacity of the foundation!

In Nashville Tennessee we have a high relative humidity under a high temperature in the summertime. As we ventilate the crawlspace we not only are bringing in air for dilution, we are bringing in humidity with it. When the air enters the crawlspace it lowers in temperature, the moisture precipitates out of the air.

This condition will not be the same in every part of the country.
This is simply a case of one shoe does not fit all.

The primary purpose of venting is to allow air quaility flow through the house in unoccupied areas such as the raised foundation, and attic, if the house did not breath stale air will cause the air quailtly to be offendsive most doing the winter months, I wanted to explain before I submitted the answer.

at any point you open the or slide them open you possibly will allow animals to enter the attic or raised foundation area some animals find electrical insulation very tasty! and if you have a floor furnance that is a very warm spot for the critters!

Animal relief "piles" are very toxic, some cats build up a pile under a customers bedroom area under the house over the years and the occupants that was sleeping over that floor space got very sick from the emmitting oder, as a result the flooring had to be removed and the piles removed and the foundation area treated.

The wife ended up in the hospital with respitory failure and other health problems. 

Dominic, clean up on aisle 11.