Understanding low point drains and what is possible and functional
One of the most common anxiety producing events in a homeowners experience with real estate occurs during the sale of the home, and is the pest dryrot and structural inspectors assessment of groundwater problems in the basement or crawlspace, and how to deal with them.
In my experience, I have found that many of these home inspectors know a few buzz words, but simply do not understand home drainage.
Pest dryrot inspectors often make statements like, adjust the low point drain in the crawlspace. Grade the crawlspace. Install a sump pump.
They might mention hand excavated french drains and call them curtain drains. Most often these inspectors do not have much of a grasp of the fact that unless you remove groundwater prior to it entering the crawlspace or basement, you are fighting a losing battle.
The low point drain, which is a piece of 3″ abs pipe poured into the concrete foundation stem wall and contains a backflow device, is many times constructed too high for the vent to work at all, and other times is not even connected to a properly installed vent, such as a daylight or drywell.
These are aspects that cannot be changed, and it is necessary to ignore them most often, and concentrate on the hand excavation of french drains on the outside of the foundation to prevent the groundwater from entering in the first place.
You can comply with the city and lender requirements for replacing the low point drain, but it is the removal of groundwater on the outside of the foundation that will prevent groundwater entry below grade.
Often the low point drain was originally installed correctly at the soil grade level, but because of wetness and perhaps even rain when the floor joists were being installed, the ground has fallen lower than the grade for which it was originally intended.
You cannot add soil in front of the low point drain and make it work, because groundwater does not run up hill. Besides, where ever you take soil from in the surrounding area of the crawlspace, to raise the grade at the low point drain, you will have a low area where the soil was taken, which will just make for another groundwater puddle when groundwater enters.
Sometimes the answer is to install a new low point drain that is actually a hand excavated french drain that passes under the foundation footing at a slope, and vents to a hand excavated drywell or daylighted vent outside the foundation. This works best on sloping sites, where the ground slopes away from the foundation if a daylighted vent is to be installed.