Should You Install A Secondary Drain Tile On The Inside Of Your Basement?
As a builder, you may be faced with the question, “is an inside tile worth the extra expense?” We will attempt to lay out the facts about it so you can make your own conclusion.
First, an interior, or secondary drain tile is not required by most city codes. Currently, Miami County, KS is the only jurisdiction that does require it.
Having an understanding of how water enters a basement is the key to understanding if an interior drain tile is worth the extra money. All drain tile (exterior and interior) are designed to keep the water table from pushing up on the bottom of the basement slab. If you can imagine the water table doing this, you can get a clear picture of how it works. During rainfall events, the ground beneath the home becomes so saturated that the water table rises like a lake upwards towards the floor slab. The water will take the path of least resistance. Hopefully, the home that you build has a good working drain tile system so that path of least resistance is not the cracks in the floor!
An interior drain tile is simply one more place for this rising water table to take as its path of least resistance. It is a backup or extra help for your exterior drain tile.
However, there is 1 more avenue that this water table can take besides the drain tile. It is the gravel bed that is directly under your basement slab. A good bed of clean ½” or ¾” gravel (4” thick or greater) will allow a lot more water to pass through it than a drain tile can. This is because the gravel bed is placed across the entire basement, vs. just next to the footing. Generally, larger, clean, & rounded gravel will allow the most water to travel through it. There are many things that can happen to you to cause the gravel to not be able to do the job. Plumbers who dig in the ground rough pipes can sometimes leave dirt trenches causing dams in the gravel bed. Footings are sometimes placed in the middle of a basement, causing a dam. Dirty gravel, crush & run gravel, or pea sized gravel won’t allow for the proper flow of water. In, these cases, the gravel may not be a good source for the water’s path of least resistance.
An average price for an interior drain tile is about $ 1.20 per lineal foot. An average size home would utilize about 180’ lineal feet to circle a basement, or cost you about $ 220.
Sometimes, an interior drain tile may be added on a lot by lot basis. In summary, installing inside drain tile is definitely better than not, but you have to decide if the extra cost is worth the extra piece of mind.
