Foundation Drain Tile Installation TIPS
- Use 4-inch white perforated pipe
- Cover with 2 feet of large, washed gravel
- Protect gravel with straw or tar paper
- Extend pipe to daylight – sumps suck
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Foundation drainage tile systems are one of the most important aspects of residential construction if your home has a full basement or crawlspace.
Drain tile systems are also one of the most misunderstood parts of the average home – both by most uninformed builders and homeowners
Hidden From Sight
Because these systems are usually deeply buried and cannot be easily modified or corrected, it’s vitally important that they are installed correctly. Foundation drainage systems which are installed properly can serve a dual roll.
Covered Swimming Pools
Many homes around the nation have full or partial basements. These basements are really reverse swimming pools.
The basement, before the house is built on top of it, looks just like the typical in-ground swimming pool. Once the house is built, this swimming pool gets covered.
But most people don’t want water in their basements. Foundation drain tile systems are the means by which ground water can be transported away from your basement. If you want a dry basement, you must have fantastic drain tile and waterproofing on the outside of the foundation.
Water in Soil
The water content in the soil surrounding your house can fluctuate seasonally. There’s always a point at which you can dig and hit water. Geologists often refer to this as the water table.
This water table rises and falls in response to the amount of precipitation in any given time period. The water table in many parts of the country can rise to within a few feet of the surface during wet spells.
Water Moves Sideways
The water in the soil is moving all the time. Gravity is pulling it to the oceans around the world.
Most people think that the water in soil moves straight down but in reality it moves sideways through the top soil and upper layers of the B horizon of soil.
Almost all homes are built on some sort of slope, so if you have acres of land above your home, the water in the soil is all marching and flowing towards your house.
Path Of Least Resistance
Water will take the path of least resistance. It can choose to go sideways through a crack in your foundation, or it can go down alongside your foundation through clean, washed gravel into a pipe.
I’m sure that you will agree that it is a better idea for the water to go down the pipe.
A foundation drain tile system has four main components:
- Drain tile pipe
- Gravel Protection
- Water outlet
All of these elements must be installed for the system to function properly.
Drain Tile Pipe
The drain tile or pipe is usually 4″ in diameter and is perforated or has pre-drilled holes along its length. Depending upon the type, it can be purchased in rolls up to 250′ or in 10-foot sections. Fittings are available to allow you to go around corners or interconnect the pipe.
I’ve never been a fan of the rolls of black corrugated drain tile with the slits in the cracks. I prefer the more rigid white plastic pipe with two rows of drainage holes drilled into the pipe.
The filter media or gravel is used to cover the drain tile. Water can flow readily through this gravel and find its way to the pipe.
I always installed a layer at least 2 or 3-feet thick. More is better.
One customer wanted me to ensure his room addition basement never had water in it. He was willing to pay to have the high-side foundation wall that pointed upslope filled completely with the nice rounded gravel.
There was no way water was going to ever try to force its way into his basement when it had the chance to go straight down to the drain-tile pipe.
Remember, water takes the path of least resistance. Some soils, heavy clays, resist water movement.
If your soil is like this, the water would rather go sideways into your basement than down through the clay soil to the drain tile. The gravel that is used most often is large 1 – 1 1/2″ diameter washed rounded gravel. This gravel is about the size of a walnut or large grapes.
Some parts of the USA have crushed gravel this size. It’s not rounded, but that really doesn’t matter. All that matters is that you just put in this rock and no sandy gravel. Sand slows down the movement of the moving water.
You must protect the gravel with a barrier. It prevents silt and mud from the soil from clogging the gravel or the drain tile pipe.
During excavation, dirt removed from the hole is fluffed. This means that it is disturbed and broken up.
It’s volume usually increases about ten percent. It’s loosened and disturbed more during back filling procedures.
As the soil gets disturbed, small dirt particles, or silt, are created and separated. These are carried through the gravel by the rain water or snowmelt which enters this soil.
Very few builders take the time to compact the soil around the outside of a house so Mother Nature does it using water and gravity.
Without a barrier of some type covering the clean gravel, these silt particles immediately clog the gravel and drain tile and render it useless.
IMPORTANT TIP: Most builders often do not install this barrier. It’s a HUGE MISTAKE to eliminate it. Do NOT ALLOW them to tell you it’s not needed. They’re either ill-informed or lying to you.
Gravel Protection Materials
The materials commonly used to stop the silt from getting to the gravel are straw or tar paper.
If you use straw, just scatter a 16-inch layer on top of the gravel before you put in any soil on top of the gravel.
Tar paper is easy as you just cut the correct width and lay it on top of the gravel.
The water outlet is simply the place where the collected water flows to. It can be one of two places:
- Daylight – downslope from your home
- Sump Pit – inside a basement or crawlspace
If you build on a hillside, your drain tile will simply ‘daylight’ or come to the surface. This happens naturally because the drain tile pipe is installed nearly level and as the ground falls away from the house at some point the pipe will be visible.
This is the best situation, because your system depends entirely on gravity to work.
If you build on level ground, you have to install a sump pit. A sump pit is usually installed inside the basement of your home.
The pit is nothing more than a buried plastic container that resembles a garbage can. It’s large enough for a sump pump to rest at the bottom.
The drain tile pipe runs beneath the footer to this sump. The collected water is then mechanically pumped from the sump.
Dry Wells – No Way
Some people say to extend the drain tile pipe to an underground dry well. A dry well is a large subterranean pit filled with gravel.
The drain tile pipe runs to this pit and the water fills this pit.
These pits work well only in places that have very open gravel soils. Not many places have this soil. In most places the soil is dense clay and the dry well fills with water and the water then backs up against your foundation.
Drain tile pipes work best when placed along side of a foundation footing, instead of on top of the footing.
By placing the pipe alongside the footing, you lower the water table below your basement floor another 6-8 inches.
In new construction, install the drain tile immediately after the footing forms are removed. Cover the pipe with gravel to a level flush with the top of the footer.
If you choose to wait until the foundation is poured, there will be less room to work in, the side walls of the excavation could cave in, or extra concrete from the foundation pour could fall into the hole and have to be removed. Believe me, it’s faster and easier to install the drain tile pipe and first layer of gravel without the foundation walls in the way.
After the foundation walls have been water proofed you begin step two. Backfill over the pipe with at least a three-foot-thick layer of gravel.
If you can afford it, backfill with gravel to within 18″ of the finish grade. You must think long term. Remember, it will be virtually impossible to dig up and add gravel in the future when your basement is leaking. The extra money spent now is well worth it.
Once the gravel is in place, cover it with a 16-inch thick layer of straw or a single layer of 15# roofing felt paper. This barrier will prevent the silt from the backfill dirt from clogging the gravel and drain tile.
To really ensure your basement or crawlspace stays dry, install a Linear French Drain around your home once it’s built. I created a fantastic step-by-step DVD showing you how to do this.