Foundation Waterproofing & Drain Tile Systems
! ! ! See Author's Notes at Bottom of Column ! ! !
Did you know that there is a big difference in exterior foundation waterproofing treatments? I'll bet you think that your new home foundation has been waterproofed. Yes, you saw that black stuff sprayed on so you are in good shape. Isn't that right? WRONG! Fewer than 1 in 50 houses in the Greater Cincinnati housing market have waterproofed foundations. Most are damproofed. What do you think is happening in your city?
What's the Difference?
Concrete soaks up water. If you place moist earth around an unprotected foundation, your basement will be damp. Surely you have been in an older basement and smelled this moisture. Older homes rarely had any treatment on the concrete or stone.
Beginning in the 1950's there was widespread use of asphalt on new foundations. This was hand brushed or troweled onto a new foundation by laborers. The asphalt did a great job of minimizing water soaking into the foundations. However, it did not possess the ability to bridge or fill a crack which may develop in the foundation. You see, after a period of time, asphalt becomes somewhat brittle. When a foundation treated with asphalt cracks, the asphalt cracks too!
Approximately 10 to 15 years ago Owens Corning modified standard asphalt by adding some rubberized compounds. The result was a compound that had a certain amount of flexibility. Other companies developed synthetic rubber compounds that have far greater elasticity than the modified asphalt. Even before either of these products was available, commercial builders used cardboard panels filled with bentonite for waterproofing. Bentonite is a special natural clay product that swells when wet. Water carries the clay into the crack, it swells and plugs the leak! The bottom line is that you can truly waterproof your foundation. It just takes a little homework on your part to select the right product for your particular building situation.
Drain Tile - REALLY Important
If you decide to have your new foundation waterproofed, the company doing the work will most likely insist that they install or monitor the installation of your drain tile system. Very few builders that I'm aware of take the time or interest to adequately install drain tile.
Water naturally flows toward your foundation. This is especially true if you live on a hillside or even a slight slope (which, by the way, most of us do!) Water moves horizontally through soil. Water occupies the void spaces between the particles of soil. The deeper you go into a soil, especially if it is clay, the less space there is for water.
To make matters worse, the soil that is use for backfill around your house is rarely compacted. When it is dumped around your house it has huge amounts of air in it. This dirt was fluffed up and pumped full of air when it was dug from the ground. It can takes years and years for this ground to naturally compact. In some cases, where overhangs protect the dirt, it may never truly compact. It can always have more air in it than the soil that is only 5 or 6 feet away. This can spell BIG trouble for your foundation if it is not waterproofed AND if you have a bad drain tile installation.
From the above discussion, you can see why draintile is important, I hope. The point is this: the backfill soil has the capacity (because of the large volume of air) to hold large quantities of water. You need to collect this water rapidly and get it away from your foundation. That is the job of the draintile.
Another Quality Installation
That is a phrase I often used to tease my coworkers after we would finish a task. It was an inside joke. However, the phrase applies to drain tile. You generally only have ONE chance to put it in. It gets buried deeply. It can clog up if not installed right. It's expensive to redo. For these and several other reasons, you need a quality installation.
I always like to install the drain tile on the side of the foundation footer. Many builders simply install it on top of the footer. Installing the draintile on top of the footer means that your water table will be at the top of the footer. My method puts the water table about 6 inches below the top of the footer. You want the level of water as low as possible.
I recommend that the drain tile be installed the day after the footers are poured. I used to help strip the forms and then put a 1 to 2 inch layer of 1 inch gravel along side the outside of the footer. I would then install the drain tile continuously around the footer. Finally we would cover the drain tile with 1 inch gravel flush with the top of the footer. This would complete phase one of the operation.
There are advantages to doing the job this way. First, the space between the side of the footer and the wall can fill with collapsed dirt and/or concrete overflow from pouring the foundation wall. This stuff is tough to dig out and remove once the basement walls are poured. Besides, it is tough to work in the narrow area left along the foundation after the walls are up and poured.
Once the foundation is waterproofed, you can continue the drain tile installation. I recommend that you install an additional 2 to 3 feet of 1 inch gravel cover above the footer. On top of this, install tar paper or a 6 inch thick layer of straw before installing any backfill dirt.
The elimination of the straw or tar paper is a huge mistake. The backfill dirt is fluffed up. When it gets wet, small silt particles will be carried into the gravel. This will clog the gravel. If your soil has enough fine particles, you may clog your draintile! All of your work will have been for naught!
So where does the draintile water go? Good question! If you are lucky, it drains out somewhere on your lot. Here is what I mean. If you are building on a sloped lot, maybe you are lucky to have enough fall within your property line whereby the draintile can daylight. There is no need for the pipe to have a slope. It can be laid virtually perfectly level from the footer until it daylights. The net result is that you are simply providing a resistance-free path for the water around your foundation to escape.
If you are unlucky, like me, you need to install a sump within your basement. The draintile pipe gets to the sump either through or under your footer. I always install a 6 inch pipe under the footer right where I know I will install the sump. I actually install this pipe before the footer is poured. It's tough to tunnel!
An electrical pump pumps the water from the sump to either the outside of your house or into a storm water drainage system. Never allow the sump water discharge pipe to dump the water along side your foundation. This simply soaks the soil again!
Battery backup sump pumps are available to assist the regular pump in the event of primary pump failure or a storm related electrical outage.
Backfilling Basement Walls
Many a foundation crack is related to backfilling. Very few homeowners realize the risk of backfilling a foundation too quickly.
Don't forget that your foundation walls are simply beams or retaining walls. The walls act as a beam once the basement floor and the first floor subfloor are attached. Without these two elements, a foundation wall can tilt inwards, crack, or even slide off the footer! Don't allow your builder to backfill until these floors are in place!
Also, did you know that it takes approximately 28 days (under ideal conditions!) for concrete to reach 75 percent of its design strength? I know of builders who backfill foundations within 4 days of being poured! I have seen huge cracks develop from foundations that were backfilled prematurely. Don't let it happen to you!
Model building codes mandate that the soil must fall away from a foundation. They actually state that there must be 6 inches of fall within the first 10 feet of horizontal distance away from a house. If lot lines are too close for this to happen, then there must be some sort of drainage channel that allows gravity to pull water away from a foundation.
Furthermore, once this water is away from the foundation it needs to be directed to the lowest part of the lot. In other words, the lot grading plan needs to be completed so that water drains off the lot much like it did before a house was built on the lot. It is a common sense issue. This can be easily accomplished if the house foundation sticks up out of the ground and backfill soil creates the needed slope.
If you have ponding problems now and it is too difficult to re-grade your yard you can drain these swampy areas fairly easily. All you need to do is install a linear french drain system in the yard. This is a simple trench system that contains perforated drain pipe and gravel. The trenches are just 6 inches wide and about 18 to 24 inches deep. They follow the contour of your yard until they go past your house. Then the bottom of the primary trench levels out and before long the pipe will daylight!
You may wonder if my advice is worth anything. Well, read what Jim Sanders wrote to me when he was at the end of his rope:
"Hi, I just wanted to write to give you the results of my "Trench Drain". I have had a wet crawlspace for 15 years. Water would fill the crawlspace at times, so we actually had to drill weepholes at the base so that it would enter the basement and eventually, the sump pump.
I have tried everything. Several contractors said that the only thing we could do was to bring the water into the house via drainage tile and let it enter the sump pump. That would work, but because I live on a 6' elevation, there is no reason that I should have water problems. It became like clockwork...when it rained, we would rush home from the lake or wherever we were vacationing so that we could be prepared to start the backup generator, in case the power failed. We even had our alarm company put a sump alarm on our system, so they could notify us if we had a power failure. Battery backup was not an option, because sometimes we loose power for days and during any rain, our sump would run every 7 minutes...just like clockwork.
I found your site and read the article on the trench or French drain. At first, it sounded a bit like "holistic healing" to me. I failed to understand why a 2 ft. deep trench, 4 ft. away from the house would do any good. How could this simple thing correct an extreme water problem that has plagued me for years, cracked my foundation, settled my garage floor and ruined almost every vacation?
I decided "what the heck". I had to dig by hand using a trenching spade and a pick-axe, because the builder back-filled our property with brick and blacktop. It took quite a bit of time. Because the ground level varies so much on that side of the house, I was not able to achieve exactly 2 ft. deep. It varied from 18" to 30" in spots, but the slope was downhill. The trench is about 80 ft. long. At times, I thought about filling it all in, because I just didn’t believe that it would work.
I stoned it, put tile in, and filled it with #1 round stone. I socked the pipe just for safety measure and I also used geotext fabric on top, so I could cover with dirt and grass. I also ordered some clay and pitched from the house to the drain.
Result? For the last month, we have had 7 or 8 torrential rains, the worst of which was last night. It rained so hard, that our lawn washed out in spots because of the high clay content. Our sump pump, that normally ran every 7 minutes during and after rain, has not turned on for 4 weeks. The silt at the bottom of the sump well is now dry and cracking. Our crawlspace has not shown a trace of water or even moisture.
Since I couldn’t see correcting the foundation cracks or the garage floor settling and tilting until I corrected the problem's source, I waited to see if the trench drain worked first.
This week, I had a company come in and perform sort of a "mud-jacking" technique on the garage floor, which worked perfectly. Also, during the past few weeks, I parged the cracks in the foundation.
I just wanted you to know how this worked. I stressed for many years over this issue and the solution was nowhere near as difficult as I thought it would be.
As a side note, I went to the end of the drain tile during a hard rain to see what was happening. Water was running out of the drain tile in about the same exact volume that it previously ran out of the weepholes in my crawlspace. This winter will be interesting, because last year, the ground next to the house was so saturated that during a thaw, my sump would run constantly. I'm guessing that the ground between the trench and the house will probably be drier now going into this winter."
- Jim Sanders, Upstate area - New York