The Pros Don’t Always Get It Right
There are plenty of online articles explaining how to install a French drain around your residence to keep water in the soil from infiltrating the foundation. Plenty of them, but some of the advice in them is wrong…at least for this old cowboy. I’ve got my own style when it comes to pretty much anything. Constructing a drainage system for the first time in my life is no exception.
When the decision was made in October of 2009 to build a home with earthbag walls on our off grid acreage, it seemed obvious a separate setup would be needed for drainage. Most earthbag “authorities” strongly recommend doing a “rubble trench” under the foundation itself with layers of various materials providing enough drainage to keep the walls dry.
Instead, our home (still under construction but getting there) is built on a perimeter foundation of simple concrete blocks, just sitting happily on the ground. A separate French drain is now being put together around the entire perimeter of the residence. $408 to use a trencher for a day? Forget that, too! Back to ye olde trusty #2 shovel and go from there. The procedure:
1. Using twelve inch spikes as stakes and a roll of nice, bright string as the border marker, outline a section of trench along one wall. In this case, the trench is fifteen inches wide and the house-side edge is also fifteen inches from the foundation. These numbers made sure the foundation wasn’t compromised (wouldn’t cave in) and also made sure that rainwater falling straight down from the eaves would land directly over the trench.
2. Make an initial “shovel-cut” for the full length of the trench. Theoretically, it shouldn’t make any real difference to do it this way rather than going full-depth from the beginning, but it feels more like something is actually getting done.
3. Shovel out the rest of the dirt to reach the desired depth and width. In this case, the average trench depth is roughly twelve inches. That’s deep enough to get the job done and little more, which is actually a good thing. Beyond that depth in this high-clay, high-caliche desert soil, it’s best to use power equipment–unless you want to spend a full day scraping out another inch or two. It’s deep enough to accept four inches of perforated drain pipe with eight inches of gravel cover…and it keeps the amount of fill gravel you have to buy down to a low roar.
Here Come Da Controversy
Some of the advice by professionals looks logical. I certainly can’t argue with the idea that it’s a good thing to have the in-trench drain pipes laid with a slight downslope or at least level. Duh.
But here we part ways.
Every online article I checked before grabbing the shovel said to be sure the holes in the perforated drain pipes were on the down side.
I call B.S.
Yup. The holes in our pipes will point up, not down. Additionally, said pipes will not be surrounded on all sides by gravel but will rest directly on bare earth. And finally, the gravel fill will not be topped with, um, topsoil, but will go all the way to the surface.
Lots of drain systems clog up over the years. With holes pointed toward the Earth itself, that should be no surprise. (Ah! To clarify: Perforated drainage pipe has rows of holes predrilled on only one side, not all the way around. Okay?) So, whether you put a bit of gravel under the pipes or you don’t, it’s going to be easier to get those holes clogged up by far if they’re on the bottoms of the pipes. Duh. Likewise, placing the (un-holed) bottoms of the pipes on bare earth is no problem; it gets the piping “as low as it can go” and maximizes flow. Rhymes, too.
The other anti-clogging technique involves stacking the trench completely full of gravel and in fact adding that top-gravel “sideways” as well…so that in the end, the house will have a “gravel walkway” extending from the foundation out over and past the trench. While some soil will erode from the trench sides into the gravel and eventually reach the pipes, there is no soil whatsoever directly above the pipes. True, you can’t plant flowers next to the house if you do it this way, but so what?
The final feature to discuss is: Besides seeping into the soil around the house itself, where will the system end up sending all that excess water every monsoon season?
The answer: As it happens, we have a bit of an “open pit” sitting just thirteen feet north of the residence’s northwest corner. A bit of trenching, a bit of piping, and an “open discharge” exit becomes available. It really did just happen that way, too. There was a great pile of dirt sitting there after the septic system trenching was done last summer. After roughly 1200 sandbags were filled with that dirt to make up most of the home’s four walls, the shallow pit was left behind. Might as well use it.
Pipeline exit into the pit.
The West-Wall Trench
The first part of today’s work shift was taken up by two activities, to wit:
1. Fiilling in the north-wall trench with gravel.
2. Trying to explain to the truck driver who brought us a load of rocks that those stones were definitely larger than 1 1/2″ diameter. Of course he assured us the size was right. It wasn’t. However, if he was forced to go back, dump that load , and bring us the right stuff…it probably wouldn’t happen today. Then we’d run out of rock during the weekend. Besides, bigger rock just means bigger air spaces between rocks in the trench; great for getting rainwater quickly to drain pipes. So: No harm, no foul. I took the rock.
Afrter the friendly driver pulled out of our driveway, I also called his company. Four minutes after closing time. Button-punched my way through the menu. Got the general manager’s voice mail. Left a message, you know, not complaining or anything, FYI, your driver’s an idiot. No, not in those words.
But check out these rocks.
SPECIAL NOTE: The people who run the rock company are top hands. When I let them know about the wrong-sized rocks a few days later, they made it right. We discussed how much of the load I might actually use. After I estimated that I’d probably use something close to half of the load and be stuck with half a load of leftovers, they informed me that the next time I order (and there’s sure to be a next time), I’ll have credit for a half load–that is, seven and a half tons of rock. Can’t be fairer than that.
That Accursed Caliche
Today was Friday, February 26, 2010. The plan for today was to top the north side trench with gravel, dig the west side trench, lay the pipe in that one, and top that, all by the time to sun went down.
It might even have happened but for that notorious Cochise County caliche. In case you’re not familiar with the term, it refers to a form of limestone rock that makes power trenchers bounce and makes manually wielded shovels scream with frustration. It also occurs in layers. Fortunately, the layer along the north side of the house allowed a foot-deep trench to be dug by hand with no problem. So did most of the west side trench…
Except for one twelve-foot section.
You know when you’ve hit caliche. Can’t miss it. Instead of sinking the shovel head full depth by simply standing on it, you wind up working from the sides of the trench, scraping across the excavation, shaving off maybe a quarter inch of mixed clay and little, white, highly amused specks of limestone with each pass. No big boulders, but it’s sort of like Mother Earth is wearing chain mail under her dress. By the time the other 28 feet of trench were completed, I still had two good hours of sunshine left in the day. By the time the sun had dropped over the horizon, those final twelve feet were finished…barely. The caliche layer had shown itself at a depth of four inches beneath the surface and contested every millimeter of depth beyond that point.
Which makes another point: A French drain is really needed here…because caliche doesn’t let water pass easily, either. If a dandy monsoon cloudbuster pours out several inches of water in a single day and there’s no system to channel the runoff, some of that water is going to seep under the concrete block foundation and into the home’s subsoil. After all, if the caliche won’t let the water go down easily, it’s still got to go somewhere. Anyway, final tally for Friday: North side…done! West side…dug! Gotta focus on the positive here….
West Side Completion
Today (Saturday) saw the finalization on the west side leg of the trench. There were a few minor glitches, though nothing drastic:
1. One small length of drain pipe is “bent over” to the “house side” of the trench rather than continuing in a straight, dead center line. This happened when I got careless and dropped a load of rock over the pipe too quickly without making sure both sides of the PVC were “rock braced”. It’ll still do the job, though.
2. Using the bigger rock (delivered in error yesterday) has one advantage, namely bigger air spaces between stones, thus the capacity to drain rainwater more quickly than the smaller gravel. These oversized mini-boulders are not something Pam’s permanently injured feet can walk on comfortably, though, so the leftovers can’t be used on any of the high-traffic walkways around the homesite.
3. Lack of focus resulted in dumping back-to-back wheelbarrow loads of rock without control. The second of these loads landed in an “okay” position and produced no real downside…unless you count my turning the air blue for a moment or two. The first out-of-control dump, though, went the other way, spilling half of the stuff all over the piled-up dirt that had been removed from the trench. Couldn’t force myself to pick all that up and clean it at the same time, so some of it’s still there, a mute but graphic testimony to the builder’s stupidity. At least it’s behind the house, not visible to the average visitor.
When all was said and done, the shift went all right. Although I did soon realize another trip to Home Depot was going to be essential: Four inch landscaping/trenching PVC takes a lot more glue than the one inch water line. Duh.
A Rain Day, Sort Of….
It rained off and on all day Sunday, but that’s no reason not to dig drainage trench. True, the gravel already in place had to be removed as the digging progressed. Likewise true, the only sensible place to stand while digging was directly under the downpouring water that sheeted from the eaves on the south side of the house. So? What’s a slightly damp spine have to do with it? Gonna wuss out, are ya?
Nah. Fair weather buiding may be okay in some cases, but when you’re building a house by yourself, you can’t afford the time loss. Besides, there were benefits:
1. Benefit: The dirt was nice and soft. Gumbo-sticky, sure. That’s clay for you. But no hardpan.
2. Benefit: New discoveries. The discovery for today involved a method for dealing with the mud accumulation on the shovel. A single stroke could stick enough gumbo to the shovel head to make the tool heavy, awkward, and inefficient. A friend had emailed me about using Pam or a similar nonstick cooking spray. I tried that, and it worked a bit, but my Pam quickly pointed out there was a better way: Used oil. I had half a barrel of the stuff on hand…and it was free. Worked like a charm. Sure, picky authorities might get on me about oiling up the soil if they watched me do this, but the actual amount of petroleum product returning to the Earth is minimal–certainly less than our septic installation contractor dumped from his old backhoe with the multiple leaking seals.
3. Benefit: Photography. Besides a number of cool project photos, a great one of the Huachuca Mountains begged to be recorded (and was, of course).
4. Benefit: Chicken fried rice. Pam felt bad, watching me out there spading away in inclement weather, so she got her cooking cap on and went to work. Result: Chicken fried rice from scratch, swiftly cobbled together from supplies on hand and better than 95% of the Chinese restaurants produce. Chicken fried rice also just happens to be my very favorite dish. Yay, wife!
By day’s end, the trench was only a little more than half done, but that’s still a whole lot more than zero.
It took a few more days to wrap things up. One thing does concern me: Inside the house, that wettest south wall area is…well, the soil is still damp as far as three feet in from the perimeter. Hopefully, that’s just because the cool temperature in there makes dry-out a long, slow process. We’re supposed to have rain again in a few days and are hoping to see evidence that, at least, it will no longer get wetter. Hopefully.
At any rate, the drain is now fully in place, the four inch perforated pipe running completely around the perimeter of the house, with a solid covering of rocks and an open outlet heading northward into the handy dandy “drainage pit”.
Happily, the house just feels a lot more complete with the drainage field installed and gravel both covering the trench and providing a walkway all the way around.
Cost: $147 for pipe…$17 for primer and glue…$13 for a new pair of tennis shoes…$226 for rock…total $403, exactly $5 less than one day’s power trencher rental. Which ought to be a true bargain, come monsoon season.
Update: New Year’s Day 2012
The French drain system described and illustrated on this page was installed during the spring of 2010. Since that time, we’ve had the opportunity to see how well it works through three full summer monsoons.
It works very well.
I have to make sure to maintain the drainage ditch that moves excess water on down the slope (there’s a very gentle, maybe 1% drop from where we sit) and out of our way. On an average of 3 times per summer, in the midst of super-heavy rains that attempt to overwhelm the system and push water right back up into the drainage pipe, I’ve had to trudge out in the downpour and muck out whatever needed to be mucked out…but that’s it. From the day the French drain was completed, we’ve never had so much as a hint of unwanted moisture under, or even right next to, the house.
Young desert cottontail rabbits tend to use the pipe as an extra-safe (170 feet long!) burrow during the dry months, but once the first flash flood washes them out for the summer, they move on to safer homes until the rainy season is over.
All in all, we couldn’t be happier with the way it all worked out.