French Drains and How they Work

French Drains and How they Work

Let’s look at how french drains work to help move water in Minneapolis/St. Paul yards.  French drains are trenches dug in your yard, lined with fabric (to keep all dirt out), then filled with a drain pipe and loose rock.  This allows water, once it enters, to flow easily to wherever the pipe takes it.  As long as the pipe goes downhill, this will be the easiest path for water to follow.

A french drain is sort of a tube and rock surrounded on all sides by landscape fabric, like a burrito!  Any water that goes through the fabric will end up in the tube and float away.  On top of the burrito, we add an inch or two of soil, maximum, and sod.  A variation is where you don’t want or need sod over the top, in which case we can use any decorative landscape rock over the top instead.

Why Would You Need a French Drain?

It’s common in Minneapolis and St. Paul landscapes to see areas of the lawn which don’t drain well.  There may be a low area which collects water.  Or often in newer developments, the property line between two houses form the low spot where all the water from the roof and yards has to flow in order to drain off the property.

Depending on your soil, certain areas may be unable to handle all the water they get.  Either the water doesn’t drain at all, or it doesn’t drain quickly enough, or dry out quickly enough, so it becomes a soggy area which may still be there when the next rain comes.  A french drain can help collect and move the water more quickly, to prevent these areas from puddling or becoming soggy messes.

How are French Drains Installed?

Our goal is to be able to dig the drain into your existing yard carefully, and replace your own sod back over the top, so that when it’s done, you barely know it’s there.  Usually we can cut the sod out where the trench will be and set it aside to reuse.  We then dig the trench to accommodate the 4″ perforated drain tile and drainage rock.  Typically this will be a trench 8-10″ deep and 8-12″ wide.  It’s doesn’t need to be huge or deep… we just want to give the water and easy way to get out of the area.

If you have heavy clay soils, we usually can’t reuse any of what we dig out.  In any case, much more dirt must come out than will go back in, so we will have to move it away in wheelbarrows and haul it away in our trucks.  For a longer trench, this actually can be a lot of dirt coming out.

We then line the bottom and sides of the trench with fabric to make sure no dirt can get into the drainage.  This would clog it all up eventually and the drain would no longer function.  We then lay our 4″ perforated drain tile “with sock” (which means the tube itself also has fabric around it) in the bottom of the trench, and cover it with loose rock.  The rock can be pea gravel, river rock…. it doesn’t really matter what the rock type is.  Anything will work.  We stop filling when we’re 1-2″ below the height of the bottom of the sod.

We then fold the fabric up over the top of everything (burrito-style) so dirt can’t get in from the top.  Then we add good soil on top, and relay the sod.

How much do French Drains Cost?

Depending how long the run of tube is, installing french drains can be a surprising amount of work.  It’s not something we can just send a couple guys with shovels to go do because we have to have a Bobcat and dump truck out front to load up and haul away all the dirt which comes out.  When we do french drains, it’s as part of a larger landscape project where we’re already building a patio or wall and the drainage is a part of the overall job.  That way the Bobcat and trucks are already there, and we’re already taking out dirt, so adding in a french drain (or other types of drainage) fits with what we’re already doing.

Pricing can vary a lot depending what type of soils you have.  It takes a long time to dig a trench through nasty clay, for example.  But nasty clay is typically where a french drain can really help!  Just a week ago, as I’m writing this, we spent nearly an entire day digging in trenches for drain tile at a property in Plymouth with really bad clay soil.  But now that the pipes and drainage rock is all in, their lawn areas are already much drier.  It can make a huge difference.  Whether that difference is worth the money it costs to install is up to you!

As part of an overall landscape project, if you needed, say, 75-100 feet of french drain installed, figure it could cost in the range of $1,000-1,500.  This assumes you have an existing lawn, so we’d be cutting out the sod, setting it aside, cleanly digging and removing the dirt, and putting your old sod back on at the end.

As I was telling our client in Plymouth last week, when you see how much work this actually is, and see how cleanly we do it, it makes sense why it costs so much.  If it can help keep water moving away from your house, further lowering your likelihood of a wet basement, it may be totally worth it to do.  That’s for you to think about!

Thanks for Reading!

As always, if you have any questions, we are always available by email or phone.  Head over to our photo galleries sorted by price to get more of a feel for what various landscape projects cost.  We’re around anytime, so feel free to call or email with any questions about your Minneapolis/St Paul landscaping project, or if you see something you want!

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