awl51
New member
I hope to tap some of the experience from TBNers who have been there, done that.
Background: I'm helping my son tear up his backyard so that his new Man Cave doesn't get wet from a sometimes-leaky basement (and, yes, I *did* tell him to do the drainage project first). He has a backyard that slopes toward the house. What we've done so far is get the tractor back there, level an area extending about 20 feet away from the back wall of the house across its entire width, and dump the spoils up on the newly "terraced" rear of the backyard.
We will come back this weekend and build a retaining wall the height of the new terrace, and place filter fabric, washed crushed rock, and perforated pipe behind the wall. The perforated pipe leads to hardpipe at one end of the wall, and then drains directly out through a trench to the font of the house.
I've never built a French drain setup before, but there is a good amount of information available, and some of it actually seems noncontroversial
. Many of these depict a French drain running behind (not below) a loose-laid masonry retaining wall.
So, my question is this: should I put an impermeable barrier between the back of the retaining wall and the rock and perforated pipe? I understand that the perforated pipe and the orientation of its holes is designed to handle groundwater coming up from below. However, without a barrier, once the groundwater level reaches the first course of the retaining wall, won't it just seep through the loose-laid block and never get to the level of the perforated pipe? Conversely, if I lay an impermeable barrier against the back of the wall masonry, won't the retaining wall heave in the winter from the water trapped behind it?
I've been actually thinking of taking a middle road...putting a barrier behind the wall, but then poking a few holes in it; the thought being that a real gullywasher would make the groundwater level rise quicker than than the few holes could drain, and thus reach the perforations where the French drain could do its work; and yet it would still allow slower and "leftover" groundwater risings to drain through the holes in the barrier. But I'd appreciate anyone weighing in with how and why they think this should be constructed. Thanks in advance.
Background: I'm helping my son tear up his backyard so that his new Man Cave doesn't get wet from a sometimes-leaky basement (and, yes, I *did* tell him to do the drainage project first). He has a backyard that slopes toward the house. What we've done so far is get the tractor back there, level an area extending about 20 feet away from the back wall of the house across its entire width, and dump the spoils up on the newly "terraced" rear of the backyard.
We will come back this weekend and build a retaining wall the height of the new terrace, and place filter fabric, washed crushed rock, and perforated pipe behind the wall. The perforated pipe leads to hardpipe at one end of the wall, and then drains directly out through a trench to the font of the house.
I've never built a French drain setup before, but there is a good amount of information available, and some of it actually seems noncontroversial
. Many of these depict a French drain running behind (not below) a loose-laid masonry retaining wall. So, my question is this: should I put an impermeable barrier between the back of the retaining wall and the rock and perforated pipe? I understand that the perforated pipe and the orientation of its holes is designed to handle groundwater coming up from below. However, without a barrier, once the groundwater level reaches the first course of the retaining wall, won't it just seep through the loose-laid block and never get to the level of the perforated pipe? Conversely, if I lay an impermeable barrier against the back of the wall masonry, won't the retaining wall heave in the winter from the water trapped behind it?
I've been actually thinking of taking a middle road...putting a barrier behind the wall, but then poking a few holes in it; the thought being that a real gullywasher would make the groundwater level rise quicker than than the few holes could drain, and thus reach the perforations where the French drain could do its work; and yet it would still allow slower and "leftover" groundwater risings to drain through the holes in the barrier. But I'd appreciate anyone weighing in with how and why they think this should be constructed. Thanks in advance.
