Draintile for concrete block wall...where to place?
Draintile for concrete block wall...where to place?
(OP)
I am rebuilding my garage and am wondering what is the ideal depth to place the draintile. The existing garage is completely demolished and I am getting concrete today. I have an alley garage and I walk about about 6 feet to my back yard to the east. The north wall will also be buried approximately 6 feet. I also have a wing wall on the south wall that heads approx. 6 feet east toward my house that will be used for the steps. I am planning on placing draintile along this wing wall, then along the east wall and also along the north wall and then daylighting it to the alley at the northwest corner of the garage. See the attached PDF for a better idea of what I have going on. I am wondering what depth I should place the draintile. A couple things to consider: the alley at the northwest corner is about 1 foot above slab grade and this is the only spot I can daylight the draintile. Should I place the draintile as low as possible and then use crushed stone (or pea rock?) filled up all the way to near ground level? Or just use about a foot of crushed stone? Or, am I better off placing the draintile a couple feet below grade?
To me, I think I should place the draintile as low as possible, and then fill a 1 foot trench with crushed rock up to about a foot below finish grade. Then I will probably put some fabric over the rock and fill the remainder with topsoil for a planting medium. Can somebody either confirm this or recommend a better solution? Thanks.
To me, I think I should place the draintile as low as possible, and then fill a 1 foot trench with crushed rock up to about a foot below finish grade. Then I will probably put some fabric over the rock and fill the remainder with topsoil for a planting medium. Can somebody either confirm this or recommend a better solution? Thanks.





RE: Draintile for concrete block wall...where to place?
Do you have frost-susceptible soils?
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928
RE: Draintile for concrete block wall...where to place?
RE: Draintile for concrete block wall...where to place?
Bozhe moi
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928
RE: Draintile for concrete block wall...where to place?
Put crushed rock ~3/4'' about 4-6'' below and on top within about ~6'' of grade. Put geoteck "sock" on tile FIRST. You could even put a layer of poly over rock and under soil - if you think you will be there more than about 20 year.
Fill in with soil and grass....
RE: Draintile for concrete block wall...where to place?
Did you get a building permit for this structure? A few things that you might want to consider:
1. On the west side of the building the footing is an 8" thickend slab. If you are in Minnestoa I think that the frost depth is 4'.
2. On the north & east sides of the building the CMU walls stop at 1'-8" below the floor joists so they have to act as a cantilevered retaining wall instead of like vertical beams spaning between the floor slab & the upper floor joists. The footings shown won't act like a heel for a cantilevered wall.
RE: Draintile for concrete block wall...where to place?
So, despite the poor overall design of the structure, what is the ideal location for the draintile to minimize the chance of foundation wall failure?
RE: Draintile for concrete block wall...where to place?
RE: Draintile for concrete block wall...where to place?
RE: Draintile for concrete block wall...where to place?
Are you suggesting placing the floor trusses directly on the CMUs? It doesn't seem to me that this will add much, if any, strength the wall. Am I missing something here?
RE: Draintile for concrete block wall...where to place?
Normally, any wall that has earth against it must resist that lateral earth pressure. The horizontal forces, usually, in a basement wall are resisted by vertical bending in the wall - the floor of the basement and the floor of the house act to resist those lateral forces.
In your case, you do not have anything at the top of your block wall to push back against the earth. Thus, the wall has to span horizontally instead of vertically and the distance appears way to far for typical 8" block to span - even with a bond beam on the top course of the wall.
I'd suggest you get some help on this as you are going to have problems with it.
RE: Draintile for concrete block wall...where to place?
No, I am suggesting that you build your CMU wall up to the bottom of the TJI's (wood I joists) that are supporting the floor above the garage. Once you put the sheathing on the joists the floor diaphragm will become a horizontal beam that can be used to resist the lateral load from the soil at the top of the wall.
Of course, you have to design the anchor bolts to plate, diaphragm chord and plate to joist connections.
RE: Draintile for concrete block wall...where to place?
For those that are curious, I demolished the existing garage that was there. The reason for this was the east wall was failing. This wall was a 4" to 6" poured concrete wall. It only lasted about 100 years, with no rebar or any other type of reinforcement. It was framed with 2x6 walls, 2x4 trusses and 2x8 floor joist. I think the new design is a bit of overkill, but I don't want to have to replace it again. Attached is a picture of the old garage during demo. Again, this lasted for about 100 years.
Back to the original question, what's the ideal depth to place the draintile?
RE: Draintile for concrete block wall...where to place?
MiketheEngineer answered the question about drainage.
About the old garage, it looks like the east wall was supported by studs that were balloon framed from the garage slab to the upper floor level. These studs were probably what kept the concrete "shoring" from pushing the wall over.
You should heed JAE's advice and get a structural engineer to design this entire new structure for you or drainage will be the least of your problems.
RE: Draintile for concrete block wall...where to place?
So, how to minimize both of these things. Well, first all backfill within about what you show on your cross section should be non-frost susceptible granular soil. Then, to avoid plugging the drain, use a clean sand or a clean sand and gravel. That will not heave and it will not plug the drain. The sand fraction of the sand and gravel acts as a filter against silt movement with water flow.
I'd also opt to seal the ground surface and divert surface water around the garage with a swale up there. A clayey topsoil would help a lot, even though it will heave some.
On holding that block wall agaist earth pressure, well, if you had the chance, built it as a mechanically stabilized earth wall (MSE) (do a search for that in Google or here), with geo-grid laid back into the soil towards the house. Then it is designed to hold that earth pressure. Even though the wall may be up, as long as it is not backfilled, you might be able to make it work.
so you see it is not only that drain pipe that you need help on
RE: Draintile for concrete block wall...where to place?
You said the alley at the NW corner is above slab grade, but there must be some place lower than the floor slab or surface water will stand in the garage. If so, put the drain tile along side the thickend slab below the floor elevation and take it to the low point so it can drain. Put a heat tape inside and insulation outside to keep it open during cold weather. Or run it to a dry well (a hole full of gravel - deeper than frost depth) if regulations allow.
The second floor diaphragm may not resist the lateral soil pressures because you have two walls with no backfill and the front wall is nearly all door. I'm with Oldestguy on this; get some good geogrid, lay it into the block joints and run rebar thru it, make it as least 8 feet wide and use plenty of layers. It won't work well unless you compact the backfill, but just use a gas-engine wacker and don't try to compact within 2 feet of the walls. Or you can use crushed stone for all the backfill. Do the same with the wing wall and detach the wing wall from the garage because it is going to move.
I like concrete sand-gravel mixture for backfilling around the drain and up the wall to about 12 or 18 inches from the surface. Be sure at least 25% by weight is particles larger than the perforations. If you do this, you shouldn't use a sock.
Frost will penetrate the backfill horizontally several feet. If you put two inches or more of styrofoam against the wall before backfilling and the sand-gravel is at least two feet wide, you might be OK as far as frost pressures against the walls. Keep the styrofoam well below the wood framing and siding because termites can use it to access the wood.
Your floor slab and exposed footings are likely to experience frost heave. You can bury more styrofoam sloping down outside the footings to reduce the exterior cold source. The only way I can think of to prevent frost under the floor is to insulate and heat the interior. Your wife will love getting into a warm car with clear windows, so this will pay for itself.
Here's the disclaimer, my friend: these are concepts to consider. You need local professional advice for the specific dimensions and details.
Good luck