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Community and Q&A

Brick Drainage at Stone Patio

user-7709149 | Posted in GBA Pro Help on

Hello, we are building a custom house with brick siding. We have a stone patio in the back of the house which rests on the foundation and supports the brick (see picture and engineer drawing). All that we have to do now is put the flagstone and slope it.

However, the brick weep holes are located at the bottom course right on the concrete slab level. If we put 2” flagstone, 0.4” grout and slope it, the weep holes will get completely covered.

As a fix, we could drill new weep holes a course higher but that won’t solve the drainage issue as the flashing is at the bottom course and any large amounts of water would pool up there. My contractor also suggested taking out a brick and pouring some liquid mortar to fill the gap behind the first course of brick thus elevating the drainage plane. Would this work or create additional headaches?

What would you recommended I do? The last option would be to remove the bricks and redo it again with a higher water drainage pane (two or three brick courses higher).

Your advice is greatly appreciated. Thanks

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  1. Expert Member

    User ...149,

    I don't want to sound alarmist, but that whole detail is quite worrying. The rim-joist is vulnerable to any water making it's way into the vent channel behind the brick from above, but also from the patio itself. I'm not sure what the best solution is and will be interested to hear what other posters suggest.

  2. user-7709149 | | #2

    I kind of agree, the detail there was a bit odd, but it was one of the more reputable engineers that designed it. He’s done hundreds of houses in the area with similar designs so I assumed it must be ok.

    As an added layer of protection I had my roofer torch on the roofing membrane all around the patio to the sheathing so no water could get in there, going up 12” onto the sheathing and 6” over the patio slab. Even without brick on, no water was getting through with rain and snow. Even if some water collected between the brick and sheathing, I doubt it could get through that membrane as the seams are sealed, unless if it pooled to over 12” which is not likely.

    That said, any suggestions on what we can do to have a proper long term solution would be appreciated so we don’t have issues down the road. Thanks

  3. user-7709149 | | #3

    I have attached a photo of the roofing membrane flashing over the concrete patio slab and sheathing.

  4. Expert Member
    Akos | | #4

    This might a good discussion to look at.

    There are two issues here:
    -providing air flow to dry the cavity behind the bricks
    -draining bulk water away from the wall

    Adding in new weep holes fixes the first but doesn't help with the 2nd, if anything it makes it worse as now there is an nice path for water to drain into this area which is now essentially a mini trough.

    So, we need a way to manage bulk water. The best would be a covered patio.

    Outside of that most options are a bit of a hard to build. For example you can add a drainage path from the base of the wall trough the concrete slab similar to the trench drain in the discussion I linked to.

    A simpler but more of a hack would be to drill through the slab beside the existing brick weep strips and allow for the walls to drain into fill under the slab. This is likely to clog overtime though.

    Thinking about it more, the best scenario would be to include both above ideas. This way bulk water is managed by the trench drain and anything that makes it into the wall cavity can drain down and away from your rim joist.

  5. JustusM | | #5

    How much slope is on the existing concrete?

    1. user-7709149 | | #6

      Currently there is no slope, but we were going to put some tiles over the concrete slab and build a 2% slope with the tiles.

      1. JustusM | | #8

        That is not a good idea. If you are in an area with frost. Water will get through the stone and mortar, freeze and pop.

  6. Expert Member
    ARMANDO COBO | | #7

    2021 IRC R404.1.6 Height above finished grade. Concrete and masonry foundation walls shall extend above the finished grade adjacent to the foundation at all points not less than 4 inches where masonry veneer is used and not less than 6 inches elsewhere.
    I always wonder why so many folks that are in the business of designing and building homes never read the Building Codes. Really!

    1. user-7709149 | | #9

      I agree with your point, although technically I don’t think that it’s in breach of building code since the foundation does go more than 4” above finished grade (assume that means the ground). But it’s the rear patio concrete pad that’s elevated and sitting on the foundation itself that’s the issue in this case. We have the same issue on the front porch, though on a much smaller area.

      I’m sure there are hundreds of houses in this area with similar designs. I wonder how they dealt with this. How likely are we to have bulk water behind the brick? If it’s condensation it should dry out. I’m wondering if building channels could make things worse.

    2. Expert Member
      ARMANDO COBO | | #10

      NO. Sorry, but that detail you posted does not meet code. The fact that everybody is doing it that way, does not make it right. The fact that that is allowed by code officials is scary. The fact that the Architect and Builder don't know any better, it's sad.
      If you, your Architect, Builder or Building Official don't agree, any and all of you can argue with ICC, or better, y'all could write your proposal for ammendment on the next code change.
      EDIT: "How likely are we to have bulk water behind the brick?" Use a garden hose to spray water on a wall where you see the weepholes open, and watch water pour out of the weepholes in a short while. This is not rocket science.

      1. user-7709149 | | #11

        Thanks Armando. It’s sad to see that people who we trust, and pay considerably, don’t follow the basics of building code.

        Unfortunately, as a homeowner we’re left to deal with the consequences. What would you suggest I do in this case? Would building a small channel below the stone tile say about an inch or two wide and 3 inch tall for the water to escape from the weep holes to it, and then out the sides be acceptable? I could also drill some holes so water can drain below the concrete slab as well.

        Alternatively, I could get the brick guys to remove a course of bricks and raise the flashing to the second or third row of bricks?

        If neither solution works, is there an alternative? At this stage we can still make changes at a cost, but once everything is finished it will be that much more difficult to do.


      2. Expert Member
        ARMANDO COBO | | #13

        I've never have had to fix an issue like this. The concrete slab should be at least 4" below the top of the concrete basement wall. I would imagine that would be an expensive fix now.
        Even if you remove some brick to flash behind, some moisture could get behind the foam above the wall. Maybe some of the guys here that are more familiar with remodels or fixing stuff have a good idea.

  7. Expert Member
    Deleted | | #12


  8. user-7709149 | | #14

    We could create a channel drain below the patio tiles adjecent to the first course of bricks as shown in the diagram below.

    We could shave off an inch or two of the concrete slab to make part of the channel go below the top of the foundation, and have it slope to the sides of the patio deck for drainage.

    Also, we can torch another layer of roofing membrane over the channel, just below the tile, so that no surface water can get into the channel, but only the water that comes from the brick weep holes can go in there.

    In addition we can drill some holes in the channel all the way through the concrete slab down to the gravel below for extra drainage. Also we’d put some steel mesh at the exits of the channel drain to make sure no critters can get in there.

    Let me know if you think this can work. It’s not ideal, but think it should be ok. Your thoughts are appreciated.


  9. Expert Member
    MALCOLM TAYLOR | | #15

    User ...149,

    That looks like a good solution to me.

  10. user-7709149 | | #16

    Thanks for the recommendations everyone, and especially Akos. I think this is the only feasible solution, outside of tearing up the whole patio and brick siding.

    The only issue is how big does the channel need to be? Would 4” high by 1.5” wide be sufficient? Or should I go 5x2”? I can likely go 1.5” into the concrete slab without affecting its integrity given it’s 6” thick.

    Any other concerns with this approach, please let me know. Thanks

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