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Waterproofing/setting elevation vs. grade

Nat . | Posted in General Questions on

This feels like a stupid question but just to make sure I’m not missing something obvious here.

New construction, I’ll have a full basement. Typical framing would sit my 12″ ground floor joists on my plate on my wall. If I want a min. of say 8″ of concrete above grade that puts me close to 2ft above grade. This means at least 3 or 4 steps in. I can live with that at the main entrance. At the rear I’ll have a patio (pavers on base) – It would be nice to not go down/up 3-4 steps to the patio and I see lots of patios flush or down one step.

After inquiring I’ve got on architect that says they just run the basement wall waterproofing up and cover the sheathing and plates to do a flush patio. This feels like a tremendous amount of faith in the watererproofing to me.

The only other option I can think of is that at the one patio wall we bring the top of concrete wall high to match top of joist, then put our plate directly on the wall thus getting an extra ~12″ of concrete and maybe save a step or two.

Anything I’m missing here as to a typical way to do this?

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Nat,

    This has come up a couple if times here over the years. Some builders, like David Meilland, have done as your architect suggested, applying a waterproof membrane covered by protective flashing, and leaving a gap between the patio and wall. Some like Martin, believe it's just not a good idea. My own feeling is that it's a detail that needs a really good builder (like David) and conscientious owner to work well over time.

    One alternative is to extend a portion of the thickness of the foundation up to the level of the subfloor where the patio will be, leaving enough at the regular height for either a sill-plate, or just enough for the rim-joist and the joists get supported on hangers.

    Whichever option you choose, remember to think through how the patio transitions to the height of the regular grade on each side. You will need steps or retaining walls, and whatever protection you use at the patio needs to extend beyond the sides for some distance.

    A third option is extend the concrete ledge detail right round the foundation, so the whole house shares the friendly transition to grade, much as you have with slab construction.

  2. Expert Member
    Michael Maines | | #2

    Nat, I would not risk relying on foundation waterproofing to be a long-term solution, but I regularly provide a shelf in the foundation so the floor joists can be dropped closer to grade. The foundation contractor will just rip rigid foam to the dimension needed. According to the IRC, the foundation wall just needs to be at least as wide as the wall above.

  3. Shaun A | | #3

    We have used floor trusses and done a top chord bearing truss. Which is kind of what you are talking about. The foundation wall would come all the way up and your top chord would bear on top of the wall. This would obviously call for using trusses and not typical joists.

  4. Nat . | | #4

    Thanks. Sounds like there are no tricks. I can't stomach relying on the waterproofing.

    If I was starting over I'd do the ledge detail but I've got a signed concrete contract in place and a lot of other details drawn. To provide a ledge at this point I'd have to thicken my wall (currently 8"). I may just have to live with the steps down. I am considering raising the wall locally only at one side where the patio is, this is a parallel to joist condition so no ledge to worry about. If I do that though they'd have to get the wall step spot on or the subfloor will need some work. Seems like steps are the safe bet at this point.

    1. Expert Member
      Malcolm Taylor | | #5

      Nat,

      You probably don't want a deck or you wouldn't be asking the question, but what about a hybrid? You could have the patio a few feet from the house and a small width of deck linking the flush entrance to it.

      For different reasons I ended up with a hybrid patio. This is the view looking down from my from my upper garden.

  5. Expert Member
    Akos | | #6

    You can use top flange hangers for your floor joists and hang them off the bottom plate directly inside your foundation.

    https://www.strongtie.com/topflangehangers_engineeredwoodconnectors/its-mit-hit_productgroup_wcc/p/its.mit.hit

    Bit more work, but not that much extra. I've used this detail for hanging joists of I beams, can't see why it wouldn't work here as well.

    1. Expert Member
      Malcolm Taylor | | #7

      That would work well. Probably a lot easier than monkeying around with the foundation walls.

      Another option along those lines would be to set a pt ledger into the inside of the forms, and use regular joist-hangers.

    2. Expert Member
      Michael Maines | | #8

      I like this idea. I like the top-chord bearing truss that Shaun A mentioned as well, but to meet code they would likely need to be covered with drywall, whereas 2x10 or 2x12 joists can remain exposed. Some people want finished basements but in my experience that's usually something that happens well after moving in. Of course if a fire started in the basement the top-flange hangers would be the first thing to fail...

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