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Tying a concrete pad into a foundation

Discussion in 'Hardscaping' started by DLCO, Mar 12, 2013.

  1. DLCO

    DLCO LawnSite Member
    from Ontario
    Messages: 14

    I have read some conflicting opinions on whether this is a good practice or not. In an area where heaving is probable, is it a wise decision to drill rebar in to the house foundation? This was the practice of my previous employer, but some of what I have read is that this could cause the foundation to crack from the heaving of the pad. Some suggestions say that the pad should be completely seperate with expansion joint between the foundation.

    Assume also, that the grade has a good slope off, the clear base is very well compacted, the concrete is 6" thick and is very well enforced.

    I am starting on my own this year and do not want to be building pads for flagstone installation incorrectly

    Opinions? Experiences?
  2. alldayrj

    alldayrj LawnSite Gold Member
    Messages: 3,793

    Ive never doweled into a foundation unless it was an extension. I wouldn't do it.
    Posted via Mobile Device
  3. shovelracer

    shovelracer LawnSite Silver Member
    Messages: 2,008

    I've seen pads pinned to a foundation in the past and never seen it crack. I've never done it, but I could understand the concern as I see pads lift 2-3" in the winter from time to time. I vote expansion joint.
  4. DVS Hardscaper

    DVS Hardscaper LawnSite Fanatic
    Messages: 6,602

    Yes, i have seen slabs doweled into foundations all the time. And we have done this ourselves.

    Think about a walk out basement. With a door. If there is a concrete slab outside that door - chances are......the slab is doweled into the foundation. This way it doesnt move and no one trips.

    (dowelling into a swimming pool - different story. Dont do it.)

  5. dstifel

    dstifel LawnSite Senior Member
    Messages: 928

    I have never done it and i learned from my dad who has 40 plus years in concrete. We always use and expansion joint and caulk it so that water can't get in and freeze pushing the pad away from the foundation. But to each its own i suppose.
  6. JMMack

    JMMack LawnSite Member
    from PA
    Messages: 16

    the best (most expensive) way to do this is either pour the slab with a turn down frost wall or build a frost wall and pour on top of it. this is what I coordinate with our structural engineer on all commercial/school buildings for zero chance of slab heaving creating trip hazards or interfering w (and most importantly) the exterior door swinging open (as they do in all commercial/public buildings)

    no doweling into foundation
  7. shovelracer

    shovelracer LawnSite Silver Member
    Messages: 2,008

    This is what was done at my shop when they built it. I believe they went 18". The inspector expressed concern in the most severe winters, but apparently there was no violation so he didn't say any more, he was there for another reason. It has held up fine so far. On the the other hand we have a gov. account that had 6000sqft of walk tossed right up against the foundation with no expansion and not dowels. I has caused all sorts of problems with door opening, overdig settlement, and in one spot some expansion wall damage. So you need to do something.
  8. JMMack

    JMMack LawnSite Member
    from PA
    Messages: 16

    check local frost depths

    most of our projects frost walls/turn downs are 42" deep.
  9. shovelracer

    shovelracer LawnSite Silver Member
    Messages: 2,008

    Frost is 42" here as well. In our case the structure was at 42", but the pad was independently floating. I agree that the pad could lift and block doors at 18", but it is on 2' of gravel and in 3 years has not moved any measurable amount. It would theoretically be possible for an exterior pad with perimeter frost wall to lift as one entire unit if bad subgrade or moisture conditions existed under the pad. Most common scenario for a turn down to frost depth would be a walkout basement. If a pad existed outside the walkout I would keep it completely separate regardless of installation method. The only way I personally would tie it in would be if the entire structure was down to frost depth like you would commonly see in a front door masonry staircase. I would not interlock the block though as is sometimes done, because by doing so creates a situation where exterior deterioration could result in water infiltration into the structure. In that case I would say appropriate to have a separate structure doweled to make one semi permanent unit.
  10. bigslick7878

    bigslick7878 LawnSite Senior Member
    Messages: 809

    I have busted out tons of pads near foundations and can't remember one that was tied in to it. Always an expansion joint or just poured up against but never doweled in. (I will say most of these were poured long ago, very few new construction)

    I mean if you what happens if you have to remove it near the foundation for some reason? That would be fun.

    Unnecessary IMO. That pad isn't going anywhere.

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