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Footing sizing - concrete walls or light stick walls? and snow load question

Discussion in 'Residential Foundation Codes' started by Dylan, Nov 7, 2017.

  1. Dylan

    Dylan Member

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    Hello All, this is my first post.

    I am trying to size a footing for a 7' ceiling height basement that will have a slab and 6' concrete poured walls (measured from top of footing to top of concrete) retaining 5' of dirt. supporting 1 wood frame story on top.

    this is in Seattle, here is our SRC:
    http://www.seattle.gov/dpd/cs/groups/pan/@pan/documents/web_informational/p2631466.pdf

    TABLE R403.1(1) is for light frame construction walls.
    TABLE R403.1(3) is for cast concrete walls.

    the stem walls are obviously going to be concrete, but then on top of that is my light frame construction... so which material are my "walls" and thus which table do I us?

    I am also trying to determine what the "snow load" is for my area. Any idea where I can find this?
    Thanks all
     
  2. cda

    cda Sawhorse

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    Welcome

    Home owner?

    Builder ??

    Designer ??

    Other?
     
  3. Dylan

    Dylan Member

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    All of the above, thanks
     
  4. Dylan

    Dylan Member

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    This is for a small extension on our house, I’ve done all sorts of work before but this is my first foundation work
     
  5. JBI

    JBI Sawhorse

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    Use the light frame wall table. These tables assume concrete foundation walls.
     
  6. JBI

    JBI Sawhorse

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    For snow load look in the beginning of Chapter 3, if the map is not clear, ask the local Code Official.
     
  7. Francis Vineyard

    Francis Vineyard Sawhorse

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    Dylan, the (ground) snow load is 25 psf. Use Table R403.1(1) for light frame construction with basement.
    Seatle.JPG

    Typically the soil is default at 1500 psf unless known or provided from the Building Official.

    In accordance with the footnote the footing may be reduced based on the following assumptions:
    18 ft. of tributary roof area
    16 ft. of tributary floor area
    8-ft. third floor height
    9-ft. second floor height
    10-ft. first floor height
    10-ft. basement wall height, 10-in. basement wall thickness, basement wall material weight of 125 pcf

    Footing.jpg

    It seems the Seattle Table values are different than my 2015, just saying.
     
  8. Dylan

    Dylan Member

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    thanks all!!

    This is great information, and I recognize the snow load stuff in CH3 now, so I must have found it previously at some point and forgotten.
    So if I use light frame (makes sense) and I assume 1500 for ground, 1 story plus basement, and 25 psi snow load I arrive between 18 " wide for 20 psi snow, and 19" wide for 30 psi snow. So my footing should be 18 1/2" wide. Does the fact my concrete wall will be 8" thick affect this sizing? (Due to more than 4 ft retained and seismic area D, it needs to be 8").I could in theory reduce the width a bit since the biggest distance from my existing structure is 12 ft. the chart says 32 ft with wall in middle, so this would be 16ft in my situation, that extra 4 ft would allow me to knock 4" off my width if I wanted, correct?

    It would also appear that I only need to put 1 #4 rebar (R403.1.3.1) in it all the way around with hooks corresponding to the necessary for my wall( #4 at 48 inch max spacing.) sound right? I will dowel this piece of footing rebar into my existing footing to tie the two together with 30" splices it looks like i need. It appears that I should have 12" of penetration into the existing footing! If this qualifies as a joint per 404.1.3.3.7.8

    thanks!
     
  9. Dylan

    Dylan Member

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    as a side question, do you usually put a hook right at the corner or 2 hooks, one just each side of the corner?
     
  10. Pcinspector1

    Pcinspector1 Platinum Member

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    Hook? Anchor bolt?

    See R403.1.6 and R403.1.6.1 for foundation anchoring, some of the spacing is dictated by your seismic zone and number of stories. Here we typically see an anchor bolt at 12-inches from the corner and every 6-feet with a minimum of two anchors in each plate. Also were there is a door opening we like to see an anchor on both sides of the rough opening a minimum of 6-inches back from the plates end.
     
  11. Dylan

    Dylan Member

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    sorry, I should have been more clear, I am not doing a monolithic pour since my walls are thick and tall, so footing first, then wall. I am referring to the rebar hooks that connect the footing to the wall.
     
  12. Dylan

    Dylan Member

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    anyone? I'll be doing the forms and rebar starting tomorrow.
     
  13. Msradell

    Msradell Sawhorse

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    The number and spacing of verticals coming out of the footing into the wall varies from area to area depending in many factors including soil conditions, seismic load factors, code cycle etc. The only way to be sure you do it correctly is to consult your local building code officials or a structural engineer that practices in your area. Even we splice length and spacing of Bars varies considerably.

    Without knowing these factors it's hard to say what you should use but quite often you see #4 bars @ 12"-18" spacing with a splice length of 2'
     

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