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pier construction question?

Discussion in 'Residential Foundation Codes' started by Pcinspector1, Nov 9, 2011.

  1. Pcinspector1

    Pcinspector1 Platinum Member

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    Plans have been submitted for a 12x12 storage room attached to the back side of an existing garage with no entry into the garage from the storage side. The plans call for the storage room to have a pier placed at all corners and every 6ft. (Total of 9 piers) The piers closest to the garage back wall will be pinned into the garage foundation with rebar. Rebar extending from the piers will be connected to a 6" slab with rebar above the top of the piers. All of this appears to be a way to get around pouring a footing. Has anyone seen this done before, would it be allowed by code?

    pc1
     
  2. JBI

    JBI Sawhorse

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    Sounds like they're taking the 'scenic' route.

    Will the soils support the loads being tranferred throught the piers?

    Are they aware that they could leave three feet between and just have a slab floor?

    Is there a DPR seal/signature on this non-prescriptive design?
     
  3. Keystone

    Keystone Sawhorse

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    From the information provided, piers are okay so long as these are the carry/points of load but rebar from piers into existing foundation can be problematic. You have know way of definitively knowing how deep the existing foundation is and no way of knowing how the slab is tied into the foundation. A concern would be uneven heave during periods of weather changes such as periods of rain causing saturated ground, dry periods, cold periods.
     
  4. iggentleman

    iggentleman Bronze Member

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    Sounds like a carport with walls.

    I was called in to fix a project like that last year. Enclosing a covered porch, turning it into a family room. A contractor had started (without a permit) and abandoned the job when the inspectors shut him down. We looked at doing the walls with double 2x beams at the top and bottom of the columns, to carry the roof on one and the wall on the other, but because of the frost heave and windbracing problems we had the new contractor tear it down and start over.
     
  5. Mark K

    Mark K Platinum Member

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    Piers are often used when there is a concern about poor quality soil near or where expansive soil is a concern. Piers are addressed in the IBC.

    It is not uncommon that if the original structure was on pier foundations to place the addition on piers also.

    Would normally expect such a design to be engineered by a registered engineer.
     
  6. DAYWALKER

    DAYWALKER Bronze Member

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    I always require the applicant to grab a posthole digger and determine the depth of the existing foundation.

    Then match existing to avoid differential movement. Piers.......are always engineered.
     
  7. rktect 1

    rktect 1 Gold Member

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    Attached to the back of a detached garage or attached garage.

    As an accessory structure I could allow this but if attached to the house then it would need to be signed and sealed.
     
  8. Darren Emery

    Darren Emery Sawhorse

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    Pier and beam foundation - we have one contractor locally that uses this on residential all the time. The beam must be designed to carry standard loads, as well as resist uplift from frost/expansive soils. Not in the book - PE required.
     
  9. steveray

    steveray Sawhorse

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    I think the 2009 IRC clarified this and says all post and pier structures are to be engineered......or something to that affect.........
     
  10. gbhammer

    gbhammer Platinum Member

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    Dig big hole, drop in contractor, fill hole, and call geotech engineer.
     
  11. Keystone

    Keystone Sawhorse

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    So pier and beam foundation have to be engineered, then what say you on decks?
     
  12. mtlogcabin

    mtlogcabin Sawhorse

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    Are you talking about masonry piers or sono tube piers?
     
  13. steveray

    steveray Sawhorse

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    R602.10.7 Braced wall panel support. Braced wall panel support shall be provided as follows:

    1. Cantilevered floor joists, supporting braced wall lines, shall comply with Section R502.3.3. Solid blocking shall be provided at the nearest bearing wall location. In Seismic Design Categories A, B and C, where the cantilever is not more than 24 inches (610 mm), a full height rim joist instead of solid blocking shall be provided.

    2. Elevated post or pier foundations supporting braced wall panels shall be designed in accordance with accepted engineering practice.

    3. Masonry stem walls with a length of 48 inches (1220 mm) or less supporting braced wall panels shall be reinforced in accordance with Figure R602.10.7. Masonry stem walls with a length greater than 48 inches (1220 mm) supporting braced wall panels shall be constructed in accordance with Section R403.1 Braced wall panels constructed in accordance with Sections R602.10.3.2 and R602.10.3.3 shall not be attached to masonry stem walls.

    See # 2......no BWP...its OK
     
  14. JBI

    JBI Sawhorse

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    steveray, you can't grab a random section from chapter six and apply it to footings. It doesn't work that way, read the applicability of chapter six. There are however provisions in chapter four that speak to the subject. For 'continuous' footings, the requirement is specific to supporting exterior walls (see underlined portion of R403.1 below from 2009 IRC). Decks have no walls (otherwise it'd be a porch) therefore continuous footings are not required. Columns are also specifically addressed, and are to be sized based on tributary load and soil bearing capacity (see underlined portion of R301.1.1 below). You are correct that a Design Professional may not be required, but took the wrong path to get there... The OP is clearly not a prescriptive approach and will require a DP to design.

    SECTION R403 FOOTINGS

    R403.1 General. All exterior

    walls shall be supported on continuous solid or fully grouted masonry or

    concrete footings, crushed stone footings, wood foundations, or other

    approved structural systems which shall be of sufficient design to

    accommodate all loads according to Section R301 and to

    transmit the resulting loads to the soil within the limitations as determined

    from the character of the soil. Footings shall be supported on undisturbed

    natural soils or engineered fill. Concrete footing shall be designed and

    constructed in accordance with the provisions of Section R403 or in

    accordance with ACI 332.

    R403.1.1 Minimum size. Minimum sizes for concrete and masonry footings

    shall be as set forth in Table R403.1 and Figure R403.1(1). The footing width,

    W, shall be based on the load-bearing value of the soil in accordance with Table

    R401.4.1. Spread footings shall be at least 6 inches (152 mm) in thickness, T.

    Footing projections, P, shall be at least 2 inches (51 mm) and shall not exceed

    the thickness of the footing. The size of footings supporting piers and columns

    shall be based on the tributary load and allowable soil pressure in accordance

    with Table R401.4.1. Footings for wood foundations shall be in accordance with

    the details set forth in Section

    R403.2, and Figures R403.1(2) and R403.1(3).
     
  15. steveray

    steveray Sawhorse

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    Thanks JBI.....not speaking specifically about footings, the whole force resisting system as a unit and how each piece transmits force to the next....if you just take that section as it reads, you can't really do cantilevered floors with exterior walls....but you find that in chapter 5....anyway...rooms on piers have been allowed around here for a long time (without engineering) and I am trying to find every way possible to educate the builders as to why they need a DP for these, and I think you have just given me one more code section for my reasoning...

    The column issue is that there is no tables in the IRC that address column bearing capacity.....I have spent far too much time with builders that have no clue about loading that are attempting to post down 25,000+ pounds in a Mcmansion.....and when lally columns start failing and I have to check for compression perpendicular to the grain on the PT sill, someone is working waaaay past their ability.....
     
  16. Francis Vineyard

    Francis Vineyard Sawhorse

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    Guess I haven't seen it because it doesn't work; why to attach it to the garage other than aesthetics and if the eave height is less than 10 ft. would simplify to build it as a free standing accessory structure with piers or no piers.

    2009 exempt permit for accessory structures 200 sf. or less.
     
    #16 Francis Vineyard, Nov 17, 2011
    Last edited by a moderator: Nov 17, 2011
  17. righter101

    righter101 Gold Member

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    Good topic.

    I finished building my new house earlier this year. Got my CofO.

    Now I want to build a covered porch over one of the doors. Basically, bear on the existing top plate, come out 8 or 9 feet to two posts, and have a roof over that area. (and covers part of a deck, less than 30 inches above the ground)

    Can that be done prescripively, with the posts supported on piers???? Why or Why not?

    This has been a subject of disagreement amongst our staff and I would like to have opinions of others.

    One of the opinions is that IRC 301.2.2.2.5 "Irregular Buildings", specifically #2, "When a section of floor or roof is not laterally

    supported by shear walls or braced wall lines on all edges."

    would govern a covered porch.

    I don't subscribe to that arguement, but would be curious to other opinions.

    Don't mean to hijack the thread, but it is a similar train of thought.

    thanks
     
  18. Pcinspector1

    Pcinspector1 Platinum Member

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    Francis, good question?

    Our city municipal code requires accessory structures to be 10ft from the main structure. This property for one is on a corner lot reducing the applicants ability to use parts of the lot due to the property's road side yard being treated as a front yard required by zoning rules. The backyard has a large swale and wide utility easment which a building can not be placed apon. The property has a large deck which takes up a large precentage of the back yard. While helping this residence he ask could a shed be attached to the back side of his garage. The classification changed to attached storage from a U-classification and the plans were submitted with piers instead of footings, which was IMO to save money. A shed over 200sf is exempt by building code as you have posted, but our city requires a permit for sheds as well as an addition to the main structure. There is no entry from the storage room into the garage as I previously posted, the garage has existing exterior siding and drywall which will remain inplace. I would have prefered footings be used instead of piers and this was the first time I have delt with this type design and application.

    pc1
     
  19. Francis Vineyard

    Francis Vineyard Sawhorse

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    pc1,

    I've had similar dealings with our zoning department; when we discussed what they considered attached which is different than the building code we realized their definition was ambiguous and difficult to enforce; could be attached with a rubber hose. Just my 2 cents as a possibility may be worth looking into.
     
    #19 Francis Vineyard, Nov 18, 2011
    Last edited by a moderator: Nov 18, 2011
  20. globe trekker

    globe trekker Sawhorse

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    Since it is an attached structure, won't they have to comply with fire resistance construction

    also ( refer to Section R302.1, 2009 IRC )?

    .
     

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