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Fndtn height above grade?

Discussion in 'Residential Foundation Codes' started by rktect 1, May 5, 2015.

  1. rktect 1

    rktect 1 Gold Member

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    2006 IRC

    So, I have a person who wants to place an all aluminum framed, non conditioned, sun room at grade. They want to cut through the existing concrete patio, 12" wide and pour a trench foundation to 42" below grade. It will be even/level with the existing patio at grade. But section 404.1.6 requires the foundation to be 6 inches higher than grade. The commentary for the code says this is for termite control as well as for minimizing the chance of decay.

    Well its aluminum, so neither of those will affect the structure. A reduction is specifically called for if masonry exterior is being used. You can drop to 4 inches.

    Common sense?

    How about, where in the code does it allow for the 16 foot wide entry through the overhead garage door to be reduced to grade level?
     
  2. mark handler

    mark handler Sawhorse

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    Covered, enclosed Patio

    Approved, as submitted
     
  3. jdfruit

    jdfruit Registered User

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    If the sun room is a complete package and "listed" such as ICC eval report; then the foundation must comply with the listing. Most I have dealt with recently called for a min of 4" from concrete floor slab to adjacent exterior grade (earth or pavement).
     
  4. mark handler

    mark handler Sawhorse

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    Never seen one that specifies the "floor"; just the footings
     
  5. retire09

    retire09 Silver Member

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    The finished floor level of habitable spaces are to be 6" above grade for drainage purposes. The termite and decay concerns can be dealt with by using all weather materials. If the space in considered habitable you also have heat, ventilation and electrical requirements to provide. Just like the garage you mentioned.
     
  6. mark handler

    mark handler Sawhorse

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    Covered, enclosed Patio Not habitable space
     
  7. retire09

    retire09 Silver Member

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    I agree. Just like the garage.
     
  8. Frank

    Frank Registered User

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    Ummmm where does it come from that the floor of a habitable space cannot be below grade? 404.1.6 talks about the top of the concrete foundation wall. What about walkout basements and habitable rooms in basements? What about slab on grade construction with same level entrance slab for accessibility? Section 506 for concrete floors has no distance to grade requirement. R310.1 talks of bedrooms in basements. Drainage does have to be assured--for commercial accessibility MAXimum slope of 1:48 at landing and for drainage Minimum of 1:50 slope-- hope your concrete guy is very good and your ground does not move with the seasons
     
  9. steveray

    steveray Sawhorse

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    Attached or detached?
     
  10. JBI

    JBI Registered User

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    2012 IRC Selected provisions (none of which require clearance above grade BTW)

    R4031.7.3 Foundation elevation On graded sites, the top of any exterior foundation shall extend above the elevation of the street gutter at point of discharge or the inlet of an approved drainage device a minimum of 12 inches (305 mm) plus 2 percent. Alternate elevations are permitted subject to the approval of the building official, provided it can be demonstrated that required drainage to the point of discharge and away from the structure is provided at all locations on the site.

    R403.3.1.1 Attachment to unheated slab-on-ground structure.

    Vertical wall insulation and horizontal insulation of frost protected shallow foundations that adjoin a slab-on-ground foundation that does not have a monthly mean temperature maintained at a minimum of 64°F (18°C) shall be in accordance with Figure R403.3(3) and Table R403.3(1). Vertical wall insulation shall extend between the frost protected shallow foundation and the adjoining slab foundation. Required horizontal insulation shall be continuous under the adjoining slab foundation and through any foundation walls adjoining the frost protected shallow foundation. Where insulation passes through a foundation wall, it shall either be of a type complying with this section and having bearing capacity equal to or greater than the structural loads imposed by the building, or the building shall be designed and constructed using beams, lintels, cantilevers or other means of transferring building loads such that the structural loads of the building do not bear on the insulation.

    R403.3.1.2 Attachment to heated structure.

    Where a frost-protected shallow foundation abuts a structure that has a monthly mean temperature maintained at a minimum of 64°F (18°C), horizontal insulation and vertical wall insulation shall not be required between the frost-protected shallow foundation and the adjoining structure. Where the frost-protected shallow foundation abuts the heated structure, the horizontal insulation and vertical wall insulation shall extend along the adjoining foundation in accordance with Figure R403.3(4) a distance of not less than Dimension A in Table R403.3(1).

    Exception: Where the frost-protected shallow foundation abuts the heated structure to form an inside corner, vertical insulation extending along the adjoining foundation is not required.
     
  11. rktect 1

    rktect 1 Gold Member

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    It is an attached, covered, not heated or cooled aluminum structure with glazing. It will be given a foundation that is 12" wide and 42" below grade. But they want the top of the foundation set equal to the patio. The patio is at grade or maybe 1" above grade.
     
  12. mtlogcabin

    mtlogcabin Registered User

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    Appendix H cover patios and refers to R506 for slab on grade. No minimum height above ground is defined
     
  13. retire09

    retire09 Silver Member

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    Back in the 80s under the uniform building codes, I would have sworn that there was a minimum finish floor height of 6" above grade for buildings in addition to the 12" plus 2%. Was that never there? Was that just a common detail shown on foundation plans?

    I'm old and I sometimes remember things that never happened.
     
  14. Builder Bob

    Builder Bob Sawhorse

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    General requirement, garage floors must slope towards opening -SECTION R309 GARAGES AND CARPORTS

    R309.1 Floor surface.

    Garage floor surfaces shall be of approved noncombustible material.

    The area of floor used for parking of automobiles or other vehicles shall be sloped to facilitate the movement of liquids to a drain or toward the main vehicle entry doorway.

    - specific
     
  15. Pcinspector1

    Pcinspector1 Platinum Member

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    Patio covers are NOT considered habitable rooms requiring it to be conditioned.

    Might let the customer know that a six inch snow could melt and over time could find away to migrate into the new space.

    The dude that builds it will be the one cursed at down at the local cafe!

    pc1
     

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