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Thread: 3" Pad Rule

  1. #1
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    Default 3" Pad Rule

    I just wanted to confirm what others are doing in regard to the 3" pad rule for being in place under the exterior AC system. Are you still calling out a "missing pad" when the (newer) unit has built-in feet at the lower frame?

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  2. #2
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    Default Re: 3" Pad Rule

    I call it out as a recommendation, not as a requirement. I've never seen feet like that. Highly doubt those are factory, I'd write'em.

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  3. #3
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    Default Re: 3" Pad Rule

    Quote Originally Posted by Markus Keller View Post
    I've never seen feet like that. Highly doubt those are factory, I'd write'em.
    They're not factory, but they are required.

    We have to have an "engineered" hold down strap in these parts as well, or else the permit won't get approved.


  4. #4
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    Default Re: 3" Pad Rule

    Quote Originally Posted by Dom D'Agostino View Post
    They're not factory, but they are required.

    We have to have an "engineered" hold down strap in these parts as well, or else the permit won't get approved.
    And those are not "engineered" and would not, should not, be approved by the inspector.

    Jerry Peck, Construction / Litigation Consultant
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  5. #5
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    Default Re: 3" Pad Rule

    I'm not sure why you would call out the supports as NON Engineered. They look like they have been secured to the unit and to the concrete to keep the unit from moving which is much better than sitting the unit un-secrued on a 3" pad.


  6. #6
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    Default Re: 3" Pad Rule

    Permit/approval search warning.

    Appears to also be encroaching/blocking required maintenance and egress/exit pathway and if the block wall/fence is a sideyard deliniator, possibly zoning. Presumptively this is located at a sideyard of the building.

    Generally those units also require "free air" space of a minimal distance on the side(s). Panel of the appliance and fittings require clearance/access.

    Unknown topography, may have required higher elevation - depends on the site plan, drawings, etc. required to bave been submitted when the instant unit was installed (with a permit, approval, and inspection). Note, the vast majority of your state has differing seismic zones and fire control zones, of significance as well.

    Looks like isolation springs such as when shipping bolted to pallets, top-heavy, vibration sensitive equipment in non-air-ride-equipped van-trucks.

    Last edited by H.G. Watson, Sr.; 04-01-2011 at 10:17 AM.

  7. #7
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    Default Re: 3" Pad Rule

    Quote Originally Posted by Rod Butler View Post
    I'm not sure why you would call out the supports as NON Engineered. They look like they have been secured to the unit and to the concrete to keep the unit from moving which is much better than sitting the unit un-secrued on a 3" pad.
    The reason those are installed is to tie the condenser unit down to the pad, and the only way to do that properly is to have an engineer determine the proper wind loading (and other applicable loads), and assess the strength (or lack thereof) of a given strap, and to specify how many of what size anchors (fastener screws) are needed from the strap to the unit and from the strap to the pad to resist the loads previously determined.

    Just Friday afternoon the owner of the major manufacturer of tie-down clips spent the afternoon in our office talking with the building official and myself, during the conversation I made several suggestions that he will be putting into his product and the engineering for his product. Changes which should make it easier for the mechanical contractor to install the tie-down clips properly, and which would also make it easier for code inspectors to properly inspect and approve the tie-down clip installation.

    If you live inland with limited wind speeds, you probably only need to anchor the condenser units down with anchors down through the bottom of the unit to the pad, but ... "how" do you know that the method of anchoring will be adequate? That answer, even in inland areas, is "was it done in accordance with the engineering?"

    The old easy was was to just shot pin the unit to the concrete pad, but there was no engineering which said what size pins, what strength/alloy metal, how much penetration into the concrete, what size washer, etc., and without that information how would you know if it was adequate?

    Now add height above grade to that equation other factors such as mounted on one-story, two-story, three-story, seven-story, etc., building with higher wind pressures and the anchoring changes.

    Oh, they are also not "supports", they are "restraints" as in "tie-down restraints" to hold the unit down and in place, versus "supports" which would support the unit and hold the unit up.

    Jerry Peck, Construction / Litigation Consultant
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  8. #8
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    Default Re: 3" Pad Rule

    Jerry and HG please read the OP question he was asking about the PAD not the hold down straps.


  9. #9
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    Default Re: 3" Pad Rule

    Quote Originally Posted by Mike Inspector View Post
    Jerry and HG please read the OP question he was asking about the PAD not the hold down straps.

    Mike,

    Please read the quoted posts I am replying to.

    That should end your confusion as to what is being said and why.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  10. #10
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    Default Re: 3" Pad Rule

    The absent pad wouldn't both bother me. The clearance around the sides would.

    Eric Barker, ACI
    Lake Barrington, IL

  11. #11
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    Default Re: 3" Pad Rule

    I have never heard of a requirement for an engineered anchor for a condenser on a slab on grade. That must be a local requirement.

    I have heard about a planning dept. requirement that they be at least five feet from a property line and I suspect this one is between a dwelling and a side yard property line. Some jurisdictions require a specified distance to any neighboring window.

    As to blocking an egress path, the front door is the only required egress door unless the dwelling is over 3000 sq. ft. There may be another path of egress on the other side of the dwelling if one is required.

    The clearances required to obstructions vary from one manufacturer to another. Some require 6" to 10" clearance on one side and more on the remaining three sides but since they are different with each maker, i look at the installation instructions.

    Another thing to consider is does the manufacturer allow the unit directly under a roof overhang. Several require a rain diverter over the unit.

    It wouldn't hurt to secure the liquid-tight within 12" and bit of foam where the lines come through the vent to keep out mice.

    Where is the disconnect?


  12. #12

    Default Re: 3" Pad Rule

    Quote Originally Posted by Markus Keller View Post
    I call it out as a recommendation, not as a requirement. I've never seen feet like that. Highly doubt those are factory, I'd write'em.
    Those are not "feet', they are seismic hold downs to keep the unit from walking away during an earthquake.

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  13. #13
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    Question Re: 3" Pad Rule

    I'm not sure what this 3" pad rule is.


  14. #14
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    Default Re: 3" Pad Rule

    Quote Originally Posted by David Bertrams View Post
    I have never heard of a requirement for an engineered anchor for a condenser on a slab on grade. That must be a local requirement.

    I have heard about a planning dept. requirement that they be at least five feet from a property line and I suspect this one is between a dwelling and a side yard property line. Some jurisdictions require a specified distance to any neighboring window.

    As to blocking an egress path, the front door is the only required egress door unless the dwelling is over 3000 sq. ft. There may be another path of egress on the other side of the dwelling if one is required.

    The clearances required to obstructions vary from one manufacturer to another. Some require 6" to 10" clearance on one side and more on the remaining three sides but since they are different with each maker, i look at the installation instructions.

    Another thing to consider is does the manufacturer allow the unit directly under a roof overhang. Several require a rain diverter over the unit.

    It wouldn't hurt to secure the liquid-tight within 12" and bit of foam where the lines come through the vent to keep out mice.

    Where is the disconnect?
    Obviously not new construction photographed.
    Secondary escapes, EEROs require exit paths under earlier California Codes.

    This new 3,000 sq. ft. threshold exemption for EERO exit paths in California, please provide citations.

    I am interested to learn more about this rodent barring "foam" you suggest. Please provide details.


  15. #15
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    Default Re: 3" Pad Rule

    Quote Originally Posted by H.G. Watson, Sr. View Post
    Obviously not new construction photographed.
    Secondary escapes, EEROs require exit paths under earlier California Codes.

    This new 3,000 sq. ft. threshold exemption for EERO exit paths in California, please provide citations.

    I am interested to learn more about this rodent barring "foam" you suggest. Please provide details.
    EERO shall open to a yard, court or public way. Nowhere does the code require an unobstructed path from the rear yard to the street. The 3000 sq. ft. is derived from the occupant load factor that triggers a requirement for a second exit and has nothing to do with an EERO. The foam is insulation. The foam gets used to seal the bottom of freon line chases and small openings at foundation vents. It looks terrible and is a lazy man's fix but it seems to work.


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