When Plans Examiners Try to Apply the “CODE” to Pole Buildings
Today’s example happens to come from the State of Michigan, however it could happen in any Building Permit issuing jurisdiction in the U.S.
What is most interesting to me about this particular example is, last November I was invited to be a presenter at a meeting of Building Officials representing pretty much the northern half of the non-UP (Upper Peninsula) portion of Michigan. The topic was how the Building Codes apply to post frame (pole building) construction, and it was determined as a resultant, the Building Code could not be applied directly.
Let’s have some fun with plan reviews, shall we?
(plan reviewer comments in yellow, referenced Code in italics below)
Footing size indicated is too small, (minimum 28″ round x 12″ thick) for sidewalls, or provide load calculations for each column. R403.1 to MBC 1805.7
All exterior walls shall be supported on continuous solid or fully grouted masonry or concrete 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.
Following this section of the Code is a Table which gives footing requirements for conventional light-frame construction, 4-inch brick veneer over light frame or 8-inch hollow concrete masonry, or 8-inch solid or fully grouted masonry.
The Code reference does not address footings for isolated, widely spaced columns.
Carrier beam size indicated is too small, three – 2” x 12” carriers minimum, required to carry truss and roof load. Table R502.5 (1)
The Table referenced is for exterior bearing walls in stick frame construction, where the dead load weights of shingles, roof sheathing, and gypsum drywall must be accounted for. It also is based entirely upon ground snow loads, without factoring in the allowable adjustments for this particular building being heated, as well as having a slippery steel roof.
Footnote for most of my readers who are in parts of the country where trusses are attached directly to the columns – this particular pole building is designed with a single truss every four feet, sidewall columns every eight feet and a header (aka “carrier beam”) attached to the columns to support the trusses.
The Table is also based upon a uniform load, which would be applicable for instances where trusses were placed every two feet (ala stick frame construction). Instead the carrier beam, is supporting a concentrated load at the center and every other truss rests directly on top of a column. This effectively reduces the load being carried by the beam by 1/3!
Think of the load applied from a truss at two foot centers as being X. In an eight foot area, there would be an X at two, four and six feet or 3X. A truss at four foot only would carry twice as much load as a truss at two feet, or 2X. 2X divided by 3X = 2/3.
Carrier beam nail fasteners are sized too small and additional fasteners are required. Alternate structural screws, lags or bolts may be used. Submit revised fastener design. R 602.2
In my humble opinion, the Plans Examiner meant to reference R 602.3 which lists fastener schedules in Tables. The Tables do not even begin to address the connections found between a “carrier beam” and a column. The Plans Examiner appears to have possibly neglected to note the design presented has the carriers notched into the faces of the bearing columns, resulting in only enough fasteners being required to resist the uplift loads.
Buildings with an eave height 10′ or greater will require knee bracing or a full length diagonal brace in each corner. R301.1.1 to MBC1609.0, 2303.2
Buildings and structures, and all parts thereof, shall be constructed to safely support all loads, including dead loads, live loads, roof loads, flood loads, snow loads, wind loads and seismic loads as prescribed by this code. The construction of buildings and structures shall result in a system that provides a complete load path capable of transferring all loads from their point of origin through the load-resisting elements to the foundation.
It appears the reviewer’s comments are some sort of a local interpretation of how to handle the requirements of R301.1
I do believe I have previously presented an overwhelming case as to why not to use knee braces: https://www.hansenpolebuildings.com/blog/2012/01/post-frame-construction-knee-braces/
But what about a diagonal brace?
The entire concept of a diagonal brace in a wall is to assume the siding (in this case steel panels), lacks the ability to carry the shear loads being applied to the building.
Having been personally involved in the testing of light gauge steel panels, I can attest to their ability to carry a significant amount of load. (Read more at: https://www.hansenpolebuildings.com/blog/2012/08/this-is-a-test-steel-strength/)
Going back to the assumption of the siding not being able to carry the load, the building being reviewed has 1841.8 pounds of shear force being transferred to each endwall. Keeping things simple, let’s look at what it takes to even attach the suggested braces.
Generously assuming each brace would carry ½ of the applied load, each end of each brace must be able to have a connection adequate to carry around 921 pounds of force. A three inch long 10d common nail (3” x 0.148” diameter) driven through a 1-1/2 inch thick member into another member (assuming the weakest commonly used framing species) will support roughly 128 pounds. It is going to take a lot of nails in a very small area to make the connection work.
To have made this entire process quick, easy and simple for all involved, and to keep the Building Permit issuing authority out of the potential liability problems for being possibly construed as becoming the engineer of record, would be to simply require all pole building plans to be submitted with the seal of a registered design professional (engineer or architect) as well as the supporting calculations.
Which is exactly what this particular client opted to do. Case closed.