Tag Archives: deflection limits

Stucco for My Post Frame Home

Stucco For My Post Frame Home

Reader SHAWN in WASHINGTON writes:

“I’m about to build a 110’x 50′ pole frame house using sono tube piers and wet set brackets. I am wanting to use the 1 coat (lighter weight) stucco on full exterior my question/ concern is what options do Ii have for my grade board contacting earth and also the transition of bottom of stucco on face of grade board? I have so much money in my land that I was really trying to save by not pouring a footer. Galvanized metal grade board? Wrap bottom and face of grade board with a custom j metal trim? Want it to be appealing to the eye with stucco stopping a few inches above ground level and just a few inches of grade board showing. Just want my grade board to last longer than 30-40 years since I will have roughly $600,000 in my house. My initial house design, but have changed it to stucco only with no rock more like other photo.”

Mike the Pole Barn Guru says:

Of concern with your use of stucco, in general, is limiting wall deflection to L/360. This can be accomplished, however it will often require larger dimension and/or higher graded wall columns (often glulaminated). Wall girts will need to be bookshelf style. In order to confirm deflection limits are indeed adequate, your post frame home’s structural plans should only be designed by a Registered Professional Engineer. Failure to meet this high degree of frame stiffness will result in failure of your stucco.

Successful stucco installation obviously requires a solid substrate (typically OSB or plywood). Either of these must be no closer to grade than six inches, unless properly pressure preservative treated (or a material otherwise impervious to decay). You might want to consider sheathing lower four feet of your wall with Foundation Rated (FDN) CDX plywood or cement board, so you can run it even down to grade, if desired.

Your grade board (splash plank) can be special ordered as UC-4B pressure treated. This level of treatment is good in the ground for longer than anyone alive on our planet to witness it failing. Our clients, who have been using stucco, have merely finished the bottom of it with a weep screed and called it a day. In all reality, no one except you is ever going to look at or notice how this is detailed.

Staging Deliveries for DIY Pole Buildings

For those who are considering a Do It Yourself (DIY) post frame barndominium, shouse or just a good old barn – not everyone can work at it expediently, or rouse enough person power for a barn raising. There do exist some options.

Reader LEE in LOUISIANA writes:

“I am in the process of conceptual design for an implement barn. However, my preference is to skin the exterior barn with old, milled reclaimed fir that I have available to me. From what I have found online, most Pole Building companies offer standard designs with conventional metal siding. However, it is my understanding that the same structural design for a metal building will not be adequate for the extra weight of woodplank siding, in lieu of the higher static and dynamic structural loads. Additionally, I would like to do most of the construction labor myself (with assistance from friends with construction background), in the interest of spreading out the construction process in different phases. As such, for this case, I am inquiring about a service to provide custom, stamped plans for a pole barn. I have read the advice and recommendations regarding engineered, stamped plans, and that it is not Hansen’s position to be in the ‘plans’ business. However, in this particular case, could Hansen work with me to provide custom, stamped plans to accommodate my preferred execution plan? I look forward to hearing your response. Thank you, Lee”

Mike the Pole Barn Guru  writes:
Actually structural design changes in post frame buildings are due to deflection limitations. Walls supporting other than just steel siding and/or steel liner panels do not have to be as stiff as ones to support other products (such as your reclaimed fir). While we do not supply engineered plans only, we can work with you to stagger deliveries to meet your phase schedule. If an impending price change to a component would occur, you would be given an option to either take delivery, or to delay delivery and pay differences in component costs. Your Hansen Pole Buildings’ Designer can further discuss this with you.

I would recommend using a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) under your barn boards, in order to keep any potential moisture from passing through your walls from outside.

For extended reading about Code requirements for Weather Resistant Barriers please see: https://www.hansenpolebuildings.com/2019/04/ibc-requirements-for-building-wrap/.

Gypsum Board on Walls

If it is weird, strange or otherwise just bizarre, when it comes to pole buildings, chances are it will eventually come across my desk. Otherwise I would have run out of material to write articles about a long, long time ago.

And it is rewarding to know I’ve got lots of loyal readers – like my friend Vincent….when technology failed last week and an article wasn’t up right away one day last week, he let me know how saddened he was, as he reads them every day at lunch!!

Back to the otherworldly….

We have clients who are constructing two fairly good sized buildings for the growing of green leafy substances which are entirely legal (although highly regulated) in two states currently – Colorado and Washington. The buildings were ordered with framing to support steel wall liner panels, so evenly spaced up the walls, the girts are every 34-1/8 inches on center. All well and good, for steel.

However, the clients have now determined they would like to have gypsum board drywall (aka sheetrock) on the inside of the exterior walls. It appears this decision may be due in part to their Building Official deciding the Building Occupancy Classification F-1 structures are somehow not allowed to have steel liner panels over insulation….we’re awaiting the section of the Code (2012 International Building Code) which would have this stipulation, as currently we have been unable to find it.

The determiner on whether gypsum board will work in any given application is going to be deflection.

“IBC 1604.3 Serviceability. Structural systems and members thereof shall be designed to have adequate stiffness to limit deflections and lateral drift.”

green-drywallIBC TABLE 1604.3 DEFLECTION LIMITS addresses the allowable deflection as “l” – the distance being spanned divided by a given unit of acceptable deflection. For exterior walls with flexible finish (such as gypsum drywall) under a wind load, this limitation is l/120. And from Footnote “f” of the table, “The wind load is permitted to be taken as 0.42 times the “component and cladding” loads for the purpose of determining deflection limits herein.

The Vult design wind speed for this structure is 110 mph (miles per hour). The net lateral pressures on the walls are greatest in Surface 1E (near the corners) of 17.697 psf (pounds per square foot), with a components and cladding wind pressure of -19.6 psf. 19.6 psf X 0.42 = 8.232 psf.

I called the good folks at USG (United States Gypsum – www.usg.com) to get their take on whether their 5/8” thick Sheetrock™ would span the 34-1/8” on center spacing of the wood framing without undue deflection. Being it was late on a Friday afternoon, the feedback was limited in its scope, however, they did email me the “Gypsum Association Properties of Gypsum Board”, which turns out to have some useful information. On Page 3 of 5 of the document copyrighted by the Gypsum Association is a table for “Negative Wind Load Resistance”. For ½” thickness over wood framing at 16 inches on center the allowable load is 80 psf, for 5/8”130 psf.

Allowable deflection is based upon the span^4. This makes the deflection at 2.84375 feet (34-1/8”) 20.692 times the deflection of 1.333 feet (16”). Using 130 psf / 20.692 results in a maximum psf of 6.28 which is less than the calculated 8.232, so 5/8” gypsum drywall would not be an adequate design solution. Under these load conditions, the maximum span of the 5/8” gypsum drywall would be 31.9”.

What about ½” drywall over 24 inch on center supports? The deflection at 24 inches on center is 5.0625 times the deflection at 16 inches. 80 / 5.0625 = 15.8 psf, which would prove adequate given these loads.