Tag Archives: drywall

11 Reasons Post Frame Commercial Girted Walls Are Best for Drywall

11 Ways Post Frame Commercial Girted Walls are Best for Drywall

Call it what you want, drywall, gypsum wallboard even Sheetrock® (registered brand of www.usg.com) and most English speaking adults know what you are talking about. In post frame (pole) building construction, wall girts (horizontal version of studs) are placed in bookshelf fashion, resisting wind loads and providing framework to attach sheathing and/or siding to exterior and a material like drywall on interior. Learn more about commercial bookshelf girts here: https://www.hansenpolebuildings.com/2011/09/commercial-girts-what-are-they/.

It turns out horizontal framing lends itself well to vertical application of Sheetrock® and here is why (horizontal being used to describe drywall run long direction left and right):

1 – Defective Seam – Horizontal rows needing more than one drywall panel creates (instead of avoids) butt-joint humps, which are not flat and are a twice (minimum) effort defect. Outlet and switch cover-plates, window and door trim, baseboards, pictures, mirrors and cabinets don’t sit flat. Using any “butt-joint product” erases all “claimed” benefits of Horizontal!

2 – Unsupported Seam –Light switch and countertop electrical boxes within a horizontal seam equals more weakness and butt-joint doubled, minimum, efforts.

3 – Structural Defect – Horizontal only reinforces a vertical studwall height of 4’ or less, a full-height studwall’s top-plate is never connected to the bottom plate. As in and due to #2 above, Frictional Contact is minimized (instead of maximized by Vertical).

4 – Seam Deception…4’x8′ Panels – Example 1: 48” tall by 102” long wall, Horizontal = 48” (technically) and it’s a 24” wide butt-joint or a minimum of doubling 48″ (Vertical = the same, generously, 96” but they’re easy 6” wide joints). Example 2: 96” tall by 102” long wall, Horizontal = 222” with 50% being 24” wide butts (Vertical = 192” of 6” wide easy joints, yes less)…in a Kitchen Horizontal = 100% of 24” wide butts (Vertical = 0%). Yes, Horizontal does taper area twice (minimum) in order to hide its butts, so very minimally just another 24” was added and #5 below was not factored into Horizontal’s monumental fraud.

5 – Self-Defeating Angles – Horizontal only uses one of a panel’s tapered edges and puts other taper at ceiling corner and baseboard creating (instead of avoiding like Vertical) a twisted angle having to be shimmed or additionally mudded. This too, instantly erases all “claimed” benefits of Horizontal by doubling seam amount, patching itself to equal Vertical!

6 – Unfriendly Seams – Horizontal celebrates chest height seams and pretends there’s no 24”-wide floor to ceiling butt-joint and ever present baseboard bevel of unfinished work. (Vertical has easy joints and top is screwed, taped and mudded later with ceiling corner and baseboard spots can also be done separately).

7 – Unsafe Installation – Horizontal needs two people for a safe installation and panel is airborne, literally creating chances to cause injury (Vertical easily tilts-up with just one person). Using a panel lifter is not even as easy and safe as Vertical’s tilt-up.

8 – Additional Waste – When correctly covering a knee wall, half wall, tub front, column or soffit by first removing both tapered edges, Horizontal can’t use these tapers elsewhere (Vertical can and does). And, Horizontal wastes four times as much mud on their completely unnecessary butt-joints and baseboard bevels…if ever done.

9 – Destructive Ignorance – Foundation and Framing crews go to great pains to make everything flat, level, plumb and square. Horizontal destroys those efforts with their defective humps and baseboard bevels (Vertical keeps this perfection).

10 – Costly Slow Complication – Horizontals depend upon pricey special muds and even messy tape or taping tools wasting mud. Taping tools still require a second step of knifing tape and muds require a mixing step. This is more expense, more time, more tools and equipment and more water…for an inferior job! Vertical’s superior with cheapest ready-mix bucket muds and dry self-adhesive tape. Again, Vertical’s seam treatment is just for looks.

11 – Fire Rating Fail – Most Single-ply or Single-layer drywall for Commercial Work is required to be installed vertically, to obtain drywall’s actual fire rating. 

Post frame construction and vertical application of drywall –  faster overall and immensely better in every way.

When a Contractor Ignores Building Plans

I realize this may come as a surprise, but there are more than a few times I have discovered building contractors have made errors in building assembly due to failure to examine the provided building plans.

Shocking.

Our client STEVE in HINES writes:

“Good morning, my building is framed, sided and roofed. However, yesterday we discovered that the sidewalls girts should have been 2x 8’s but 2×6’s were used instead (same as the endwalls). I know this is my problem to fix, but before I tell the contractor, I’d like to know if you have ever heard of this happening and if so, what they had to do to fix the problem. As it stands, it definitely does not meet wind code anymore. I’m not asking for a fix, but only some direction as where to start pursuing one. Could very well become a messy job!

Thanks.”

Well, to begin with, I was a post frame building contractor in a past life. At times we had as many as 35 crews erecting buildings in six states. Most of these crews were very, very good. Some of them were not quite as good. Overall this mix did give me an interesting perspective – if something could be done wrong, one of my crews figured out how to do it. Along with this, chances are I have had to come up with a fix for these unexpected challenges.

In Steve’s case, actual reasoning for 2×8 sidewall girts was so his building could have a flush interior surface to drywall – known as commercial girts. (Learn about commercial wall girts here: https://www.hansenpolebuildings.com/2011/09/commercial-girts-what-are-they/)

Our curiosity question was – what did the builder do with the 2×8 material supplied for girts? It turns out client had a pile of 2×8 left over when the pole building was completed. They ran short of 2×6, so building owner just assumed someone had stolen them and more were purchased!

Anyhow – there are several possible fixes. 2x4x12′ could be ripped and nailed along length of  2×6 installed where 2×8 should have been, or 2×4 could be placed vertically (3-1/2″ face against girt inside face) every two feet’ to provide a surface to attach drywall. Whichever choice is decided upon, a revision should be done to plans and sealed by Engineer of Record to verify adequacy.

Bookshelf Girts or Stud Walls?

Why Use Bookshelf Girts Rather Than Studs?

Long time readers may recall my Grandpa Pete was a home builder and his sons – Sid (my father), Neil, Lyle, Gil, Dave and Amund were all framing contractors. https://www.hansenpolebuildings.com/2011/06/before-the-pole-barn-guru/. Besides being raised with “wood is good”, I had a concept of vertical stud walls permanently ingrained in my head!

Stud walls led to my losing my posterior erecting my first post frame (pole barn) building. I struggled with this 90 degree ‘flip’ in framing concept far more than I needed to. Luckily, I was able to wrap my head around left-to-right rather than up and down when it came to my second building and I actually made some very good money!

Reader TRENT in WALLA WALLA writes:

“I am currently working on plans for building my first post frame home. It will be 30×48 single story. I am trying to figure out the best wall girt design. I am looking at going with 2×8 bookshelf wall girts or vertical stud walls between the posts. I see more people going with bookshelf girts vs vertical studs. Is there any drawbacks or reasons not to use vertical stud wall framing between the posts?”

Mike the Pole Barn Guru responds:

Installing a ceilingPretty straightforward – vertical stud walls will take more lumber. Besides increased material investment, more pieces mean more connections and more labor.

Imagine, if you will, a pole building with a 10′ eave height and columns every 12 feet. Bookshelf girts take (1) 2x4x12′ pressure treated, (4) 2x8x12′, (2) 2x4x8′ for blocking girts ends and (2) 2x4x12′ to attach drywall at the ceiling level – 98.67 board feet of lumber. For stud walls (1) 2x6x12′ pressure treated, (7) 2x6x10′ studs, (1) 2x6x12′ top plate, (1) 2x4x12′ to attach drywall at ceiling level, (4) 2x4x12′ horizontally to attach steel to wall studs – 134 board feet of lumber. From a structural aspect, care will need to be exercised in attachment of the top plate and end studs to adequately transfer wall bay wind loads to columns. It may necessitate some sort of Simpson strap to properly anchor the plate to columns.

 

 

 

 

Concerns of a Post Frame Building Kit Shopper

Hopefully most, if not all, of my loyal readers are those who have concerns when it comes to investing in a new post frame building (I do know some of you just enjoy my slightly skewed sense of humor, or find my writings otherwise entertaining). For those of you who are avid kit shoppers, I try to give honest advice to any question posed to me.

Reader TRAVIS writes:

“Hello, I’m shopping around potential kit purchases and have a few questions. 

First off I’m planning to finish the interior, are the long spans between trusses you design able to handle the dead weight of drywall ceilings? 

One of my main concerns is column rot as my area is fairly wet. What type of treatment is used on the columns, where do you source them from, and do you ever recommend concrete permacolumns? 

Is it possible to use half scissor trusses and half regular to gain extra height in only certain areas? 

Thank you any help is appreciated.”

Mike the Pole Barn Guru gives advice:

Yes, we are able to design roof systems to support virtually any dead weight – including gypsum wallboard (drywall). Whether a Hansen Pole Building, or not, it is just a matter of the proper loads being applied in the engineering design phase of the truss process, then (if the trusses are spaced over two feet on center) using appropriate framing between the bottom chords of the trusses to support the loads without undue deflection.

If you intend to insulate above the ceiling, make sure to ask for the trusses to be designed with a raised heel at least two inches higher than the depth of the ceiling insulation, to allow for full thickness of the insulation above the sidewalls. Normally this has little effect upon the price of the trusses, however the building must be made taller to provide the same interior clear height.

All Hansen Pole Buildings’ structural columns (supporting roof loads) are pressure preservative treated to a minimum UC-4B specification, which is the requirement per the IBC (International Building Code). Even under extreme conditions, these columns should more than adequately support your building not only for your lifespan, but also your grandchildren’s. The longevity of properly pressure preservative treated lumber has been well documented in scientific testing.

We’ve had clients use concrete permacolumns – if your concern is properly pressure preservative treated wood not being adequate for your situation, a less expensive (and easier to build) alternative would be to pour the column holes full of concrete and utilize wet set brackets.

It is possible to mix any combination of scissored and flat bottom chord trusses throughout your new post frame building to gain extra height or for aesthetic purposes.

 

 

Properly Treated Poles, Ceiling Loads, and Uplift Plates

Properly Treated Poles, Ceiling Loads, and Uplift Plates

DEAR POLE BARN GURU: My pole barn is approximately 25 years old. My question is, does the foundation need to be treated for maintenance to prevent rotting? The wood that is underground was originally treated wood but how long does that last? The floor inside is concrete but there is no concrete around the framing which meets dirt on the outside. NORMA in CASSOPOLIS

DEAR NORMA: Despite what might be voiced by naysayers – properly pressure preservative treated lumber should, under most circumstances, last longer than you and I (or our grandchildren) will be around to see. If you are curious, excavate the top eight to 12 inches of soil around one or more of the columns and check on the condition of them. We are currently adding onto our warehouse – a 40 year old post frame building. Some of the existing columns were dug alongside and it was determined there had been no noticeable decay at all. I would suspect yours will be the same.

 

DEAR POLE BARN GURU: Can you strap a ceiling for drywall ceiling in a pole barn if the joists are 8 ft apart? TOM in BLAIR

DEAR TOM: I will do what I feel is some interpreting….where “joists” are the prefabricated metal connector plated wood roof trusses, and “strap” would refer to framing placed across (or more probably between) the bottom chords of the trusses.

If your trusses have been designed to support the weight of a ceiling load, then yes. Hansen Pole Buildings uses a 10 psf (pounds per square foot) design ceiling load for instances where gypsum wallboard will be applied. A five psf load might possibly be adequate with bare minimal framing and nothing ancillary hanging from the bottoms of the trusses. You would be well advised to consult with the engineer who designed your building, or the truss fabricator to insure your roof system is indeed adequate to support these loads.

Once truss adequacy is confirmed your engineer can specify the size, species and grade of the material to be used as ceiling joists as well as what he or she requires as a connection between the ceiling joists and the trusses.

DEAR POLE BARN GURU: What is used to hold the post in the concrete? galv nails pounded into the 6×6 treated post post? Rebar drilled through the post as a big nail? Galv-steel anti-lift brackets of some sort? GLENN in PORTLAND

DEAR GLENN: Hansen Pole Buildings now supplies (as a standard feature) one or more UP-Lift plates per each structural column (the required number will depend upon analysis by the Engineer of Record). It would require a significant number of large diameter nails to equal the holding power of a single UP-Lift plate.  Rebar through the column might prove to be adequate, however it does involve a significant amount of effort to drill the holes through the column, cut rebar to short lengths and seal the rebar at the edges of the column to prevent water infiltration. In any case, the ultimate responsibility for design of adequate uplift resistance should be left up to the engineer who designs your building.

For more information on UP-Lift plates read here: https://www.hansenpolebuildings.com/2014/05/up-lift-plates/


 

Drywall Idea, Bolt Counts? and Don’t D-I-Y This!

DEAR POLE BARN GURU: Will I have problem with moisture in the wall if I nail drywall to the gerts and leave the 6×6 poles exposed? I may put a stove for heat in it while I am in it occasionally. I have insulted the roof. Concrete floor. JAMES in NEW ALBANY

DEAR JAMES: Provided you have a good building wrap between the siding and the wall girts (read more about building wraps here: https://www.hansenpolebuildings.com/2012/11/house-wrap/), as well as a well-sealed vapor barrier between the girts and the drywall, you should be able to minimize the effects of moisture in the wall.

Now your bad news. I will take a wild guess and surmise your post frame building has girts nailed flat on the outside of the columns. If so, and you attempt to drywall to the inside face of the girts, be prepared for infinite issues with the drywall joints cracking due to excess deflection.

If there is no building wrap, a quick and easy fix is to have an inch or more of closed cell foam insulation sprayed on the inside of the siding.

I’d most probably either build a vertical stud wall between the columns, or place another set of horizontal girts on the inside of the columns. Either of these would afford an insulation cavity with enough depth to make a difference. This would allow BIBs insulation to be blown into the wall with a minimal number of heat transfer points.

DEAR POLE BARN GURU: How many lag bolts should be used in a 4 x 6? This is for the truss supports. COREY in PAW PAW.

nailing trussesDEAR COREY: My educated wild guess is your post frame building has trusses placed on top of a truss carrier (basically a header from column to column).

You can find the size and number of required fasteners by looking at the data prepared by the engineer who designed your building, as this information will be on the sealed plans.

Numerous factors would be involved in the determination of adequate fastening. If the carriers are notched into the columns, far fewer fasteners will be required, as they will only be needed to resist wind loads.

If the carriers are placed on the sides of the columns, then the roof load is typically the governing factor. The fasteners then have to resist the live loads (snow and any attic bonus or storage space) plus the dead loads (weight of roof system and covering, as well as any ceiling.

The spacing of the columns and span of the truss impact the number of fasteners as well.

If for some reason this information is lost or missing from your plans, a competent local RDP (Registered Design Professional) should be engaged to provide a connection design for you, as this is hugely critical to prevent unexpected failures which could result in bodily harm or death. DO NOT GUESS.

 

DEAR POLE BARN GURU: How can I build a strong 30 foot truss that won’t sag. LARRY in TYLER

DEAR LARRY: I hate to just throw out the obvious, but in your case I will – DO NOT BUILD YOUR OWN TRUSS.

Prefabricated metal connector plated wood trusses are nothing short of an engineered miracle. You can have them designed to support any load which you can conceive of, have them delivered to your site and engineer sealed drawings are provided to confirm the required load conditions are met.

A quick Google search of “Tyler Texas Wood Roof Trusses” will give you several possibilities to discuss your needs.

 

 

Commercial Girts Best for Drywall, Site Prep, and Condensation

DEAR POLE BARN GURU: I’m considering a pole barn for my residence but had a question about the girt placement between posts. I read in the FAQ section that they are placed like shelves between posts. Would it be possible to mount drywall directly to these for interior walls without additional bracing or building of interior wall frames? I’m trying to avoid framing an entire building within a building, it seems pointless and not cost effective. If I need to frame every interior wall to hold drywall and insulation, I can simply build a standard stick frame house. VAN in INDEPENDENCE

Installing Drywall on CeilingDEAR VAN: Bookshelf girts for insulation (e.g. Commercial Girts) is a quick and easy way to create a deep insulation cavity as well as providing the framing for your interior GWB (Gypsum Wall Board). You will want to confirm your new post frame building frame is stiff enough to prevent undue deflection from cracking the GWB joints.

Learn more about commercial girts here: https://www.hansenpolebuildings.com/2011/09/commercial-girts-what-are-they/.

DEAR POLE BARN GURU: I have property in an area that floods from time to time. For example, can a monitor barn (approx. 25×50). with side sheds be built. The idea I have is the side sheds serving as porches and under the barn would be a drive through area. there is already a modular home built in the area that is elevated about 4 ft. off the ground and they have had no problem . Thanks, MIKE in MOLINA

DEAR MIKE: You can build any sort of post frame building on your site which will be allowable under the limitations of your Planning Department. As to dealing with the flood issues, you should have your property elevations determined by a surveyor, and the site where the building will be constructed can then be built up so the floor will be above the flood plain level.

 

DEAR POLE BARN GURU: I recently purchased several 4’x50′ reflectix double bubble foil rolls. I’ve put up a brand new 30×56 post frame metal building and was going to use this product to keep the metal roof and walls from condensating not to mention I was hoping it would help keep some heat in during the winter and heat out during the summer until I truly insulate the inside. My question is, for ease of installation on my metal roof panels, is it acceptable to put the foil on the underside of the 2×6 roof joists instead of sandwiching it between the roof joists and metal? There will be no roof venting due to leaving the trusses and attic space exposed. My only real concern is that it could condensate worse installing it this way. Also I will not be continually heating the building. Only on occasion with a propane heater while I’m working. I’m not real savvy when it comes to insulation and condensation control so any advice would be appreciated. Thanks in advance! Brandon

DEAR BRANDON: While it would be easy to install the steel roofing without having to place the reflective radiant barrier between the roof purlins and the roof steel, it is going to be the easiest method to limit condensation issues, given the product you have invested in. Hopefully you have gotten the double bubble with a tab along one side and an adhesive pull strip, otherwise you will have to tape all of the seams as you work your way along the roof.

Could you place it on the underside of the purlins? Yes, however in order to work as an effective condensation control, it has to be absolutely tightly sealed against any protruding framing members. Remember the time you saved on installing the roof steel? You just ate it all up.

If you have not yet ordered your steel roofing you could resell the reflective radiant barrier online and order steel with I.C.C. (Integral Condensation Control) attached (see the article and video here: https://www.hansenpolebuildings.com/2017/03/integral-condensation-control/).

 

 

Real Estate Value, Post Brackets, and Interior Finishing

DEAR POLE BARN GURU: As a licensed Real Estate agent and looking to move, I realize how crazy the market is (at least in Michigan and the Grand Rapids Area).

Considering building a pole barn home for my wife and I when we sell our house, however what about resale value?

My concern is regarding appraisal or the possibility of having comparables should we need to sell after we build. At best I could think of manufactured, but that would depend on what the building is “labeled” as. Speaking to a professional lender he seemed convinced that I would HAVE to have a cash buyer, or someone doing a portfolio loan at 15% down.

Do you know of anyone who was able to sell their pole barn house with financing, and if so, what did the appraiser use as their comps?

Thank you in advance! GAGE in ROCKFORD

Gambrel roof pole barnDEAR GAGE: Post frame homes will have the same value as a comparably sized and featured stick built home. Think of it from this aspect – both have permanent foundations, both are constructed onsite out of wood framing. The structural system is “wood framed”. Period.

When you (or a buyer) go to get a loan, remember to use “wood framed” otherwise you will entirely confuse the lender. For comps, your appraiser will be looking at other similar sized and featured wood framed homes which have sold recently in your area.

I cannot vouch for people selling their homes with financing, however I financed and refinanced my own home and with two very elaborate post frame accessory buildings (both of which are livable spaces). Through three appraisals, never once did the question of post frame come up.

DEAR POLE BARN GURU: Wondering if you can place the 6×6 pole onto a concrete foundation with brackets that hold pole to concrete?

DEAR JOE: Yes, it can be done, provided the 6×6 is adequate to carry the loads being imposed upon it. Here is information on the brackets: https://www.hansenpolebuildings.com/2012/09/concrete-brackets-2/.

DEAR POLE BARN GURU: I have a pole barn that I would like to finish the interior on
the posts are spaced 8′, the building has 7/16 osb over the wall girts (vinyl siding), I did a cut
and cobble job of rigid foam (1 inch) . My idea is to use 7/16 osb to finish inside and Maybe add sheetrock at some point- my concern is the support of interior walls-do I just let the wall girts carry the load or do I figure a way to anchor into posts? Thanks very much, Robert in Middletown.

DEAR ROBERT: Not sure why you would want to go to the added expense of placing OSB on the inside and then later adding gypsum wallboard, other than your post frame building frame may have too much deflection to prohibit taped drywall joints from cracking.

Before adding GWB (gypsum wall board) you should verify with the engineer who designed your building to make sure it is adequately rigid to be able to support it. If you are unable to contact the engineer, then you should consult with a RDP (Registered Design Professional – architect or engineer) who can confirm it is adequate, or recommend a fix or fixes if it is not.

Once you know all is good, a set of girts should be attached to the inside of the columns to support the GWB. This will also create an insulation cavity where you can add fiberglass batts or even better – do BIBs (information on BIBs here: https://www.hansenpolebuildings.com/2011/11/bibs/).


 

How Can I Add interior Walls to a Post Frame Building?

DEAR POLE BARN GURU: How difficult is it to add interior walls to build rooms inside the pole barn. Are more materials needed to add interior rooms and do the exterior walls need extra support? PATRICIA in McMINNVILLE

DEAR PATRICIA: The beauty of post frame (pole barn) buildings is the great majority of them are designed to be clearspan – there are rarely interior columns to avoid, so non-structural interior walls can be placed anywhere!

Home OfficeThis was a great feature for my lovely bride and I, as we moved walls all around until we came up with the configuration which best met with our needs – after the building shell was completed.

There is a caveat – if the interior of your building is going to have gypsum drywall (aka sheetrock) it is important to have the structure designed to limit the deflection. Most post frame buildings are designed with only the deflection of steel siding in mind, which would cause many drywall joints to crack under wind or seismic events.

If properly designed (better make sure an engineer was involved in those original plans) then no materials should have to be added to the exterior framework in order to add interior walls. You will, of course, have to provide the materials for the interior walls themselves.

DEAR POLE BARN GURU: Can Hansen provide a kit that will work as a picnic shelter with no walls, just the poles and the roof with the triangle gable ends covered with siding? JOE in MISENHEIMER

DEAR JOE: Yes we can provide roof only buildings. In most cases, it is less expensive to cover one or both endwalls to the ground, rather than building just a pavilion style structure. Here is a link to a previous article where I expound upon why: https://www.hansenpolebuildings.com/2015/04/roof-only-pole-buildings/

DEAR POLE BARN GURU: I am doing a barn w apartment , the whole building will be conditioned space, I am looking for the best house wrap for my barn and new home?

I am wondering if insulated Tylek or insulated panels are worth it on outside since I’m framing w 2×6 and concrete lap siding? Thanks DANIEL in WOODBINE

DEAR DANIEL: Most Building Permit issuing jurisdictions are going to require a Weather Resistant Barrier underneath siding around a conditioned space, so there is probably not much of a choice. For the most part, concrete lap siding should be installed over a solid sheathing such as OSB (oriented strand board) or plywood to prevent waves in the material and to give the building adequate shear resistance. Here is the link to the first of a three part series of articles I wrote on Weather Resistant Barriers: https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/.

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.