Tag Archives: bottom chord bracing

Help Me Insulate My Pole Building

This story is sad, to me. As post frame building “experts” we (an industry collective we) owe it to our clients to educate them at design phase to avoid a situation such as reader ERIC in SPOKANE VALLEY has become happily (or maybe less happy) involved in.

Eric writes:

“I want to start insulating my pole building. 30x40x16, roof layers are metal, synthetic underlayment, osb, 2×8 purlins. My question is, can I leave an air gap between roof and insulation, as I plan on using R19 batting and covering with facing. Has an open ridge vent. Thank you.”

Mike the Pole Barn Guru responds:

Placing batts between purlins is probably not a Top Twenty best answer for several reasons:

If you do not completely fill purlin cavities, Code requires airflow from eave to ridge over top of the insulation. You have no way to achieve this without a major remodel. You don’t even want to go there.

Getting a perfectly sealed vapor barrier under purlins would be nearly impossible to achieve.

You would have to seal the ridge vent (it isn’t working anyhow, because your building does not have an air intake from enclosed vented soffits).

While installing a flat ceiling at truss bottom chord height might appear to be a quick solution, it also is fraught with some perils:

Trusses are probably not designed to support a ceiling load. It might be possible to obtain an engineered repair from the company who produced your building’s trusses.

Ventilation system would need to be addressed for newly created dead attic space.

Closed cell spray foam insulation would need to be added in the area closest to eave sidewalls.

Weighing what you have to start with, my recommendation is to spray three inches of closed cell foam insulation below your roof sheathing. This will provide a greater R value than R19 batts and provides a vapor barrier. You will need to seal off the ridge (foam installer may be able to just spray foam underside).

Also, I notice in your photo what appears to be a total absence of truss web and bottom chord bracing. I’d have to have a copy of your building’s sealed plans, a truss drawing and some more photos to truly discern.

How Could This Have Been Avoided?

Whoever provided this post frame building should have been asking some important questions:

Will you, or anyone who might own this building in future years ever want to climate control (heat, cool or both)?

If yes, what method of roof insulation is being considered? I like insulation over a flat level ceiling personally, as I then no longer pay to heat or cool the attic area. In order to do this right, energy heels (https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/) should be utilized. It also means having adequate attic insulation with soffit vents as intakes and ridge vents as exhaust.

It all could have been so much simpler.

 

Temporary Truss Bracing

The Importance of Temporary Truss Bracing

Back in my early days in the prefabricated metal connector plated truss industry, one of my clients was the congregations of a church along Highway 95 in Hayden, Idaho. The project was for an entirely new building, with the work being done by primarily volunteer help, under the supervision of a carpenter with more decades of experience under his belt than even my Father or my five Uncles.

The design called for a large central clearspan comprised of low slope trusses with a raised heel. (For more reading on raised heel trusses: https://www.hansenpolebuildings.com/blog/2012/07/raised-heel-trusses/)

Surrounding this on three sides were areas with monoslope (sloping in one direction away from the main span) trusses, which were placed first.

Once the walls for the central portion were framed, the supervisor called for delivery of the main span. As the trusses were very large, they paid extra for our crane truck to individually place the trusses (good idea). All of this was accomplished on a chilly windless day in mid-January, without a hitch. Our crane truck had hardly completed the 15 minute drive from the building site back to our manufacturing plant, when we got “the call”…..the roof had collapsed!!

I high-tailed it out to the church, to find the experienced carpenter shaking his head. The rear of this set of trusses had been braced against the previously framed roof behind, with temporary truss bracing. Before putting permanent bracing in place, the contractor had removed the temporary bracing. He said he knew it was in trouble the moment he pulled out the last nail, and in the blink of an eye, it was scrambled trusses on the ground!

From the pole building photos attached from a recent project (not the church), it is impossible for me to determine if the trusses and their attached purlins were in place or being placed when things went bad. What I can tell is this – there is no bracing of any sort to be found in this assembly which would have kept it from racking or toppling. The temporary truss bracing is AWOL.

What would have helped to prevent this pain?

X BracingAn X Brace, or braces, between the top chord of one pair of trusses and the bottom chord of the other pair would have prevented toppling (the larger the span, the greater the need for more than a single X). Also, temporarily nailing some of the wall girts to the tops of the roof purlins in diagonal fashion would have prevented the assembly from racking.

The Wood Truss Council of America (WTCA) www.WoodTruss.com and the Truss Plate Institute (TPI) www.tpinst.org have prepared a summary sheet BCSI-B10 “Post Frame Truss Installation and Bracing”, which is included in the Hansen Pole Buildings’ Installation Manual, and should be provided to anyone who is assembling a pole building using prefabricated wood roof trusses.

Trusses are very, very strong when properly installed and braced in the vertical direction for which they were designed. By using care and caution, during handling and installation, they will perform admirably for generations.

Dear Pole Barn Guru: What is the Proper Wind Shear Bracing?

New!  The Pole Barn Guru’s mailbox is overflowing with questions.  Due to high demand, he is answering questions on Saturdays as well as Mondays.

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday or Saturday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

Dear Pole Barn Guru: What is the proper wind sheer bracing for a 60’W x 80’L by 20’H monitor pole barn with a 20′ center aisle and a second story? The raised center portion has 20 foot walls, then another 6 feet to the center at the ridge.

The 2 sheds on either side are 10′ at the edge and intersect the center at about 15′. The entire structure is made of poles on 20′ centers, Lvl beams and ladder trusses for floor and trussed roofs. It is unprotected from the wind. We are in central Texas. TEETERING IN TEXAS

DEAR TEETERING: This is why it is such an excellent idea to order complete pole building packages from a company who can run all of these calculations accurately in advance. Then buildings are designed to resist the proper loads, including wind shear, without having to search for solutions in the middle of the game.

Provided all of the columns are adequately sized and embedded …..

Steel roofing should be 3′ width, minimum 29 gauge, with high ribs every 9″, attached to 2x purlins on edge spaced no more than 28″ o.c. Roofing should attach to purlins with #12 x 1-1/2″ diaphragm screws at 9″ o.c. at each purlin. At eave and top edges of panels place screws on each side of every high rib.

Provided you attach the endwall steel the same as the roof steel, you should be able to have up to 19 lineal feet of openings on each endwall without further reinforcement.

All of this should be reviewed by a Registered Design Professional (RDP – engineer or architect) for structural adequacy.

DEAR POLE BARN GURU:  Is it possible to get a quote to have it assembled? MINDFUL IN MORRIS

DEAR MORRIS: We are not contractors, however fair market value for labor is typically about 50% of materials costs.

I recommend placing an ad on Craigslist under “labor gigs” such as:

Contractor needed to assemble pole building kit package on my clear level site in Morris County. 24’x40’x14′ includes 12″ overhangs, a 12’x12′ overhead door, entry door and wainscot. I will provide all materials except for nail gun nails. Willing to pay $4000-5000 depending upon experience and references.

DEAR POLE BARN GURU: I have a metal building constructed of 2×4 square tubing and 4×4 metal posts. 3″ × 1.5″ c purlin is welded with the c side down spanning across my 2×4 square tubing roof beams. I have a metal roof screwed to the c purlin. The building wraps around an existing building and looks like an L from a top view and has a 2 on 12 shed roof with a hip. The building is “stand alone” and attached to the other structure only with a side wall transition piece. The metal roof slides under the eve of the other structure with the side wall transition on top. I also used the vented enclosure under the sidewall transition for ventilation. I also have a ridge vent at the hip with the vented enclosure under the hip cap. I have a 12″ soffit around the outside perimeter of the metal structure with soffit vents every 5 ft. I have a 4 ft cedar picket half wall around the outside perimeter with the remaining height of the wall in screens….basically a screened in party room but I plan on switching out the screens for heavy plastic sheeting in the winter. I have a hot tub inside and I want to insulate the roof and install a ceiling. 1st question: do I have to install a vapor barrier IF I am using 3/8 marine plywood for the ceiling and the attic side of the sheathing is covered in heavy vinyl….sheathing was once election signs. I am attaching the ceiling directly to the bottom of the 2×4 roof beams following the slope of the 2 on 12 pitch.

2nd question…..because I only have the 4″ depth of the 2×4 sq tubing + 1.5″ depth of the c purlin = 5.5″ total for insulation AND vent space, how would you insulate? Spray foam is too expensive for me. I want to reduce the radiant heat in the summer and I am concerned with the humidity from the hot tub especially in the winter. Any help would be greatly appreciated. TOASTY IN TEXAS

DEAR TOASTY: My guess is you are going to be creating an inadequately ventilated dead attic space. You need to have 1/150th of the “foot print” of your space, as ventilation, equally divided between the eaves and the ridge. In your case, you have no ability to adequately vent the high side of your roof, as it abuts another building.

Even though the best solution might well be to tear everything down and construct a new building, chances are you would not look favorably financially upon it as the end all.

Probably your best bet is to install an A1V reflective radiant barrier beneath the roof purlins (https://www.buyreflectiveinsulation.com) with the reflective side up. Make sure every seam is tightly sealed. This should help reduce the thermal gain in the summer. If you are going to create a dead attic space between a ceiling and the reflective radiant barrier – powered attic vents in each end could be a good investment.

As for humidity from your hot tub, install air inlet vents near the floor and exhaust vents near the ceiling line. You may also need to have one or more powered vents in the walls of this area.

Dear Pole Barn Guru: Why Do I Need Truss Web Bracing?

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU:  Hello,

I came across the link below while investigating Pole Barn House kits, but since we don’t want a concrete slab, I was wondering about how the poles work in conjunction with a crawl space.

https://www.hansenpolebuildings.com/blog/2013/03/crawl-space/

GNASHING IN NASHVILLE

DEAR GNASHING: The easiest (and most affordable) way to create a crawl space is to construct in typical pole building style, with an elevated wood floor.  This now creates a crawl space which can either have an insulated perimeter, or the floor may be insulated leaving an unconditioned area.  A far more expensive route would be to pour a continuous footing and foundation, mounting the columns to poured-in-place brackets on top of the foundation walls.  We’ve done them both ways, so it’s client’s preference.

DEAR POLE BARN GURU: I’ve hired a contractor to assemble a Hansen Pole Building kit package for me. He says he is short on trims to cover the fascias. As he was explaining to me, is that the triangle cut part of the end needs to be covered by the ‘L’ trim. Does that make sense? It does to me looking at it, but hard to write out! WRUNG OUT IN WASHINGTON

DEAR WRUNG: Your building requires 30’3” of trim to cover each fascia, when installed to match the instructions provided in our Construction Guide. A total of 63 feet was shipped to your building site, so there was plenty provided.

It appears, what has happened, is your installers have made an assumption of how to correctly apply the trims, rather than having thoroughly reviewed the directions provided. Failure to follow the step-by-step detailed instructions does occur every once in a while. Hopefully your project is not past the point of no return (where trim was improperly used).

DEAR POLE BARN GURU: What is the purpose of bracing the webs of roof trusses? Why do some webs need braces while others don’t? MYSTIFIED IN MISSISSIPPI
DEAR MYSTIFIED: The internal members of roof trusses are referred to as webs. The permanent braces sometimes required on roof truss webs are called continuous lateral braces, or CLBs. They’re typically required on a web which is in compression. The truss web bracing is intended to keep the truss web from buckling in the weak (skinny) direction.

To explain why they’re sometimes necessary, imagine pushing down on a yardstick which extends vertically to the floor from the palm of your hand. It doesn’t take much pressure for the yardstick to buckle.

Now imagine taking your other hand and restraining the yardstick halfway up from the floor. If you press down now, it takes a lot more pressure to make the yardstick buckle. In effect, you’ve added a CLB to the yardstick.

The web of a truss is much like a yardstick. It can withstand a certain amount of compression without bracing. The amount of compression a web can withstand depends partly on its size, species, and grade. But the biggest factor in determining truss web bracing requirements is the overall length of the web.

In some cases, webs can require two rows of bracing rather than one. This design is most often seen in very tall trusses.

Single trusses are only 1-1/2 inches wide and require far more web bracing than does a double truss system, where the two individual trusses are nailed directly together so as to form a three inch width member. Doubling the thickness makes the webs twice as stiff against buckling.

If one CLB is required on a web, it should be roughly in the center of the web. If two CLBs are called for, they should be at one-third points on the web.

Continuous lateral bracing won’t do any good if it’s not anchored to something solid. The CLB will just transfer the buckling, and the whole set of webs will buckle in the same direction. Typically, CLBs are anchored with diagonal braces to rigid points such as the top chords of trusses, or to a building endwall.

In pole buildings, it is not uncommon to have trusses spaced eight feet or more apart. CLBs begin to become impractical, as they eventually become so long they will buckle between the trusses. In no case should a single 2x (1-1/2 inch wide) CLB used with a length over 10’.

So how to apply truss web bracing of widely spaced trusses? By applying a 1×4 or larger brace to the top or bottom (if two CLBs are required, to both top and bottom) of the web needing to be braced, for at least 90% of the length! These braces act as a strongback, restraining the web from buckling in the weak direction. The braces should be attached with 10d common nails, placed at a spacing as recommended by the RDP (Registered Design Professional – engineer or architect) for the project.

To determine if you need CLBs, look at the drawings accompanying the trusses; they should have the locations of any CLBs on them. Many truss manufacturers also put tags on webs which require braces. For more information on trusses, visit the Wood Truss Council of America’s Web site at: www.sbcindustry.com