Tag Archives: roof purlins

Temporary Client Insanity – Truss Problems?

Temporary Client Insanity – Truss Problems? 

Long ago someone told me during the course of any construction project there comes a time when every client goes absolutely bat-pooh crazy. Personally, even knowing what I know, I am guilty of freaking out and having had a case of temporary client insanity during our own remodel and construction projects for our home.

For hyperventilation they have people breath from a brown paper bag, in my case – perhaps a plastic bag over my head and tied tightly about my neck would have been more appropriate.

Below I will share a client’s concerns. He remained much calmer (totally appreciated) during this process than I might have. He wrote to Justine (Hansen Pole Buildings’ Master of All Things Trusses):

“Justine, one more thing, the top chords of the trusses show 2×8 and the trusses were delivered with a 2×6 top chord, so all the bracing (purlins) will be hanging down. This roof is going to be insulated.

Also, the double trusses are not fastened together and I think I should have more than 1 set of scissored trusses.”

Our Technical Support response:

Building plans are drafted prior to receipt of truss drawings, so trusses as drawn on your plans are merely a depiction of what they may look like. Top and bottom chords as well as internal diagonal webs may be entirely different. The roof slopes will be accurate. Your building’s roof purlins certainly may hang below roof truss top chords, as this has no bearing upon your ability to insulate (please refer to Figure 9-5 of your Hansen Pole Buildings’ Construction Manual). As your roof has a Reflective Radiant Barrier, if you intend to use batt insulation between purlins, make sure to use unfaced insulation without a vapor barrier on underside, otherwise moisture can become trapped between two vapor barriers. This can lead to ineffective damp insulation as well as potential mold and mildew issues.

Per change order #3 your building is to have standard trusses in front 24 feet and a vaulted ceiling in rear 24 feet. With a pair of scissor trusses at 12 feet in front of rear endwall, this allows for the rear 24 feet to be vaulted and front 24 feet to have a level bottom chord.

Truss assembly people are not carpenters – and rarely do truss manufacturing facilities even have nail guns. It also avoids nail wounds from inexperienced or inappropriate use. As an example – back in 1979, I was shopping for a new employer designing and selling trusses. I interviewed with Tilden Truss, near Seattle. They used air guns firing a “T” staple to initially set steel truss plates. Their fabrication shop ceiling was covered with hundreds (if not thousands) of these “T” staples!

You will find it much easier to maneuver single trusses around your building site, than twice as heavy double trusses.

Please feel free to address any building assembly concerns to TechSupport@HansenPoleBuildings.com.

Another crisis averted.

The Ultimate Post Frame Building Experience

Hansen Pole Buildings is on a mission to provide “The Ultimate Post Frame Building Experience™”. (Read about “The Ultimate Post Frame Building Experience™” here: https://www.hansenpolebuildings.com/2016/06/ultimate-post-frame-experience/) In doing so, we often make what I will refer to as ‘tweaks’ to make not only our clients’ experiences better, but also their new post frame buildings better.

About Hansen BuildingsWe look for trends in questions asked by owners of existing pole barns – usually not even those we provided! There are a couple of these our team has decided to address and we have so far done a very poor job of letting our clients know we have done so.

Lesser of these items are folks who decide, for whatever reason, they would like to add either plywood or OSB between their new post frame building’s roof purlins and roof steel (https://www.hansenpolebuildings.com/2017/03/osb-steel-roofing-pole-buildings/).

Near universally pole barn builders and kit suppliers (as well as most truss manufacturers) have designed trusses with barely enough load capacity to meet minimums. In most instances, actual weight of materials (dead load) of roof truss top chords is around 2.5 psf (pounds per square foot). This is enough to account for truss weight, roof purlins, some sort of reflective radiant barrier or other minimal condensation control, as well as light gauge steel roofing. We have been using 3.3 psf just to give a little extra cushion (roughly 1/3rd more capacity).

½-inch plywood and 7/16-inch OSB both weigh 46 to 48 pounds per four foot by eight foot sheet or 1.5 psf. In order to account for possibilities of someone wanting to add one of these sheathings during building assembly, Hansen Pole Buildings has opted to increase our design top chord dead load to five psf for clearspan trusses up to and including 40 feet. This is DOUBLE minimum requirements.

Tomorrow, I will share with you a solution to an all too frequent challenge.

Stay tuned……

Dancing With the Posts

Reality television watchers have suffered through 384 episodes of the ABC networks, Dancing with the Stars hosted by Tom Bergeron since 2005. On occasion, it seems some of our clients (or much more often their builders) have done some posts (as opposed to pole) dancing when placing columns for their new building. A certain amount of randomization can be accommodated, as found in this real life scenario:

Our client contacted his Hansen Pole Buildings’ Designer Rick recently, with this information:

“(name withheld) has a question about what to do with the bottoms of his posts being off and how it will affect his roof purlins. 

He sent this diagram showing how his posts are off: 

pole layout

Red circle is 3 inches off 

Blue circle is 1 ½ inches off 

The question is, does he just set the tops of his columns where they are supposed to be, or does he add a 2×6 to the side of one post?”

From front to back on the left side of the building the now poured into concrete column spacing is: 120”, 144”, 144”, 144”, 119.5”. Other than the rear bay being ½” short, it is spot on.

Now, for the right side – 117”, 145.5”, 144”, 144”, 121.75”. Those of you who pulled out your calculators already know the right side is ¾” longer than the left, as well as the columns not aligning.

In the most typical (as it allows for least cost, fewest holes to be dug and more long term design flexibility) Hansen Pole Buildings construction, double trusses are notched into the sidewall columns and 2x purlins are joist hung on edge between them. For ease of construction and builder sanity, it is ideal for the purlins in each bay to be able to be cut to the same length.

There is a solution, which I passed along:

“Construction Tolerances Standard for Post-Frame Buildings” allows for columns to be 1% out of plumb, which on a 16′ eave would be 1.92″.

He certainly wants to have trusses placed on columns so as to be able to cut all of the purlins to the same length in each bay.

Working from bottom of page up –

First pair up page (diagram sent by client) – tip left column forward (down page) 1-1/2″, right rear (up page) 1-1/2″

Next three on left tip forward 1-1/2″

Rear – left corner tip outward (back) 1/2″ right corner tip forward 1/4″

The posts will easily flex this far, so it shouldn’t be a huge issue.

This is just one of many reasons why post frame building roofs should be framed (as well as sheathed) prior to any wall framing being done. In the event the walls would have been framed prior to this, solving the challenge would have proven to be difficult, at best.

Thankfully, we have a very astute client who contacted our Technical Support Department for assistance as soon as they were aware of something gone awry.

Dear Pole Barn Guru: Toe Nail Purlins or use Hangers?

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:It looks like your double truss system uses hangers between the trusses rather than the boards running on top of the trusses.

When I see these used on decks it sometimes looks like the nails that are toe-nailed into the connectors don’t do anything as they are at the very end of the board. The board splits or chips out.

Have I just seen it done improperly or perhaps I’ve seen the wrong types of hangers or nails being used?

I’m guessing you’ve seen your fair share of improperly installed connectors so I’m looking forward to what you have to say.

Thanks NOVICE IN MILTON

DEAR NOVICE: The Hansen Pole Buildings double truss system (as well as the special requests we get for widely spaced single trusses) do utilize engineered steel connectors to attach the roof purlins to the sides of the trusses.

As an experiment, I looked today at the hundreds of hangers we have installed on a 42’ x 120’ self storage building being constructed for Eric (one of the Hansen Pole Buildings owners). All of the hangers for the project are manufactured by Simpson Strong-Tie:

https://www.hansenpolebuildings.com/blog/2013/08/simpson/

The hangers installed are their LU26, LU28 and H1 brackets.

The roof purlins being nailed into are kiln dried 2×6 and 2×8 of Douglas Fir (DFir) and SPF (Canadian Spruce-Pine-Fir). All of the nails used in the hangers are joist hanger nails (#10 x 1-1/2” long) which are designed specifically for use in engineered metal connectors.

https://www.hansenpolebuildings.com/blog/2013/01/tico-10d-common-nails/

I was unable to find a single case on Eric’s large building with hundreds of joist hangers where the nails contributed to an end split in a purlin or a portion of the roof purlin being split away.

I do have some theories as to what may be the cause of what you have seen on decks.

Theory #1 – other than a few specially designed brackets, joist hangers are designed for the nails to be installed at right angles to the wood. Toe-nailing (driving the nails in at an angle) could be responsible for splits.

Theory #2 – in your part of the country, the vast majority of lumber used for decks is pressure preservative treated Southern Yellow Pine (SYP). It could very well be the SYP lumber is more susceptible to splitting than the species of wood provided for use in the building we are currently constructing.

Simpson Strong-Tie produces millions upon millions of engineered steel connectors every year – if there existing an inordinate (or any) number of failures due to the use of their products, they would be on top of making changes in the design to prevent them.

Me – if my choice is to nail a purlin over the top of the truss (which in the great majority of cases does not calculate out to be adequate structurally) or to use an engineered connector – the connector is going to win every single time.

DEAR POLE BARN GURU: I am currently assembling a Hansen Pole Building kit package. The building has a transition in roof slope from a steeper slope in the enclosed area, to a flatter slope in the open attached side shed.

In following the instructions in your Construction Guide, I note the solid wall between the enclosed and open portions is to have the wall framed and wall steel installed prior to placement of the roof steel.

My questions are these – I’m running the J trim at the top eave girt between the enclosed wall and shed.  Do I need to flow around the shed rafters with the J trim? Will I be able to square the roof if I put the wall steel on? STUMPED

DEAR STUMPED: Yes – the J Trim goes around the rafters which project through the wall. And as long as this wall is plumb before installing the wall steel, it will not interfere with being able to square up the roof.

The Great Purlins Caper

Here is the scene….

roof framing plansOur client has ordered a pole building kit package which is designed around sidewall columns spaced every 14’. For those who care, the building has a design roof snow load of 30 psf (pounds per square foot) and the actual roof dead load carried by the roof purlins (including the purlins themselves) is 1.626 psf. Our engineer designs a roof system with a pair of trusses at each sidewall column, and 2×8 #2 roof purlins joist hung between the trusses and placed 24 inches on center. The engineer prints off two sets of plans and supporting calculations, places his seal and signature on them, and sends them off to our client.

The client submits his plans and obtains a permit to build, which he proceeds to do.

Once under construction, the client sends this email to our office:

“My planning department made a notation on my plans that the roof purlins on the 14′ bays either need to be 16″ on center or use MSR 1450 rated lumber. The plans call out purlins 24″ on center and I don’t believe the wood I was shipped is rated MSR 1450. What is the resolution to this issue?”

The real issue, in my perhaps narrow mind, is a plans checker with perhaps limited ability to perform structural calculations, has made edits to an engineer sealed plan. Effectively, and probably unknowingly, this person has made themselves into the EOR (engineer of record) for this project, putting themselves and their Building Department into a potential position of liability should the building happen to fail structurally.

I wrote at length about this very issue earlier this year: https://www.hansenpolebuildings.com/blog/2013/07/building-official/

A couple of things to know about engineers (a broad generality of course) – their time does not come free, and they can get pretty bent out of shape when someone other than a Registered Design Professional questions their work.  After all, they spent considerable time and money getting their degree to be the “professional” assuming liability for every set of plans they seal.

In order to expedite a solution and keep the peace, I make a call to the plans checker. In the call I discover they have used 10 psf for the dead load on the roof purlins…..over six times the actual load! This sort of dead load would be much more appropriate for a building sheathed with OSB (oriented strand board) or plywood, with a shingled roof!

After a quick and happy conversation, the plans checker and I are now buddies, the crises is averted and the client is out building away on his building, using the plans as designed by the engineer.