Tag Archives: OSB

Truss Spacing and Design

Truss Spacing and Design for Sheathed Post Frame Roofs

In most instances, there is not a structural or Code requirement for solid roof sheathing (plywood or OSB – Oriented Strand Board) to be placed below through screwed roof steel for post frame buildings. In some cases, clients look upon this as being an easier installation when doing a DIY build. For others, it is about providing a thermal break to eliminate underside of roof steel condensation. And a few look towards minimization of potential hail damage.

Reader CARROLL in PORTER writes:

“ Wanting to build Pole Barn that is about 35’x80’x12′ My question is, if I want to install 1/2″ decking plywood or OSB decking with underlayment and metal panels how far apart will I need the trusses to be center to center or what kind of truss design will I need? I guess it could be a 4/12 or 5/12 pitch if that helps any.”

Provided you have adequate available space, you may want to tweak your footprint dimensions in order to optimize your return for your investment. As steel comes in three foot widths and lumber in two foot lengths, your most cost effective dimensions of length and width will be multiples of six feet. In your instance, I would recommend 36 feet wide and 84 feet long.

With this said, I would place a single truss on each endwall and a two ply truss every 12 feet to align with your sidewall columns. Purlins can be placed on edge, using engineered steel joist hangers, between each set of trusses and spaced every two feet to support your sheathing. Whether plywood or OSB, panels are best installed running up roof from eave to ridge (perpendicular to purlins, parallel with truss spans). If not using synthetic underlayment, you should use 30# asphalt impregnated paper (roofing felt). With Hansen Pole Buildings, we purposefully design all trusses spanning 40 feet or less with a greater than minimum requirement top chord dead load – in order to accommodate those who want to install solid sheathing.

 

Truss Spacing for Shingled Roofs

Roof truss spacing seems to be a topic with no consensus. Most Americans live in traditional stick framed houses, apartments or condominiums, where roof trusses (if they were utilized, rather than using dimensional lumber rafters) are most typically spaced every two feet.

Reader CHARLIE writes:

“Dear Hansen Pole Buildings, May I ask how far apart was the Truss placement in your “Re-roofing with Shingles” article? 

https://www.hansenpolebuildings.com/2012/01/re-roofing-with-shingles/

I’m considering a 24’x 36’ pole barn for a recording studio build but would need asphalt shingle type roof. I’m concerned that a suitable design would need additional rafters to meet the 7 lb/sq ft load requirement.

Most designs I have seen are showing the trusses 4’ OC. 

Respectfully, Charlie”

Mike the Pole Barn Guru writes:
In this particular article roof trusses were actually spaced with a pair every 12 feet – directly aligned with sidewall columns. This style of post frame construction affords several advantages:

Fewer holes to dig. There is nothing more deflating than getting down to digging one or two last column (pole) holes and hitting a rock larger than a Volkswagon Beetle! Minimization of holes to be dug reduces chances of underground surprises.

No need for truss carriers (structural headers) between columns in order to support trusses. Structural failures are almost always due to connection issues. Truss carriers rarely have adequate fasteners from header to columns and trusses themselves are rarely anchored sufficiently to them.

By far my most read article of all time has been on pole barn truss spacing: https://www.hansenpolebuildings.com/2011/06/pole-barn-truss-spacing/.

Asphalt shingles need to be installed over asphalt impregnated paper (felt) or ice and snow shield, most usually over OSB (Oriented Strand Board) or plywood. Weak link of this system is spanning ability of this underlying sheathing.

In order to be within spanning capabilities of common sheathing, dimensional lumber roof purlins, on edge, were joist hung between truss pairs, every two feet.

When you order a post frame (pole barn) kit from Hansen Pole Buildings with asphalt shingles, we automatically have our engineers design for this added load, as well as reducing deflection criteria so you end up with a nice, smooth roof. We also take into consideration Building Code requirements to account for a future overlaid reroof (even “lifetime” shingles will not last anywhere near a lifetime).


Considering a shingled roof due to how long they are warranted? You might want to read this article first: https://www.hansenpolebuildings.com/2015/03/shingle-warranties/.

The Roof, The Roof… and Sheds without Sidewalls

Mike answers questions about a Roof Line, Roofing with OSB layer, and Endwall Only Sheds:

DEAR POLE BARN GURU: What is the roof line style in the attached picture called? BRYAN in MARYSVILLE

DEAR BRYAN: The prefabricated roof truss folks would refer to this as being a Polynesian roof – one in which the outer portion is at a lower slope than the center portion. I tend to steer clear of steeper-to-flatter roof slope changes as they just increase the possibility of a future leak, however it is certainly doable. Your photo also features a widow’s peak at the center.

 

DEAR POLE BARN GURU: Hello Guru, I am Putting 1/2″ Plywood On the trusses first before the metal roof, what do U recommend to cover the plywood, for vapor barrier protection? I was just gonna use felt paper! any recommendations? Thanx MIKE in ROCHESTER

DEAR MIKE: If applying the plywood directly over trusses spaced every two feet, you will need to add purlins in order to screw the roofing down (screws into plywood or OSB are inadequate for wind uplift). Steel manufacturers recommend the use of 30# asphalt impregnated paper (roofing felt) between sheathing and roofing.

DEAR POLE BARN GURU: What is it called if I only want a structure that has a wall in the front and wall in the back but open on the sides for animal pens? I can’t seem to find ANY images of this type of building. CHRISTINE in BERTRAM

DEAR CHRISTINE: I would call it a loafing shed with both eave sides open. It could be either single sloped, or have peaked endwalls.

Sometimes There Are Just Not Words: Hansen Building Disaster

Sometimes There Are Just Not Words to Express…  Building Disaster

How horrifically a build can be botched.

 

In a scene from 2013’s box office flop The Lone Ranger – Tonto (played by Johnny Depp) and the Lone Ranger (played by Armie Hammer) the heroes get themselves buried in the sand up to their necks. After looking at the photos provided by our client of what a “professional” builder did in framing his building, I am thinking tossing a coin to decide the builder’s fate might be appropriate. Heads – buried in the desert to the neck, or tails – boiled in scalding safflower oil (as we would not want the builder to meet his demise due to saturated fats).

These photos are of the front endwall of a Hansen building. The areas where the OSB (Oriented Strand Board) are visible are shearwalls. These are needed in order to carry the horizontal loads imposed on the building due to wind from the roof to the ground. In most cases, the steel siding is adequate to carry these loads. In this particular case, a large endwall door opening precludes this as a design solution.

In order to function as a shearwall the OSB has to be nailed on all edges, hence the 2×6 which is visible on the face of the columns. The engineered plans for this building happen to show the verticals as being 2×4, however this did not stop the builder from hacking up 2×6 which was ordained for somewhere else on the building. The trick to attaching the OSB at the edges (next to the columns) is to mount the provided 2×4 half onto the column, the other half projecting past the column so the OSB can nail to it.

Oops – ignored this part of the plan (and obviously never opened the Hansen Pole Buildings’ Construction Manual where this assembly is shown in step-by-step fashion).

But wait, it gets even better (or worse for the poor building owner)! Stay tuned tomorrow for the next installment .
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