Tag Archives: Truss

Roof Truss Costs, Moisture Barriers, and Integrated Condensation Control

This Wednesday the Pole Barn Guru addresses reader questions about “the most cost effective length to procure, transport and install of a Post Frame Roof Truss 4/12 Pitch; 36′, 40′ or 50′?” a suitable moisture barrier for a shed, and Integrated condensation controls.

DEAR POLE BARN GURU: Typically, what is the most cost effective length to procure, transport and install of a Post Frame Roof Truss 4/12 Pitch; 36′, 40′ or 50′? Question is relevant to a mixed-use agriculture building. Thank you for your assistance. LYNNE in EDINBURG

DEAR LYNNE: Transportation can often be a limiting factor. In order to avoid pilot cars and over width permits, maximum truss height is limited to 102″ (8’6″). A 50′ span, 4/12 slope truss will normally be roughly 108″ tall, plus any overhang “tails”. So, this would entail an over width permit. Now most truss companies purchase year-long over width permits for their trucks, so this cost is negligible. Most states do not require pilot cars, unless loads are 12 foot or greater in width. This allows for 60 foot span trusses to be hauled without expensive pilot vehicles. As to procurement, while you will pay more per lineal foot of truss as spans increase, you will also need fewer trusses. For an agricultural building, I always encourage clients to build as large as they can economically justify and have space to build on, as it will never be too big. Keeping your building length to three times building width will also help with your budget, as these ratios are typically within shear load carrying capabilities of properly fastened steel roofing and siding.


DEAR POLE BARN GURU: I have a 12′ x18′ unheated shed framed and ready for the metal roof and siding. The roof will anchor to untreated 2″x4″ purlins. Is it ok to use Tyvek or a similar wrap to cover the seams from the top of my purlin ends and hang over the rake rafters that will be covered by the metal siding???? Is this an acceptable secondary water barrier between my roof and wall seam? My shed will most likely have a crushed limestone floor. It will be unheated and “unfinished” on the inside. No windows and 2 barn doors across from each other. Thank you so much. MACK in BATON ROUGE

DEAR MACK: Before placing your limestone floor materials, install a well-sealed vapor barrier (I recommend 15mil in order to minimize potential for punctures). This will help to minimize, or even eliminate condensation challenges. Order your roof steel with an Integral Condensation Control (Condestop, Dripstop or similar) factory applied. Cover walls with Tyvek or similar before installing wall steel.

If purlins cross rake rafters on endwalls, install 2×4 blocking between them to seal any open spaces.

Order steel Rake/Corner trims to cover last rib of roof steel and top of endwall steel (similar to below):


DEAR POLE BARN GURU: Building a 50x36x12 pole barn with 4:12 roof pitch. Attic space will be unconditioned with blown in cellulose insulation in ceiling and batten on walls. Attic will be vented with soffit and ridge vent. Walls will have exterior house wrap under metal panels. Question is, what to put under the roof panels? Just a vapor barrier or a dual purpose vapor/radiant barrier? I hear different opinions on placing radiant barrier under roof. STEVEN in SUGAR LAND

DEAR STEVEN: I would order your roof steel with an Integral Condensation Control (Dripstop, Condenstop or similar) factory applied. You can read more about these products here: https://www.hansenpolebuildings.com/2020/09/integral-condensation-control-2/



Dead Load, Sliding Barn Doors, and Truss Spacing

This weeks PBG discusses a bottom chord dead load, installing sliding barn doors, and truss spacing.

DEAR POLE BARN GURU: Ok, just to make sure I understand that 10lb psf dead load rating would cover the bottom chords supporting ducts either resting on or suspended from them inside the conditioned space? My thinking is if the vents are within the conditioned space I would need minimal insulation to prevent surface condensation. ROB in ANNAPOLIS

DEAR ROB: 10 psf dead load is primarily to cover weight of ceiling gypsum wallboard. Your relatively light duct could be placed anywhere within roof system without adverse effects. A down side to placing duct work within a conditioned attic – effectively insulating roof slope plane and endwall triangles. For practical purposes this can only be achieved with closed cell spray foam. While being highly effective as an insulator, about R-7 per inch of thickness, it comes with a price tag not for those who are faint of pocketbook – usually around a dollar per square foot per inch of thickness. If you go this route, you need to eliminate venting eaves and ridge.

DEAR POLE BARN GURU: Good morning,

Figure 27-5

I need to get some pricing on a (2) 6’-0” wide x 8’-0” high sliding barn style doors for an agricultural building in Ware county Ga.


I have never purchased, or installed a door like this, so I was hoping you could help me get started.



DEAR DAVID: Thank you very much for your interest. Hansen Pole Buildings only provides doors along with an investment in a complete post frame building kit package, due to high incidence of damage when shipped independently. We do have installation instructions available online: https://www.hansenpolebuildings.com/2016/07/build-sliding-door/.


DEAR POLE BARN GURU: What would the truss spacing need to be in our area that has a 40lb snow load? RODNEY in REPUBLIC

joist hangersRODNEY: In most instances a true double truss (not two single trusses spaced apart by blocking) will be most cost effective, as well as adequate to carry applied loads (along with properly sized roof purlins). However, depending upon a myriad of other factors such as eave height, truss span, roof slope and building length some other spacing may result in cost savings.

This will be just one reason I recommend consulting with a post frame building kit supplier who has sophisticated design software able to do a near instantaneous analysis of multiple possibilities. This supplier should also be able to provide site specific plans for your building, sealed by a registered design professional.



A Silly Extreme Example

I’m a voracious reader. A large portion of my daily reading is devoted to learning as much as I can about my industry and expanding my knowledge base.

On LinkedIn, I am a member of the “Truss, Panel & Building Components” discussion group. One of the members, Gene Marcoux, from Florida, had postulated, “If we have a chance to reshape the way things are going to be done, wouldn’t it make sense to have the whole structure engineered for structural integrity….”

I happen to personally agree with Gene’s statement. If a design professional did not do the structural design of your new pole building, then who did?

Building Code Book

IBC Building Code Book

Keymark Enterprises, Inc., of Colorado, provides structural engineering and precision manufacturing of wood components (such as trusses and wall panels). Their account representative, Steve Cummings had this take on the subject:

“In perhaps a silly, extreme example, think about a 20×24 garage on a farm in Kentucky. Right now there is no government check that it will conform to current code, no engineering requirement, no permit required, no inspection necessary. We all know, from experience and training, how to build this garage. What is the value of the increased requirements vs. the cost of building departments, inspectors, engineers and designers?”

In my humble opinion, while an industry expert may know how to properly construct this pole building, not everyone is an expert. All it takes is one error in the design of a connection (too few nails, nails too closely spaced, an incorrect hanger, etc.) or sizing of a structural member and a catastrophic collapse could be the result.

The Building Code purpose “is intended to provide minimum requirements to safeguard the public safety, health and general welfare through structural strength, means of egress facilities, stability, sanitation, adequate light and ventilation, energy conservation, and safety to life and property from fire and other hazards attributed to the built environment”.

In having no permit requirements, there is no one to insure the goals of the codes are met. Are we willing to sacrifice a life or lives, due to deficient design, all in the name of saving a few dollars?