Tag Archives: Design Solutions

Weather Resistant Barriers, LVL Notches, and Design Ideas

This week the Pole Barn Guru answers reader questions about weather resistant barriers, a caution to not attempt to notch LVL rafters, and a recommended design solution for a new build.

DEAR POLE BARN GURU: We are in process of designing our barndominium with hoping to start building next spring. Do you have a recommendation as to what water resistant barrier (WRB) to use with closed cell spray foam? Planning on using a standing seam metal roof and wainscot siding at this time. I know that a reflective barrier is useless without an air gap behind it. Using spray foam prevents its use. I’ve researched several, like zip system, Tyvek, and others. Thanks for answering my question. GREG in CARROLL

DEAR GREG: In your climate zone I would typically not recommend using spray foam other than as two inch thickness applied directly to steel roofing and/or siding in order to control condensation. This does result in having to mechanically control humidity as your building will now “dry” to inside. As standing seam steel does not provide shear resistance, it must be installed over solid decking – and you can spray foam directly to this decking underside.

In any case, it is not recommended to use closed cell spray foam applied to any WRB. For extended reading: https://www.hansenpolebuildings.com/2020/04/spray-foam-insulation-3/


DEAR POLE BARN GURU: I got a pole barn I’m putting up. The purlins were designed to run over end rafter bit that makes eve low. Can a 1 ½” x3 ½”(2×4) notch for outrigger for eave support and run end rafter up like others in the center. Notch would be 1 ½” deep on an 11 ¾” lvl. One in center span and one at top of roof. This is on the shed roofs only. MIKE in RAVENSDALE

DEAR MIKE: Absolutely do not cut or notch into your end rafter. You need to lower end rafters to allow purlins to go over top of end rafters without any notching.

While you are at it – have your building’s engineer recheck those shed rafters and purlins closest to main endwall to confirm they are adequate for snow drift loads. Usually purlins closest to endwalls have to be much closer together to adequately support those loads.


DEAR POLE BARN GURU: I want to space my poles 8′ apart and use to 2×12, one inside and one outside at the top to place standard trusses on the top so i can add an insulated ceiling in it. Any comments on this, and how deep do my posts have to go into the ground? LARREN in DAVIS CREEK

DEAR LARREN: Personally, I would throw away your proposed design solution.

In most instances, you are better served with sidewall columns spaced every 12 feet. Use a true two-ply truss, aligned with every sidewall column (https://www.hansenpolebuildings.com/2018/09/true-double-trusses/) and notched in. Trusses should be engineered to carry a ceiling (bottom chord dead load – BCDL). Use five (5) psf (pounds per square foot) for a steel ceiling and 10 psf if sheetrocked. Between bottom chords of pairs of trusses, joist hang 2×6 #2 24 inches on center.

In any case, raised heel trusses should be utilized to allow for full depth of insulation from wall-to-wall. https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/
Column depth will be determined by engineer who is designing your plans. They need to be deep enough to go below frost line (not an issue in California) as well as to resist overturning and uplift. Building dimensions, applied wind loads and soil bearing capacity will all impact depth of holes.

Pole Building Specs- Design Solution!

Sometimes prospective clients educate themselves just enough to be dangerous – most often dangerous to their own pocket books. I much more prefer a client who comes to us looking for a design solution and assistance in best fitting a building around their needs for today and the future. This is rather than one who has preconceived notions of what pole barn specs should be for their particular building – perhaps without even knowing why it is they want what they are asking for.

My question: “Do you mind sharing why (fill in the blank) is important to you?”

Here are some excerpts from a recent request from a client:

Building:  42’wide x 80’ long, 13’ height, 8’ truss spacing, 6/12 roof pitch, 2/12 lower chord, peak height 25’, soffit height 14’3.5”

My all time most read article happens to address truss spacing: https://www.hansenpolebuildings.com/2011/06/pole-barn-truss-spacing/

There does seem to be some dimensional mismatches when it comes to heights. Working backwards from the 25 foot peak height, would make the eave height at a 6/12 roof slope 14’6”.

The client has some specific overhang requests:

Overhangs: 12” boxed vented overhangs (6” fascia) w/ gutters and downspouts on 80’ sides, gable ends 12” non-vented overhang (6” fascia)

Working again from the overall height, which gave us an eave height of 14’6”, the roof will lose six inches of height across the foot of overhang, a 2×6 beveled to a 6/12 slope would measure 4.75 inches and the soffit is a half inch thick. This puts the underside of the soffit at 13’6.75”.

Foundation: pre cast concrete pier with bracket to attach to laminated wood columns above grade

There are some folks who just do not feel confident in placing pressure preservative treated wood in the ground. I’ve never quite understood the rationale behind having a rather heavy precast chunk of concrete shipped in, when a hole could be filled with concrete and a wet set bracket placed into it: https://www.hansenpolebuildings.com/2012/09/concrete-brackets-2/

Siding and 36” wainscot: 26ga ribbed steel panels, fastened with stainless screws

Roof: 26ga ribbed steel panels fastened with stainless screws

Frankly 26 gauge steel is going to be overkill – the steel skin is not the weak link of the building system.  Here is an in depth article on steel thickness: https://www.hansenpolebuildings.com/2012/01/steel-thickness/.

The stainless steel screws are just another way to run more dollars through someone’s till: https://www.hansenpolebuildings.com/2017/03/use-stainless-steel-screws-steel-roofing-siding/.

Want to get the most post frame building for your investment?

If your answer is no, then Hansen Pole Buildings is probably not going to be the best fit.

Yes – tell one of our highly skilled Building Designers what your vision is of your ideal dream building (what problems will it solve and goals will it help you achieve) and we will provide for you the Ultimate Post Frame Building Experience™.