Tag Archives: bottom chord dead load

Overhead Doors and Eave Height

Putting a 14 Foot Tall Overhead Door in a Short Eave Height…

I’ve been doing post frame buildings now for a couple of years. Okay, maybe a couple of couple of years, as in 37 (ouch, am I seriously this old?). I’ve learned a certain amount of clients (and builders) are seemingly dimensionally challenged when it comes to fitting overhead doors into buildings. Quote request, after quote request has come across my desk, for the overhead door height and the building eave height to be the same!

Newer readers might want to review how eave height is measured on post frame buildings: https://www.hansenpolebuildings.com/2015/02/eave-height-2/.

Hansen Pole Buildings’ Designer Doug posed this question of me earlier today, which came from a client of his:

“Do you offer a vaulted bottom chord that would allow us to lower the sidewall height and keep 15’6” at the 14’ overhead door?”

And Doug added…..

“My instinct and experience says we need minimum 2’ especially with a 14’ high door but it never hurts to ask.” (This would be needing two feet of eave height greater than the overhead door height)

The building in question has a 40 foot wide endwall. With placement of the overhead door at the center of the endwall, here is my answer to Doug:

The bottom side of the top jamb will be at 14’2.5″ above grade, 15″ to clear = 15’5.5″. Door is 12′ wide, so allow an extra 6″ of width for the tracks. This means at 13’6″ from the sidewall, you need to have 15’5.5″ above grade. With a standard gabled roof and 2×6 top chord on the trusses, the door just fits.

If the scissor truss bottom chord was a 1/12 slope, the eave height could be lowered to 14’10.5″; 2/12 13’9″; 3/12 12’7.5″.

 

 

Now the kicker – with scissor trusses, your client had better drive straight into the building and not want to park close to one of the sidewalls, because those trusses make a nasty slapping sound when they get hit, right before the roof caves in.

Because the scissor trusses are going to require adding to the exterior slope of the building, the overall building height is going to be the same or more, and scissor trusses are more expensive than standard trusses – probably making the entire project more expensive, with less net interior clear space throughout the building.

Can he do it? Sure. Is it practical or safe? Probably not.

Will My Trusses Hold Added Ceiling Dead Load?

Understanding the Needs of Load Bearing Finish

I sadly hear this story all too often. A brand new post frame building which quite possibly will not meet the load needs of the owner due to lack of due diligence upon the part of whomever sold the building. Here is the story and my response:

DEAR POLE BARN GURU: I have a newly constructed 30 x 40 pole barn, truss spacing 8′ o.c., 2×6. 5 PSF. I am wondering if I can cap the ceiling and insulate without over loading the bottom chord? Recommended material used for this? In laymen’s term how do I determine how much dead weight can be applied to bottom chord? At the time of construction I did not understand the load bearing needs of interior finish. Thank you – JUSTIN in MONROE

Dear Justin: Yours is one of the two most frequent issues following completion of a new post frame building, the other being insulating. Most post frame builders and building suppliers are afraid to have this discussion with potential new building owners – for fear the increase in price will scare them off! In my humble opinion, part of delivering “The Ultimate Post Frame Building Experience” is to discuss important issues such as this with clients BEFORE the building design process gets too far down the line. Shame on whomever you invested hard earned dollars with for not having had this discussion with you.

You should have been furnished with engineer sealed truss drawings for your building. If you were not, call whomever you purchased the building from, and request them. On the truss drawing will be a section which outlines all of the live and dead loads which the trusses are designed to support. If the number next to BCDL (Bottom Chord Dead Load) is less than five psf (pounds per square foot) then the trusses and the building are not designed to support a ceiling.

Take heart, if the design BCDL happens to be less than five, you can contact the truss manufacturer and for a nominal fee they can usually (especially with smaller truss spans like yours) get an engineered repair (or fix) to upgrade the trusses to support the load of the ceiling. This is never as inexpensive as having it done right to start with.

In order to install a ceiling in your building, you will need to ventilate the dead attic space you will be creating. More reading on ventilation is available here: https://www.hansenpolebuildings.com/2014/02/pole-building-ventilation/

Once past the truss loading and ventilation stages, the adequacy of the footings for the building columns to handle the extra load could pose a challenge – IF your new building was not designed to support a ceiling load to begin with. You should consult with the engineer of record who sealed the plans for your building, to verify the ability of the footing to properly transfer the loads from your building to the supporting soils. If you are unable to contact him or her, a competent engineer should be contacted to confirm what you have works, or to design a repair if not. Don’t overlook this step, or assume what you have will handle the load – we all know what assuming ends up causing – nothing but grief and having a column settle due to the added weight is not a problem you want to have to solve.

Ceiling joists will need to be installed between the bottom chord of the trusses. To support 5/8″ gypsum drywall, #2 (not standard & better) grade 2×4 or 2×6 can be placed 24 inches on center supported at each end with 2×4 joist hangers.

Planning a new post frame building? If you feel you or anyone after you who uses your new building will ever have the desire to install a ceiling (trust me – it happens a lot), at the very least have the trusses designed to support a ceiling load, as well as make provisions for adequate ventilation. The headache you solve, may very well be your own!