Tag Archives: floor joists

How to Properly Design a Barndominium Wood Floor Over a Crawl Space

How To Properly Design a Barndominium Wood Floor Over a Crawl Space

Reader JERRY in HAWESVILLE writes:

“If one were to build a post frame home on a crawlspace and the floor joists were sitting on a 3 ply 2×10 center beam on post spaced 8-10 feet apart, how does one support the joists at the outer walls? Do you need another 3 ply beam on each side and how would you attach those to your posts? If you could show a diagram, that would be great. Thanks.”

Well Jerry, a simple answer is yes, you need to support floor joists at the exterior wall. Beyond this things begin to get more complex and should only be done with a Registered Professional Engineer being involved.

Let’s begin with your interior floor beams, we will check for a beam spanning 10′:

fb: bending stress from live/dead loads
P = (D + L) = 10 psf + 40 psf = 50 psf
W = 50 psf * 8′ / 12 in./ft. = 33.333 pli (8′ is tributary area being carried by 3 – 2×10 #2 SYP members)
M = (33.333 pli * 120″2) / 8 = 60000 in.lbs
S = b * d2 / 6 = 3 * 1.5″ * 9.25″2 / 6 = 64.17 in.3
fb = M / S = 60000 in.lbs / 64.17 in.3 = 934.99 psi
934.99 ≤ 800 x 1.15 (Increase for repetitive members) so over stressed in bending by 1.6%

Not a very practical design solution.

If beam span is reduced to 8′, then allowable tributary area could be increased to 12′ (e.g. 6′ on either side).

Moral is your proposed 3 ply 2×10 beam is probably not a best solution.

Beams also need to be checked to meet Code required deflection limitations of  l/360 where “l” is the span of beam between supports. In this instance, bending will dictate design.

Hopefully this alone shows a fully engineered solution is best, as an engineer will confirm all needed grades and dimensions, as well as best connection methods. He or she will also design column footings to be adequate in diameter to properly distribute added weight (both live and dead loads) being added due to your floor system.

Builder Warranty Example

Example Builder Warranty

Disclaimer – this and subsequent articles on this subject are not intended to be legal advice, merely an example for discussions between you and your legal advisor.

I cannot express strongly enough how important to both builders and their clients to have a written warranty in any agreement. 

WARRANTIES: There is no warranty applicable to the building and is expressly in lieu of all other warranties available under any State or Federal laws, expressed or implied, including any warranty of all labor, material, product and taxes will be paid for and there will be no potential lien claim against Purchaser’s property upon completion of the work and following final payment by Purchaser to Seller.

Products supplied by third party suppliers, manufacturers and sub-contractors to the project are warranted only to the extent that the suppliers and manufacturers of those products provide a warranty.

In the event that a defect is discovered in one of these products, Seller will assist Purchaser in securing repair or replacement of these products under the warranty provided by the third party supplier or manufacturer. Warranty work is work which was correctly and completely done initially, but becomes non-operational or dysfunctional following occupancy or use by Purchaser. No retainage or holdback will be allowed for warranty work.  

Seller expressly warrants to the original noncommercial purchaser(s) and only the original purchasers.  

That if any part of a Seller constructed post frame building, as covered by this warranty, proves to be defective due to materials or workmanship, under normal use and service, for two (2) years, that defective part will be repaired or replaced, subject to the terms and conditions contained in this Warranty.

Seller hereby assigns to Purchaser all rights under manufacturer’s warranties. Defects in items covered in manufacturer’s warranties are excluded from coverage of this limited warranty, and Purchaser should follow the procedures in the manufacturer’s warranties if defects appear in these items. 

 For ten (10) years.

Any solid sawn or glu-laminated (pressure treated to a minimum UC-4B) structural columns that fail due to decay or insect damage, unless said column has been exposed to animal wastes.

The original building roof structure, if damaged directly by snow loads because of the failure of any prefabricated roof truss or trusses to meet design specification. Subjecting your roof system to greater loads than those set out on the face of this Agreement, any unspecified ceiling loads, or modifying the trusses in any way voids all Warranties.

Any major structural defects which are defined as being an actual defect in a load-bearing portion of the building which seriously impairs its load-bearing function to the extent that the building is unsafe. For purposes of this definition, the following items compromise the structure of the building:

  1. Load bearing columns,
  2. Floor or ceiling joists,
  3. Beam, trusses and rafters.

For Two  (2) Years:

Any roof leaks due to defects in material or workmanship, expressly excepting where the building has been connected to an adjoining structure, in roof valleys, or at roof slope changes to which cases, no warranty applies. 

Any other building parts which prove to be defective in material or workmanship.

This warranty period shall commence on the date of the acceptance of the building by the Purchase or Purchaser’s occupancy of the building, whichever comes first.

This warranty contained wherein is void in situations where:

  1. Installation is not made in accordance with the instructions supplied by Hansen Buildings.
  2. The actual operation or use of the product varies from the recommended operation or intended use.
  3. There is a malfunction or defect resulting from or worsened by misuse, negligence, accidents, lack of or improper performance of required maintenance by the original purchaser.
  4. The building is altered or added onto, unless by Seller.
  5. Seller is not notified within twenty four (24) hours of problems due to snow loads.
  6. Purchaser fails to take timely action to or damage.
  7. Anyone other than Seller’s employees or agents or subcontractors have been on the building roof.
  8. Purchaser fails to make final payment per terms of sale.

Equipment such as fans, HVAC, gutters, downspouts, walk door locksets, other equipment not manufactured by Seller, site work, concrete, doors, windows, interior finishes, mechanical or electrical systems are excluded from this warranty.

The Purchaser expressly agrees to fully and timely pursue all available remedies under any applicable insurance agreement before making claim under this warranty.

In the event Seller repairs, replaces or pays the cost of repairing or replacing any defect covered in this warranty for which Purchaser is covered by insurance or a warranty provided by another party. Purchaser must assign proceeds of such insurance or other warranty to Seller, to the extent of the cost to Seller, of such repair or replacement.

Any claims for defects under warranty must be submitted in writing to Seller within the warranty period and promptly after discovery of the claimed defect, describing the defect claimed and date of building completion, before Seller is responsible for correction of that defect. Written notice of a defect must be received by Seller prior to the expiration of the warranty on that defect and no action at law or in equity may be brought by Purchaser against Seller, for failure to remedy or repair any defect about which Seller has not received timely notice in writing.

Purchaser must provide access to Seller, during normal business hours to inspect the defect reported and, if necessary, to take corrective action. A reasonable time should be allowed for inspection purposes. If, after inspection, Seller agrees, at its sole option to repair or replace only the defective materials or workmanship within the first three months from date of building completion at NO COST to the Purchaser. Thereafter Seller shall assume the cost of material and labor for any warranty work upon advance payment by the Purchaser of a one hundred dollar service payment for each incident under this warranty. The obligation of Seller, under this warranty, shall be performed only by persons designated and compensated by Seller for that purpose, and is subject to all other provisions of this warranty.

The provisions of this Warranty are the full and complete warranty policy extended by Seller, and are expressly in lieu of all other warranties, expressed or implied, including any warranty of merchantability or fitness for a particular purpose. These warranties may not be transferred or assigned. The liability of Seller shall not exceed the cost to Seller for repairing or replacing damaged or defective material or workmanship, as provided above, during the warranty period. 

THE WARRANTY STATEMENTS CONTAINED IN THIS LIMITED WARRANTY SET FORTH THE ONLY EXPRESS WARRANTIES EXTENDED BY SELLER FOR ITS BUILDING AND THE PROVISIONS HEREOF SHALL CONSTITUTE THE PURCHASERS EXCLUSIVE REMEDY FOR BREACH OF THIS WARRANTY. IN NO EVENT WILL SELLER BE LIABLE TO THE PURCHASER FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND FOR BREACH OF AN EXPRESS OR IMPLIED WARRANTY ON THE BUILDING; PROPERTY DAMAGE, PERSONAL INJURY , OR ECONOMIC LOSS IF OCCASIONED BY SELLER’S NEGLIGENCE, EVEN IF SELLER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. 

Some states do not allow the exclusion or limitation of incidental or consequential damages, so the above limitations or exclusions may not apply to you. This warranty gives you specific legal rights and you may also have other rights which vary from state to state. 

Purchaser shall promptly contact Seller’s warranty department regarding any disputes involving this Agreement.

Seller and Purchaser agree that this limited warranty on the building is in lieu if all warranties of ability or workmanlike construction or any other warranties, express or implied, to which Purchaser might be entitled, except as to consumer products. No employee, subcontractor, or agent of Seller has the authority to change the terms of this warranty.

A Floor Raising Exercise: I Joists

For some obscure reason people planning new buildings tend to scrimp on height. In most instances, designing a new fully engineered post frame building – whether for a barndominium, shop house (shouse), garage, shop, etc., just a little bit taller is a relatively inexpensive proposition and can save many more dollars and mental anguish than having to alter after construction.

Reader CHRIS in SNOHOMISH writes:

“I have a pole barn with a center door for Rv, above is an additional living space, the width is 12’6” depth of 41’ height of 13’, I need to shorten the truss’s so I can gain 6” height , current truss are HY floor joists, question is can I put 2×6” spaced every 8”’s and have the same weight carrying capacity?”

Mike the Pole Barn Guru writes:

HY floor joists are wood prefabricated I joists. Let’s take a look at Chris’ proposed design solution (please keep in mind, any structural design solution should be reviewed by your building’s engineer to confirm structural adequacy):

FLOOR JOIST DESIGN

Assumptions:

Joist span 12.5-ft.
joist spacing = 8″ o.c.

joist  live load = 40 psf
joist_dead_load = 10 psf

Fb: allowable bending pressure
Fb‘ = Fb * CD * CM * Ct * CL * CF * Cfu * Ci * Cr
CD: load duration factor
CD = 1 NDS 2.3.2
CM: wet service factor
CM = 1 because floor joists are protected from moisture by roof
Ct: temperature factor
Ct = 1 NDS 2.3.3
CL: beam stability factor
CL = 1 NDS 4.4.1
CF: size factor
CF = 1.3 NDS Supplement table 4A
Cfu: flat use factor
Cfu = 1 NDS Supplement table 4A
Ci: incising factor
Ci = 1 NDS 4.3.8
Cr: repetitive member factor
Cr = 1.15 NDS 4.3.9
Fb = 900 psi NDS Supplement Table 4-A
Fb‘ = 900 psi * 1 * 1 * 1 * 1 * 1.3 * 1 * 1 * 1.15
Fb‘ = 1345.5 psi

fb: bending stress from live/dead loads
fb = live + dead load * joist spacing / 12 / 12 * (sf * 12 – 1.5)2 / 8 / (b * d2 / 6)
fb = 50 psf * 8″ / 12 in./ft. / 12 in./ft. * (12.5′ * 12 in./ft. – 1.5″)2 / 8 / (1.5″ * 5.5″2 / 6)
fb = 1012.5 psi <= 1345.5 psi so okay in bending

Δallow: allowable deflection
Δallow = sf * 12 / 360 IBC 1604.3
Δallow = 12.5′ * 12 in./ft. / 360
Δallow = 0.4167″

Δmax: maximum deflection
Δmax = 5 * live load * joist spacing / 12 / 12 * (sf * 12 – 1.5)4 / 384 / 1600000 / b / d3 * 12 from http://www.awc.org/pdf/DA6-BeamFormulas.pdf p.4
Δmax = 5 * 40 psf * 8″ / 12 in./ft. / 12 in./ft. * (12.5′ * 12 in./ft. – 1.5)4 / 384 / 1600000 / 1.5″ / 5.5″3 * 12
Δmax = 0.423″ > 0.4167:
2×6 #2 DougFir joists will not work at 8″ on center due to not meeting deflection criteria

Chris’ options are to buy #1 or Select Structural graded 2×6 DougFir or go to 6″ on center spacing.

Designing a Dream Barndominium Loft

Designing a Dream Barndominium Loft

Reader BRIAN in PETOSKY writes:

“ Hi Mike,

Mindi told me to email you my lofted floor question for our project.

To avoid messing with truss-support floors, we were planning to build a full 26×60 main barn with scissor trusses the full length. Then on one end, we would make a 20’x26′ loft. Have the floor joists run parallel to the barn, perpendicular to the trusses, so we’d have 20′ floor joists. These would be supported by the gable end wall and interior posts 20′ in.

We live in a barn home with this configuration and it works well. Allows consistent and uninterrupted ceiling space the length of the barn but still get a 2nd floor in where we want it.

The question is, I guess, what, if anything needs to be conveyed to the engineer for this design? Does it influence anything on the gable end wall? How far apart can the posts be on the interior end? Can stairs be free-standing next to this loft?

Thank you!”

When I used to call on Home Depots, Petoskey was one of my stops. Every time I was there the weather was gorgeous, making it difficult to get motivated to move on to my next appointment!

There are some challenges with running dimensional lumber floor joists to span 20′. Even using #2 & better 2×12 Douglas Fir joists, they would need to be 12 inches on center! Other popular specie of framing lumber has lower MOE (Modulus of Elasticity) values, so will not even begin to approach being able to span 20’. Chances are good there will be both a fair amount of spring to this floor, as well as a non-uniformity in deflection from joist to joist.

For extended reading on floor deflection, please read https://www.hansenpolebuildings.com/2015/12/wood-floors-deflection-and-vibration/

This would be my recommendation – we can use prefabricated wood floor trusses to span 26′. Doing so would allow there to be no interior supports within this 26′ x 20′ area. As long as stairs run perpendicular to the floor trusses, no columns would be needed where they attach. When you and Mindi have your building details finalized, she will relay this information forward on your Agreement with us, so everyone will be on the same page. Further, we send plans to you for a final once over prior to engineer sealing them, just in case.

Wood Floor Trusses

When I was first in the metal connector plated wood truss industry back in 1977, my employers – Dutch Andres and Tom Vincent at Spokane Truss, had just invested in a machine which would fabricate what would be called a 4×2 floor truss.

These trusses revolutionized the way floors could be constructed – freeing up areas below them from the need for load bearing walls and columns in all of the most inconvenient places!

Rick Ochs is new to the inside team at Hansen Pole Buildings, and earlier this week, he posed a question:

“Hey Mike,

No rush… I have been viewing tutorials from WTCA (Wood Truss Council of America) on trusses and structural building components.  I was wondering why we don’t spec floor trusses instead of the traditional 2×10 with hangers.  Cost I presume.

Thanks!”

Here is my response to Rick:

Floor trusses will be significantly more expensive.

Let’s say you have a 2×10 at .6285m (current price at The Home Depot®) so a 12′ would be $12.57.

(“m” happens to be lumber people’s secret code for 1000 board feet)

If they were even 16″ o.c., you are talking 0.79 per square foot for the cost of joists.

Floor trusses are going to run around $4.40 per lineal foot, spaced 2′ on center, this makes the cost per square foot for the joists at $2.20.

For a floor span of over 24′ trusses are certainly the way to go.

To which Rick responded:

“I’m thinking it would take a little more math on the builder/customer part to compare against labor cost savings of setting floor truss vs time required to set hangers, cut and nail joists.”

Personally, I have metal connector plated wood floor trusses in two of my personal buildings – in one case spanning 30 feet and the other 48 (yes a 48 foot clearspan floor).

Here are some of the benefits of using wood floor trusses:

  • Larger sheathing attachment, with 2×3 or (usually) 2×4 nailing surface,
  • Spacing up to 24” o.c. maximizes efficiency, decreasing installation time.
  • Each unique truss is engineered to proper codes and loading.
  • Speeds up mechanical installation (think heat ducts) with the open webbing thus saving dollars.
  • Span longer distances than conventional lumber or I-joists.
  • Special bearing, cantilever, and balcony details are easily built in.
  • Less pilferage, it is unlikely a 20’ truss is going to walk off the jobsite.
  • Faster jobsite build times, saving jobsite labor, construction loan interest, vandalism, and environmental damage.

Wood floor trusses can also be designed to limit the deflection and vibration, read more here:

https://www.hansenpolebuildings.com/2015/12/wood-floors-deflection-and-vibration/

In the global scope of life, having a wood truss supported floor is a fairly economical upgrade, which is certainly something worth investigating.

Scary Pole Barn Design

Scary Design

A one-time potential Hansen Pole Buildings’ client, who is a friend of mine on Facebook, didn’t invest in one of our engineered post frame buildings. Most likely it was due to price – people so easily believe they have gotten a great deal, when instead they set themselves up for nothing but potential grief.

He proudly posted the photo above on Facebook of the progress of his new building.

Disclaimer – in case you, gentle reader, were unsure – his new building is NOT a Hansen Pole Building.

I will let you in on a secret which truly frightens me about this building…….

loft floor framingIf a load approaching what the loft should be designed to support is placed upon it, I venture to wager it will fail. Do not stand underneath it, by any means.

As near as I can tell from the photo, the columns which support the second floor are spaced roughly 12 feet on center. It appears the floor joists are 2×12 spaced 16 inches on center and each end of the joists are supported by what seems to be another 2×12.

Building design and construction are only as good as the weakest link.

The building is in the deep south, so we will go with the premise the lumber being used is Southern Pine.

The floor joists are not a problem – they would easily support double the normal design floor live load of 40 pounds per square foot (for residential loading). The problem comes from the beams which support them at each end.

Here is the formula for design of the beams:

(Live plus dead loads) X ½ the distance to the next beam X Beam span^2  /  8 X 31.6406 (the Section Modulus of a 2×12) X Fb (for 2×12 Southern Pine 750) X 1.15 (Cr – repetitive member increase)

(40 + 10) X (72”) X 12’^2 / 8 X 31.6406 X 750 X 1.15 = 2.37 when it has to be less than or equal to one to work.

The floor, as built, is overstressed by 237%!! Or – think of it this way, it will only support 42% of what it should support by the BuildingCode!!

In either case, it is frightening.

Don’t construct (or have constructed for you) any post frame (pole) building which has not been designed by a Registered Design Professional (RDP – architect or engineer). To do so is scary pole barn design and nothing short of playing Russian Roulette.