Tag Archives: parallel flat chord trusses

Footing Size? A “Reverse Barndominium?” and a Loft Bedroom?

This week the Pole Barn Guru answers questions about the footing size for an open car porch and why a person should use a registered design professional, building a “reverse barndominium” where one build a post frame shell around an existing structure, and if one can build a loft bedroom in a footprint of 20’x 30′.

treated postDEAR POLE BARN GURU: I am building an open car porch, the inside will be connected to another building and on the outside I planning on using 3 – 8 inch x 8 inch x 8 feet posts 12 feet apart. The open car porch area is 24ft x 24ft and the roof is 6 on 12 with 2 x 6 rafters and joists landing on the outside plate. What size footing will I need for each pole? JAY in MORGAN CITY

DEAR JAY: This is a question best answered by the Registered Professional Engineer who designed your building, as he or she will be able to do a complete analysis including soil bearing capacity, design wind speed and wind exposure. With columns only eight feet long, I am guessing you are planning on using wet set brackets into concrete piers https://www.hansenpolebuildings.com/2019/05/sturdi-wall-plus-concrete-brackets/. I would not be surprised to see piers up to three feet deep and two foot diameter in order to adequate resist uplift forces.

DEAR POLE BARN GURU: Are you aware of anyone ever building a “reverse barndominium”? Usually barndominiums are built shell (outside walls) first then the interior, but what about building entirely around an existing structure? I really want to buy this historic house built in 1861. It is currently gutted down to the dirt floors, needs a roof, garage, etc. Why not just enclose the whole thing and DIY the interior without dealing with the outside elements? The primary structure is 19’x38′, but the side structure is an additional 20′ (39′ total wide) with a 6/12 roof. The eave height is 15.5′ and about 20′ at the ridge. The basement is about 4′ deep. I could go 42′ wide with a structure and have the exterior posts completely outside of the current footprint. The lot is 60’x150′ and I’m looking at a 40×80-ish building with a second story.

Is this feasible or have I succumb to the Dunning-Kruger Effect? I have attached an image of my sketchup drawing to give a better idea of my concept.

Thank you great guru. I love your philosophy and transparency throughout your blog posts. I have learned a lot at the cost of otherwise being productive at work. JAMES in WESTON

DEAR JAMES: Thank you very much for your kind words, although I am not as certain your employer would be as happy with me 🙂

Perhaps surprisingly, you would be far from the first person to attempt such a project. Is is entirely doable and actually becomes very similar to what people do with a PEMB (Pre-engineered metal building aka red iron) or a weld up barndominium, where a shell is erected and a building is built inside of a building. You just happen to have your insides prebuilt!

Outside of my loyal readers, most have never heard of the Dunning-Kruger Effect (https://www.hansenpolebuildings.com/2015/01/dunning-kruger-effect/)


DEAR POLE BARN GURU: I’m interested in a residential building approximately 20ft x 30ft. How tall would the walls need to be to include a loft bedroom with headspace to approximately 4ft from the sides? JUDE in DUPONT

DEAR JUDE: I will answer your question from a standpoint of you getting best value for your investment – meaning using both floors from wall to wall.

Assuming a concrete slab-on-grade for main level, bottom of framed ceiling would be at 8′ 4-5/8″ this allows for 5/8″ drywall on ceiling and 1/2″ at bottom to be able to account for any variances in your building slab and to keep drywall from soaking up moisture from floor, plus 3-1/2″ for actual thickness of a nominal four inch thick slab.

I would recommend using premanufactured wood floor trusses between floors (https://www.hansenpolebuildings.com/2014/09/floor-trusses/). Plan on a 20 inch thickness, plus 3/4″ for subflooring and 8′ 1-1/8″ putting bottom of roof trusses at 18′ 2-1/2″. In Pennsylvania I would recommend R-60 blown in attic insulation (just under 20 inches thick), resulting in needing a 20 foot eave height.



Hangar Doors in Eave Side of Buildings

Hangar Doors in Eave Side of Buildings

Reader KEN in ZEPHYRHILLS writes:

“To facilitate use as an aircraft hangar can the sliding doors be located on the side rather than the end walls?”

I have been involved in more than a fair number of airplane hangars, starting way before my days in the post frame industry – as my father was a private pilot. You can read more about this story here: https://www.hansenpolebuildings.com/2013/09/hangar-n3407s/.

In most instances, airplane hangars are designed with the large hangar doors on the gable (peaked) endwalls. This allows for the greatest amount of usable door height as clearspan trusses can be used to span the opening. If needed multiple end trusses, with appropriate added bracing, may be utilized to support the weight of some or all of the door or doors.

My first adventure into the realm of hangars with sidewall door came when I was managing the prefabricated light gauge metal connector plate truss plant for Lucas Plywood and Lumber back in 1979. My client was Lindahl Lumber who was constructing two post frame “T” airplane hangars in Chehalis, Washington.

One of these was a T hangar (which you can read about here: https://www.hansenpolebuildings.com/2013/09/airplane-t-hangar/). The other a Nested T (https://www.hansenpolebuildings.com/2013/09/nested-t-hangar/).

As a post frame building contractor – I had my first up close and personal experience with a hangar with sidewall doors here: https://www.hansenpolebuildings.com/2013/09/t-hangar/.

Whether a T hangar or a hangar for a single plane, doors can be placed in sidewalls. There are a myriad of methods which can be used to support the weight of the doors – cantilevered trusses or beams (whether they be parallel chord flat trusses, structural steel, glulams or LVLs all of which are beams).

pole building with carportThe challenge of any of these support methods is deflection. Even in areas with no snow, the support for the door or doors is going to deflect (sag) even under just the weight of the roof being carried and the weight from the door. We recently provided a hangar with a full hipped roof in the Carolinas, where the building owner was originally distressed to find the beam for his door deflected significantly (albeit within Code and sound engineering practice limitations).

If a hangar door system absolutely must be located in a sidewall, then my personal preference would be to use a parallel chord truss system, as they can be designed for a minimal amount of deflection under design loads and can be fabricated with some upwards camber in order to hide some of the deflection. Most clients are unwilling to go this route, as they do not want to sacrifice the height of the truss – which is going to be several feet tall.

Regardless of where one wants to locate a hangar door, chances are excellent a post frame building is going to be the most economical and practical design solution.


How to Clearspan the Juncture of L or T Shaped Pole Buildings

How to Clearspan the Juncture of L or T shaped Post Frame Buildings

There are some instances where either an L or a T shaped building is the design solution of choice. In some cases it is due to the shape of the property being built upon. Other times it is a result of ideal materials flow either for storage, manufacturing or a combination of the two. It could also be for aesthetic reasons – to create a particular look or feel.

Factors which will influence the structural solution are many, and can include a combination of the following:

  • Distance (or span) of the structural member which will be carrying the load.
  • Will the structural member also be carrying a portion of the roof load in the direction away from the span to be carried?
  • Width of span being carried – the structural member will have to support one-half of the span of the roof being carried (the other half being transferred to the columns on the opposite wall).
  • The live, snow and dead loads to be carried by the roof.
  • Design of the columns at each end of the structural member – both in adequacy for carrying the larger compressive (gravity) loads, as well as the wind loads which would have normally been carried by the columns which were replaced by the structural members.

So, with all of the above in mind, what are the possible solutions?

  • If the spans and loads are relatively small, the first choice and least expensive is to use a “girder” truss or trusses. Trusses from the span to be carried would be connected to the bottom chord of the structural member girder truss. Most often the limitation of this system is the load capacity of the connecting hanger.
  • Steel “I” beam – brings back fond memories of the first construction project I did working for my dad and uncles as a teen. We had to fire wrap steel columns and beams being used in otherwise wood construction with seemingly layer upon layer of fire resistant gypsum . Then there are the connection challenges of steel beam to wooden columns and wood trusses to steel beam. I tend to avoid this choice as a possible design solution.

  • Parallel chord flat trusses – can carry fairly large loads, but start to get fairly deep. The spans being carried can connect over the top chord of the flat trusses, making for a relatively simple connection. If headroom below is not a challenge, these can prove to be an affordable solution.
  • LVL or Glulam beams – LVLs can be obtained which have higher Fb (fiberstress in bending) values than glulams. If the span of the beam is very great, deflection of the beam can become an issue to be reckoned with.

Have an interesting building in mind which may pose structural challenges with other building systems? If so, then a post frame building might be the design solution of choice.