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We're trying to raise the roof on our 1.5 storey pole barn. We're intending on just replacing half the roof as shown below. each truss is supported by 4x6 columns (the long side of the 4x6 is bolted to the 2x12 truss beams). the second floor is supported by 2x12s. Each member is joined by the standard metal plates for roofing, but the trusses are bolted to the 4x6 columns.

  • County doesn't require engineering review or any inspections for residences that are owner built and occupied.
  • We get hurricanes/tornados from time to time. No earthquakes
  • 30 minutes from coast.
  • The barn has already withstood the last 2+ decades no problem.

How well does this design work? Are there any glaring changes that need to be made.

Planned design is below: enter image description here

Current design is this: current design

For context, a shot of the building overall as planned: enter image description here

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  • $\begingroup$ the modification to the right wall of the building in the top picture is similar to doubling the size of a sail on a boat ... you really need to hire a structural engineer for this ... the courts and insurance companies will take a dim view on well, the guy on the internet said that it's ok to make the changes $\endgroup$
    – jsotola
    Commented May 21, 2023 at 1:11
  • $\begingroup$ Well, the wife is an engineer but this isn't really her field. And you're correct about the sail analogy. However, for the most part, the wind comes from the south here which is from the left of the photo. That's why i'm thinking of extending the right side instead of the left. Is that correct? do you have any resources that would be helpful in calculating loading and stress for this structure? $\endgroup$
    – Joe B
    Commented May 21, 2023 at 1:43
  • $\begingroup$ yes, a structural engineer $\endgroup$
    – jsotola
    Commented May 21, 2023 at 2:27
  • $\begingroup$ Lol fair enough $\endgroup$
    – Joe B
    Commented May 21, 2023 at 2:31
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    $\begingroup$ Considering where most of the wind comes from is moot unless you expect most of the wind to be capable of damaging your structure. Consider worst cases and factors of safety instead. Reference building codes for your area. IBC is pretty popular... $\endgroup$
    – Abel
    Commented Jun 20, 2023 at 13:33

2 Answers 2

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I'm sorry to tell that, but it's difficult to tell which design is worse in terms of construction.

In both designs, structure is suboptimal.

What can be seen on the cross-section view: The beams are not supported on the joints, so joints take lateral load from connected beams, and those are not supposed to. All of the beam joints should end on a column or another beam that takes load longitudinally, at least if you want it to be rigid, not just for visibility of structure. There is no single triangle in this design! Well, I see a small triangular object serving as a shear wall, but it ends in the middle of a beam, and the beam would take lateral force and tend to break. The presence of such an element is a sign of helplessness of the overall design which would fall apart without it. Also this particular triangle does not add much to overall rigidity of the construct.

Both constructs could be make order of magnitude more solid with the same amount of material if you go with a proper construction engineering.

Look at different types of roof truss elements. For example here: https://engineeringdiscoveries.com/roof-truss-elements-angles-and-basics-to-understand/

Just look how many triangles are there in those proven constructs!

Here is a screenshot of that website in case it is unavailable: enter image description here

You need something similar to Gambrel, at least you need some of them as an intermediate supporting construct for the roof to be solid! enter image description here Again, look at the triangles. Every single joint between beams on this drawing has a supporting beam ending right in the joint. If you want your construct to be solid, it should literally consist of triangles. I'm not telling you that any structure that consists of triangles would be solid enough, but if a structure does not contain a single one - this structure is questionable.

What can be seen on the isometry view: There is no support of the entire construct besides the material of the walls. You need shear walls or inclined webs to support the roof, otherwise it could collapse (40' direction on the isometry view). It might be standing only because of the strength of decoration materials and shingles on the roof, but without those a single person strong enough shake it with bare hands and eventually collapse it.

I hope you will make your own research and hire a good construction engineer for your project before building. They should show you a computation made in a CAD program for structural strength of every element that is taking load.

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It doesn't matter what we think. You need a to get a building permit; and it looks like you want to make a residential space out of a space that wasn't originally permitted as such. This will probably require a redesign of the entire structure to comply with current residential building codes. Assume you will have to strip and replace all plumbing and electrical systems. It would likely cost as much as leveling the place and putting up a prefab.

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