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Old 01-06-2012, 11:45 AM   #1
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2x4 floor truss for Barn


I am planning to convert an old wooden barn (approx. 100 years) to living space. Ground level will become a garage/workshop, upper level will become an appartment. The barn is 30' wide and 50' long, gambrel roof. I would like to keep the garage space open and support the first level floor with trusses made of 2x4s, 24" deep, 30' long, 16" on center. I'm planning to use the warren truss design.

Here is the problem: the roof is supported by 8 vertical, evenly spaced beams that go from ground floor to the roof. (2 rows of 4 beams, along the 50' length of the barn). Does anyone have experience if the floor trusses will be able to support the concentrated load of these beams?
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Old 01-06-2012, 11:54 AM   #2
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2x4 floor truss for Barn


I think you need to bring an architect/engineer in to tell you what can span what depending on loads.

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Old 01-06-2012, 12:05 PM   #3
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2x4 floor truss for Barn


I must not understand your plan. You state that you plan to support the first floor using trusses (rather than conventional floor joists). Then you state that the roof is supported by vertical posts that extend from ground level to the roof. Then you ask if the trusses can support the point load of the posts.

What I don't understand is why you need to support the posts on the trusses. Is it because you want to eliminate the posts between the ground level and the first floor? If so, you are going to need very special, engineered trusses to support the large point loads from the roof. These will almost certainly not be stock trusses, they will need to be custom fabricated. You must load a truss at the joint, not between joints, so the trusses would need to be designed to have a joint directly under each post, and of course the joint (and the truss as a whole) would need to be strong enough to support the specific load of the post. This is clearly a job for a competent structural engineer, working with a truss manufacturer.
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Old 01-06-2012, 12:22 PM   #4
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2x4 floor truss for Barn


Yes, from the ground to the first floor, the space should be open. From the first floor to the roof, the vertical beams could stay in place. And I have been debating how important the open space for the garage/workshop would be. It is more of a nice to have than an absolute necessity.

So, if I were to leave the vertical beams in place as they are now, based on all the information I have read, the design should hold up. Depending on additional information, I will most likely not tackle the removal of those beams.

Thanks for your input.
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Old 01-06-2012, 12:38 PM   #5
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2x4 floor truss for Barn


I'm not even positive of the guy means roof or floor trusses. Him calling posts beams...
I guess he means floor trusses...sounds like he wants to build them himself...

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Old 01-06-2012, 04:16 PM   #6
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2x4 floor truss for Barn


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Originally Posted by titanoman View Post
I'm not even positive of the guy means roof or floor trusses. Him calling posts beams...
I guess he means floor trusses...sounds like he wants to build them himself...

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You are right titanoman, I did call posts beams and I do want to build the trusses (floor trusses) myself. If I were as smart as you are I would not spend my time in this chat room. I appreciate encouraging and supportive comments.
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Old 01-06-2012, 04:27 PM   #7
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2x4 floor truss for Barn


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Originally Posted by carpyta View Post
You are right titanoman, I did call posts beams and I do want to build the trusses (floor trusses) myself. If I were as smart as you are I would not spend my time in this chat room. I appreciate encouraging and supportive comments.

Do you have any experience in truss design?
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Old 01-06-2012, 04:50 PM   #8
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2x4 floor truss for Barn


OK, so let's get to the design. You need trusses 30 feet wide, you want to make them from 2x4's, you plan to set them 16 inches OC, and you have abandoned (at least temporarily) the idea of supporting the posts on the trusses. You are converting a barn, which is considered unoccupied space, into occupied space.

The conversion of unoccupied space into occupied space triggers a whole series of complex code issues, at least if you are required to get a permit, and plan to build to code. This issue has been discussed repeatedly on this forum, I suggest you do a search for "conversion" and see what you find. At a minimum, you are going to need to address floor loading, egress, electrical, plumbing, firestopping, HVAC and insulation issues. Perhaps you have looked into all of this, a lot of these issues bear directly on the design of the trusses.

The fact that you are planning to have an apartment suggests you plan to rent it out, which may get you into an entirely different section of code (it does in my state). Different loading, different fire regulations etc. Some of the factors may influence the truss design.

As for the trusses, which is what you originally asked about, design of a 30 foot truss supporting a floor would normally be done by a truss manufacturer, using relatively sophisticated design software. Or they may have standard floor trusses available in 30 foot lengths which will support the required dead and live load, plus point loads. DIY trusses are unusual, because most people lack the equipment generally used to make trusses (typically a pneumatic gang nailer is used). It is certainly possible to design and build trusses using standard lumber and standard fasteners (nails), however you have to get the design just right.

I don't know how much money, if any, you would save designing and building your own trusses. Certainly you should at least look into commercially available trusses. You obviously need to discuss the project with your local building inspector, assuming you have a local building inspector, as this is a complicated undertaking that needs careful planning.

I recently worked on the sale of a house with an old barn, and had occasion to examine the cost to convert the barn to living space meeting current code. The cost was so high that the owner concluded it was not cost effective, so they left the barn as is.
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Old 01-06-2012, 07:36 PM   #9
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2x4 floor truss for Barn


Carpyta; As you are aware, floor trusses are engineered and form an assembly, they work together. A 30' span is not huge but big enough where you can easily have failure of the floor system if you don't do it right. I suggest you have an professional engineer design the trusses if you are constructing them yourself, or, as your building code may effectively prohibit you from construting them yourself as it will be too involved and costly to have the constructed trusses certified, go to a truss manufacturer and have them engineer them and manufacture them. You can transfer the load of the posts to the exterior walls where the load is posted down. I haven't seen large loads transferred with floor trusses but usually transferred with a different engineered product, e.g. laminated beams, LVLs. A PE definitely is needed on that. The engineer can also look at how the existing barn is posted down and determine if it will support the additional load. A barn can sag and move a bit and nobody notices, but as soon as habitable space starts to move or settle it causes problems with things like doors, windows, plumbing, and squeaks. Sounds like a good project. good luck.
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Old 01-06-2012, 08:25 PM   #10
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2x4 floor truss for Barn


This project is not going to be cost effective, but it is going to be interesting, like a hobby of sorts. I am relatively familiar with regular floor joists. The span tables are pretty standard for residential use. Under normal load and use conditions engineering consultation is not an absolute necessity.

I expected that span tables for trusses for residential load would work similarly. The information I have found is that for 30' with modified warren truss design, the required load would be supported (necessary tools are available).

So far, all indications are that this is not a typical diy project.

Thanks for your insight.
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Old 01-06-2012, 09:56 PM   #11
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2x4 floor truss for Barn


The main thing you can't replicate at home (anybody can run "w" struts throughout and double up the uprights at the bearing points and have a pretty strong assembly) are the gang plates. Nails or screws aren't going to be able to keep it solid very long. Even if you sheeted both sides with 3/4 plywood (well, maybe then) it wouldn't be as strong.
Oh what a nightmare if it started sagging in the middle.
Just a thought, and good luck. Sounds like a fun project.

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