Modified post and beam framing question

I'm working out how to use nail laminated 2x4 lumber in a modified post and beam structure.
Posts are simple to figure, but the beans is more complicated.
Some illustrations I have seen shown two 2x6 on either side of a post,  either notched into the post or setting on cleats,with blocking in between.
I'm working  with  2x4's, so I would rather stack one top of the other,  for more supporting  material in one place.
It would look something  like the picture below.
I think it should work as I desire, but I'm afraid I'm missing something.
I am going out of my way to use 2x4's due to costs-I get them for free from huge pallets.

I have stacked dimensional lumber to make a beam as shown, but I was using full 2"x4" roughcut material, and I went three high. I still kept the span fairly short.

I screwed strips of vertical 2x4 to the sides to try and keep everything in place.

The structure was temporary and taken apart after maybe 18 months. While it did survive snow loads and windstorms at time of dissassembly found a number of snapped #10 screws and loosening nails, and it looked like the eventual failure mode may have been the components of this beam separating.

It was a woodshed, built in a spot where nothing would be damaged if it failed.


If I was building something permanent and finding something more suitable for beams was not an option, I would use more than two 2x4s per beam... perhaps a pair on edge with a third on the flat above?

Hey William, you mentioned you get those 2x4's for free, consider two more on the backside, at angles with ends mitered and butted and with plenty of fasteners, to the pair that are stacked, almost creating triangulation like in a truss. I attached a drawing (I'm not an artist) to show what I'm trying to explain. I think it will greatly increase the strength and load capacity of the double 2x4 beams.

Why the need for a beam?

This is a serious question, and there may be a reason that I am unsure of, that is why I ask?

But I also ask because I build out of 2x4's a lot. In my carpentry, I use the humble truss to get the frame built. I built a 30x48 foot barn, 4 foot on center, using 2x4's, and with proper bracing, and using plywood gussets, it is plenty strong enough. I will admit that I do use 2x6's for rafters, but I am not sure it is needed. The old Tiny House I live in now, is made out of 100% 2x4's, and has been in place for 80 years.

If you could salvage your free 2x4's, then use plywood gussets, and truss framing, you might be able to build a lot without building beams.

Here is a picture of my 2x4, truss beamed barn.

Dillon,  your report is bad news for me,   but exactly what I needed to know .

Travis, I'm trying to create more floor space while not exceeding 200 square feet.
That means a second floor,  and all the strength that will need.
I won't need that space right away, but I'm trying to plan ahead.
I want  be able to span 8 feet,  enough for a single vehicle to enter.
I googled DIY 2x4 floor truss while researching for this project  and found a lot of warnings against attempting them, but I would like to know what you think.
Are floor trusses harder to do than roof trusses?



I was seeing 6 posts,  with beams in between, forming an 8x16 rectangle.
This would leave room to expand three feet on either side,  of the vehicle  bay, and still stay under 200 square feet.


James, I like the looks of your sketch, heck it has lots in common with a truss, triangular shapes distributing weight,adding strength.

I think that a truss is a better solution than a built up beam.. if you have the height to burn.

The asymetric natuure of the one shown bugs me tho. Given the small size of the structure maybe the answer is one more layer, to make a sandwich style truss-beam?


It may also be possible to build large bay windows onto a structure like this, making them below the height limit so they do not count as floorspace... obv. local law dependent, but can provide excellent seating and bed type space ifnthe loophole is applicable.


I wouldn't be afraid of DIY trusses, as long as there were serious fasteners used. I use screws for most stuff for ease of repurposing, but garden variety screws aren't strong enough to trust in a truss.

Probably I would use stout spiral nails combined with construction adhesive... but structural screws would also seem acceptable to me.


Travis, I've seen your nifty truss-barn mentioned before, but have you talked about the construction in more detail elsewhere?

I am a bit sketched out by 4ft on center... are the purlins iust 2x4s?

There is nothing to be concerned about with 4 Foot on Center Construction. I have a 24x48 barn here that my Uncle built that is over 30 years old. And in the 1960's and 1970's, a lot of the chicken houses that were built, are also still standing. Those were 80 feet wide and 200 feet long, and 3 story tall behemoths. The rafters on my latest barn are 2x6, but it is also a very low pitched roof, and is 52 feet long in length. It is a truss, and its longest span is 12 feet, so it can easily handle the load. But four foot construction is quite common here...

As for adding a second story, a truss made out of 2x4's will be vastly stronger than a 2x4 beam. That is because strength comes from depth, and not from width. By that I mean a 2x12 is going to be ten times stronger than a six inch wide beam, that is 3-1/2 inches deep.

Just study the shapes available for floor trusses and then make your own, using plywood gussets. I would probably have a 2x4 top and bottom cord, spaced 12 inches apart. I would then make 45 degrees cross bracing to in-fill the middle of the truss cord.

The one aspect I failed to mention was, you MUST use plywood, or OSB as a gusset material because it does not split. If you use regular boards, they will. But you can make a lot of gussets out of a sheet of plywood. I built my whole 30 x 48 barn out of something like (4) 4x8 sheets of 1/2 inch plywood. A few sheets of plywood, makes a lot of gussets! I have used OSB, and it works, but plywood is a lot better and is only a few more bucks per sheet.

Trusses it is then!
Stacking two bus would be simpler,  but I suspect learning to build trusses will pay off big time.
I am pretty crappy with a hammer and I use deck screws for most projects,  but I think I will buy a low end framing nailer to build this minibarn.
Nails are cheap and nail guns are fast,  plus I have read that screws simply do not have as much shear strength to be used in framing.
Scrap plywood is not hard to find, but I might buy it to be certain of the quality.
OSB is crap to me, as it seems unable to survive getting wet,it never seems strong to begin with,  and cutting it throws of noxious particles.

Travis, do you glue your gussets?
I am hoping to avoid the mess and expense of glue.

Weird question, could one cover the entire side of a truss with plywood, instead of just at the joints?
Would it be stronger that way?

I was hoping  to cover the second floor in two layers of pallet slates, run perpendicular to each other.
That might be too light too much work, in which case I will use 2x4s
I am thinking to top that with plastic, nylon window screen, and a coating  of cement mortar.
Unconventional , but it worked in a chicken coop and for my kitchen counter,  and I want to try it here.
The second story structure will be a  greenhouse or hoop house,  so the floor needs to shed water fairly well.

I'm not sure where to put the stairs,  or how to build them,  ideas on that are welcome.

No, I do not glue my gussets on. I have never had a problem just nailing them. I do use plenty of nails, but with a nailing gun, that is pretty easy to do.

You will like truss construction. Where else can you take short, thin framing and build something sturdy out of it? I mean, if you need a 2x4 24 feet long, and all you have is 8 foot long lumber, you just make (4) gussets 3-1/2 inches wide, two feet long, and the put (3) 8 foot long 2x4's together and nail them with no loss in strength. The rafters on my barn are 52 feet long from doing this! Obviously I cannot span 52 feet in width, the widest is 12 feet, but that is how long my rafters are.

The only thing a person needs with truss construction is confidence. It took me a day and a half to cut all my truss parts for my barn, and then nail the trusses together. But by the end of the second day, the barn was framed (a half day to put up). But as you are cutting, you just have to have confidence that it will work. Most people like to piece-meal a carpentry project, but that is not how truss construction works.

First you figure out what you need for a truss frame.
Then you cut up all your parts, always starting with the longest members first.
Then you nail up the frames (remembering on the first and last frames, the gussets are only on one side)
Then you start raising each frame. The first one is the hardest, but gets easier as you add more, and have something to brace off from.

This was my barn, framed after the second day. Total cost for the 30 x 48 foot barn was $4450.

You could think of Warren trusses, similar to a bridge used on railway lines.
using Travis's advise and a warren truss which is similar to a rectangle with triangular segments

The framing you used in your barn is inspiring. However, I can't find any info on the web about this kind of construction. I would really like to know more.

I'm in the very early stages of planning a straw bale house and I decided on a modified post and beam frame. Looking to cut costs and labor as much as possible, I felt confident in using 4x4's.But now I wonder if I can cut down even more.

2x4 framing like this seems very efficient.

When a truss loads up, the top chord goes into compression and the bottom cord goes into tension.
Its the same inside a  beam, and thats why beams are deep. IE 6 , 8 or 10 inches .
As Travis said, its the depth of the truss or beam that is important.

BUT, what is a 'modified post and beam system' ?

If you want to create a span by cutting costs and labour, maybe you should not build the beam!

Trusses or built up beams  need material in the proper place to function as a chord and that takes time and fixings.

If you need to save those costs, I would not start building in the manner planned.

There's lots of info around in building trusses  usually  we use gang ail plates on the connections rather than long screws much stringer than long screws.
Plywood or timber cleats will also work.
Plywood shell beams also work well  this link will give you some engineered tables
https://img.bretts.com.au/long_span_beams_span_tables.pdf