Calling all truss experts

[Innovate1]

The design with the truss plates and mixed sizes is stronger than plain rafters with a solid 2x6 "joist" for your storage space. You need to realize the load in your storage space is all transferred to the top cord of the truss. The horizontal 2x4's don't act as joists at all, they are in tension only.

You are correct that the load is transferred to the top cord. But the horizontal lower cord does act as joists supporting the load (maybe only their own weight or the drywall ceiling) between vertical or horizontal members that go to the top. All members in the truss are considered to be in tension or compression only, as if the joints are hinges. That's a conservative case as the joints can withstand some torque, especially the members that are continuous but the main strength comes from compression/tension.

 

[Bert_]

You are correct that the load is transferred to the top cord. But the horizontal lower cord does act as joists supporting the load (maybe only their own weight or the drywall ceiling) between vertical or horizontal members that go to the top. All members in the truss are considered to be in tension or compression only, as if the joints are hinges. That's a conservative case as the joints can withstand some torque, especially the members that are continuous but the main strength comes from compression/tension.

I get it. Needs to be said as plainly as possible for the point to get across though

 

[Mike_72]

With all other portions of the truss unchanged, wouldn’t the same design with a 2x6 lower chord all the way across be a stronger design?

 

[Bert_]

With all other portions of the truss unchanged, wouldn’t the same design with a 2x6 lower chord all the way across be a stronger design?

Doubt it would make much difference. As noted many times the 2x4 is in tension. It doesn't carry much downward force. It main function is to keep the walls from spreading.

 

[Mike_72]

Doubt it would make much difference. As noted many times the 2x4 is in tension. It doesn't carry much downward force. It main function is to keep the walls from spreading.

Okay thanks, would there be any benefits to having the webs 2x4 rather than 2X3? I assume it wouldn’t make much of a difference in the webs that are in tension, but would the compression webs benefit from the additional strength?

 

[Daniel Dudley]

Mike, there are 10s of thousands of trusses all over the country. They have been making them for a long time. Those little plates have the equivalent of fifty to a hundred nails in them pressed into the wood. The engineering is all done by math, and the trusses will easily hold the load they are rated for with no detectable deflection.

It doesn't matter how they look, or how you feel about them, as they are a proven product. You can't out think the math with speculation, or improve the product with guesswork. Trusses are designed to replace heavy, unsupported, solid span timbers with lighter reinforced components. They are designed to be installed as a unit; not being built up on the building, they save materials, money, and time.

You can trust them, and they make a heck of a lot more sense when you are looking at a whole bunch of them installed instead of a drawing of one in profile. Floating in space, a truss is a floppy thing. Installed and tied into a building, they are strong and unyielding. They like a load, and they are comfortable with it.

They just don't look like what you are used to seeing.