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Discussion Starter #1
So I am curious..
currently I have 2x6 upper and lower beams and 2x4 supports with an open center. the 2x6 span the whole top and the bottom only has two joined.


The truss company designed my contractor is using for the addition designed..
2x4 uppers, lowers, and supports, with a center support. The 2x4s upper and lower are spliced together at every support point.


Is this just a minimum code thing? is the 2x4 stronger?
Why are they changing the layout design? They came and measured the old so its not sight unseen.
This new design makes it very hard to traverse through the attic for persons and duct and whatever else have you.


My house is over 60years old with a main room that spans the full length of the existing trusses (30footish),... I have zero cracks in my plaster ceiling.


I don't feel comfortable with these going onto the addition. The blueprints depict the original design and 2x6's, but they don't call out for it.
 

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For trusses, code doesn’t care if the lumber is 2x4 or 2x6. The code spells out minimum top and bottom chord live and dead loads within permissible deflection. If the engineered truss meets those criteria, it meets code. If you want something different, ask if the truss company can design it to meet code. Their software designs to meet code in the most cost efficient way unless they input something else.
 
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retired framer
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Some one should have told the truss company what you had.

Different designs do have different loading limits, and maybe the standard has changed over the years.
 

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Truss loading and design is pretty simple math, especially for a computer.
They plug in the span, roof dead loads, local wind loads, snow loads, etc and computer will spit out design that provides sufficient strength. If the size and shape of the addition is different than your original attic, or code requirements have changed, the truss design may be different too. I doubt you need to be concerned about the strength of the truss. For sure one of the considerations in truss design will be using minimum of material --- material = $$. Truss attics can a bee-itch to walk through, that is common. I doubt ability to walk/crawl through was even considered at all.

If the trusses have been built and delivered, they aren't changing them now. If the trusses only exist on paper, you can ask your contractor for a different truss design with more open area --- possibly he will charge you for any extra costs.
 

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Framing Contractor
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I bet that 7 web design is just as strong, or stronger than your 4 web ones with the 2x6 tops and bottoms. If your concern is the access, trusses can be made with fewer webs using larger chords, aka timber type trusses. Think of an attic truss. Without the need for the room, the truss would most likely be all 2x4 construction.
 

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You may ask. At 30 feet with a standard 25 lbs snow, 10 dead weight, you should be able to get the exact same Fink trusses as what you have before. (unless the city have changed the code for win and/or seismic load).

It all depend on the length of the trusses. It sometime also depend on the species of the wood.

The Fink trust (the old one) you have are often recommended for 12 to 32 feet. At 30 Feet, you often end up with 2x6 because of the length between support of the top cord. Said, it is 30 feet. -- 15 feet per side -- 7.5 feet of top cord between support.

The double Fink (the proposed one) are often recommended for 40 to 60 feet. However, they often permit to use 2x4 for the top and bottom cord. For example, at the top cord, the space between support is 5 Feet... and this can be accommodated with some specie of wood in 2x4.

Also note that the trusses are computed to the exact same "load". Consequently, what ever the model of trusses you retain, they will have exactly the same "Flex" and shall not cause problem with the drywall.
 

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retired framer
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We must live in a different world up here. We have roofs with multi shapes and an average house may get trusses of 8 or 10 different shapes and styles. They are numbered and they are put exactly where their plan puts them, often not on layout.
Every truss comes with it's own stamped drawing. After we have stood them and done all the normal angle bracing and 1x4 cat walks and sheeted it. We go back inside and go thru and add the required extras that have to be added to the truss.

Often those extras use 300 to 500 lineal ft of 2x4, we call that process the engineering of the trusses.

The on site engineer and the city inspectors also got a copy of that pile of stamped drawings and the both inspect o see if we have missed anything.

The last thing we worry about would be what the insulater has to do to walk around up there.
 

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Hammered Thumb
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We must live in a different world up here. . .
You are describing the process anywhere, but I think the OP is just skiddish because the new trusses don't look like the old ones and look a little bit "daintier" with the 2x4s. Hofefully yours and everyone's comments have provided some assurance for him.
 

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Discussion Starter #12 (Edited)
The last thing we worry about would be what the insulater has to do to walk around up there.
insulator being me.
I also spend more time in the attic than normal home owner. lol

THank you everyone for your inputs.

As for the "different world" THis is a farmhouse style.. all trusses are identical. porch lays on top.

The designer came to the house. took measurements of existing. THe Plans depict 2x6 but dont specify any sizes.
I feel he should have brought this to attention... "hey would you like them to match the house and plans or just build the house brand cheepo design?"

PRobably going to retalk with the contractor and possibly the truss company.
 

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Discussion Starter #13
Ended up using another company to make the trusses, no resistance. and actually was cheaper.

Not sure why the other one resisted so much.
 

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Neal was on the right track.
Some truss members are under compression and some are under tension. It is not necessarily easy to tell which is which by looking at them. Members under tension are being stretched so they don’t need bracing. Members under compression are subject to bending and failing, so they get braced. When I was a county inspector, I got a copy of the truss engineering drawing because it showed where to put bracing. At inspection time it was easy, verify that it was built to the drawings with the proper fasteners. You can do that, too, just to be sure.
 

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retired framer
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Truss companies are just like engineers, some will work with you to make you job easier and others are just dictator want to be"s and always think it is some kind of insult if you make a suggestion.
 
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