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Parallel Chord Floor Trusses

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I am building a 2 story garage the outside dimensions of the garage is 30'deep and 34' wide. I wanted a clear span in the garage area so I chose to use parallel chord floor trusses. I will be installing a 42" stairwell. My question is about using a girder. Since the stairs will be against the outside wall and the truss layout will put two trusses within 4" of each other rather than tripleing the trusses I wanted to have girder pockets installed on the ladder truss and the first two on the other side of the stairwell. My thought was I could set the girder on the outside wall and pass it through the first two trusses on the other side of the stair well to distribute the load even though they are not side by side.

Will this work? What size 2x material would I need to build the girder? (there will be 3 trusses dead-ended into the girder a 42" span) How would the bottom chord of the dead-ended trusses carry any weight? Should I use steel strap for the bottom chord or end nailed or nailed up through the bottom chords? How to you specify to the manufacturer where you want the pockets for the girder? (by the size of the stairwell or end of the truss? I'd also want the webs to line up so do you need to specify from which end of the truss?

I also need to brake the stairs on a landing. Rather than a stiff leg support under the landing my thought was I could suspend the floor load by a 1 1/2" steel pipe passed through the bottom chord of the 8 over 4 roof trusses. I am concerned that I do get a large point load on that corner of the landing. Any Ideas or suggestions? or should I just go with the conventional stiff leg to the floor?

(post #178278, reply #1 of 9)

30' clear span floor trusses will need to be at least 24" deep, and may have some "bounce" in them even at that.

As for headering off around the stairs, why not just build a wall around the stairs ? Then you don't have the header/girder worries. Make sure the truss manufacturer knows exactly what you're planning when you order the trusses, so he can design them correctly.

Assuming you use a girder and beam, it would probably be simplest to make the shorter trusses top chord bearing on the beam. The supporting girder truss(es) should have a beam pocket built into them to accomodate the beam. You may have to block up the end of the beam to get your height set right.

Suspending the landing from the roof trusses is a bad idea, unless you buy a girder truss specifically designed for the point load. Even then, I'm not sure you wouldn't have problems with the roof wanting to make seasonal movements and causing trouble.

Make sure you check local codes before you start, also. I've heard mention of restrictions about placing residential areas over garage space.

(post #178278, reply #2 of 9)

Pretty much what Ron said,


(post #178278, reply #3 of 9)

Am I missing something here? I thought trusses always came with engineered drawings that specify exactly how they are to be installed. These engineeed drawings are based on the structure's architectural drawings - or are these stairs an after thought?

(post #178278, reply #4 of 9)

Whats a parallel cord floor truss? (still hearing terms for the first time)

Saw a garage this size with full upstairs living area. Wide flange steel went down center, now just 15' span. Could the wfb act as your girder? Wouldn't have to be exactly in the center...

(post #178278, reply #5 of 9)

Ron I've only worked with floor trusses a couple of times and each time I worked the dumb end. (show up and work hard) This is the first time I've had to be in the lead. The Span for this garage is actually 29'6" and the truss book I looked at specified 20" deep with 16" oc for 29'9" span or 19.3" oc 22" deep or 24" oc 24" deep. Yes I agree, I will have bounce but I will have a clear span down stairs.

Part of the bounce is the deflection side to side on the trusses the 3/4" osb floor on top and cross framing on the bottom chords will help. I remember from the previous jobs that the trusses at the stairwell needed doubled. In this case the layout truss and the truss at the stairwell will be just a couple of inches apart. Do I need a third truss to keep them tight or will it work ok with the small space between the trusses? My thought was to build the girder beam out of two 2x8's laminated and passed through the bottom side of the top chord in the girder pockets on the outside wall and the first two trusses with the small space on the other side of the stairs. Will this distribute the load effectively or should I be concerned about lateral movement from the trusses. (reason for the doubling?)

I suspected the suspension Idea was bad I was looking for ways to free up more workshop space under the stairs it's not uncomon to put storage under the stairs with a wall. Thanks for the input

(post #178278, reply #6 of 9)

Jeff -

The reason I suggested going 24" deep minimum was to try to reduce the "bounce" as much as possible. Reducing spacing doesn't help this.

> Part of the bounce is the deflection side to side

You're right, but it's not all that much. Stick with the deepest trusses you can stand.

> cross framing on the bottom chords will help

By this, I assume you mean 2X6 strongbacks. Yes, they will help, but depth will help more.

The "first 2 trusses" you mention need to be special girder trusses, not just standard floor trusses. The manufacturer can build a beam pocket into the floor, and determine what loads the girder needs to be designed for.

Most of the questions you ask would best be answered by the people you plan to buy the trusses from. Just take them your plans, and let them figure out what to do. That's why us truss guys get the big bucks................(-:

(post #178278, reply #7 of 9)


Thanks, I got the feeling the truss guy was "selling" me something. He acted inconvenienced by my questions about the size of the trusses, and if I should use a girder or header. His attitude was just let me reach into your pocket lets see how much mone you have then I'll let you know what you need. I thought it would be nice to be a little better informed when I go back to order from this jerk.

I really appreciate the info.

(post #178278, reply #8 of 9)

Why order from them ? There are plenty of truss companies out there who build floor trusses. I'd be curious to hear what company you're dealing with and/or what geographical region you're in. You can email me privately if you don't want to air it out here.

Best of luck with your project......

(post #178278, reply #9 of 9)

parallel cord floor trusses meen the top and bottom members parrell each other.

Mr Chokreff if you do try and hang something from the trusses either floor or roof it is very importian to load then from the top member that is why roof trusses for examply the one im my garage are labled 35-7-5 for 24" on center the first number if the live load on top of the truss the second the dead load on top of the trusses and the last number the dead load on the bottom cord such as drywall my 250 plus poinds gets scary on the bottom members. it doesn't seem here in Utah there is much compititiom amound truss manufactures