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Existing 2x4 garage truss storage

Existing 2x4 garage truss storage

Existing 2x4 garage truss storage

(OP)
Gentlemen: There is a 2x4 roof truss system over my garage I plan to use for light storage. I am a Product Research Engineer and know little about truss loading, but the geometry of the truss system looked very good, so I proceeded. Although I am a Solids CAD designer, my youngest son drew the attached for me, so I'm going to use it to explain what I've done. What are your thoughts and opinions?

RE: Existing 2x4 garage truss storage

Helpful sketch, thank you. A couple of questions please... 1) What is the approximate geographical location and 2) is the body shown already there as an existing dead load or is this representative of the future intended loading condition.

RE: Existing 2x4 garage truss storage

(OP)
Thanks for the reply. We live mid-state in Pennsylvania. Snow loading is usually light and the garage has a very steep roof. The worker shown in the sketch was placed there by my youngest son who thought someone should be standing on the platform. It is, however, where we plan to place stored items. I have been thinking about adding 5/8" plywood gussets at the peak of the truss (both sides) held with 4 3/8" lag bolts and the same at the bottom of the vertical members.

RE: Existing 2x4 garage truss storage

Depending on how recently your home was constructed trusses that can fit a 42" high x 2' square rectangle should have been designed for limited storage loading. The code prescribes this as 20 PSF minimum. I'm not sure how old your home is, but if it relatively recent I believe this has been in the code for awhile.

If your anticipated loading is going to exceed 20 PSF or if your home is older I recommend contacting a structural engineer in your area to review.

RE: Existing 2x4 garage truss storage

(OP)
I've got to take some action immediately. I have already laid the 5/8 chip-board (not particle board). The attached drawing shows what I propose to do to strengthen the 2x4 trusses. What are your thoughts.

Beiswenger Research
http://www.beiswenger.com

RE: Existing 2x4 garage truss storage

Ah yes, a deadline. Jdgengineer asked some pertinent questions, and what is lumber species and grade, and what are metal plate sizes and gages, and what is truss spacing, and is drywall ceiling a part of the original construction, and are the trusses showing any signs of distress, and I for one, would not be drilling lag bolts into a truss, especially the bottom chord, and... I kinda go along with jdgengineer and suggest you hire a local pro.

RE: Existing 2x4 garage truss storage

(OP)
Ok, gentlemen. I agree. I will let everyone know what the engineer says.

Beiswenger Research
http://www.beiswenger.com

RE: Existing 2x4 garage truss storage

(OP)
I spoke with a structural engineer and he said, if the height of the area above the chord is greater than 43 inches, then, by code, the PSF capability must be at least 20. This, however, does not satisfy my wife. I met also with a builder and he said I can bolt a gusset to the bottom chord if the bolt passes through the point where the vertical members create a V. I looked at my drawing and that seemed to make some sense. Can I trouble you guys again for your thoughts?

Beiswenger Research
http://www.beiswenger.com

RE: Existing 2x4 garage truss storage

1. Can your engineer design the reinforcement for you? It's really not hard, just needs to be done correctly.
2. he may be right on the 43 inch thing, but jdgengineer above made a good observation as to the age of the house and the relevant codes at the time, suggesting the possibility that the trusses were designed prior to that 43" detail being inserted in the code, and therefore your trusses not being designed with that capacity. i do not know on this one, just trying to make a helpful observation. if i was your engineer, i would research this exactly.
3. was your engineer appraised as to the age of your trusses?
4. you're assuming the truss manufacturer built it to code, which is not unreasonable, but i'd work out that age thing first.
5. i really would avoid drilling bolt holes through that bottom chord. i am thinking you may be reducing the capacity of the truss on the order of 10% to 20%.
6. any reason why your builder is recommending reinforcements and your engineer is not?
7. 20 psf is not a lot. i tried to look up the psf weight of a box of books but couldn't find it quickly, someone else will have it. 42", 3 1/2 feet of somethings is a lot heavier than 3 1/2 feet of other things.
8. last time i strutted my stuff as an engineer over my wife's objections, it broke.

RE: Existing 2x4 garage truss storage

(OP)
Thank you, Triangle. I am determined now to strengthen my 2x4 truss system with 5/8 plywood gussets on both sides at the apex joints and at the node joints (see attached drawing by my youngest son). With what should I fasten them? Being a product design engineer (www.beiswenger.com), I was thinking about using 5/16 bolts with washers and nuts, but that would mean drilling a clean 5/16 hole through the chord at the node joint. Problem? I could just use 5/16 lag bolts. I could also add glue to the process. What about nails? I hate to both you guys again, but my wife is getting anxious. What do you suggest?

Beiswenger Research
http://www.beiswenger.com

RE: Existing 2x4 garage truss storage

Best I can tell so far is that the 20psf code provision, that has been referenced in this string, first appeared in the code in the 2003 IBC, which would mean it was not widely implemented until years later, and in some locations may still not be enforced much. That's from a friend who has been designing these trusses for 20 years, but also he did not reserach it deeply as to the precise date, but he did say it is a recent code development. There will be others in this forum with more exact information on date and history of this provision. But based on what I've seen so far, if your residence is older than 2003,4,5-ish, it's likely that the trusses do no accommodate this 20 psf that has been discussed.

RE: Existing 2x4 garage truss storage

Typically, the repairs you show would not be needed. But then again they could be.

Roof trusses, as you show, the additional loading would more often need the truss plates at the bearings and bottom chord splices repaired. Possibly a 2x addon in the panel of additional loading.

Personally, I prefer to use nails/screws repairs and not bolts for wood trusses.

As for will the trusses fail, that depends on how much load you add to the trusses. Whether the trusses will see the code maximum design load at the same time is also a concern.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

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