reinforce truss for attic storage
reinforce truss for attic storage
(OP)
I have 2x4 "fink" (or W) trusses spanning 20 foot on 24 inch centers. I'm not sure the pitch of the roof, but it is pretty steep. I can include pictures if it would help.
I want to use this attic space for storage, but after doing some searching it appears 2x4's on 24" centers aren't going to support much.
Would I gain anything by sistering a 20' 2x10 or 2x12 next to each bottom chord? My floor would then go on top of the 2x10 or 2x12.
I don't plan on using this for liveable space, only storage. I'm an electrical engineer, so go easy on me... :)
I want to use this attic space for storage, but after doing some searching it appears 2x4's on 24" centers aren't going to support much.
Would I gain anything by sistering a 20' 2x10 or 2x12 next to each bottom chord? My floor would then go on top of the 2x10 or 2x12.
I don't plan on using this for liveable space, only storage. I'm an electrical engineer, so go easy on me... :)





RE: reinforce truss for attic storage
I have 2X4 trusses with a 24' span on a 4:12 pitch and manage to store relatively light items, with some tax records, clothes, suitcases - that sort of thing. No problems for me.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: reinforce truss for attic storage
i'd say heavier stuff than your average person, but no engine blocks or anything that heavy.
RE: reinforce truss for attic storage
Garth Dreger PE
AZ Phoenix area
RE: reinforce truss for attic storage
i guess my main question is:
if i sister a 20' 2x10 or 2x12 next to this, will my psf go up, down, or stay the same? will i be doing more harm than good?
RE: reinforce truss for attic storage
Garth Dreger PE
AZ Phoenix area
RE: reinforce truss for attic storage
RE: reinforce truss for attic storage
Garth Dreger PE
AZ Phoenix area
RE: reinforce truss for attic storage
Is there anyway to reinforce the connections of the truss if I were to sister a 2x10?
So, another thought popped into my head last night:
what if I just run a 2x10 or 2x12 right next to the truss and the only connection points would be at the load bearing walls. In other words, the bottom chord of the truss would never be sistered to the extra 2x10 or 2x12 that I would be adding, taking the truss out of the equation.
Would I get better psf since it is just a single board? i guess it would be like a floor joist.
Do I need to be careful not to exceed the strength of the load bearing wall?
RE: reinforce truss for attic storage
RE: reinforce truss for attic storage
RE: reinforce truss for attic storage
RE: reinforce truss for attic storage
Can anyone give me the psf numbers on what the "floor joists" will hold? And will the load bearing walls be able to take the extra load?
RE: reinforce truss for attic storage
Garth Dreger PE
AZ Phoenix area
RE: reinforce truss for attic storage
WHOA there nellie!
If you have sheetrock on the underside of the bottom chord of the trusses, you'd better attach the additional 2X members to the truss or you will likely pop the sheetrock off the bottom of the truss as the 2X12/s are not going to be as strong as the truss and have more deflection under load.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: reinforce truss for attic storage
hadn't thought about the sheetrock... any idea where i can find the max deflection under load?
if i do attach it to the truss, then we are back to the extra loading issue on the joints of the truss.
so is there any way to reinforce the joints?
right now they have those pressed on metal connectors. maybe if i add some plywood "plates"?
thanks for the replies guys, i'm learning quite a bit!
RE: reinforce truss for attic storage
If you only plan on loading the the middle panel of the fink (which should be about 6'6" on a 20' span), then a single 2x8 x 12' scab centered on the truss will be sufficient. The oversized scab will allow you to get about (3) nails in each intersecting web to cover the increase in force in the web just in case the tooth holding of the plate is not sufficient. If you are worried about eccentricity on the joint, apply a 24" scab centered on the back face of the joint and use (2) nails per face per web. For the heel joints-1/2" plywood x 16" wide x height to match the pitch on each face. The peak joint - 16" x 16" x 1/2" plywood cut to fit.
Alpine makes the nail-on Trulox plate (I'm sure Mitek has an equivalent), so instead of using the oversized bottom chord scab, you can apply the trulox plate to each face at the bottom chord panel and then use a single 2x4 scab on the bottom chord. Same goes for the peak instead of plywood. i would still use plywood on the heel joints unless you want to cut a wedge to fit into the heel that the trulox can nail in to. The wedge is to prevent the trulox plate from buckling where it is not in contact with wood, which is common on steep pitches.
RE: reinforce truss for attic storage
Yes, plates are the week spot. But before you start adding a bunch of wood "joists" or some sort of system to provide additional strength to the plates, talk to a truss engineer or structural engineer in your area. They can calculate what your truss can support. I'm not sure on the price the truss engineer would ask but shouldn't take them more than 1/4 hour at about $80per hour for a technician to run. Maybe they can just run it while you're on the phone. Just a matter of finding a truss guy willing to help you since this is not the type of work they normally do.
But if you would rather beef up the existing trusses, OSB gusset plates work well when glued and nailed.
Jim Houlette PE
Web: www.evstudio.us
Online Magazine: www.evstudio.info
RE: reinforce truss for attic storage
Since it sounds relatively easy to beef up the joints as KRW7 proposed, I think I will go ahead and do that.
If someone is willing to, I can post a picture with the measurements and if you could calculate the loading, that would be awesome.
Again, thanks for all the replies. I appreciate all the help!
RE: reinforce truss for attic storage
RE: reinforce truss for attic storage
That's a lot of material for just some storage area.
I'm curious jake65892, have you made your choice and started work?
Jim Houlette PE
Web: www.evstudio.us
Online Magazine: www.evstudio.info
RE: reinforce truss for attic storage
I thought about that, essentially making floor joists. Someone stated earlier on that they would bend under my load and cause problems with the sheetrock ceiling in the garage.
jhoulette:
I haven't started the work yet (have to finish running electric to the shed), but I think I am going to follow KRW7's advice, as it seems the easiest (and cheapest) with the best reinforcement.
RE: reinforce truss for attic storage
RE: reinforce truss for attic storage
Jim Houlette PE
Web: www.evstudio.us
Online Magazine: www.evstudio.info
RE: reinforce truss for attic storage
The analysis showed that the front half worked just fine, but the back half would require plywood or osb gussets at the joints. It would be worth your while to get paperwork from a PE even with a simple fink (mine were modified queen post trusses-low pitch).
On a side note, I've seen repairs to attic frame trusses to allow them to support steel beam winches, so its almost all do-able, just a question of what to do.
fyi
Mike
RE: reinforce truss for attic storage
Larry
RE: reinforce truss for attic storage
RE: reinforce truss for attic storage
Third, Never install a "hoist" to the trusses unless they have been designed for this. A hoist will result in Impact loads which may cause the joints to fail. Consult your truss Manufacture or an independant P.E.
RE: reinforce truss for attic storage
How hold the trusses are and under what code they were designed, depends on if these checks were done.
RE: reinforce truss for attic storage
This is the perfect thread for my similar questions about strengthening a truss for attic floor use. My situation has a bit of a twist, though. I have moved into a home where the attic space above a garage has been altered for storage. Here are the raw details:
- The floor is 8'X14' square foot OSB flooring, screwed into adjoining framing members
- The floor sits above six 2X4's laying perpendicular above the bottom cord of five trusses
- A load bearing wall holds one end of these perpendicular members
- Trusses are a standard 20'X65" design, with three web members meeting together at the bottom cord, one vertically in the center and two laterally
- The bottom cord is comprised of two 2X4's that is joined with the web members via one large gusset plate
- A six foot 2X4 has been sistered in the middle with the bottom cord on all trusses and bolted in six places with 1/4" bolts/nuts/oversized washers
- Standard framing hardware was used at each joint and intersection of the framing pieces
- Based upon a receipt found under the flooring, this project was completed in 2001
Now, I have no idea if this was professionally done, but doubt it. The previous owner was pretty handy and I think that he just did what he thought would work. I don't even know the kind of storage load that he put up there, but it all seems to have worked for several years. Nonetheless, I can see a tiny crack in the seams of two large ceiling sheetrock pieces. It runs the length of the garage, but shows no bowing or other deformity. Here are my questions:
1. Does this sound safe?
2. Could the 1/4" bolts drilled through the 2X4's mentioned actually lessen the strength of the bottom cord?
3. Does such a design alteration sound like it could hold minimal storage weight (like mentioned previously)?
4. How might I properly reinforce the trusses for the existing flooring? I am willing to tear down the ceiling and retrofit full length members if needed.
Nope, there is no legal liability with anyone's answers and any response is just hearsay. I would be interested in getting an engineer to look at this, but can't seem to find anyone who will take on such a small job.
Like the guy who started this thread stated, "I'm an electrical engineer, so go easy on me." Well, I am a firefighter, so I only really know how to dodge when a truss fails...
Peace,
Dr. Z.
RE: reinforce truss for attic storage
like most of what I've seen, I doubt it would fall down, but the long term effects (like cracking or bowing sheetrock) you are probably already seeing. There are typically some safety margins built in (particularly with visually graded lumber, and metal connector plates). The actual trusses may or may not have been designed for the attic storage load (and you would only see minor differences in the design anyway- for typical garage spans.
What is scary to me is even with the code changes that mandate running the LAS loads for residential, the software (like Mitek) will now run trusses that depend heavily on the moment carrying capacity of the plates and non-engineer types are encouraged to design trusses. I have been seeing more than a few non triangulated designs for garage trusses in the past couple of years and its the triangulation that gives a truss its strength and stiffness.
anyway- my .02$
Mike
Murphys law 28th corollary- If there are five ways for something to go wrong, and you circumvent all five, a sixth will promptly develop.
Kwazai's addition- if you circumvent the sixth a seventh will develop, etc. etc.