Breaktime Spotlight

How to Reinforce 2x6 Ceiling Joists to Handle Heavy Loads

comments (17) February 9th, 2011 in Blogs

Scott Gibson, contributing writer

Can 2x6s hold up to heavy lumber?
2x6 celing joists can do a fine job of keeping the walls from spreading, but what if Leo wants to store piles and piles of heavy lumber up there?
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Another view of the shop

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Can 2x6s hold up to heavy lumber?

2x6 celing joists can do a fine job of keeping the walls from spreading, but what if Leo wants to store piles and piles of heavy lumber up there?

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Photo: Leo Meilak

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That's Leo's delimma, as he explains in this Breaktime post. The recently completed 16- by 24-foot building has 2x4 walls and a roof with a 2x10 ridge and 2x6 rafters.

It was only after the building was up did Leom realize he hadn't figured in the added weight of the lumber on the ceiling joists.

"The 16-ft. 2x6s are there to keep the 2x6 rafters from spreading," he writes. "This is a pretty basic design, designed by an engineer and approved by the town. I only wish I mentioned it earlier that the attic might be used for storage. If I had mentioned it earlier what would I have done differently? I don't want a beam or posts running down the middle for obvious reasons."

If he doubled up every other joist, would it be enough to handle the weight of "a lot of hardwood." His engineer does, but what about everyone else?

A little sag, but it won't collapse

The 2x6 joists will sag, no doubt, says DanH. "They will probably not collapse, and the load will probably not compromise the structure. Many a garage has been loaded down for decades the way you suggest, and out-and-out failures are rare, in spite of the rather inferior garage construction techniques used 60-80 years ago."

But, DanH adds, that assumes Leom uses common sense and doesn't overload the overhead storage area with wood.

The sag could be reduced or eliminated by installing king posts, or Leom could sister 2x8s to the 2x6 joists to "roughly triple" the load-bearing capacity of the ceiling.

"Since this isn't a floor, then the allowable deflection tables don't really apply," adds Jigs-n-fixtures. "They are mostly there to keep people walking on the floor comfortable, or prevent inflexible flooring like ceramic tile, from being damaged. The structure would be sound with considerably more deflection."

Even a stack of wood a foot deep would mean a load of 50 lb. per sq. ft. (psf).

Engineer 10 is skeptical.

"Tell your engineer that another engineer says that doubling 2x6s doesn't work for heavy loads," he writes. "If he/she still insists that doubling is OK then ask for a signed and sealed letter to this effect."

Engineer 10 adds that a No. 2 2x6 over a 16-ft. span can carry 10 psf while a 2x8 will carry 20 psf. Sistering the two together means a load-carrying capacity of 30 psf.

"This is based on bending strength only not deflection, therefore a load larger than that will cause collapse," he writes. "The load can be considered permanent dead load since it will be there for months at a time which makes everything worse because of material fatigue.

"In addition to that the deflection will be so noticeable from below that it will look frightening to a casual observer."

I-joists would have been a good bet

Calvin suggests that I-joists would have been an alternative to consider at the start of the project. In his own garage, he used I-joists with 2x4 flanges for a 30-ft. clear span.

"No sistering or modification of I-joists to the existing situation," he says.

There's a problem with I-joists, Sandcastles points out. Leom is already concerned there isn't enough room between his double top plate and the roof to wedge in the additional 2x8s, and the minimum I-joist Sandcastles knows of is 9 1/4 in.

"You probably have to even more significantly trim the 9 1/4 I joist, cutting it more than manufacturers will allow," Sandcastles says.

Also, says Leom, the load rating for an I-joist is 100 psf live load, 20 psf for a dead load, and that doesn't help his situation much because lumber stored overhead for long periods of time is dead load.

Piffin had this variation on the I-joist option:

"What I would do is to add a 2x4 to the top and bottom of each joist, using glue and structural screws to convert each joist into an I-joist in place," Piffin writes.

"You could even possibly introduce a good crown to each by holding the bottom chord in place with a slightly long 2x4 post under the center as you install it. Do bottom chords first, then the tops. Leave posts in place until all fasters are in and the glue kicks well."

Or, use LVLs in a limited area

JAlden wonders whether Leom actually needs storage over the full 24-ft. length of the shop. Would, say, 8 ft of storage be enough for the amount of wood he has?

"If so, go buy 4 pieces of 9 1/4 inch [laminated venner lumber]," JAlden writes. "Last time I bought them they were about 3 bucks a foot so we are talking 200 dollars here.

"Cut the ends at the angle of your roof and see how long you can make them and still get some bearing on your top plates. You may get full bearing if you have some roof overhang to slide one side into. Get as much bearing as you can. Even half of the plate is sufficient.

"Sister these to every other 2x6 and you'll have 8 feet of beefed up area."

Come back next week to find out what Leo did to solve this deflection dilemma

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Comments (17)

Alisyaya writes: I have just purchased a two-story home with lots of attic space. I had a contractor come out to estimate finishing it out. He said that all the ceiling joints would have to be changed out to floor joists which would been extensive and raise the floor. It seems to me that I read somewhere that you can reinforce the ceiling joists in such a way as to give them the strength of floor joists. I want the space to be an area for kids to play and maybe have a couple of beds. Any suggestions?
Thanks
Posted: 5:32 pm on May 31st

sawdustmaker49 writes: ok blair633,what would you suggest to solve the problem?
Posted: 12:07 pm on March 6th

Tubba writes: It has been proven that sandwiching 3/4 in plywood glued between 2 2x6 will increase the load capacity 10 fold.
Posted: 11:15 pm on February 9th

barkeatr writes: YOU could strengthen the clg joist system by adding plywood on top of the clg joists. I think you would get more bang for the buck with the sistering solutions listed above but if the person was thinking he would like sheathing up there anyway, then the sheathing might get him the reduction in deflection he is looking for. Of course it has to be done right, as far as fasteners and glue. and there cannot be any gaps between plywood sheets. Essentially you are adding a top flange to each joist as you would see in the top of an I beam,or better, a T shaped beam. I have seen this done and the T and G is cut off to create a stronger butt joint to better resist compression forces.
Posted: 9:03 pm on November 14th

JLNels writes: You could install an UPSET beam down the center in the attic. Bearing the new beam on the end walls, install joist hangers on each of the 2x6 ceiling joist (one on each side of the new beam) to reduce the span and increase the load capacity of the attic space.
Posted: 4:35 pm on March 19th

CableRigger writes: To prevent sag in 2x6's and strengthen at same time, you could secure lengths of stainless steel (or galvanized) cable - attach at each end of individual ceiling joists, have cable go over a one or two "spreaders" or strut projecting down from the underside of the ceiling joist maybe 12"-14" or so as not to lose too much headroom (these could be 2x4's fastened to ceiling joist with a plywood gusset sandwich, the longer the 2x4 is, the more mechanical advantage there is), and tension the turnbuckle in each cable assembly so cable taught.
I would guess doing so every third ceiling joist would keep your dead load from making the ceiling joists sag.
Added bonus is you wouldn't be adding more material to the dead weight as you would be by adding more dimensional lumber to the whole equation.
Would look good too.
Posted: 10:42 pm on February 20th

pilgrim writes: we should "think out-side the box" with this one..go outside your building and determine where it would be really neat to have an access door (or panel) ABOVE the in question 2x6's..1;this is where you will slide in what ever you need to strenthen the joists from ABOVE ..glue lams,whatever..I would also block the 2x6's below the area where the lam would be placed to give you a good purchase area to tie them(2x6's and lam(s) together)..and 2;now you have a good access area Outside you building to handle longer stock that,as we all know,is not fun to handle with tools and benches in our work space.(I ASSUMED we all know the lam(s) would be supported at each end)..

I'm really the only PERFECT person I KNOW,

PILGRIM,OREGON
Posted: 8:36 am on February 16th

garymac writes: I'm thinking tie the rafters and ceiling joists together to make a funk truss and add some decking in the open centre portion to help spread the load. Use blocking and 5/8 gusset plates to tie every thing together
Posted: 12:09 pm on February 15th

ekt_tim writes: I agree bonding & screwing a 2x to the bottom of each joist might be sufficient, but you could halve the effective span by hanging the joists along the centerline under the ridge with gusset plates and vertical 2x4's. This would change your stick built roof framing to trusses.
Posted: 8:17 am on February 15th

chinuga writes: run a beam under the joist,no post needed, create a beam pocket at one end with double 2x4 cripples and 2x12 double simpson hanger at overhead header. Use 2x12 and 1/2 plywood glued with PL400 and your done.
Posted: 6:18 pm on February 14th

sawzall316 writes: CubanOriley's method is typical, it's not rocket science for the guy to have the engineer come up with something to give him ease of mind.
Posted: 5:50 pm on February 14th

CubanORiley writes: I've done this application before. Used what is termed as a spaced beam, which requires 2x6 blocking at various points, (engineer determined) glued each side, patterned nailed with an additional continuous joist on the opposite side. Blocks are sandwiched between the two joists. This would occur at every joist. I've been instructed usually to use 2x6x24" blocks at 4"o.c. where I've stored various amounts of dimensional lumber. Have not had any sag or concerns.
Posted: 4:57 pm on February 14th

pvarchitect writes: I'd be prone to looking at creating a truss involving the ceiling/floor joists and the roof rafters; perhaps by adding vertical or diagonal leg components from the rafters to the 1/4 point of the ceiling floor span. Involving a competent and experienced structural engineer is a MUST however, because in addition to shear and stress points of the construction lumber, the connections must be designed as to any reinforcement and number of fasteners or bolts, split rings or washers. Adding a 2 x 4 along the bottom chord of the 2 x 6 ceiling/floor joist maybe helpful in stiffening the joist as well. Gluing and screwing a 3/4" attic subfloor and providing solid bridging should also be considered.
Posted: 3:50 pm on February 14th

MichaelENG writes: Must agree with blair633. For a horizontal span, divide the span by the depth, don't go beyond 20 without consulting an engineer. If loads are extreme (storage loads can be extreme), consult an engineer anyway. In this case, 16'/5.5" is 35. Would it break if you walked across it? Probably not as long as the joist didn't have a big knot midspan. Would it break if you loaded it at 100 psf? dunno, but I wouldn't want to stand under it.

In defense of those hesitant to call an engineer, too many engineers fail to do their job. Their job it to make sure that an assembly is 2-3 times stronger than it needs to be. Too often, they make it 6 times stronger than it needs to be. A century ago (back before engineers were terribly involved in construction), the engineer's marketing slogan was, "An engineer can do for a dollar what any fool can do for two." Having been a professional engineer for over a quarter of a century, I see fellow engineers designing things that are back to costing two dollars or worse. Not all engineers, or even most, but enough to give the profession a bad name.
Posted: 3:00 pm on February 14th

blair633 writes: I am a structural engineer, and am amazed articles like this get published, none of what is shown is even close to meeting building code loads. A 16' long 2 x 6 does not have any load capacity for storage. These are simple calculations for an engineer, you should always consult an engineer in lieu of guessing
Posted: 2:32 pm on February 14th

MichaelENG writes: If the garage has a simple peaked roof, dropping 2x6s free of large knots from the peak and tying them into the center of the ceiling joists would cut the span in half. Half the span means 4 times the load carrying capacity from a strength standpoint, the deflection would be 1/16 that of the full span. This scheme is predicated on achieving serious load carrying connections (well thought out and installed A-35 or L clips should to it) at all joints: tie to roof rafters at peak, tie to ceiling joists, roof rafters to ceiling joists at the eaves. The ceiling joists create a truss to begin with, I'm suggesting adding another member to the truss. In general a truss if much more efficient than beams, but you gotta respect the joints. In this case, you would be creating many trusses which lead to redundancy which leads to a good nights sleep.

Michael
Posted: 2:04 pm on February 14th

kfield writes: I'm not an engineer but I wonder what extra strength could be gained when sistering the 2X6s with 2X8s if plywood was glued between them. Staggering the joints in the plywood so they all did not line up and were not at dead center.
Posted: 1:59 pm on February 14th

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