# 2 x 4 Strength?



## mopowers

How much weight can a 10' doug fir 2 x 4 hold if the 2 x 4 is supported at the ends by joist hangers? In other words, the 2 x 4 is laying horizontal like a joist w/ the 4" side vertical.

THANKS!!!


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## Daniel Holzman

The amount of weight a horizontal element can hold depends on the bending strength of the element (in your case Doug Fir, need the grade), and the distribution of the weight. The worst case in terms of maximum bending stress on the beam comes from a point load at the center of the span. The best case for bending comes from a pair of point loads directly located over the support brackets. A distributed load creates a lower maximum bending stress in the beam than a point load of equal total weight at the center.

Example:

A 10 foot long 2x4 carrying a uniform load of 40 pounds per foot (400 lbs total load) will have a maximum bending moment at the center of the span of 1000 ft-lbs.

The same 10 foot long 2x4 with a point load of 400 lbs at the center will experience a maximum bending moment of 500 ft-lbs.

Whether the beam fails or not is also a function of maximum shear stress, although in most home applications bending moment controls.


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## mopowers

Thanks for the explanation. I'm trying to plan a storage shelf in my garage.

The garage is 10' wide and I'd like to make the shelf 2' out from the wall. I will put a 2x4 ledger on three sides. The fourth side (running from wall to wall), will have joist hangers holding up a 2x4. Then I was going to connect the two 10' long 2x4's with studs every two feet. Then sheet it with 3/4" plywood.

I'm just trying to determine if I should run a couple supports from the ceiling down to the suspended side of the shelf.

Here is a quick drawing of what I'm trying to do. Do you think this will be strong enough, or do I need supports in the middle?


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## Proby

Interesting, I'd like to hear what Daniel has to say about this.

What are you going to be putting on the shelf? 

Is there any reason (clearance underneath) that you can't use a larger 2X in front?


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## Jack Olsen

First off, I am in no way an expert. So take this like you'd take helpful advice from some guy just walking past your garage. 

Without a center support, I think that is going to sag. Just the weight of the shelving will eventually make it sag. 

How to avoid this? You could do a diagonal brace below it, a diagonal brace up above it, or you could tie it into the roof with a vertical piece connecting to a ceiling piece that spans at least three of the ceiling joists. 

Or you could use a 2x8 for the piece running the span. It depends on how much weight you're going to put on it.

My personal rule of thumb is to never have a 2x4 span more than 4' when it's being laid out up to 24" on center. (A 2x6 is good for 6', a 2x8 for 8', etc.) So by my reckoning, the ideal piece for that would be a 2x10. But that might be overkill if you're just storing Christmas decorations up there.


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## johnnyboy

throw a 4x4 in there instead.


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## concretemasonry

It looks are you are trying to build a "park-under" shelf at the end of your garage.

Just add another 10' 2x4 to cut the span of the that intermediate 2x4 (that should be elimimated) because it is over-building for a 12" span between joists.

I have built several systems (usually 2 spand in a 24' or 30 wide garage with a post in the middle) in my homes through the years. Usually the rear 2x4 was anchored or attached to the rear wall. The only criticism I get is that they are "ungodly" strong and will attract people in a tornado warning. When I weighed 285#, I got up there and noted it no inkling of deflection. - If your are considering something like a 5.7 liter (350 ci) engine the concentrated weight might be a problem. If it is a 1000 hp Formula 1 engine, it is no problem.

Being supported on three sides, cutting the load on a 10' span by going to 12" spacing and eliminating the 2x4s from front to back makes a waorld of difference. - Fewer 2x4s, fewer hangers and much more rigidity and strength. Just edge nail the 3/4 plywood well, but think I used 1/2" plywood on the first couple.

Dick


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## Scuba_Dave

Might want to consider extending the side 2' 2x's out to 32" to catch the next stud
I'd span the 10' distance too


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## concretemasonry

What is so sacred about spacing at 16" o.c.? I just used 12" o.c. because it worked for 24" shelf depth (any more depth is really unusable and impractical) to reduce the load on an individual 2x4. Since your are using 3/4" plywood and attach it well it has been proven to be stable. 3/4" plywood properly nailed to a 2x4 provides all the continuity that is needed. - It just a storage area for 20-30 years or until you change your mind and not a prescriptive, no-brain code "life-safety" problem. If you expect to pile up 8' of junk on the shelf, then there could be concern.

I just went out and measured mu present garage and found it was 23' wide (clear) and I used a center post and a 24" long 2x4 beam to spread the load out from the joist in the center of the 24" distance from the back wall to the front 2x4. - The center 10' long 2x4 carries far more load than the back wall (continuously supported" or the front 2x4, but in my case it is spanning about 11' - 6".

Too often, people look at the standard, "no-brain" tables and spans and practices without looking at what is really needed. - Than when you have to do and what is correct and not what is habitual.

I have designed many multi-story buildings and am only risking a dented hood on my two cars IF there is an earthquake, wind, snow and a dynamic load at the same time. - Not a code issue, but a casual use.

Dick


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## mopowers

Proby said:


> Interesting, I'd like to hear what Daniel has to say about this.
> 
> What are you going to be putting on the shelf?
> 
> Is there any reason (clearance underneath) that you can't use a larger 2X in front?


I'll be storing random boxes of parts to my hotrod project, gallon buckets of paint for the house, christmas ornament, rarely used tools, etc.

The self will be above a garage door, so the larger the beam, the less space I will have available.



> First off, I am in no way an expert. So take this like you'd take helpful advice from some guy just walking past your garage.
> 
> Without a center support, I think that is going to sag. Just the weight of the shelving will eventually make it sag.
> 
> How to avoid this? You could do a diagonal brace below it, a diagonal brace up above it, or you could tie it into the roof with a vertical piece connecting to a ceiling piece that spans at least three of the ceiling joists.
> 
> Or you could use a 2x8 for the piece running the span. It depends on how much weight you're going to put on it.
> 
> My personal rule of thumb is to never have a 2x4 span more than 4' when it's being laid out up to 24" on center. (A 2x6 is good for 6', a 2x8 for 8', etc.) So by my reckoning, the ideal piece for that would be a 2x10. But that might be overkill if you're just storing Christmas decorations up there.


I can't brace the underside since the garage door is under it. I could diagonal brace above. How would you atach the diag. 2x braces to the wall and shelf?

I also may weld up some angle iron 'T' brackets to lag to the cieling joists and screw to the front beam.




> It looks are you are trying to build a "park-under" shelf at the end of your garage.
> 
> Just add another 10' 2x4 to cut the span of the that intermediate 2x4 (that should be elimimated) because it is over-building for a 12" span between joists.
> 
> I have built several systems (usually 2 spand in a 24' or 30 wide garage with a post in the middle) in my homes through the years. Usually the rear 2x4 was anchored or attached to the rear wall. The only criticism I get is that they are "ungodly" strong and will attract people in a tornado warning. When I weighed 285#, I got up there and noted it no inkling of deflection. - If your are considering something like a 5.7 liter (350 ci) engine the concentrated weight might be a problem. If it is a 1000 hp Formula 1 engine, it is no problem.
> 
> Being supported on three sides, cutting the load on a 10' span by going to 12" spacing and eliminating the 2x4s from front to back makes a waorld of difference. - Fewer 2x4s, fewer hangers and much more rigidity and strength. Just edge nail the 3/4 plywood well, but think I used 1/2" plywood on the first couple.
> 
> Dick


So you're saying I should get rid of the short studs and just run another 10'er down the middle attached to the 2' ledgers?

I hadn't though of that. Hmmmmm... 



> Might want to consider extending the side 2' 2x's out to 32" to catch the next stud
> I'd span the 10' distance too


They will be extended down the sides as well because I plan on extending the shelving down the sides. I just left them off my scetch for simplicity sake. Thanks!! What do you mean you would "span the 10' distance too?" Isn't that what my drawing does? I'm not quite sure I understand you. 


Here is a picture of where I'll be building this shelf. I'd like the shelf to be just above the torsion rod. Thanks for all the help guys! I really appreciate it!!!


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## Gary in WA

Depends on the species of wood used, and the grade. A #2, *Doug Fir, 1.7*, 24"o.c. will span 10' and carry *15# sq.ft*. or *150#.*
pp #11, table C-1: http://www.awc.org/pdf/STJR_2005.pdf

Dave, 99% of the time, front garage side walls are laid out for the *exterior sheathing*- from the outside corner, not the inside drywall. You're thinking, though! 

Be safe, Gary


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## racebum

if load carrying is a concern and a 45degree bracket is out of the question due to where it would fall, depending on construction using cable at the corners running straight up to the truss would greatly increase the amount of weight you could put on the shelf since the end of your shelf would not be floating out in space anymore.


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## baum

Do what I did, 

I have the exact same application, however i only have 2 walls to support (back and 1 side). I created a 2x4 frame just how you are, 1/2" ply for the decking. I bolted the back and side using lag bolts, and used chain and eyebolts from the front of the frame to the ceiling joists. I spaced this every 4 ft. 

I have so much crap on it you wouldnt believe. wheels/tires, tools, x-mas goodies.


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## mopowers

Thanks for the input guys. I just talked to my dad, who's a carpenter. He suggested using the erector set looking straps they use for garage door installs and dropping a few straps form the ceiling joists grabbing two joists each.

Also, do you folks think it would be better to use short studs like my picture to connect the two joists, or span a middle 10' joist as Dick suggested. Which way is stronger???

Lastly, (stupid question time)- What is difference between kiln dried 2x4s and green studs? What would be best in this application.

Thanks a lot guys!! I'd ask my dad these questions, but he's really busy and I don't want to bother him with my stupid questions.


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## mopowers

Do any of you folks answer this question for me? Maybe I'm not explaining myself very well.

Would it be better to use short studs like in my sketch to connect the two joists, or span a middle 10' joist instead as Dick suggested. Which way is stronger???


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## Jack Olsen

Now that I see your application, I would get three 10' 2x4s. Use one 24" piece on each side if it helps you tie them together. Beyond that, whether you need a center piece going up to a ceiling joist depends on how much weight you're putting up there. 

I would not go with short pieces parallel to the long walls, as in your original drawing.

(Then again, I'm a writer, not a carpenter.)


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## Yoyizit

mopowers said:


>


Assume 800,000 PSI for the modulus of elasticity [MOE] for the 2x4 as a worst case, I = 5.4 and y = 3.5/2 = 1.8".
http://www.engineeringtoolbox.com/beam-stress-deflection-d_1312.html
Each short 2x4 will be very strong.
I'd worry more about shearing off the four wall fasteners.

Try it. Cut a 2x4 to length, support it at each end 1/8" above the floor, stand on the center of it on one foot and see if you can see any bending at all at midspan. 
You can also use this method to measure the MOE for your particular wood.


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## concretemasonry

The design tables have little real value since this is a unique application and probably not under a code and the design tables do not usually cover shelving for design loads. They might be intersting from an academic standpoint.

The important thing is that is it strong, functional and stable, which could be limited by the connections and the structure it is attached to.


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## kwikfishron

I agree with no short joist and do three the long direction.

If you’re worried about sag use 2x6. Woods cheap right now.

Don’t limit yourself to 24”, find the studs in the wall if you find one at 20-24” great otherwise go to the first stud beyond that. 

You’ll end up with a stronger shelf and a little more space.


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## Gary in WA

Concretemasonry, there is a ceiling joist table, on post #11 = *150# total load*.

If the short 2x are omitted and the span is 2' ----- it's the *same load*. To add another 10' 2x4, at 2' span, or 12"on center, you carry the load = *15# per sq.ft.* on the middle one and on the rim one =* 15#* together* total 30#.* OR *300# total load*. 

As Ron said, change to one *2x6 *in front and 2x ledger with/without the short spacers, *total load is 756# or 75# per sq.ft.* for Doug fir.

Be safe, Gary


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## concretemasonry

GBR - I do not believe in absolute use of joist tables even though I have been involved in the creation and code writing while being a structural engineer. They are basically for code purposes, which are based on a load capacity where failure would be a problem with human safety (life safety) if a building fails. I don't see this to be a ceiling joist or floor joist for code compliance. I don't see this as a code controlled situation, so the tables are just a guideline depending on the expected use. If it was a code problem, then I would recommend getting a permit and inspection, which is insane, but it would drive a plan checker and inspector insane and they would not want to get bothered.. Deflection is also not a problem.

As you correctly pointed out the elimination of the short 24" 2x4s and substituting a 10' 2x4 does double the load. This coupled with the 3/4" plywood will give a very robust storage area, especially since it is 24" deep so there is little room for a person and any appreciable space to occupy. If it was deeper, then the possibility of more load increases.

It is obvious that a 2x6 would be stronger, but the height would be decreased.

Attach the 24" long sidewall 2xs as well as possible, because this is where the real load is.

All too often, people involved in the strict use of codes in the U.S. and can get out of touch with the real world and practicality. I have a structural engineer friend in South America that has designed a number of projects with 1 to 10 - partially reinforced loadbearing masonry buildings using 6" thick block walls with no concrete or steel columns or beams that ranged from 10 to 22 stories. They have been doing this since 1972 when the first building were designed using the existing U.S. standards. When I asked him what codes and standards they used, he said "We use your codes and standards, but use them better based on experience, technological improvements, construction practices and prudent enforcement".

Dick


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## mopowers

Thanks for all the help guys. I got started on the shelving today.



> Attach the 24" long sidewall 2xs as well as possible, because this is where the real load is.


How would you attach them? I was just planning on running (2) 3" screws on every stud it hits. Keep in mind the side ledgers won't be 24"- they'll be about 5' for more shelving down the side. I just omitted that from the sketch for simplicity sake. 

Thanks again!!


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## Proby

mopowers said:


> How would you attach them? I was just planning on running (2) 3" screws on every stud it hits.


I'm curious what people have to say about this. Screws would have less tendency to pull out, but nails have a stronger shear weight rating. Lag bolts would split the difference I believe.


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## fabrk8r

I'd certainly use lag bolts to anchor the ledgers. There is going to be both shear force and lateral (pulling) force on the fasteners.

I would use at least 5/16" x 4" lag bolts with flat washers.


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## mopowers

fabrk8r said:


> I'd certainly use lag bolts to anchor the ledgers. There is going to be both shear force and lateral (pulling) force on the fasteners.
> 
> I would use at least 5/16" x 4" lag bolts with flat washers.


one per stud? or 2?


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## Gary in WA

http://www.awc.org/calculators/conn....0&submit2_LLSS=Calculate+Connection+Capacity

Be safe, Gary


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## fabrk8r

mopowers said:


> one per stud? or 2?


One per stud should be sufficient. Pre-drill the ledgers and pilot drill into the studs to prevent splitting.


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## Scuba_Dave

You could also install the side 2x's lower & have the 10' 2x's sit on top of these
Then add blocking between them


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## Yoyizit

GBR in WA said:


> http://www.awc.org/calculators/conn....0&submit2_LLSS=Calculate+Connection+Capacity
> 
> Be safe, Gary


I would call you a master of Internet searches. :thumbsup:


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## Gary in WA

You should see my bookmarks library.......... lol.

"You could also install the side 2x's lower & have the 10' 2x's sit on top of these
Then add blocking between them " -------- from Dave. 

Using a hanger, LUS 2x4 (L= lumber, U= shape, S= shear) rather than putting 3- 10d into the 1-1/2” of meat bearing there with very possible splitting out. 

The hanger has a shear resistance of *490# *using 10d*,* below toe-nails (3-16d = *561#*), but less chance of splitting.
http://www.strongtie.com/products/connectors/hangertables/face_ss-df1.asp

http://books.google.com/books?id=_C...esnum=10&ved=0CC4Q6AEwCQ#v=onepage&q=&f=false

Good for CA and FL., though no inspection required in this application. This will help hold the side walls together in a high wind or seismic area, especially tall walls that will flex at mid-height. I’d hate to find all my storage stuff on my car windshield for lack of using a shear hanger over toe-nails.

Be safe, Gary


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## mopowers

Thanks guys. I finally made my over storage shelf. Here are a couple pictures. Now I need to make one above the door in my 2-car garage. I ended up not putting a support in the middle because it seems solid as a rock. Before I put the plywood down, I was doing pull-ups on the outside joist and it wasn't budging.


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## Jack Olsen

Looks good. 

And here's the deal: if it DOES start to sag sometome down the line (and I honestly don't think it will), you could always sister some 1x6 pieces along the face edges and have a built in 'stop' to keep things from sliding or rolling over the edge and down on whatever's parked below.

(Living in earthquake country, you think about that kind of thing.)


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## Yoyizit

xxxxxxxxxxxxx


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## fdecker

*Similar project, question about design*

I have a similar shelf I need to build. I would appreciate any comments or suggestions about how to properly construct it. I have 2 pictures showing the same design with the rafters going in different directions.

1. This is a hanging loft shelf 10' wide by 4' deep
2. It will hold storage boxes, nothing very heavy
3. It will mount against the wall above the garage door opening
4. There is a wall to the left 2' from the shelf. I could extend the shelf if needed to use that wall, but then I have to deal with a 12' wide shelf
5. The ceiling is supported by a huge I beam and is the floor of the bonus room above
6. Should the shelf rafters go left to right or back to front?
7. Should I double up the front 2x4 or use a 2x6 as shown? I'm wanting the extra space since there is the garage door opener rail below the shelf, so leaning towards the 2x4.
8. Should the top hanger rail be just a 2x4, or should I bolt 2 2x4's together on the 4" face, then bolt them to the ceiling rafters over the sheetrock, and then bolt my hangers to the 2" faces?
9. Am I ok on the 10' span without having to double up or put a middle hanger in there?
10. And what about the back mount? I have a top plate there using a 2x4 for the shelf to sit on and then bolt the back shelf 2x4 to the garage wall. I also have to put 2x4's between the vertical beams because they sit out 1.5" from the wall. So the 2x4 spacers would make a flush mounting surface. I then would have to be careful of where the mounting bolts for the 2x4 spacers go since the shelf back 2x4 has to mount to the spacer. So my idea is to bolt the spacer to a vertical beam and then bold the shelf back to the spacer anywhere in between.

Thanks again


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## illnastyimpreza

general rule for constructing something that will NOT sag. 

1'' of dimentional lumber per foot of span. 2x4= 1.5'' x3.5'' will go 3.5'. or 42'' long. If you are going more than that, you need posts or other supports. It also helps to create a sandwich. Get some 3/4'' Plywood and sandwich it between 2 pieces of whatever lumber you are using. The Plywood is MUCH more rigid than the pine.


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## tony.g

Daniel Holzman said:


> in most home applications bending moment controls.


What about deflection!!!!!!!!!!!!!!!!


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## ElleNavorski

Daniel Holzman said:


> Example:
> 
> A 10 foot long 2x4 carrying a uniform load of 40 pounds per foot (400 lbs total load) will have a maximum bending moment at the center of the span of 1000 ft-lbs.
> 
> The same 10 foot long 2x4 with a point load of 400 lbs at the center will experience a maximum bending moment of 500 ft-lbs.


Switch the final answers above for a simply supported beam: The uniformly loaded beam maximum moment is 500 ft-lbs. The point loaded beam maximum moment is 1000 ft-lbs.


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## nightowl5473

Daniel Holzman said:


> The amount of weight a horizontal element can hold depends on the bending strength of the element (in your case Doug Fir, need the grade), and the distribution of the weight. The worst case in terms of maximum bending stress on the beam comes from a point load at the center of the span. The best case for bending comes from a pair of point loads directly located over the support brackets. A distributed load creates a lower maximum bending stress in the beam than a point load of equal total weight at the center.
> 
> Example:
> 
> A 10 foot long 2x4 carrying a uniform load of 40 pounds per foot (400 lbs total load) will have a maximum bending moment at the center of the span of 1000 ft-lbs.
> 
> The same 10 foot long 2x4 with a point load of 400 lbs at the center will experience a maximum bending moment of 500 ft-lbs.
> 
> Whether the beam fails or not is also a function of maximum shear stress, although in most home applications bending moment controls.


The above scenarios are reversed. A beam loaded with a distributed load will have a lower bending moment than one loaded with a point load that equals the total distributed load.

Dave Y.


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