Joist Weight Concerns

[Striker]

Evening:

I'm finally tackling my garage attic project. However, I have one concern in the back of my mind that is nagging me. I have a 20x22 ft garage built with 2x10 for the joists (24 in center). The outside walls are 2x4s on 16 in centers, but the wall opposite of the garage doors is 2x4s on 24 in centers (no weight load on it). The joists run back and forth to the two walls on 16 in centers.

I just installed 3/4 attic decking that covers about 75% of the attic. Once I install drywall I'm starting to wonder the type of weight load I'm putting on the building. The attic will be used for light storage, but a few items will weight 25+ pounds.

Normally I'd consult an engineer, but it will be almost a week before he gets back to me due to his work load (friend doing a favor for me). So, I'm asking the construction experts out there. Am I worrying over nothing or do I have a legitimate concern here? Any help is appreciated. Thanks!

 

[mmhouse]

So to clarify, you have 2x10 ceiling joists on 16" centers spanning about 22' and you will be drywalling the ceiling and using a portion of the attic for storage, is that correct? Do you know the species and grade of the 2x10's (you should find grade stamps on them)?

According to the American Wood Council's span calculator and using 2x10 Hem-Fir #2 for ceiling joists the maximum span allowed would be 19' 3". Link to calculator follows:

http://www.awc.org/calculators/span...bmit=Calculate+Maximum+Horizontal+Span#answer

Now don't get overly concerned until we confirm the actual span, what species and grade of lumber you actually have and other details. I'm just giving you the calculator example to illustrate how you figure this stuff out.

You shouldn't have any problem with your walls providing that you have adequate sheathing or other lateral bracing. Wood stud walls are extremely strong, even 2x4's. However, you do need to make sure there is something to keep the walls from racking. Are your walls solid sheathed on the exterior with plywood or OSB? What thickness? If not, do you have some sort of wood or metal diagonal bracing let into or on top of the studs?

 

[Striker]

So to clarify, you have 2x10 ceiling joists on 16" centers spanning about 22' and you will be drywalling the ceiling and using a portion of the attic for storage, is that correct? Do you know the species and grade of the 2x10's (you should find grade stamps on them)?

Ceiling joists are on 24" centers. The house was built in the early 1970s so it should be old growth lumbar. I can't find any stamping on the wood nor do I know the species. The joists are just under 20 ft long.

Now don't get overly concerned until we confirm the actual span, what species and grade of lumber you actually have and other details. I'm just giving you the calculator example to illustrate how you figure this stuff out.

I'm not too worried...yet. I've visited the above mentioned site before for another project a year or so back.

Are your walls solid sheathed on the exterior with plywood or OSB? What thickness? If not, do you have some sort of wood or metal diagonal bracing let into or on top of the studs?

There is no exterior plywood siding. The outer wall layers are 2x4, felt paper, and then hardiplank siding. There is cross bracing running diagonal from the bottom to the top for about 8 ft at all the corners.

 

[portcity]

taking a hem fir 24 oc carrying 20psf live, 10psf dead, l240 would give you a length of 16'. now change that to 12"oc and it gives a length of 22'7". So you could just go in and add a extra joist in the middle of your existing ones to meet load requirements. Heres some load charts to help

 

[Striker]

All the joists run one way (parallel to the garage doors). Are you saying I should add one perpendicular in the middle? If so that is going to be one big modification to the structure.

 

[gesoffen]

I think portcity is suggesting add another 2x10 in between the existing ones - that will change the joist spacing from 24" oc to 12" oc.

 

[little d]

striker, 20' for a 2 by 10 is a pretty good span, heres what i would sugest. crossing your ceiling joist, come out 5' from outside walls, take a 2"by4" and nail or screw it down through your decking into your ceiling joist. now take a 2" by 10", or 12" standing up and atach that to your 2 by 4,this is what is called a strong back, basickly, your bracing the joist from the top instead of the bottom. this should stiffin up your ceilin/floor a bunch, good luck and if ya need anything, just give me a shout, little d.

 

[bigdav160]

I don't see your location but in my area thousands and thousands of homes were built just like you describe.

Those 2x10's are just collar ties keeping the walls from spreading. Adding plywood and sheetrock is going to add, maybe, 3-4lbs of dead load. I don't see a problem.

 

[mmhouse]

Sorry for mis-reading the joist span on your original post.

Since there is no grade stamping on the wood, it's difficult to tell exactly what you have. Knowing what part of the country you're in and when the garage was built could give a good clue. Southeast is often yellow pine, northwest is often fir or hem-fir, etc.

Using hem-fir on 24" centers gives you a maximum span of 16' 0". This is allowing a 20 lb/sf life load (i.e. storage) and 10 lb/sf dead load (this is flooring, drywall, insulation and other stuff "attached" to the structure). This also allows for certain deflection or bending of the members under load.

Knowing what we know, the ceiling is obviously not as strong as would be required if it was built today. It will deflect or bounce a lot when you put weight on top of it. It will probably hold up just fine with drywall and even with your plywood for flooring but in my opinion you shouldn't be storing much if anything up there. You will get some feel for that when you stand on top and see how much the floor bounces (probably a lot!).

Portcity's suggestion of adding a 2x10 joist between each existing joist to take the spacing from 24" to 12" is the best solution. This would allow you to comfortably store stuff that's not too heavy without concern about anything failing, but would obviously cost a few bucks. I think this is the way I'd go.

Little d's strongback suggestion is good too but still doesn't really get you to where you should be. Adding cross bridging or solid bridging between the joists would also help some with deflection but all of this is really not going to get you to where you could store much stuff without worry.

Remember, you will almost always end up storing more up there than you plan.

 

[Striker]

Morning:

I am located in Texas and as previously posted the house was built in the early 1970s. You can't stand up as the ceiling is only about 5ft high at its highest point. It's more of a giant crawl space than anything else. It does have enough space for me to use plastic storage containers.

 

[mmhouse]

Morning:

I am located in Texas and as previously posted the house was built in the early 1970s. You can't stand up as the ceiling is only about 5ft high at its highest point. It's more of a giant crawl space than anything else. It does have enough space for me to use plastic storage containers.

Southern Pine takes you to 16' 11". Pretty much any way you look at it you technically shouldn't be putting a floor up there and storing things without somehow strengthening the structure. My guess is that you'll be okay with just a drywall ceiling but I wouldn't put a floor on as that means there will be stuff up there and there really shouldn't be.

Adding intermediate joists as suggested earlier is the best and most certain solution.

Another possibility would be to scab a piece of smaller dimension lumber (i.e. 2x6 or 2x8) onto each existing 2x10 joist - in other words nail it to the side of the existing joist. I wouldn't be able to tell you what size would be necessary but obviously the bigger the better.

Your diagonal corner bracing is likely sufficient. I wouldn't worry about that. Your concern should be the strength of the ceiling after you add the weight of drywall and plywood and then start putting stuff in your new attic.

 

[tcianci]

Oh, go ahead and load it, it always sags slowly

 

[lilredex]

For what its worth......... Bought my place twenty years back and it came with a frame 22 X 24 garage, the ceiling joists were 2 X 4's (on 24" centers) and some were sagging a bit. My guess is, that this was a "Beaver Lumber" garage kit (from the sixties), where they off load all the pieces on to your driveway and you put it up. At least this is what the guy next door remembers and he was here since 1958. So, there must have been a bit of thought put into the selection of all the parts. We have no magic materials around here........we have spruce, more spruce and even more spruce. Spruce is everywhere.

So.......I look at it and think WTF? What to do as I have a lot of junk I want to store up there on those puny joists. My solution was to put my floor jack under those "saggers" and "sister" on another 2 X 4. Then I took some 1 X 6's (thrown out from an old fence) and hooked them to the rafters to keep them in place......kind of like bridge building. I then got a few 1 X 10's (more Spruce) and dropped them along over top of those "new" joists, leaving a walkway between to accomodate my ladder. So, we now have four runs the length of the garage holding up multi boxes of junk. In addition, I have some shorter runs up closer to the peak to accomodate a few wheels and rads, etc.


And you guys are worried about 2 X 10's being under powered? I know there are thousands of garages around here that are similarly constructed and they didn't fall down either. The only other extra support I added was a diagonal 2 X 4 brace across the back wall, it was racking something serious. I pulled it back in place using a chain and turnbuckle diagonally.

It is this one...........

 

[portcity]

mmhouse idea of scabbing a smaller 2x beside it is another good idea, and would probably be pretty easy. Ive had to do that before for an engineer to pass inspection. You would essentially just be building beams

 

[Striker]

I looked at possibly adding more joists and that is going to be a lot of work. The existing joists are directly connected to the roof rafters. There is no place that I can see where I can connect new joists.

 

[little d]

striker, the strong backs will work, ive done it manny times, your call though, good luck, little d.

 

[jkuro]

If you just want to beef it up a little you can add some solid blocking, this is about the easiest to do. This will help spread the load on the floor a little more evenly and help keeep it from sagging. I would add two blocks per span.

 

[6768rogues]

Joists usually do not just break in half. They will sag and if not braced will rotate and fail. Span tables take into account the amount of deflection that is considered acceptable. If you go a little further than the table (within reason), you will have more deflection (bounce when walking on them). If they do not have bridging or other equivalent support, they can rotate and fail. The top of the joist is under compression and the bottom is under tension, so they want to rotate.
For floors, one unit of deflection for 360 units of length is usually used. For roofs, it is one unit of deflection in 180 units of length.

 

[CUSTOMMANCAVES.COM]

For reference:

2 x 12 Douglas Fir, 12" o.c., 20' span, hung with joist hangers on a 2 x 12 rim joist. Rim joist supported every 4 ' with 2 x 4's. Rated weight? Lots!

 

[Striker]

I wanted to update everyone on the project. After sharing the ideas from this thread and discussing the structural aspects with the engineer we came up with a plan. I married additional 2x10 joists to the existing joists with bolts and nuts. I then installed 3 rows of 2x10 blocking to prevent the joists from rotating. Additional vertical 2x4s were added or replaced due to a few not passing visual inspection.

For the most part the garage is built very well, but you can tell the framers took a bit of liberty when it came to their choice of installing 2x4s. It was almost like they ran out and scrounged around. Some were perfect up until near the ends where they were chunks missing (like they screwed up nailing in the wood and took a crowbar to pry it out).

Once those issues were fixed I was cleared to use the attic. Thank you everyone for your insight and advice. It definitely came in handy.

 

[mmhouse]

Thanks for the update. Now you can store stuff up there and sleep well.