floor live loads, lumber storage

[tim vadas]

I'm cautious about how much wood i can store in my garage . . .

A few years ago, i had my attached 24x24' garage partly finished into a shop and a second floor installed. A beam was installed down the center of the garage between the garage doors only supported at the ends, and the second floors is 12 ft lengths of 2x8s installed over each garage stall, 16" on center, with advantech 3/4" subfloor over top. I have the beam information, but i'm not completely sure how to interpret it. The load say 10 PLF dead load, 40 PLF live load. The product says 1-3/4 x 16 x 2.0E CP-Lam LVL 4 ply.

I'm unclear, but is 40 PLF the same as pounds per square foot?

I'd like to store some dried lumber up there. I've had it cut and stored outside a couple years, but the mice keep chewing through the tarps, and living in my wood pile, so i get sections of rot. I have about 2000 bd. ft. of mostly red oak, 20% white oak. If i assume about 3.5-4 lbs/bd. ft. (is that right?) for the wood, i've got up to 8000 lbs of wood. If the floor holds 40 psf, that's up to about 23,000 lbs spread evenly across the floor. So i'm safe putting all this wood up there? It just seems like a lot of weight compared to what we normally have on our floors. Am i missing something?

[Jim Neeley]

I'm going to throw in my $0.02.. I'm an Electrical / Mechanical engineer, not a Structural, so hopefully one will jump in and correct me if I misspeak. First, I'm going to assume that you are looking at this document:

http://www.coastalforestproducts.com/catalog/files/2012%20p21%20Cp%20lam%20properties%20EWPCatalog.pd f

If this is so, and if the building was built to their guidelines, then the floor would provide a support for 10#/ft2 dead and 40#/ft2 live load.

The 10#/ft2 dead load is anything that remains in place for a relatively long time... like wood storage, if it's going to be in place for any extended period.
The 40#/ft2 live load is for short-term loads.

Why the difference? The phenomena is akin to shelf sagging. If you build a shelf that is too wide for it's thickness and load, it may stand up OK initially but it will sag over time. For example, if you had a shelf that wouldn't sag with 10#/ft2 over time, you could put several times as much weight on the shelf and not have it break; it would be "safe". If it was left there it would, over time, damage the shelf.

What this means is that with your wood, if you were to spread it evenly all over the floor, it is rated for you to put 24'x24'x10#/ft2= 5,760# on the level. I'll defer to one of my illustrious Structural colleagues on how much more you can load it, if any, for your application. :-)

Jim

[Michael W. Clark]

I have always heard PLF referred to as pounds per linear foot. It would be the same as PSF (pounds per square foot) if your joists were on 12" centers? Your rating may be even less than what Jiim describes, however you reach the same conclusion.

I'm a mechanical engineer too, not a structural, so wait on one of them to chime in.

[Thomas Bank]

Registered architect, but I spent ten years working directly for structural engineers. PLF is pounds per lineal foot. So basically, you take the area supported by a foot of the beam and you're allowed 40lbs live load on that area - the dead load takes care of the floor structure itself.

So, consider that for each bay you have half of each 2x8 supported by the side walls and half supported by the beam (in idea conditions). That means that you have twelve feet of the second floor (six feet either side of the beam) that is supported by the beam. So you'd have 40lbs divided by that 12 square feet. You can see that there isn't a whole lot of capacity there...

Is this actually a full floor? Or a loft space? I cannot imagine anyone designing a full floor with 2x8s spanning 12' in good conscience. That sounds much more like a ceiling rafter design with some fairly light storage requirements. There is no way I'd store lumber up there.

[tim vadas]

Thanks for your help so far.

Jim, I was looking at the coastal products page, but the 40 psi that it states in the footnotes doesn't quite make sense to me because you can't support an unlimited area.

Thomas, what you say about the PLF and contributing load area makes sense to me, but if 40 PLF is correct, it could barely hold up the 2x8s and plywood. I'm assuming i'm reading the beam information wrong on the printout from the lumber store.

I found this pdf on coastal products page, http://www.coastalforestproducts.com/catalog/files/2012%20p24%20Cp%20loads%20EWPCatalog.pdf, and I've got 4 ply, 16" beam. The relationship between number of plys and PLF is linear, so for 4-ply, it would have 540 PLF. If that means the beam can carry 540 PLFx 24' / (12'x24'), that gives me about 45 psf across the contributing area to the beam. The rest of the floor would carry load to the side walls, which already supports the roof, and is a 2x4 wall over a concrete slab. I'm assuming that can take a similar load?

That gives me a lot more weight bearing, but i'm still not sure about the adequacy of a 2x8 carrying the load back to the beam. I checked some span tables for douglas fir no. 2 common, and it says a 2x8 joist, 16 OC, can go 12'9" for a floor that is 10 psf dead, 40 psf live load.

I'm an environmental engineer, so i've taken some basic statics courses, but I'll defer to the more experienced structural people. Thomas, does what i came up with sound reasonable to you?

[phil harold]

As a carpenter I I have a few questions
You have a clear span of 24' with a single 16" lvl?
or is 4 lvls with a 24' clear span?


If you are storing lumber it will be a dead load not a live load !!!
Live loads are temporary, of short duration, or moving.

[Kurt Cady]

I am a licensed structural engineer and it seems to me that it would be well worth a couple hundred bucks to call one out to check/calc it out.

Never in a million years would I give design/load advice out on the Internet

Theres A whole lot more to it than picking a number out of a table

[Thomas Bank]

Along with Phil's questions, the next question about the LVL span is what is it bearing on?

And I agree with Kurt, you should really have it evaluated by a professional. As mentioned, beyond the calculations there are the questions on how everything is connected and how the loads are transferred. My earlier post was pretty much just walking you through the reasons I would not even consider storing anything up there. Sounds like what I had calculated was based on some erroneous numbers, but my simple answer still stands at that I wouldn't consider storing lumber up there.

My workshop is automotive/metalworking on the first floor and woodworking on the second floor. I've got 2x10s at 12" oc spanning 12' and resting on 16" deep steel beams supported on steel posts. My total load capacity is over 150psf.

[Jim Andrew]

It would be interesting to know what size and what the beam itself is, as well as the species and grade of the 2x8's. There is a lot of difference between syp or douglas fir and spf, or even hemlock. It was common to build homes that had a width of 28' with 2x8 floor systems, some cheap home builders even went to 24" centers where the stair opening cut the span. A few years ago, the span charts in the code book was updated to compensate for poorer quality lumber, and started causing floor systems that same size to be 2x 10.

[tim vadas]

Thanks for the replies.

The beam is made up of 4 1-3/4x16" lvls, over a 24' span. 2x8's are dougl fir no. 2 common.

I thought it would be more straightforward than you guys make it sound, given that most residential systems do not require a structural engineer and i thought beams, joists, etc. were decided by contractors based on tables. I guess my main question was whether this floor sounded like a 40 psf live load floor as are most residential floors, or maybe less, as for an attic. I never discussed specific weight requirements with the contractor, just mentioned i'd like to store some material up there. I'm not looking to put the maximum possible weight up there; i'd stick to 25-50% of the rated load.

However, i understand there are differences depending on uniform vs. point loads, or how wood is joined, etc. I'll check with a professional just to be safe. Thanks again.

[Thomas Bank]

Although a lot of homebuilding is done from tables or by the lumberyard for LVLs, trusses, and such, when you start talking about storing 3.5 to 4 tons of wood... Obviously, there isn't a whole lot in the way of furniture and such in the average residential home that is going to be 4 tons... You're playing in a different ballgame here.

[Greg Cuetara]

I am also a licensed structural engineer and I will concur with Kurt that if you are that concerned pay a few hundred bucks and have someone look at it.

Just to be clear any lumber stored would be considered a live load. A dead load is anything that is the actual structure that will never move. A live load is considered anything that would be stored up there etc. The basic difference between the two is that a dead load is a very well known quantity, the actual structure, whereas a live load is an unknown, the lumber that you may store up there. If it can be moved around it is a live load. There is no time frame given to distinguish between the two. I could store lumber for 500 years and it would still be considered a live load. Again pay a few bucks and gets someone to look at your situation. There are always special considerations to connections, member sizes, spans etc. and you just can't pull that stuff off the internet or out of a book.

A suggestion would be to go to this website and email them to ask about someone in your area that does residential work... http://www.ct-sec.org/

good luck,
Greg

[Jason Roehl]

One thing I haven't really seen mentioned is the deflection of the floor. So, if the beam is rated for 10 PLF dead load and 40 PLF live load, that doesn't mean that it will accept floor construction of 10 PSF for any distance out from the beam. The floor joists have to be deep enough and closely spaced enough to stay within the desired deflection (L/480, L/360, L/240, etc), but if the design is too robust (very little deflection due to deep joists and/or closely spaced), you may exceed that 10 PLF dead load rating.

It can all be done from tables for simple, straightforward situations, or even a call to your local building inspector, but it doesn't hurt to have a structural engineer take a look, either.

[Jim Andrew]

Sounds like your upper floor is pretty well built. I'd go ahead and put some up there. The closer you can pile it to the outside wall the better, as more of the weight will rest on your exterior walls. If all else fails, you could put a post under the beam near the center of the building. That would about quadruple the strength of the upper floor.

[Joe Angrisani]

.....If all else fails....

How à propos....

[John Lifer]

Sounds like your upper floor is pretty well built. I'd go ahead and put some up there. The closer you can pile it to the outside wall the better, as more of the weight will rest on your exterior walls. If all else fails, you could put a post under the beam near the center of the building. That would about quadruple the strength of the upper floor.
You're not seriously saying go ahead and put 4 tons of wood up there are you?
Like the OP, I love it, 'If all else fails" Unfortunately, when it does fail, it will be too late.

[Jim Andrew]

I was saying you could put some wood up there. Did I write 4 tons? And I did mean you could quadruple the amount you could put up there if there was a post in the center of the garage. Cuts the span of the beam in half.

[Tom Scott]

Adding the post only increases the capacity of the beam, not the joists. So, can't really say it increases the capacity of the floor. Not trying to pile on, but the joists could easily be the weak link in the whole floor.

[Joe Angrisani]

.....but the joists could easily be the weak link in the whole floor.

"Could easily be the weak link"??? Twelve foot 2x8s on 16" centers? Where's the "could" in that under-build? I'll bet a shiny quarter that floor will flex at midspan under the weight of a 200 pound man....

[Jim Andrew]

I have a barn that's over a hundred years old. It has a loft built with 2x8 doug fir on 24" centers. It also has 4x6 beams on 12' centers. When I was young, we used to pile baled hay in that loft about 12' high. They were heavy bales of alfalfa, about 70 pounds each. Haven't had hay in it for years, but I have that loft full of lumber, about 8' high.

[Tom Scott]

"Could easily be the weak link"??? Twelve foot 2x8s on 16" centers? Where's the "could" in that under-build? I'll bet a shiny quarter that floor will flex at midspan under the weight of a 200 pound man....

I don't know species or grade, but assuming S-P-F #2 2x8 joist, it should deflect less than 1/4" with a 200# man in the middle. Those 2x8's at 16" o.c. are theoretically good for about 10psf DL and 40psf LL, but are maxed out for stress and deflection. Would I load it up with a bunch of wood? No.

[Tom Scott]

I have a barn that's over a hundred years old. It has a loft built with 2x8 doug fir on 24" centers. It also has 4x6 beams on 12' centers. When I was young, we used to pile baled hay in that loft about 12' high. They were heavy bales of alfalfa, about 70 pounds each. Haven't had hay in it for years, but I have that loft full of lumber, about 8' high.

There is a HUGE difference in the wood we had 100 years ago. In fact, there is a difference in the wood we had just 20 years ago. The Southern Pine Council recently lowered the allowable stress values for certain visually-graded lumber by about 1/3. Their design values are based on testing and there has been a steady decline...attributed to research developing faster growth trees.

[David Gutierrez]

SPF 2x8's at this span and load are limited to 12'-3" with a deflection of L/360. A ton, 2000 lbs, of wood spread out over 50 square feet does not exceed the floors capacity. plenty of capacity to store lumber if you are smart about it.

[Michael W. Clark]

Seems like mouse traps or some Decon would be a lot easier.:)

Mike