I’m going to remove a 17′-3″ length of interior wall and replace it with a beam. Load above is the attic–full dimension 2×6 ceiling joists (two pieces lapped in the center over the wall I’m removing), total span about 28′. The attic has a partial plywood floor and some contents stored in it. The roof is stick framed with 2×6 and there are no truss-type diagonal braces or anything else bearing on the joists.
Desired beam is a 4x and posts are to be at the ends. Is the sizing of something like this covered by the ‘prescriptive’ part of the code, or is it something an engineer would have to look at?
Replies
David:
Don't quote me on this, but a booklet I have on LVLs says a clear opening of 17' and a span of 28' with a live load of 40 PSF and a dead load of 12 PSF needs a 5-1/4" x 14" LVL. For an 18' clear opening, 5-1/4 x 16.
This seems like a pretty major project to me. A little engineering might be in order.
Al Mollitor, Sharon MA
Al, when you say clear opening of 17' and span of 28', what does the 28' refer to? The beam, whatever it's made of, would be just over 17' long and would be supported at either end either by 4x4 or 6x6. I'm getting the feeling it's 6x6...
My question is mostly an academic one and does not mean I'm about to wing it in a client's house. Whatever goes in will be reviewed and approved for a permit. I'm just wondering if it's possible to look this stuff up. The building department here seems to have software for double-checking beam sizing, so if I come up with something they will check it too.
I was looking at a book of tables provided by the beam manufacturer. The 17' would have been the distance between the posts that support the beam. The 28' would be the 14' 2x6 joists you have on both sides of the beam.
If you actually do this, the people that make and sell the beam may be able to spec the proper size for you. Obviously, the posts that support the beam must transfer that load to a foundation.
The 5-1/4 x 14 would be three 1-3/4 x 14s fastened together. Unless you want to get these guys that have had their hernias repaired to lift it, you could lift them one piece at a time. They're not as heavy as you might think.
Al Mollitor, Sharon MA
I don't ever size beams for people without looking at the situation personally. But you seem to have a pretty good handle on the situation.
Clay comes pretty close in his load calcs, but I don't think the loads he used are heavy enough. But I'd be surprised if a 3 1/2 X 16" or 18" LVL didn't work in this case PROVIDED that you've told us everything.
Your codes may have something in them that changes the design. Like BOCA requires 30PSF live load in some situations, and 40 PSF in others.
If you go to a lumberyard, they can probably help you out. Their sources for engineered beams will have the software and expertise to get you a beam design. Most of them can come up with an engineer's seal if your building requires it. And they'll be familiar with your local codes.Do not do an immoral thing for moral reasons. [Thomas Hardy]
Don't take on this un-necessary liability. Get a pro's advice.
Go to http://www.gp.com/build/literature.aspx#Engineered%20Lumber
You not only need to size the beam properly, you also need to have a proper bearing dimension. A single jack and king stud won't do for the length you are refering to.
You will probably have to double or triple the LVLs to create a beam - very heavy. I haven't looked up you situation but from my recent experience, fabricating the beam is alot of fun and reqires some (lots) of organization. Getting the beam in place is another story. We used a couple of Baker scaffolds to get the beam to height (almost) and then used bottle jacks. Screw jack columns might have been easier than bottle jacks in retrospect. We are doing another beam in 2wks and will try the screw jack method for comparison. I think it will be more stable due to less components.
F.
Might I suggest a flinch beam; 2 C8 x 11.5 steel channels on either side of the stud wall bolted through the existing studs with 2x fillers between studs. This can be erected prior to cutting out the studs etc. Bearing at each end can be steel jack post or 2 x 4 built-up columns. Exterior of channels can then be furred in with stapping and drywall.
I removed a middle column and a bearing wall, and installed a beam to support the tile roof and a cathedral ceiling. Span between supports was about 26 ft. The engr spec'd a 3x18 glulam, with at leasst 2 studs supporting each end...I used three.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
There was an article in FHB a couple of years ago describing a similar project. What they did was cut the joists and install the beam so the bottom of the beam was flush with the bottom of the joists. Installed joist hangers and when they were done, the ceiling was smooth across where the wall had been.
If you want 4" of beam showing, you could do the same thing, only have the beam hang down 4-1/2" below the bottom of the joists. If you did that, the beam could be however deep it needs to be for engineering purposes, because only the 4" you want would show below the ceiling, and the rest of it would protrude up into the attic.
Taunton has a book, engineering for builders, that has all the tables except the engineered lumber that you need.
That doesn't sound like that big a deal, I assume your wall is perpendicular to the direction the ceiling joists are running. Attic space has lower dead/live loading weights to contend with than living floors. Maybe a doubled 2x12 over that distance, with hangers from the cut ceiling joists onto the new beam? You'd have to look it up. In this situation it would only be one side's loading determining the sizing of the beam. Adjustable steel posts, like the basement style, will bear relatively large loads down to the foundation. The foundation would be an issue, particularly if one side ends up in the middle of a slab either slab-on-grade or transmitted down to a basement slab, you would probably need to jack hammer it up and pour a proper spread footer.
The roof is irrelevant unless my understanding is incorrect. The force at work in your description is one tending to bow the walls out, which would be counteracted by the existing ceiling joists and collar ties if present - but not a force that relates to needing a larger beam size. Proper fastening of the new beams and cut joists would be necessary to counteract the spreading effect.
remodeler
Another system that goes along the lines Uncle Dunc suggested is to install what we call an upside down beam. To do that we install the beam on top of the joists so that it's depth is contained in the attic space. Then extra-long joist hangers are installed hanging the joists from the beam. In this case you would have to remove the attic decking to accomplish this. Obviously this doesn't work when the space above will be finished. In some cases for this system we have to have steel hangers welded to get the neccessary depth.
Then extra-long joist hangers are installed hanging the joists from the beam. That works as long as the designer & contractor knows that the hangers are open-ended, and there's nothing to keep the joist from falling out the back of the hanger. Also, there's not enough strength in the standard hangers to resist the outward thrust of the joists. It's a solvable situation as long as it is understood.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
Ed;
I am assuming that the joists are already scabbed to their mates on the opposite side of the wall ... true it may not be that way and then it should be done. Usually we use double hangers in a case like this so that the two joists act as one and provide rigid linear positioning for each other. If the joist lengths are not sufficient to provide a decent overlap it is best to cut them so that they butt in the middle of the beam and then scab an addional length to them before hanging them in a double hanger. It is also doable to use angle iron as hangers but you have to get permission from the structural inspector first if the work is going to be inspected. They can be fussy about such things. A good point you raised though ... sometimes I forget to give all the details ... and they ARE important.
The space is used for storage, and although I had thought of flush-framing the beam, the rooms have 9' ceilings and a beam below the ceiling level is OK. Flush framing would require a fair amount of hardware to enable the joists to continue resisting the lateral thrust of the roof. I was hoping to use 4x rough-sawn fir but based on the beam sizes folks are mentioning so far it doesn't sound likely. Maybe this will have to be a painted glu-lam. Another thought I had was to use a 3x tube steel and wrap it with VG fir.
David,
Your local codes folks have the main piece of info needed to answer the question. a 40 - 50 # live load would be needed for living space, but an unfinished attic would only need about a 15# live load design. Since you use thisthis for some storage, you need to know how much and whether that impacts the local code requirements.
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David; This is fairly straightforward. Your supported length will be 14 feet (this is half of your 28 foot total joist span ... you can see that the other half of the load will rest on the outside walls). For the minimal storage that you describe you can get by with 20 lbs/sf live load and 10 lbs/sf dead load. Basically we are treating this as a light duty floor beam. Your beam span is 17 foot 3 inches as you stated. Now we add up the live load and the dead load to get 30 lbs/sf. We multiply that by our supported length (14 feet) to get the lbs/lf (pounds per lineal foot) that will be resting on our beam. This number turns out to be 420 (lbs/lf). According to my Glulam tables that will require about a 3" by 15" beam. You can use these figures to consult the tables for the specific beam product that you purchase (because they do vary depending on exactly what you get). This is predicated on the idea that you are using the space in the attic only for occaisional light storage. If you want to build it for regular use, possibly even finishing the space someday, you will need to add another 10 lbs/sf live load (or 140 lbs/lf). Thus requiring a beam that will span 18 feet while holding a load of 560 lbs/lf. Also check with your building department to see if they have more stringent requirements that you will have to meet (these are typical). Your local lumberyard can probably give you any additional help that you need (don't expect much from the big box stores on things like this ... you need a real professional lumberyard).
Here is another nice source. They have a demo program you can download. the real program costs $90. But if you do much desing and building it could be handy
Beam Check by AC software