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Homeowner Forum / Construction / October 2006Beam in garage supporting upstairs room
My house (built in '86) has a family room (size 16' x 26') above a two-car garage. All that's supporting the floor across the span of the garage are 2x8 floor joists running across the 16' length. Because there are no supports in the garage, the family room floor is bouncier than I'd like. What I'm thinking of doing is putting a beam down the 26' length in the garage, supported at each end by a metal post. The floor to finished ceiling height in the garage is 10'. Anyone have any suggestions on what size beam to use? My first thought was a steel I-beam, but maybe I can do it myself with (say) three 2x12s bolted together. Of course, that might depend on whether I can find 26' long 2x12s. Think 2x12s will do the job and provide rigidity over that large a span? I guess manufactured beams would be another possibility. If so, what size? Sorry, meant 2x10 floor joists running across the 16' length (every 16"), not 2x8. > My house (built in '86) has a family room (size 16' x 26') above a > two-car garage. All that's supporting the floor across the span of the [quoted text clipped - 9 lines] > large a span? I guess manufactured beams would be another possibility. > If so, what size? Just an update. I visited my local lumber supply store and was quoted $1,100 for a manufactured beam (the guy did the calculations on what size was necessary). The person I dealt with suggested I go with a steel I-beam, because it would cost less. I then got a quote on the steal beam and that was $500 (delivered but not installed). On the other hand, I can get three 2x12s for $150. The lumber guy said he thought the 2x12s would do the job, but, not being an engineer, he couldn't say for sure. The suggestion of sistering the joists is probably a good one, though I hate to pull down all the drywall (well, actually, it's the thought of reinstalling it that I hate). > My house (built in '86) has a family room (size 16' x 26') above a > two-car garage. All that's supporting the floor across the span of the [quoted text clipped - 9 lines] > large a span? I guess manufactured beams would be another possibility. > If so, what size? Chack out engineered lumber. I would look for an LVL I-beam at your local hardware store. For a 26' span you can probably use two or three of them bolted together. Google for manufacturers specs once you know what is easily available in your neighbourhood. Carolyn  SignatureCarolyn Marenger In a previous post verivin@yahoo.com wrote... > My house (built in '86) has a family room (size 16' x 26') above a > two-car garage. All that's supporting the floor across the span of the [quoted text clipped - 3 lines] > 26' length in the garage, supported at each end by a metal post. The > floor to finished ceiling height in the garage is 10'. You could accomplish the same effect by doubling up the joists. In fact the "doubles" don't even have to run all the way across the 16 feet. Buy some 12-foot pieces. Jack the existing joists to level or slight above. Glue and screw the new pieces on and take out the jacks. Re-install the sheet rock SignatureBob Morrison, PE, SE R L Morrison Engineering Co Structural & Civil Engineering Poulsbo WA bob at rlmorrisonengr dot com > My house (built in '86) has a family room (size 16' x 26') above a > two-car garage. All that's supporting the floor across the span of the [quoted text clipped - 9 lines] > large a span? I guess manufactured beams would be another possibility. > If so, what size? In the case of what you're anticipating doing, the 2X12 would only serve as a nailer, not doing the actual support. You would need a steel plate 3/4" I beam. The 2X12s could be put on both sides of the I beam via bolts. The 2X12s don't have to be continuous, can have 2 on either side of the I beam. 3 2X12s over each other is doable, but the span is too great. SignatureJonny > In the case of what you're anticipating doing, the 2X12 would only serve as > a nailer, not doing the actual support. You would need a steel plate 3/4" I [quoted text clipped - 3 lines] > -- > Jonny Thanks for the suggestions! I understand suggestion #1 (use manufactured beams) and #2 (sister the 2x10s), but I don't fully understand #3 (I-beam with 2x12s on each side). If the 2x12s aren't doing the actual supporting, why bother with them at all? I don't have to nail anything to the beam, it can be exposed. I believe what Bob was referring to (in #2) by doubling the floor joists, was to add additional section modulus to the joists in the middle of the span (where deflection and hence, bounce, is greatest.) The greatest moment occurs at mid span, doubling the joists there will give you something similar to a 4x10 section. You could probably build up a beam out of shorter 2x's (considering only if it was glued and screwed or nailed well), but you could not count the outer layers as being effective (they would act as a splice section only). And you would also have to create columns at each end to carry the load of the beam into a concrete footing (can't go just into the garage floor unless you are prepared for cracking and settling.) Bob's suggestion was probably the most cost effective (considering all the alternatives, including the beam itself, the additional cost of the columns, and footings necessary to support the loads) and would produce a very rigid floor above. >> In the case of what you're anticipating doing, the 2X12 would only serve >> as [quoted text clipped - 12 lines] > doing the actual supporting, why bother with them at all? I don't have > to nail anything to the beam, it can be exposed. In a previous post PPS wrote... > I believe what Bob was referring to (in #2) by doubling the floor joists, > was to add additional section modulus to the joists in the middle of the > span (where deflection and hence, bounce, is greatest.) The greatest moment > occurs at mid span, doubling the joists there will give you something > similar to a 4x10 section. That is exactly what I had in mind. This is one of those things that might fall under the heading of "Engineer's Secret Tricks" SignatureBob Morrison, PE, SE R L Morrison Engineering Co Structural & Civil Engineering Poulsbo WA bob at rlmorrisonengr dot com OK..the votes were in and Bob's idea seemed to prevail. So...I went ahead and pulled down the first of about 12 sheets of drywall and to my surprise found not 2x10s, but trusses! (I was assuming 2x10s because that's what the builder used on the main floor, which also has long, unsupported stretches.) What they are are two 2x4s laid flat (top & bottom) connected on each side by pieces of metal. I took a picture, which I'll send to anyone who is interested. What does everyone think now? Is sistering the joists out and we're back to the beam? BTW, the trusses are 11 1/2" high. In a previous post verivin@yahoo.com wrote... > OK..the votes were in and Bob's idea seemed to prevail. So...I went > ahead and pulled down the first of about 12 sheets of drywall and to my [quoted text clipped - 4 lines] > which I'll send to anyone who is interested. What does everyone think > now? Is sistering the joists out and we're back to the beam? Probably not, but you might want to get a local engineer involved in this one. When you say the top and bottom are connected by pieces of metal, are there diagonals that connect with the metal or is the web of the truss a continuous metal sheet. You can send a copy of the photo to the address below. SignatureBob Morrison, PE, SE R L Morrison Engineering Co Structural & Civil Engineering Poulsbo WA bob at rlmorrisonengr dot com To All: I've seen the picture and the joists are indeed a form of manufactured truss. Here's the advice I gave the OP. Life gets more difficult, but I don't believe it would be impossible to sister on something. These being trusses I would stay away from adding a support in the middle. The trusses most likely were not designed for such a support. I'm still thinking that one might use a 2x12 (11-1/4" deep) x 12' long flush with the bottom and screwed to the truss on one side. You will need to take the sag out of the trusses with temporary shoring before you do this. SignatureBob Morrison, PE, SE R L Morrison Engineering Co Structural & Civil Engineering Poulsbo WA bob at rlmorrisonengr dot com > > In the case of what you're anticipating doing, the 2X12 would only serve as > > a nailer, not doing the actual support. ... ... ... > understand #3 (I-beam with 2x12s on each side). If the 2x12s aren't > doing the actual supporting, why bother with them at all? I don't have > to nail anything to the beam, it can be exposed. My interpretation is that he was thinking you were planning on splitting the existing joists and using the beam to hang them on--the side pieces would be for hanger supports. IIUY, you intended to simply insert a beam under the existing joists at the midpoint for support. I vote w/ Bob M as the neatest solution...but I ken not wanting to rehang a ceiling, but then again, _I_ don't have to... :) |
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