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OT: Header Beam Clear Spans

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  • OT: Header Beam Clear Spans

    I am in the design stages of a "lean-to" type shelter on my deck that is going to require a 16 ft (+) clear span under the roofline (about a 10ft wide roof). This lean-to is to be a free standing shelter; not attached to the house. The back of the shelter is of no concern, it can have posts where warranted along a standard nailed/screwed 2X? beam. However, in the front, I want no obstructions.

    I can find no common beam construction technique that will clear span what I want. Even 4-2X12 can span only around 12-14 ft. So I'm looking at gluelam beams like in this random link:

    http://cmfac.groups.et.byu.net/tharm...am%20guide.pdf

    But the more I look, the more ignorant I become. I don't know terms like "allowable moments", "moment of inertia", "modulus of Elasticity", or most of the other design terms. I simply want a built-up beam that can take a northern Indiana snow load over a 16 or so foot span. The roofing material will be something like the Ondura panel or metal, so the actual construction load on the beam(s) will not be great. I just don't want to see it come crashing to the ground when the snow flies... and if last year is any indication, it WILL definitely fly!!

    So, does anyone know of a "beams for idiots" website or reference so I can design to the correct size? Also, I know that these engineered beams are vacuum laminated but, using the correct water resistant glues, can I duplicate strength on my own (home built)?

  • #2
    16ft isn't hard with engineered beams (many garages have that above the door ) but not so easy with 2x built up timber. If you have access to quality grades of lumber, like SELSTR (select structural) etc, it isn't hard to make your own beams. You don't need to glue vertical 2x together if you follow the correct nailing/bolting schedule. "Bolts/lags" have changed in the past 10 years. Now you can get 3/8" engineered screws than perform like 1/2 and 5/8.

    There isn't much beam loading with a 10 foot rafter span - remember, half the load is taken by the back wall. Contact your local supplier of glue lams, LVL, paralam etc etc.; they will have calc software to size the beam for many suppliers. Also, go directly to the beam manf websites (like, Parr, LP, Boise Cascade etc) - they have simplified design guides with tables for different snow loading, span and width.

    For heavy snow or floor loads and built-up with engineered lumber, I use LVL - it's comes in 2x (1.75 nominal), 4x and 6x, but much deeper than timber. For 10 foot roof span you won't need much depth. You nail/bolt the 2x together as specified. For a decent design guide (all manf of beams have similar), glance though this. If depth is a limitation, Even with a 20 foot rafter span, and 40 psf live 115% snow (doubt you need this in your area), you can get away with 5.25x11.25 for 16 foot; for 20 psf live and 115% snow, it's 3.5x11.25.

    http://parr.com/PDFs/LP%20LVL%201.9E.pdf

    Clear-span loading is one thing, but you need to figure you how you are going to provide lateral bracing. A typical garage portal will have BP "Braced Panels" or APB "Alternate Braced Panels" (narrower, but more timber and tighter nailing schedule) increased on each end. You might consider post/pole construction where the posts are buried deep in concrete provided both lateral and uplift restraint.
    Last edited by lakeside53; 08-10-2014, 05:26 PM.

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    • #3
      What limit are you using for figuring deflection-L/480 (most conservative but most common) or L/320?
      the latter may open your choices. If it doesnt need to be solid, you could look into trusses. If you're not limited to 12" depth, a 16-20" depth truss might suffice.

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      • #4
        When you say 16' clear span with no posts/obstructions in front I think you are planning to cantilever the beams out from the house and not support them at the other end?

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        • #5
          What about a Flitch beam?It's an old standby for large garage door openings.Two 2x12"s with a piece of 1/4 x 10" flabar sandwiched in between and bolted through with carriage bolts.

          It's strong as an Ox,you would still be connecting to wood afterwards and no welding required.
          I just need one more tool,just one!

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          • #6
            Min 8x2 at 400mm ctrs,, span in feet express as inches, eg 16 feet is 16", divide by 2= 8" x 2, min fot 1500 n/m2 load, defn about 10 mm with CLS 24 timber, preferred 9 x 3 cuts defn to 1/10 inch
            Mark

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            • #7
              Your in the "lake effect" snow load area as I am so call your local real lumberyard & see. I think a 2 or 3 ply lvl bolted properly won't be too tall, maybe 12" as your only carrying 1/2 the width plus the overhang. If you use steel roof & a decent pitch it won't hold much snow in most cases.

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              • #8
                Indiana. You get wind and snow there. Local code and buildingdepartment rules your project to some extent. However so long as you select your roof system members to resist the loads and can point to some table or manufactuer's info you should be OK.'

                I suggest this book. Ramsey Sleeper "Archictural Graphic Standards". It's a common reference to be found in most public librarys. In it you will find tabulated data for sn, and AIA publication. It contains sow and wind loads for various parts of the country and the wood members recommended to resist them. The page numbers may vary with edition. I have the 7th edition and the infomation you may seek starts on Page 298.

                If you track this book down (you don't want to buy it, it's fearsomely expensive) budget extra time to browse. It's full of construction and archectural info with tons of illustrations to make everything crystal clear.

                I dig my copy out about once a year to dig out something specific then get distracted by the bounty of tchnical info ("geek porn," Barbara calls it) and after a couple of weeks of intermittant browsing, I return it to its place on the shelf.

                Appatently you're concerned about preserving your view. A steel beam needs to be about half the depth of wood for equal strength. If you pack out the web with wood you can install standard joist hangers to connect the joists for a clean non-intrusive eve that still allows slope for drainage.
                Last edited by Forrest Addy; 08-10-2014, 08:44 PM.

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                • #9
                  If you are under a local body for permits and inspection (building inspectors) then I would suggest that you contact them and tell them what you are doing. They can probably tell you what you need, not only for the snow load, but to satisfy the local requirements. Otherwise, you may wind up building it twice, once before it fails inspection and again after.

                  Even if you are out in the woods, you can talk to the building inspectors in the nearest town for their advice. May cost you some coffee and donuts.
                  Paul A.
                  SE Texas

                  And if you look REAL close at an analog signal,
                  You will find that it has discrete steps.

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                  • #10
                    As usual, many great suggestions. I figured I could get some direction here. I am indeed dead nuts in the snow belt; last year was the second worst on record (I think it was my 'welcome the new guy to the area' gift).

                    Not sure if this project will need inspection, the deck itself did not. However, good idea to run it by someone first.

                    The rafters will be a kind of modified truss (exposed and pretty), again no longer than about 10 ft. The trusses, framing and roofing material will be fairly light, kind of like a pole barn roof. This structure is little more than a giant grill cover, with a bit of seating and a couple of ceiling fans. It will cover less than a third or so of the actual floor surface. Canvas curtains will be strung along the back side on cables so we can cut wind, rain, or exposure to the neighbors at will. I will have access to the grill year round, unless we get the snows from hell again.

                    And it is important to have no post in the center of the deck floor to run into... should I get a little tipsy some fine evening, or want to chase the little woman around. Or both.

                    So far, in order, I will call inspector, visit my high end lumber joint, start looking at newfangled (to me) hardware, and keep looking for a home made plan that can be executed here without emptying my wallet.

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                    • #11
                      Not wanting to start another thread .. I am also in need of a beam. Replacing a load bearing wall
                      in a house. I have a Glu-lam beam in my pile that is perfectly the right size (4"x12"x17') Wonder if you
                      guys can tell me how bad the weather affects it. Its not damaged at all but is pretty weathered.

                      Mike A
                      John Titor, when are you.

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                      • #12
                        Originally posted by mikeamick View Post
                        Not wanting to start another thread .. I am also in need of a beam. Replacing a load bearing wall
                        in a house. I have a Glu-lam beam in my pile that is perfectly the right size (4"x12"x17') Wonder if you
                        guys can tell me how bad the weather affects it. Its not damaged at all but is pretty weathered.
                        The beam should be fine in and of itself if it has no delaminations (gaps between the plies).
                        "Patriotism is the last refuge of a scoundrel"

                        Comment


                        • #13
                          The OP is in a lake effect snow area and the applicable roof snow is subject to determination by the local authority for his exact location because of extreme local variations.

                          If the roof design snow load is 40 psf and the structure weighs 15 psf then we have 55 psf total and 275 lb per foot on the beam. Rounding to 300 plf on the beam allowing for beam self weight we get a bending moment of 9600 lb ft for a span of 16' between centers of support and for a deflection limitation of L/240 on the total load we need a Moment of Inertia for the beam of 290 in^3 assuming engineered lumber.

                          For the case described you could use almost get by with a 1 3/4" x 11 7/8" MicroLam (LVL) with a little more deflection or a 14" would easily meet the requirements. The 14" would weigh about 120 lbs. and could be good for up to 70 psf total on the roof.

                          There are some approximations in the above and loads could possibly be reduced if some other factors are considered.
                          "Patriotism is the last refuge of a scoundrel"

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                          • #14
                            If Jep is correct I'd use 2 11 7/8 bolted ending up with 3.5"thick & 2 hanger to put them inside the post.

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                            • #15
                              Originally posted by jep24601 View Post
                              ... Moment of Inertia for the beam of 290 in^3 assuming engineered lumber.
                              in^4

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