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Old 09-04-2011, 11:38 AM   #1
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Laminating a Beam


I want to laminate a beam for a small 4 foot porch roof. The spans on the roof are 18 and 20 feet I'm using 2 x 6 for the support beam. How far from the posts can the seams be, the ends of two 2 x 6 butted together, or must they be directly over the support posts. I live in BC, if that's any help.

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Old 09-04-2011, 12:42 PM   #2
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Laminating a Beam


apply and be accepted to engineering school.

finish.

start engineering beams.

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Old 09-04-2011, 02:25 PM   #3
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Laminating a Beam


Usually I go with jcrack's approach, but perhaps I can be of some assistance. I am not going to comment on your sizing of the beam, since I have no idea what load you are designing for. So let's assume you got the size correct. You did not state how many 2x6's you want to laminate, the number of 2x6's has a substantial effect on the design of the laminations and the fastener pattern. I also don't understand the meaning of your words "small four foot porch roof". Did you mean there were going to be four posts at the corners?

If you post a diagram of your design, I can help you develop a fastener pattern for laminating the beam.
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Old 09-04-2011, 03:02 PM   #4
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Laminating a Beam


I am laminating three 2 x 6's together. They are sitting on 6 x 6 posts, the span between the post would not exceed 10 feet. If you measured out from the wall, it would be 6 feet to the edge of the eave. Sorry I said 4 feet before. Once again the length of these beams will be 18 feet for one and 20 feet for the other. So my question is; I start with a ten foot 2 x 6, the second 2 x 6 is only eight feet long, and the third is 10 feet. As I carry on laminating this beam, the 2 x 6 in the middle can now be 10 foot long, etc. If the distance between the posts are 10 feet, I will have a seam two feet short of the beam. Do these seams have to be atop the posts or can they be that two feet short? I tried drawing this in excel and uploading it, but it wouldn't let me.
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Old 09-04-2011, 03:38 PM   #5
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Laminating a Beam


Wouldn't go as far as J Crack Corn but I would just buy a section of glue lam somebody else already engineered before buying timber and bolting it together. Or even a piece of steel and wrap it so it does not show.

Agree it is hard to know what you are attempting without seeing a diagram. I am envisioning a roof, over a porch, coming four feet out from the house and running 20' long?

What is your framing member on the house side of the porch going to look like? A ledger plate anchored to what?

I assume you are trying to span 20' with as few posts showing or something? Aren't you going to need the posts just to look decent aesthetically?

What is the roofing material, its weight, and loads on it with weather conditions and all?

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Old 09-04-2011, 07:35 PM   #6
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Laminating a Beam


OK, let's assume you got the size correct, based on the load. Unless there is a local building code requirement (check with your building inspector), it is not necessary to make the joints (you refer to them as seams) line up with the posts. It is necessary that you have adequate overlap and an appropriate fastener pattern.

The overlap is no problem, since your 2x6 pieces are at least 8 feet long. If you use 16d nails spaced every 6 inches, staggered top and bottom, you are going to have plenty of shear capacity. This means the beam will not fail in horizontal shear, which is a good thing. However, the beam could fail in bending, if three 2x6's are inadequate. Since we have no idea what the load is, no one can offer any insight as to whether three 2x6 elements is sufficient, but you didn't ask, so I am going to operate on the don't ask, don't offer an opinion policy on that question.

There are alternatives to 16d nails, including structural screws, lag bolts, and threaded bolts with nuts. The required pattern depends on the allowable shear in the fastener, and on the strength of the wood, however use of nails is simple, fast and effective. You can also purchase a laminated beam, however I sense that financial considerations are important, so I suggest nails. By the way, you can also use structural adhesive as a SUPPLEMENT to the nails, not by itself, however it is not necessary.
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Old 09-06-2011, 10:28 AM   #7
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Laminating a Beam


Why not just use a 20' 6x6?
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Old 09-06-2011, 12:13 PM   #8
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Laminating a Beam


I am understanding that the beams are for the rafter tails (birds mouth) to sit on, am I right? It also depends on your snow loads as the size you will need.

I disagree with some people who are quick to want to call out an engineer. I know Daniel and some of the other engineers here know their stuff but there are some engineers out there who are dangerous and should not have a license. I know of one in Memphis who signed off on a two story house with 20 foot 2X8 floor joist with no support under the span at all. That was one of the biggest messes I have ever seen and it was a rich man's house. Sorry, to rant but but some folks who come here can't afford an engineer in their budget. They are here to ask our help and yes there are times an engineer is necessary because there is no way we can see all that is going on on a job site.
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Old 09-07-2011, 11:36 AM   #9
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You're right jiju 1943, in many of your statements. I don't know about some of the rest of you, but hiring an engineer was not an option and we are allowed, by the building code to make our own beams. My back deck is in excess of 53 feet, and we laminated, in accordance with the blueprints, a beam made of 2 x 10's. However the question here has only been addressed by one person, that question is simply how far from the post can a joint be, when laminating a beam. Let's just assume that everything else is correct, as to loads etc.
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Old 09-07-2011, 11:50 AM   #10
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Laminating a Beam


Robbie, laminate away. As long as the joints are not within 3 foot of each other and you have one continuous member between each post, you're okay. I'd glue with a construction adhesive and screw it together rather than nail it. If I'm reading your post correctly, you are making 2 beams- one 18 foot and one 20 foot. Just order 3 2x 6- 18's and 3 2x 6-20's and there would be no joints to worry about.
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Old 09-07-2011, 11:54 AM   #11
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Thanks TrapperL, we would have just bought the proper lengths but in this backward part of BC they don't come long enough to do that.

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