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Old 10-06-2009, 04:52 PM   #1
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Raising Wall Heights


I am considering raising the height of our home's walls while adding a second story. I have heard of using a laminated beam along the top of the existing wall to do this. But, I don't understand how that eliminates the "hinge effect".

Can someone explain why this works but building a 14" mini-wall on top of the existing wall does not?

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Old 10-06-2009, 11:36 PM   #2
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Raising Wall Heights


We do have an engineer on this site , maybe he will chime in soon..... I've seen two instances where they added a 4x12 and a 6x12 all the way around the perimeter on top of the walls. Then through bolts every 24" to keep it there. One was because the framer figured the wall height wrong after the fact. The roof system - trusses and plywood was lifted off the house intact by a 50 ton crane, framer installed header stock, lowered roof back on. I only heard about that one from the framer. I laughed along with him as it was 5 weeks after the fact....
Be safe, Gary

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Old 10-08-2009, 03:56 PM   #3
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Raising Wall Heights


Maybe a picture will help. I don't understand why a stick frame addition to the wall height will not work, but a lam beam will.
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Old 10-08-2009, 04:03 PM   #4
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Raising Wall Heights


The simple answer is that a Lam beam is much stronger
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Old 10-08-2009, 04:07 PM   #5
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Hum. Thanks, but I still don't get it.

The wall itself is stick-framed. So the only strength I can think of -- that a lam beam offers -- is a horizontal shear strength, not a vertical one.

But, to my understanding, that is what plywood sheathing is for.
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Old 10-08-2009, 04:21 PM   #6
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Raising Wall Heights


Structurally, either way you have a hinge between the existing wall and whatever you attach to it (studs or laminated beam) unless you use the proper connecting hardware AND connection methods (nails do not really do well). If you are just nailing a short stud wall or a laminated beam, it makes little difference, they are equally poor.

The question of a "hinge" is important with any horizontal loads (wind, seismic, etc.) and it very difficult to eliminate with wood construction, because continuity is very poor. Don't really sweat the vertical loads.

If you are adding another story to your house, you need some professional help and not just a "nail benders" opinion.

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Old 10-08-2009, 04:44 PM   #7
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I don't understand the so called hinge effect. There is no hinge in either case, as a hinge is defined as a connection between two elements that allows for rotation of the elements, as in a hinged arch bridge. There are no hinges whether you install a laminated beam or a stick built section, PROVIDED as previously noted you properly connect the new section (stick or lam) to the existing wall. If you did not connect the two elements together at all, you would have a hinge along the horizontal axis, which could lead to buckling of the assembly, but of course you are going to connect the pieces.

That said, you will certainly want professional advice on the proper attachment technique for the lam or stick built section to the existing wall to eliminate the potential for lateral buckling. Beyond that, either technique could be made to work, provided the new section is correctly designed. The stick built is effectively an I beam, the lam is a rectangular beam. For my money, I would probably go with the stick built, likely considerably less expensive.
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Old 10-08-2009, 04:54 PM   #8
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Raising Wall Heights


Thanks everyone. I got my answer.

I brought up the "hinge effect" because that is what someone told me some time ago when I first brought up the idea. I didn't understand it then any more than I understand it now. But thanks to everyone here I now know my options are open and -- most importantly -- it can be done with the proper connections. Those connections I will get from my local architect.

Thanks again everyone. Much appreciated.
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Old 10-08-2009, 06:01 PM   #9
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Daniel - You don't understand the effects of a hinge in a structural element (wall, beam, etc.)?

It is the same thing as the classic problem of a 4' masonry foundation wall topped with a 4" wood frame wall, except in the roof raising situation, the "hinge" is closer to one end that at the middle, but it is still a hinge. At least with a basement knee wall, you have a fair amount of weight compared to a light stick addition above everything else around.

Obviously, it is very easy to transmit the vertical and shear loads with a nailed connection, but the ability to transmit the continuity of the wall(s) is difficult to do without some hardware and specific connection methods between the hardware and the two different wood elements. Toe nailing a laminated beam certainly is feeble and requires some thought and hardware. - Would you suggest a that a wall made of two 4' high sections is as structurally sound as a continuous 8' high wall? It is like playing basketball with a bad knee!

The future problem will only show up at critical times like seismic or high winds - sort of like a situation where the "nail bender"/framer did not put the nuts on the anchor bolts and the house went over when it should not have. - If you sign off on it, it is your liability.

Based on 30 years as a P.E.

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Old 10-08-2009, 07:31 PM   #10
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Well, between us I guess we have 60 years as PE's. But about that hinge.

As I mentioned, the definition of a hinge is a connection that does not transmit moment in one or more planes. So, assuming the two elements are properly connected (and the OP did note that he would get an architect to design the connection), there is no hinge there. This is no different than the connection made between two steel beams on a long span bridge, the connection is designed to transmit moment by including an adequate number of fasteners, appropriately spaced, and appropriately attached. So I would say that an 8 foot tall wall consisting of two 4 foot sections, properly connected together, is just as good as a continuous 8 foot high wall.

As always, the key is the connection.
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Old 10-08-2009, 09:23 PM   #11
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Daniel -

You are totally correct if the wall sections are properly connected. The problem is that most people (DIYers) think a few nails will solve all problems - especially if they are long enough and the hammer is big enough.

I always wonder about the structural ability of architects when they get out of their own little "world" even though they are professionals in a certain area.

Dick
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Old 10-09-2009, 12:28 AM   #12
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Raising Wall Heights


I was reading these posts with interest and, of course, to learn something. Then-Dick makes reference to the "integrity" (as I call it) of Architects vs. Engineers and I immediately think of what is going on in my home town-Albany, GA. The local Licensed/Registered Architects got together and had a judge issue a "Cease and Desist" order to the local Licensed/Registered Engineers so that the Engineers cannot draw and place their stamp on commercial building plans which they draw for the construction companies they work for. Having worked with some of the P.E.'s, and I.E.'s, and having seen their stamps on drawings they did of buildings to be/or under construction, this is going to be interesting. The Architects state that they are the only one's who are allowed to draw the plans as this is what they were trained for. This is going to be really interesting to me. Thanks, David

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