structural ridge vs flush beam vs scisso
So this house has a bearing wall to be removed. It supports an unused attic (5′ tall) . Rafters are 2×6 and 13′ long and at a 5/12 pitch. 2×6 ceiling joists are 12′ long and overlapping on the bearing wall. Everyiting is 16″ o.c.
The lumber yard told me I could put in a flush beam of three 1.75x 14″ glue lams that would span the 20′ and 7″ or I could put in three 1.75″ x 16 glue lams for a structural ridge or the architect suggested scissor trusses with no plan so they could be possibly made with the 2×6 rafters as top chords… Assuming good end support and metal connectors on the first two options…. what does anyone think in terms of labor and cost and why would the structural ridge glue lams be bigger than the flush beam. I have not discussed this with the building inspector yet as I’m trying to get my ducks in a row first.
Replies
I don't understand what you're saying. Are you taking out the ceiling joists and making it a cathedral ceiling? If so, what is the difference between your flush beam and structural ridge?
When you say flush beam, do you mean cutting out the existing ridge and cutting back the existing rafters and sliding the (3)1-3/4 x 14" lvl's up in between?
When you say structural ridge, are you saying to put the (3) 1-3/4 x 16" lvl's underneath the existing ridge? Or, remove the existing ridge and notch out the bottom of the existing rafters and make a birdsmouth on them so that they sit on top of the 3 lvl's?
Also, why even consider putting in scissor trusses on an existing house to make it cathedral? Was the plan to rip the roof off or put them inside the existing roof?
Joe Carola
Edited 11/18/2007 6:07 pm ET by Framer
Two thoughts come to mind.
First - You might be able to leave the roof alone if you put the beams in. If you use scissor trusses, it will obviously have to be torn off.
Second - A deeper beam might be cheaper. Like a 2 ply 18" deep LVL might work in stead of a 3 ply 16" beam. Less money and less pieces to handle. The place that designed the beams could check that out for you.
Get my ducks in a row while you are out herding fowl, willya?
Forget the trusses. You don't want to hae to totally rebuild this just to take a wll out.
Next - clarify that removing the wall is all you are trying to do. The ceiling flush beam will do that for you and no need whatsoever for a ridge beam unless you are also trying to do something like make a catherdral ceiling too.
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Yeah,
Just to clarify #1) the goal is to take out the bearing wall and #2) by flush beam I mean tucked into the existing ceiling joists and flush with the existing sheetrock.... so it doesn't show. I know you guys get this.... and using joist hangers to connect the existing joists to the built up glu lam beam....
Perhaps scissor ties.... site built using the existing 2x6 rafters as a top chord and leaving the roof and roof deck on would be alot of work but I costed it out and it seemed about the same or slightly more than the flush beam route even when I included the $1500 engineering stamp fee that the building inspector would want. And a guy that worked for the engineering company said I'd probably have to beef up the 2x6 rafters (16" o.c) which have a 13' span with sistered on 2x 10 rafters IN ORDER TO DO A STRUCTURAL RIDGE since the 2x6 rafters are undersized. Does this sound right.... that they'd need to be beefed up?
In everyone's experience it would probably be alot easier to do the flush beam, right?
Thanks friends.
Last clarification: the idea is take out the bearing wall yes but possibly have a catedral ceiling if the structural ridge option was choosen.
So, since your leaving the ceiling joists in, what does that have to do with beefing up the rafters? You don't have to do anything to them.
If you are going to do a cathedral ceiling, you have many options. Here's one that I did on my cousins house.
http://forums.taunton.com/tp-breaktime/messages?msg=97062.40
Joe Carola
What get confusiong is th if this if that maybe this maybe that.So - IF you just want to take out the bearing wall then yes, the flush beam iunsert is the easiest cheapest IF you want a smooth ceioing. a beam beloiw the ceiling is even easier.If you want a cathedral ceiling, you are in for a lot more work and expense acording to how you want to cgo about it and how much youy have to spendyeah i get it, but I have a hard time answering three questions in one, especially when they are mixed together. hard to doa complete structrual analysis with oine eye tied behind my back. Sorry
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It's hard to understand what's going on here. one of those cases where a picture is worth a thousand...If I understand you correctly, you have 5' of headroom in the attic as built?
I think the engineers want a structural ridge because you will be cutting through the existing ceiling joists that are also acting as collar ties.
Why not add a new beam to carry the midspan of the ceiling rafters above the existing ceiling joists and hang them? You are then simply replacing the load that was on the bearing wall with the beam and leaving the rest of the structure intact. You may need to cut a hole through the side of the house to get the new beam in. I guess it depends what type of siding you have to work with. Perhaps the hole could be repaired with a new gable vent? I dunno, that all depends on the design, whatnot. We once replaced a ceiling beam in a similar situation with a flush beam (hip roof, no way to get one in over)using steel straps to maintain the tension load across the underside of the beam from joist to joist.
Undersized rafters are another issue.
I'm sure you have thought of this, but don't forget that if you install a structural flush beam you will need to open the walls to provide adequate bearing for the beam.
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OK, sorry for any confusion. #1) I'll look into 2 larger LVL's rather than 3 smaller ones for a flush beam as Bosshog suggested. This also means that the in the wall end supports would only have to be 3 1/2 inches wide to support the flush beam. #2) Framer, I read that piece you referenced me to about beefing up the rafters on the underside to support a structural ridge. #3) If I do a flush beam I'm aware I need end supports that run to the foundation or to a 2' x 2' pad.. #4) If I do a flush beam I wasn't aware, as Piffin refered to, that I would need
steel straps under the beam (above the sheetrock) to "maintain the tension load" accross the joists. I was planning on "hanging" the joists from the beam with joist hangers on each side... would the diagonal longer nails in them not take care of this.... I never thought about this problem.
The idea of the scissor trusses was to leave the roof and rafters in tact and use the rafters as upper chords of some site built, engineer designed, built in place, home made scissor trusses..... to get rid the bearing wall, eliminate the need for end support (such as a structrual ridge or flush beam require).
I think the general concensis is that the easiest and cheapest is to put in a flush beam of LVL's. No cathedral ceiling but less expense and time and trouble.
in the wall end supports would only have to be 3 1/2 inches wide to support the flush beam
Don't bet on that. Yes, 3-1/2" would match the beam width, but you might need more studs to carry the load. Wouldn't be surprised if you needed 4 studs."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
jeff buck would just tell you to hire a pro
RE the straps to contain the tension loading...I did a flush beam insert in a very large house where an engineer had done all the specs.
He was certain that no straps were necessary.
However, we had uses some eyebolts in the outer wall top plates and cable with turnbuckles to control the wall spread and pull things snug together. We left them in place. The engineer was probably right, but it felt "righter" to have some insurnce.But for your place, with only a small roof above, I would think the extra strapping un-necessary following my discussion with that engineer.
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I also did this recently, all the dimensions were the same, except the length of the load bearing wall was only 14'. Used a 3 1/2 X 12 oriented strand beam, slung the cieling joists below it with special joist hangers. Note here: joist hangers were about $35 cdn (that's real money, not funny money!!, sorry I've never been able to say that before to you USn's) 'cause old joists were 1 7/8 wide, but because the load they would carry was huge I only needed one for each cieling joist pair. Decided against a structural ridge beam and cathedral cieling because dimensions of a room 14 X 26 wouldn't look good with a cathedral cieling. Inspector will want a sound load path from the end of whatever you put up, down to a footing, plan on a footing and lally column in the basement. Good luck ..
I like redeyefly's idea with the beam above the ceiling joists ( that is if you can get the beam up there into the space). Dont have to cut the ceiling joists to fit beam in place. Metal connectors would hopefully be easier to install.
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Dear Fast Eddie, Piffin, and Wane:
This is a very helpful discussion. OK, I'd probably need more than 4x4's to support the flush or just above the joist beam. and these would go down to the foundation below, etc. Rodger. That is a great idea to put it just above the joists and suspend the joists form it. Now, these "special joist hangers" that a carpenter, albiet a poet, from a broken nation would have to buy at perhaps $5O worthless US dollars each..... where would one get them? Simpson makes such?
Now, one more thing.... I'm a maverick and I like challenges because all of what we otherwise do all day is stand there and squeeze the trigger of this or that tool..... I also like the challenge of getting an engineer to design and spec scizzor trusses using the 2x6's existing rafters as the top chord, leaving the roof intact but pulling the sheetrock and ceiling. This would not require end bracing of an above the joist beam and it would thereby give more room for free placement of windows on the gable end without having to avoid a structural support in the center of the gable end.
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Simpson Strong tie has a connector selector software at their website for download. As I recall, these were not especially expensive or hard to get.I did not think of the beam riding above the joists like that for your situation. I was getting too confused with all the info and options.But iut is by faar the simplest and easiest way to do this most times. I have done ti twice. Once the engineer just had us use A35's to attach the joists to the beam above.The ones we use on the other looked something like this
http://www.strongtie.com/products/connectors/THA-THAC.html
But my memory is that the product name included the letter "I"About four years ago, there was an article on doing it this way in FHB by an author in New Orleans.
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This is good. From the Simpson Strong Tie catalogue I see these THAC and THA hangers which would not be able to overlap the top of the LVL's ( I think that's the name for GLU LAMS) but they are meant for hanging 2x6's and have long straps (total hanger lenght is 17 3/16 inches) to nail into the sides of the LVL....anyway I'll call Simpson and see what they recommend and the lumber yard people will have the company spec them anyway. The thing is the joists are off set from each other, by passing each for a short while above the bearing wall.... so I'd have to cut the nails that connect them together and the ones that toe nail them to the top plate of the bearing wall and then slide them under them and above the sheetrock and then slide the beam in up to them. It doesn't sound too bad except that the beam will be weighting down the joists but I think it's a great and dooable idea. I'm going to look up that FHB article you mentioned. Thanks guys.
You can set that beam above so that it is an inch above the joists
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sorry, I'm weekday contributer ... I used Simpson THAI's, that said I just saw the "gable" end word in your post, its going to be awfully wonky once the cieling (and strapping??) come down. If you cathedral that cieling back in place plan on adding some lateral support to that gable end wall, esp if more openings are planned.
LVLs and Glulams are two different things. LVL- Laminated Veneer Lumber The biggest trade name is MicroLam. It is basically a 1 3/4" thick piece of plywood.Glulam- Typically 2x4s, but sometimes larger or smaller timbers stacked and glued together to create a beam.
So what I'm exploring is slinging the 2x6 ceiling joists (12' long, 16" o.c,) from this 20 foot long beam in the unfinished attic. These THAI connectors are made for a 2x 10 but a 2x 6 would fit..... they are 20" long including the straps which are intended to wrap around the top of the beam. So I could use maybe 4 twelve inch glue lams if they spec'd right. I'd probably have to put blocking between the joists also to keep them from swaying .... to give them some rigidity as they'd all be hanging. Now I have to check the load requirements for a floor of an unfinished attic... and see if the hangers are rated for that load. I don't want to hire an engineer if I don't have to. Hey, by the way, why would I set the beam 1" above the joists?
Edited 11/28/2007 9:23 pm ET by poetwithahammer
.. warehauser will size the beam(s) for you, once the hangers are screwed there is no sway, they're rigid, the unfinished floor is new info, you'll have to pass that on to beam calc's. The beam can be set any or no height above the ceiling joists.
OK, here's the plan. Not that hard once you figure it out.... more sweat on the paper and less on the job.... The lumber yard sized it for two 16" LVL's (1.75" thick each) setting accross the joists to span the 20' and 7. The lumber yard will obtain some sort of stamp from the LVL manufacuter saying they will carry the load well. I'm required to have 3.5 inch bearings at each end buy I may beef that up and also I may use Douglas Fir. I'll tie the joists with 3" by 19 and 3/16 inches THAI Hangers (my thighs were sagging), I'll use 3" wide ones (3 and 1/8 inch) because the joists are doubled over the bearing wall (which I will remove after). Thanks very much.
Good plan. I don't think the LVL manufacturer will stamp anything. But they all publish their load tables. Someone at your yard should be able to run over how they work so you can show the inspector if he wants the calcs verified. Although I've only had to show an inspector once that my calcs were correct and it was in a situation that the beam looked undersized. You shouldn't have that problem as those two 16"s will look HUGE up in that attic. Out of curiosity, how are you getting the beam up into the attic?
The lumberyard delivers by helium baloon and I"ll have them drop it through the roof on the way by to another job. should be OK. thanks for your help.
Allright, actually, I'm pulling out the louvered vent in the attic and going through the hole. Hey. should work. thanks again. I'll let you know how it went.
A last thought...
The ceiling joists are overlapped, right?
Before removing or adding anything, run a bolt or two through the overlap of each to maintain the tension across the span
Now that is a good idea. I had forgotten the importance of mainatining the tension accross the two... to keep the exterior walls tied together.... I put some deck screws in but that would seem to be marginal. Thanks.
Um.
Don't know where you're building. Where I build , we use licensed structural engineers. Not a lot of help here I'm afraid.
skipj