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Old 03-02-2014, 11:08 PM  
slownsteady
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Hey nealtw, thanks for the link to the article. It really helped me get an idea of the process.

And just to keep the facts straight the room is approx. 24'x12'.



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Old 03-02-2014, 11:42 PM  
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If I was to truss it up instead of putting in a beam, would I get any advantage by adding additional collar ties?
This would need answers from an engineer and for a few hundred bucks they would suggest cutting the beam in.
The reason I thougt the wall or beam had bean removed was the age of the house, I assumed 40 years or more and then in the photo below the sheeting you can see 2x4 with green paint on the ends which look like newer material like someone had scabbed blocks on the sides of the joists at the joint which would indicate joist butted into each other over a wall.
Perhaps your neighbors house was built with a beam up there or with trusses and your homeowner thought he could just make it look the same.
I would remove 2 ft of drywall and put the beam in from below and replace the drywall before noon.



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Old 03-03-2014, 06:06 AM  
bud16415
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Neal has done more framing than most likely all of us put together so I respect his views a great deal on these matters. I do understand how a beam above or below and supported on the ends would carry the load and give those ceiling joists something to hang from or sit on.

I also think if it was mine and I was ripping all that drywall down and insulation out I would think about one of your earlier ideas of building a simple kingpost truss in place using what you already have as rafters and joists as members. I have built kingpost trusses on the deck before and for a builder I don’t think he would want to get involved in the time required to do this but as a home owner DIY labor isn’t the real issue as much as being able to do this without getting into foundation and posts going up thru an existing house.

In your roof like any truss the weight of roof and snow load is acting straight down and because the roof is an angle each end is holding half that weight with a horizontal component trying to push the walls out. The bottom chord is put in tension along with the collar ties. The bottom chord is also seeing the weight of the ceiling pulling down. Because that joint is just scabbed together and unsupported and being level it has no strength except those nails to react that ceiling weight. In a truss these weights are transferred around thru the members and some ate in tension some in compression. In a king post truss the lower chord is split right where yours is and there is a vertical going straight up. You have a ridge board there so you would have to invent some way of joining to it or two king posts one on each side of the ridge. The strapping and the long color ties were someone’s attempt at trying to fix this at one time. I think the plywood down the center was more of a catwalk when doing the insulation etc.

The trusses I have built used plates at all the joints on both sides cut from .5 plywood and glues and nailed. The nails were shot in mainly to hold them together as the glue dried and that method make a very strong joint.

If the ceiling height is ok below I wouldn’t personally mess around trying to vault the ceiling. But anything can be done. The word of caution from me if you are thinking of adding a collar tie to every pair of rafters and then bringing the ceiling up to that height would be the interesting point of the ties and the rafters could become a very high point of loading and you would want to run some numbers. The fact that it’s been standing 60 years gives a good feeling that the structure is ok except for the falling center. As mentioned above the lumber size would be small by todays code but would be about the size they would use in a truss I would think. If you were not planning to rip the drywall down I would never suggest trying to do this method crawling around inside the space.

Like I said I’m not a builder only another home owner handyman and I see you are entertaining this idea already. Maybe the pros will come back on and show us both why this built in place trussing wouldn’t work.

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Old 03-03-2014, 09:45 PM  
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Hmmm, are you saying that the kingpost truss would be parallel to the ridge and support the joists like a beam? Or are you saying that the truss would run parallel to the rafters? If so, how many are we talking about?

I did a little reading on the subject and i think I have a pretty good grasp of the physics involved, but I'm not too sure of the application in this instance. Of course, i would not proceed until i fully understand. That's why i'm trying to think this through now while there is still snow on the roof and way too cold to rip out the ceiling and insulation for even a day.

So here's a question: does the vertical member of the kingpost tie in to the ridge? That would seem like quite a load.

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Old 03-03-2014, 11:10 PM  
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Bud, you want to be real carefull here. What you or I would do in our own home from experience is one thing but any changes from a rafter system to a truss system should be designed by someone that understands all the loads and forces involved, a structural engineer.
My understanding of the king system is the rafter sits on top of the beam at the peak which is held up by king posts at the end. If you do that then there is no need for collar ties and you could add depth to the rafter for insulation and you have a vaulted ceiling or for a lower vault you could run new joists from the wall to half way up the rafter on the op. wall or install a new ridge board at a lower height and install rafters to that somewhat lower then the roof rafters.
Just for starters the beam I suggested would be there to take the sag out of the ceiling, half the weight of the ceiling joist, half the weight of the drywall and half the weight of insulation.
A king system will carry all of that ceiling weight the same but will also carry have of all the weight of the roof and half the weight of the snow load so the beam is in no way equal and would likely get to a fair sized engineered beam. Then before you would move all that weight to the end of a wall and a foundation wall that likely wasn't designed for that. So you would at the least open up walls to add more lumber to carry the weight down and at worst there would also be some work to make the footings bigger and then if there happened to be a door or window in the down line, it just keeps adding up.
http://www.finehomebuilding.com/how-to/qa/framing-cathedral-ceiling.aspx

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Old 03-04-2014, 07:02 AM  
bud16415
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Neal’s article he listed is an excellent read. The additional collar tie method they show in the first figure is what the OP asking about at first, or one of the things he asked about. In the article they point out doing this is a very simple truss. They also warn as I did that the rafter below the collar tie is in effect a cantilever. In doing this all the weight is going on the two bearing walls and the point on the rafter right below where the collar tie is joined is going to be a high stress point due to the cantilever. That’s where I suggested if he wants to do this he should run some numbers or hire someone to do that based on the size of his rafters.
The second figure is just a takeoff on the first if someone wanted a true open to the ridge look.

The third figure relates to what I was suggesting it shows that the ridge board can also be the beam we are talking about adding and in that example it shows how it is used to actually support half the weight of the roof. In the OP case I don’t think it would truly be half the weight but it will work with the rafters to allow some of the load to be transferred. The existing structure has been working for 60 years so that’s a good clue that the bearing walls are able to carry the entire load. They are already doing that including the ceiling weight. The question is the sagging of the ceiling because that lower chord of the triangle is broken in the middle. The simplest truss is a king post and it’s just that triangle he now has formed by two rafters and two ceiling joists with the addition of the king post and that would be a straight up and down member that goes from the peak to the center of the ceiling where the two joists join. In doing that the half the weight of the ceiling would be transferred to the ridge and back down the rafters to the walls. It wouldn’t change the loading in the walls but would add load to the rafters and the ridge beam, but at the same time make the roof system stronger as it would now become a truss with a ridged bottom chord.

That’s the simple king post truss the next level up would be the king post with one additional diagonal member on each side starting at the bottom center and going to the mid-point of the rafter. I don’t know if that would be needed or not but I would consider doing that also. Along with adding support to the ends of the ridge beam if it wasn’t too hard to do.

I agree with Neal’s first statement.
“Bud, you want to be real careful here. What you or I would do in our own home from experience is one thing but any changes from a rafter system to a truss system should be designed by someone that understands all the loads and forces involved, a structural engineer.”
To the OP any advice you will get here is subject to you knowing the source and weighing it out to your own satisfaction. If you feel it’s something you can fly by the seat of your pants or chose to run some numbers yourself or hire someone to run them is up to how you feel about doing that. Even if you take Neal’s advice of opening a strip adding a beam and done before noon, it will add weight up there and could require running the numbers as it will still be supporting half the weight of that celing.

My thoughts are right now your gable end walls are not load bearing. The ridge board is just stabilizing the roof and is compressed in spots between the rafter tops. That strapping someone put in there was a failed attempt at “kind of” forming a truss out of what was there. They could have been on the right track and I can see why it was done that way because they were limited in working up there not wanting to disturb the ceiling. A better method I would have tried once again if this was my house and be aware of the above disclaimer on advice. But I think I would have made something using hangers and having threaded rods with turnbuckles in the center and adding in to each pair of rafters. Strapping is strong but very hard to get any kind of preload into it when nailing up.

A lot depends on if you want that raised ceiling below. If you do then the collar tie method will be what you will want and I would suggest reinforcing the lower rafter leg with some kind of plywood triangles etc.

Do a Google search on King Post Truss there are many photos I won’t link them.

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Old 03-04-2014, 07:54 AM  
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A 12x20 ceiling is likley less than 1000 lbs, half on the walls and half on baering points, you are only adding 250 lbs to the gable wall and 250 lbs to the center bearing wall.

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Old 03-04-2014, 08:17 AM  
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Well if that’s the case I wouldn’t hesitate hanging it off the beam that’s already in place (ridge beam), that’s carrying no load now. Another 500 pounds spread out over that many rafters (20) is only asking each rafter to carry 25 more pounds even if the ridge beam wasn’t being loaded.

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Old 03-04-2014, 03:21 PM  
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That is not a supported ridge beam and I wonder why the engineers never say that would work and have us put beams in..

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Old 03-04-2014, 04:18 PM  
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I'm enjoying the education I'm getting from both of you guys, and I appreciate it. But let's pull back for a minute. The load is already there, supported by the rafters and the split joists. Aside from me crawling around up there during the repair, there is no additional load - except for whatever materials I add from this project: Same 1/2'' drywall that was there and maybe a little extra insulation. My gut tells me that the metal strapping stretched as all the kinks smoothed out over time. That's why i originally used the words "snug up". And don't forget it is a blind attic - no access, no storage, no peeking after it's done. I could build an entire lattice up there to distribute weight, and as long as it worked, it wouldn't matter.

I guess the simplest question I am asking is; am I adding any additional significant pressure to the roof if I tie the joists to the rafters, most of which are already tied with the metal straps.

I agree the beam is optimal. And I have no big worries putting in the beam above the joists. That's well within my skill level. I'm even ok with cutting in the beam at joist level, but it still feels like a bigger project than i would have expected for a minimal sag.

Bud, I have taken a look online at Kingpost trusses, but it still sounds to me like a real stretch, unless you are saying that I can convert my current joist/rafter setup by adding vertical supports, but that again puts the weight on the roof ridge...right?

Would it just be simpler to sister a 2x6x8 across the seam in each joist to make them stiffer? Put in a good-sized block to fill the gap where the joists overlap.

Or how about cross-ties from joist to opposite rafter - kind of like a scissor truss - to keep the two halves of the roof on friendly terms?

There is a solution out there that is between optimal and ineffective.



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