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Old 03-04-2014, 05:00 PM  
nealtw
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You are right in that what ever you have has been doing the job untill now and if you somewhat happy with that, you could build a temp wall to hold the ceiling level and then replace the metal straps with 2x4s and that should hold the ceiling up.

But, but ,but . Just because it has stood there for some time, that dosn't mean it can take that extra big snow load, that extra strong wind or a small earth shaker. The idea is to make the house strong enough to maybe not stay perfect but stay together long enough to get people out.

To me it is simple, spend some time in the attic hoping to make it strong or spend some time on a beam and know it is good. I think the beam above would work but given the choice I would be working from below rather than crawling around in the attic.



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Old 03-05-2014, 04:30 AM  
inspectorD
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Great Conversation!
Having done plenty of these fixes, I can tell you, each situation is different. Why? Snow Loads.
Your fix is only going to be fixed by an overworried engineer who has to cover their ASSets. Usually an overbuild, but worth every penny for when you want to sleep at night...or sell your house before an Inspector comes a callin.
My opinion is that this house was built back in the 30s or 40s and this was how they did it with no bearing wall ever put in to carry only the joist weight. The whole reason that crack is happening is because of the bad overlap joint at the joist. The walls only have to spread an 1/8th of an inch due to any weight at the roof/ or from wind movement to crack the sheetrock.
Installing a beam in the middle by cutting the joists does not help this issue because of the walls still wanting to spread, so you would add strapping at the bottoms to help connect the joists to each other to prevent this. This is why the beams are usually underneath the joists with a larger overlap at the joists connection.
This happens with roof pitches less than a 6 pitch most often because the roof it to shallow to distribute the weight downward instead of outward.
Installing a beam at the ridge under the rafters is another option to make this a cathedral ceiling. And will need to be carried for the point loads at each end as Neil said. However, so does a flush beam installed at the joists.
Overall, I would suggest calling in the engineer for your solution to YOUR home.Cheapest fix will be a truss type system with lots of metal hardware installed and no guarantee of fixing the issue/ but a pretty good chance of working. My opinion on installing a rafter beam and carrying the weight to the foundation would also install some roof and soffit ventilation. Be careful of this vaulted or cathedral solution because when you sister under the rafters for the insulation, you may not have enough room to the tops of the windows depending on their height. But if you can, you may get the most bang for your buck with the openness and bigger feel to the room. This however also has a downside at first. Any new wood lumber you use will shrink and cause a crack in the new vaulted ceiling.
My advice , call the engineer for 400 bucks... it will be worth it.. may even be less expensive than that.
Good luck.



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Old 03-05-2014, 06:33 AM  
bud16415
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“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?”

Yes that’s what I was suggesting simply adding the one vertical and leaving alone your rafters, roof and joists. By the sound of it your joists are overlapped now and nailed together. You might have to cut them apart one at a time and make a butt joint with a plywood plate on both sides that also attaches the vertical new member.

As to the ridge board taking the weight in a truss roof you don’t normally have a ridge beam, so how much weight would be transferred out to the ends of the ridge is questionable. Once you add the center vertical member you will have made the 4 pieces you have now into a simple truss. Actually they are a truss now and inspectorD is correct the weight on the roof wants to push the walls out and the thing that stops that mostly is the lower members, in your case the joists pulling back in. He is also correct the slighter the pitch to the roof the greater the force pushing out and in a shallow pitch roof that force can be many times what the load on the roof is.

As the angle approaches zero the forces keep going up. Think about your ceiling now as an upside down roof with a pitch of zero. Now think about the droop you see in power lines between poles. They could save miles and miles of wire if they could pull it tighter but they can’t because they would exceed the strength of the wire. That arch is by design as is the spacing of the poles because in theory if the wire could be hung level the force at the ends would be infinite. That shape is called a catenary arch. Now to your flat ceiling its acting something similar to this because of the weak joint in the middle and the weight of the drywall pulling down. As Neal pointed out if you could support the weight straight up it would only take about 25 pounds at each intersection of two joists, but the nails you have joining them are seeing this huge force because of the slight angle.

Your idea of putting longer pieces in beside the joists and making that joint harder to bend could work. They would strengthen the split joist and make it more of a beam but the span wouldn’t have changed. When you put the beam in Neal suggested or the vertical member I suggested you are cutting the span in half and doubling the strength of the existing joists.

I looked at the beam as harder because it required carrying the load out to the end walls and then having to carry it down the wall to the foundation. I saw it as you already have two load bearing walls that are already taking all the load for 60 years. There is nothing at all wrong with paying for the advice of a pro to run some numbers and you could suggest all the above to him as ideas you might want to think about. If it was mine I might also do just a little bit of pre-cambering before I did the final attachment points. By pre-camber I mean your joists and the sag have maybe taken a set over the years and I would be tempted to lift them back just a smidgen even under a little force and then attach them to the new beam or the support I suggested or the new sisters you suggested. If you try the sisters I would both glue and screw or nail.

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Old 03-05-2014, 03:27 PM  
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Hmmm (thinking!)

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Old 03-06-2014, 06:57 AM  
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As long as you are thinking. Another way to explain my thoughts on this might be right now your roof framing is not a true triangle even though you have a triangle shape made by two rafters and two joists. Almost always in a truss you will see all triangles. The triangle is the strongest shape because force applied to it anyplace will not cause any of the connections to act as a hinge. Comparing that to a square or a rectangle or any 4 or more sided shape and the legs can hinge without any of them having to break to do so. They depend on the strength of the joint. In your case you have that joint where the two ceiling joists are connected and that makes your roof a four beam member. Say a strong wind hit your load bearing wall and tried to push it in. With any kind of a truss the force would travel across the house and be reacted by both walls and the end walls. With having the unsupported connection in the center of the joist that connection could move down in the direction it’s normally trying to go and the rafter could hinge around the ridge board and move in with the wall. I’m not saying this is likely to happen just to use this thought as a way on envisioning how much stronger something gets when you convert it to triangles.

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Old 03-06-2014, 07:56 AM  
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Quote:
Originally Posted by nealtw View Post
That is not a supported ridge beam and I wonder why the engineers never say that would work and have us put beams in..

That’s a really good question in reading back over this thread and one I wouldn’t know how to answer for sure. I think inspectorD touched on the answer. Any engineer called in for a plan of repair is going to view the existing structure as an unknown commodity. And will take into account things that are known such as in this case the dimensions of the ceiling thickness of the drywall and joist size and go to a table and pick a beam size known to support that weight or half that weight as the case may be and then apply a safety factor. It’s simple and cut and dried. If there is head room he’s going to say put it below and if not he will have to do some additional work and say put it above and then have to figure a hanging method with a proper safety factor. And sleep well at night knowing there are no unknowns in his solution.

That same engineer if given the job of designing a whole new roof for this house would do nothing close to the above method. He would select trusses based around the pitch, snow loads, span, type of roof and ceiling etc. He would put as many of them on whatever center distance it took to do the job and again apply some safety factor to the design.

Adding structure into the roof as I suggested and having 100% mathematical certainty to the design would be virtually impossible and if not impossible it surely would be cost prohibitive. He would have to figure in the existing structure and how converting that structure from a classic rafter build that we know by todays codes would most likely come back as undersize, into some kind of a hybrid truss that’s to be owner built. Like Neal said in an earlier post Why he or I may do and feel comfortable with in our own homes based around experience and some science and knowing the history of the structure, might not raise to the level of an engineer signing his John Hancock to a drawing.

Not too long ago at work we need a pole put in to hold a satellite tv dish. You know the ones you see on porch posts and chimneys and screwed thru siding etc. Well they called in engineering and I watched backhoe roll in and dig a hole carpenters then came and formed up a box a steal company delivered the iron work for the post and a big prefabbed rebar unit. A ditch was dug and conduit laid and then one yard of concrete was poured and finished to form the footing for this big mast. It’s a really nice looking job but I don’t know if I would hire them to put in a mail box for me.
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Old 03-06-2014, 12:51 PM  
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Below are a couple links that might be useful. The second one is a calculator that tells you how much force is pushing out on your outside walls and possibly the reason the ceiling has had issues beyond what we have talked about. I see you live in snow country and around here we are told to use 60lbs per sq foot as a winter snow load. That comes out to be about 3 feet of snow I think and of course you also have to add in the weight of the roof to start. When you run your own numbers you might be surprised. Every winter the roof sees loading and unloading and that “could” have been working those connections more than you think. This cycling might have been what failed the drywall also and all the more reason to look at how the middle as well as the ends are attached and see if there is signs of pulling.

http://home.comcast.net/~mbiegert/Bl...lStuff/JLC.pdf

http://www.timbertoolbox.com/Calcs/raisedtiethrust.htm

http://www.timbertoolbox.com/Calcs/RafterThrust.htm

http://www.timbertoolbox.com/

When I ran this calculator I just figured 16” on center or 1.33’ x half the span of the room and put in a guess at weight + 60lbs snow load. So for example 12’ x 1.33’ x 60 snow plus whatever you figure roof weight maybe 10. Play around with the numbers and see what you think.

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Old 03-06-2014, 01:37 PM  
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Thanks, Bud. I will dig into that info. I'm not much of a math guy, but if I scratch my head enough, some stuff seeps through.

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Old 03-06-2014, 01:44 PM  
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It'll be a couple weeks before I tear off the drywall (or at least poke my head in). Probably won't decide till then. I will def report back with updated info, board dimensions, etc. In the meantime, I will continue checking this thread, so please don't think it died...

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Old 03-19-2014, 09:53 PM  
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Did find a sample of someone adding beam above ceiling
http://www.matthewghunter.com/projectexamples.htm



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