Hello everyone,
I have an old house built in the 40’s…. It’s started out as a plain old gable 4/12 roof house and was added on throughout the years… My concern now is the open garage that was added on also…. I hope I can explain this clearly to everyone, I can post up pics if need be…..
When I crawled up on the roof above the garage, I felt the roof had slight movement.. When I crawled in the attic to investigate I think I have pinpointed the problem….. The garage add on is 25′ x 12’….. The house is 48′ x 25’…… Well, the cwiling joist run in the 25′ direction….. The joist are 12′ long overlapped to make the 25′ long run….. All of which are running on top the interior walls (obviously)……. All of which is all good….
The problem is, over the garage, the ceiling joist are running the same direction as the rest of the house, the 25′ span…. Except, there are no interior walls to brace them…. So I have a long 25′ span of joist over an open space… On top of that, the roof is braced to the joist, right in the middle of the 25′ span where the two 12′ joist overlap each other……
So, I’m thinking I have to add a laminated beam in the center of that 25′ span…. Question is, do I have to add a lam beam or can I add just two 2×12’s nailed and glued together across the 12′ span…. The roof is not that heavy, it’s just a tin roof… But I do plan on removing the tin and decking and shingling the whole roof later….
I’m adding some pictures for clarity… I’m sure it sounds confusing…. What is you guys opinion on the proper course of action here?? Am I on the right track adding the lam beam and rebracing??
Thanks….
Replies
What you have there is a "truss". If the sizes of the pieces are right and they are properly joined this is a perfectly fine construction technique.
You certainly can add a "strongback" along the center to stiffen it up, but you should be careful to not (without fully appreciating what you're doing) upset the connections between the existing members.
Nit picking silly details (like insisting that it's a truss) is hardly helpful.
Actually it's not a pre-fab truss... I can see how in the pic it looks like iit but, I promise it's just individual rafters, joist, and 2x4 braces...
due to the unsupported span of joist, th deflection is BAD....
I didn't say that it's pre-fab, but it's still a truss.
Yes the 2 that are braced are truss. Now I'm no engineer but I think that with only 6 rafters 24" OC and there are only 2 truss and using all 2x4 for a 25' span, isn't enough... If they were all truss I could see this being ok, or even being 2x6 in its current configuration but not 2x4 25' long....
Yes, the ridge braces are just misaligned... If you go inside the garage, the ceiling is sagging so bad in the middle...right where the ridge braces are coming down on the unsupported 2x4 joist..... I haven't run a string on the ridge yet to see if it sags. It doesn't look like by eye, but I'm sure it is.....
Could I just install 2x6 bottom chord or (joist) and brace all the rafters in a truss configuration, instead of adding a lam beam in the center?? Would this be satisfactory??
Thanks for any input.....
Technically, a truss is anything where the members describe triangles and the members are only in pure compression or pure tension. This describes what you have to the extent that the weight of the roofing and the weigh of the ceiling are "reasonably small".
Ok, I see what you mean. Just because it isn't "Howe" or "Fink" design, the fact that it is a braced system makes the whole unit a truss..... Even the rafters with the ridge brace only.....
With the 2x4 truss spanning 25' and 24" OC, if I walk on roof, there is movement.... What can be my best course of action to fix this? I was thinking of:
. Adding 3 ridge braces on bottle jacks, I'm sure 2 would work, run a 2x4 across the bottom of joist on each side of ridge and add 3 braces on each side of ridge to support the joist, then cut the joist in the center, add a lam beam across the 12' span and reattach The joist on a ledger or hangers to the lam beam and re brach the ridge to the top of lam beam......
.Or could I just run a brace on bottle jack with slight up pressure across the bottom of joist directly in the center of where the ridge is, and remove joist one at a time and replace them with 2x6...
Would any of these methods work in your opinion??
Thank you,
Okay, now hold on there.
Careful.
Do you understand that gravity is trying to pull the ridge straight down? And that the main thing preventing that is the ceiling joists tying the two bearing walls together? True, you get a LITTLE help from the diagonal bracing from the (approx) midspan of the rafters (not the ridge) down to the center of the joist span, but that looks like a pretty steep angle in your case.
What you propose about cutting your joists, inserting a beam and reattaching your joists CAN work, but before you cut those joists, you have to also support the ridge temporarily. Sounds like the ridge is sagging so you want to jack that up anyways, but please be sure you understand the forces involved before you begin.
Now, none of us can SEE what you have there, so we're all just taking you at your word. But from the photo it doesn't look like a professionaly designed and built roof to me. Looks like someone had a basic understanding of roof framing, but used some questionable techniques. All that to say, it's possible that roof/ceiling never was straight/flat in the first place, which means simply jacking a little here, raising a little over there, and then resupporting everything (with a new beam system) might not give you three flat planes (ceiling and two roof planes) when you're done.
So you have to determine exactly what is sagging, what is not, and see if they all corespond. That is, "...if I were to lift HERE, that would force THAT up, which would in turn lift THAT, which would bring everything back into plane (approx)".
Until you can visualize through that set of adjustments, please don't cut/jack/brace anything. Without that clear understanding you lack the geometric knowledge necessary to safely reframe that roof/celing.
Do you have a headroom issue under the existing ceiling? If you decided to, could the beam go UNDER the joist mid span, instead of cutting the joists?
Or, could you cut a hole through the gable end wall and insert 2X12's AVOVE the joists, jack everything back up and then attach the newly flattened structure to the newly built up beam up in the space above the ceiling joists? The reason I asked about center post alignment was to suggest jacking everything up, then sheathing those with two layers of plywood, joints staggered, or even one layer each side, but again, joints staggered.
I know the way I explained it was probly confusing as heck.... But yes, I first explained that I would brace the ridge.... Then, build 2 temporary walls inside my garage to support the joist on either side of the ridge, before cutting anything.... I do understand the forces at play here.... If I braced everything the way I explained, it would definitely e strong enough to cut the joist and add a beam...
What you proposed sounds reasonable, based on what you've told us.
But I don't like to say for sure unless I've seen something myself. So I'm reluctant to suggest you go ahead with it.
One thing to keep in mind - A beam needs to be braced along the top edge. If you a put a beam in there that's deeper than the ceiling joists the top edge will need braces added.