I have a small room (about 13 ft. X 10 plus ft.) that was added to the back of my house. This room is under a shed roof that is tied into the main roof. I am renovating this room, and want to use drywall for the ceiling. The previous ceiling (which I have already torn out) was a kind of “compressed paper” type paneling, that my contractor said was called “homasote” (?). It was significantly lighter in weight than drywall. The ceiling joists are 2X4s on 16 inch centers that span the 10 plus feet. I have been wondering if they are sufficient to support the drywall, and when I mentioned this to my contractor, he said something like: “I will just run supports from the centers of the joists up to the rafters.” I took this to mean that he would simply attach one end of a 2X board at the center of each rafter span and the other end to the rafter above it.
Two questions. First, how can I determine if my existing ceiling joists are sufficient? Second, whether or not they are, is what the contractor proposed an accepted, standard building technique? It seems to me that it would simply be transferring some of the load to the rafters, which then begs the question of what will be the effect on them? Can they handle the additonal load?
I would greatly appreciate any enlightenment on these points.
Thanks,
JIm
Replies
Recipe for cracks
The question is not whether or not the rafters can handle the additional load (they can), but whether or not they SHOULD (they should not). Hanging ceiling joists from the rafters will almost guarantee cracked drywall as the rafters deflect under loads such as snow or workers.
The 2X4 ceiling joists will handle the weight of the drywall just fine. That is, assuming that the framing was done correctly in the first place. Adding a couple of strongbacks would be cheap insurance.
I tend to agree w/ Don ... running supports to 'hang' the ceiling from the roof rafters might spell trouble as it really isn't like a designed truss system ... it's simply transferring a point load from the roof to the center of the ceiling. Course that also dependso on the roof rafter size. If it is substantial, maybe it's OK.
As to if 2x4 is adequate ... no idea.
2x4 is not sufficient for a 10+ft. span. I would not tie into the rafters either. If the ceiling joists are undersized, the rafters may be as well. At a minimum, do what Don said, run a strongback down the middle of the ceiling joists.
Or if there is nothing in your way, run new 2x6's alongside the 2x4's. The room is so small, how many do you need 10? For $30 you can do it right.
Span Table for Structural Lumber
The load carrying capabilities, and related spans are easy enough to determine from readily available span tables which are generally based on standards established by the American Wood Council or Forrest Products Association or someone similar. An easy to use one can be found here: http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
A conservative rule of thumb for structural members would be one inch of depth for each foot of span. This would apply to the roof rafters. I would hope to see 2x10’s at 24 or something close (2x8’s at 16”). If the roof rafters aren’t in this range I would get out the calculator and then you’re going to need to know some additional information, like live loads for your area. Remember the span is the actual length of the member, not necessarily the distance across the floor below the member.
The ceiling joists carry the load of the ceiling system. Generally less than 20 pounds per square foot, a pretty light load. They also keep the horizontal load component from the roof from pushing the wall out. You have to keep ceiling joists, or counteract the roof load some other way (collar ties). I know this is not your question but it’s super important.
The same calculator will reveal that 2x6s are probably a minimum for the ceiling joists. Haldi gave good advice about adding the 2x6s. Install them next to the 2x4’s, tack them together so the 2x4 aren’t moving and run a couple rows of bridging at 1/3 points in the ceiling joist spans to keep them straight. The 2x4’s have no structural value in carrying the drywall but are still holding the wall in place. $30 will probably cover the bill as Haldi suggested.
There is no reason to connect the ceiling joists to the roof rafters in this situation. They are largely separate systems and should be left as such. You can’t improve the structural value of the roof rafters from the ceiling joists without doing some engineering on the connections.
Good Luck
Ron
Ron
Collar ties in the upper third of the roof frame are there to keep the roof from opening up from wind uplift-they serve little or no purpose tieing the rafters together and resisting the outward thrust of the walls. Rafter ties in the lower third of the roof frame hold the rafters and keep the walls together. Ceiling joists do this for example. Any ties above the one third line need a structural ridge to resist the outward thrust-collar ties or not.
And welcome to Breaktime.
Collar Ties
Calvin,
Since we didn't get a chance to finish our detailed discussion of collar ties by way of the private mail I sent you, I thought it important to post my message to you in its entirety so that there is no confusion about the response I made and the use of collar ties.
Calvin,
Thanks for the welcome to the forum ... hopefully I can provide some useful information to a small group of posters as you've been doing for the last 8 years instead of the smart ******* answers some of the people get from time to time ...
I'm writing to you about the collar tie response. Thanks for the clarification. I forgot that the poster said it was a shed roof which implies a simply supported rafter span. Horizontal load resistance in this case is negligible and the ceiling joists or collar ties, no matter where they are located could be eliminated. For your own edification, check out your statement about wind uplift and collar tie location. I've never designed collar ties to resist wind uplift and don’t think they were ever used that way in the southern part of the US where wind uplift is a serious concern. Your location and traditional building methods could be the exception. A good article on collar ties appears here on the Fine Homebuilding site.
Considering the level of detail you and I are dealing with on this item, I thought it better to contact you directly rather than confuse the original poster and anyone else who might read this dialogue (especially considering how off topic I was at that point in my response). If I’ve misunderstood your post please let me know and if I’m still wrong I will make a correcting post indicating my error. I would hate to start out giving someone erroneous information.
Thanks again for the welcome. What do you think? ... I'm following your lead.
If I've missed something important or left something out please let me know
Sorry for not responding later. I don't have much to add to the discussion. A long time ago when I learned framing, we put a collar tie every other or third rafter using leftover lineal. Why? because we did. Later when asking about eliminating ceiling joists, the inspector said we'd need either a structural ridge, exposed beam ties or cables every third rafter to hold the walls together. Again, a long time ago. Asking him why I learned that if no ties above the 1/3rd distance above the plate, the walls might spread. "What about the collar ties"?
"No way kid, they're to hold the roof together, have nothing to do with holding the walls together."
Over the yrs that is pretty much the answer I've been given from architects, other carpenters and a few more inspectors. That's it Ron. Not much more backup than that. I'll go take a look at your link and see where I've erred. Thanks
edit: "or counteract the roof load some other way (collar ties). " I replied to your origtinal post because several times here the term collar ties has been used in general to describe most any tieing member above ceiling joists.Often brought up when somebody asks about vaulting the ceiling in a remodel.
re. Mike Guertin's pc. you linked to-while he mentions no code requirement for collar ties, I don't know that it is an opinion that is agreed to across the board. Being a remodeler I don't come in contact with many roof framing inspections as I work alone-my opportunity or desire to build additions has waned over the years as I've gotten older. Whether they are required or not now I cannot say, but in some jurisdictions I've worked they were-probably from the old school thinnking of the inspector.
I have to admit, I was taught to frame in the 70's. Not formal training but the "here's how we do it" method. Luckily the guys I learned from didn't just throw it together. Bad habits can be learned by bad teachers.
BTW Ceiling Joists
2x4 Ceiling Joists with a 10' span are insufficient per today's codes. Remedy this as others suggested.
Either collar ties or ceiling joists will do the job
A tension tie below the ridge is needed to make sure that the rafters do not spread and push the exterior walls out.
This can be accomplished with collar ties or ceiling joists. Where using ceiling joists as tension ties for the rafters attention must be paid to make sure that joists are spanning continously in the same horizontal direction as rafters do and are properly fastened to rafters above exterior walls. If joists are not continous then they must be spliced with fasteners above an interior wall.
If joists do not span in the same direction with the rafters then collar ties can be used as one solution. Alternatively collar ties can be avoided but an engineer such as myself has to be consulted because the answer of how to do it right becomes much more complex, and more expensive to frame, it requires a series of blockings between joists and continuous pre-tensioned steel strap ties from wall to wall..
In the article in Fine Homebuilding the editor who answered this question seemed to be a little too sure of himself and derided proponents of collar ties use as never needed, but the truth is that it all depends on the ceiling framing orientation.
Eng...........
We have talked of this b/4 here on the board.
Collar ties
Rafter ties.
In our jurisdiction here in NW Oh. an inspector will allow "ties" that are no more than a third of the distance UP from the top plate to the ridge (if joists are eliminated)..
I also understand that collar ties are up there in the top one third.
So, when you mention either joists or collar ties..............do you mean either joists or rafter ties?
No more a valid requirement
Calvin,
Yeah, collar ties, rafter ties and tension ties are the same thing for the purpose of this discussion, tension ties being the most accurate name.
Ever since IRC 2000 came out roof tension ties can be placed as low as the ceiling level which will effectively make them serve as ceiling joists too. The location at one third height below ridge is a minimum rule of thumb because placing them higher than that closer to the ridge will require so many fasteners for connection to the rafter that will make it practically useless.
Your local inspector needs to be shown the current IRC applicable to your state to change his opinion on this.
More importantly, placing them higher will make the rafters want to bow, and heavier rafters will be required.
It depends
It all depends on the total roof width, how high up the tie is placed and so on. For the larger roof widths you are right, but for a realtively small width it may not make a difference, it is only more economical to make nthe ceiling joists to serve as rafter ties too instead of adding separate ties below the ridge.