I have a basic roof construction question maybe someone can enlighten me about 😉
I’m building a 24×30 garage with a conventionally framed roof. There is a center beam running down the length of the building upon which the ceiling joists overlap and rest with the other end being supported by the walls. The plan shows the roof rafters nailed to the sides of these ceiling joists and then meeting at a ridge beam and attached directly opposite its’ opposing joist (no offset at the ridge beam).
With the ceiling joists being two pieces of wood overlapped in the center and then the roof joists attached to the sides of those, then even in the best case the roof rafters will each have to be have to be moved 3/4″ out of perpendicular with the walls in order to meet at the ridge (1 1/2″ over the entire width / 2 = 3/4″).
Course, could move the ceiling rafters out of perpendicular with the walls that little bit or even fudge the rafters and the joists each a bit to make up the difference but either way it seems that this may cause difficulties with either my attic floor sheathing or the roof sheathing due to the members they are attached to not being quite perpendicular with the walls (like one corner of the panel may only rest about a quarter inch on the 2x it is attached to)
Possible solutions that come to mind are: 1) butt and plate the ceiling rafters where they meet on the center beam (no overlap=no problem) OR 2) offset the roof joists 1 1/2″ where they attach to the ridge beam OR 3) or figure that 1 1/2 ” adjusted over the whole 24 feet isn’t going to amount to enough to cause much of a problem.
What’s the voice of experience have to say??
Thanks!
Replies
Keep the rafters perpendicular to the wall framing. The offset won,t make any difference at the ridge. Toenail rafters in ridge even if you can just face nail from other side of ridge. Toenailing holds better than end grain nailing.This method will keep your joists and rafters square to the walls.
mike
Short answere is that no, it isn't enough to worry about. it works out to slightly less than 1/8" of deviation in each sheet of plywood.
But I don't like to do it that way.
Enlighten me a little. Are you personally doing this or subbing it out?
When you say, " thereIS" a beam, I read present tense - that it has already been installed. I normally cut butt to the ridge beam. So who decided to do it this way? Sounds like a less experienced framer or one who...well - nevermind.
The squaring issue for the roof rafters can be handled by offsetting the tails on the wall plates 3/4" either direction but then your ties for ceiling go off square a little, tho only 1/16" in each 4' sheet.
Excellence is its own reward!
Thanks for the reply,
Yes, I'm the one doing the framing (and I would fall into the less experienced framer category). The idea/plan came from a book titled "Building a Multi-Use Barn" by John Wagner.
The center beam rests in a pocket in the end walls and then the ceiling joists rest on the beam. (they don't exist yet - just planning) Your saying you would rest the beam on the top of the wall and then use hangers and butt the ceiling joists to the center beam?? That would make for an uninterrupted ceiling and solve the not perpendicular issue... :-) but the ceiling joists would have to be as wide as the center beam to make the attic floor level humm...
Thanks again for the input!
H
I guess that I got confused by the terminology here. I thought you were talking about a ridge beam for the roof rafters, but it appears that this is a carrying beam for the ceiling/floor joists. That is a more common method, to side lap them and not worry about the minor off-square since it is barely noticeable on a sheet of plywood.
Where headroom below is an issue, we raise a flush set beam and use hangers o attach the joists to it.
Sorry for the confusion.
Excellence is its own reward!
There is a center beam running down the length of the building upon which the ceiling joists overlap and rest with the other end being supported by the walls. The plan shows the roof rafters nailed to the sides of these ceiling joists and then meeting at a ridge beam and attached directly opposite its' opposing joist (no offset at the ridge beam).
There has to be an offset. If you drew a line on the ridge, one rafter you would mark to the left and the othe you would mark to the right. You can't but them oppssite because your ceiling joists are overlapping one another.
The only time you can butt them directly opposite is when you have one continuos ceiling joist, if your ceiling is running the 24' way, then you by 24' joists and put the rafters on one side of the joists then you can butt them at the ridge.
If I ever seen anyone in your situation with your ceiling joists overlapping and then bending the rafter at the ridge to butt eachother, I would throw them off the job. It's not the right way to do it Period no matter what the plans say, it's wrong. Just look at the layout that I drew for you. You will see.
Joe Carola
there is another way to do it, by furring the all ceiling joists on one side of the supporting beam 1&1/2 inches at the wall with a short block or scab,( approx. 3' )you will be able to have everything perfectly square and have the rafters exactly opposite each other at the ridge beam. however I like piffins suggestion of moving the supporting beam up to flush it with bottom of ceiling joists and attaching joists with joist hangers. if you were planning to use the top of ceiling joists for floor of attic and you don't want the beam rising up from the attic floor you can either fur up the floor or get an engineered beam out of LVL that is the proper thickness. this way again everything is on layout and square.
Skids,
You know as well as I do that the rafter will always offset in his situation and it's not a problem. In 20 years I've never seen anyone or heard of anyone bend the rafter over out of square befor.
Putting a flush girder in just so the layout can butt eachother is a waste of time for his situation. You have to cut all the beams exact and then put a bunch of hangers on for no reason.
Put a dropped girder in and by 24' ceiling joists and then butt all your rafters and be done with it.
If you have a house where you have the two outside walls and two inside bearing walls then those two inside bearing walls can be where the ceiling joists offsets the the two ceiling joists that run from the outside walls and on top of thwe two inside wall with the same layout mark and then the ceiling joists that are on the two inside walls will go on the same side as the rafters would go.
If he needs the height in the ceiling then put a flush girder in, lay it out right and then butt the rafters.
I put flush girders in all the time with hangers but these are for custome homes and additions/remodels.......
It's not a better job if they do butt eachother. In his case they can't. I see no reason to change it so that they do. When ever I can get long lenghts I get them. I just framed a garage with 24' 2x8. One shot your done and the rafters butt.
Joe Carola
Edited 8/14/2003 8:36:07 PM ET by Framer
Joe, I found from Amazon that this Wagoner that wrote the book with the plans in it was awrier and editior at JLC and has written other framing books. It appears that he knows his stuff but the drawings the poster here has described are confusing. There must be either a misinterpretation or the persons who drew the drawins for the book erred and the writer didn't catch it before printing. That happens too often in the publishing business.
I was checking on him because there are also too many books like this where some guy who can write well but has only worked on framing three houses will write a book intended for DIYs and it sells well. That doesn't appear to be the case here. Too bad he didn't have you doing the illustrations. Yours are clear as a bell! I was having hard time understanding what the original poster was saying.
Go Joe!.
Excellence is its own reward!
I found from Amazon that this Wagoner that wrote the book with the plans in it was awrier and editior at JLC and has written other framing books.
Who is this guy and what other books has he written? Just curious.
I was having hard time understanding what the original poster was saying
I was to because I've never heard of anyone throwing a rafter out of square befor to butt eachother. The thought has never crossed my mind. It's just the way you lay things out.
In this situation where his ceiling joists are overlapped in the center whether it be a bearing wall or in his case a girder for example.
Let's say on the front wall, if his rafter from left to right was layed out at 15-1/4" and X to the right and the ceiling joist will be X to the left.
The back wall the rafter would be 15-1/4" and X to the left and ceiling joist would be X to the right.
Now your ridge will have a layout mark from left to right of 15-1/4" with an X to the right for the rafter on the front of the house and the 15-1/4" mark would be marked X and to the left for the back rafter. They will always be offset by 1-1/2".
I would love to see what these drawings look like and how he can show anything different with the layout. For all layout 15-1/4" and X away for your first mark and then 16" o.c. gives you the right layout.
Left to Right I do this, 15-1/4", 31-1/4", 47-1/4" 63-1/4" 79-1/4", 95-1/4".
My rafter top plate will look like this on the front wall ------ X|R.
My rafter top plate will look like this on the back wall------ R|X.
I always lay my rafter over the studs.
It can be confusing when you have a center bearing wall and your overlapping ceiling beams. I've seen guys nail it wrong befor at the ridge only because they made a mistake with the layout not because they intended to do it.
I layout my outside walls first and then take a chaulkline and have one guy go on the back wall and I go on the front wall and we snap the lines on all the layout marks and what that does is snaps perfectly straght lines all the way through on top of every interior partition of the addition or house.
I'll then go to all the partitions myself and mark the top plates where the rafters and ceiling joists go and continue down that same line and mark the sides of the plates for the studs.
This way it is absolutely imposible for you to make a mistake with the center interior partions for the layout mark. You know how it is, if you go to take your tape out and try and mark your first 16" o.c. mark and someone calls you and asks you a question, you might have marked it wrong and forgot to double check. With a chaulkline from front to back there's no mistake.
This way you can TEACH someone how to layout and show them the marks are there for a reason and why one ceiling joist goes on one side and one goes on the other and the same goes for the rafters.
Sorry for rambling on but I hope it works out for him and for me on the job or here I always like to help and clear things up and being on the field is no better place to Teach someone or on these forums it's good that we can attach drawings because they can definitely help.
Stay out of trouble Piffin. ;-)
Joe Carola
http://www.target.com/gp/search.html/601-9553199-0769760?field-author=John%20D%2e%20Wagner&index=books
You can search Amazon or search google for him and find plenty more. Don't know him personally or have any of his books.
Excellence is its own reward!
IMO: When you are common framing a roof, AVOID puting the beam that carries the ceiling joists in the ceiling. Put the ceiling joists ON the beam.
Since it is the ceiling joists that hold the roof up and the outside walls from deflecting outward, I'd much rather have the ceiling joists nailed both to the beam (or top plate if it's a bearing wall) and nailed together than to have them simply in joist hangers.
I suppose if you live where there is no snow load it may not matter much.
Any jackass can kick down a barn, but it takes a carpenter to build one.
Edited 8/14/2003 10:40:05 PM ET by Hasbeen
I'd have to agree with hasbeen on this one--depending on where this building is, the ceiling joists may have significant tension on them. I'd spec an 18" overlap on the ceiling joists, running over the top of the girder. I'd offset the rafters 3/4" each way, just 'cause I'm anal and like everything square. Plus it's easier to nail rafters to the ridge when they're offset.
Of course, it's only a garage, can't see it from my house, etc.
Thanks everyone!
I think you've all confirmed my suspicions that skewing the rafters just so they meet opposite each other at the ridge would be a newbie mistake. It is drawn that way in the book but like one poster mentioned, there may have been some miscommunication between the author and the illustrator... Glad I got some additional input!
Thanks again!
H
Since your "Ceiling beam" is carrying a floor, I am assuming that it is larger than 1 1/2" in thickness.
Butt the floor joists over the floor beam.
set a pair of joists, nail an 18" simpson flatstrap to one side at the top, set the blocking, set the next pair of joists, simpson strap, and continue till done.
Floor joists will be inline, so no issue of "tweaking" joists or rafters... strapping the side leaves the floor level.
Strapping continues the bond from one wall to the other.
Exposed beam in the ceiling for esthetics (everyony loves an exposed beam, right?)
SamT
Grant Gilmore, The Ages of American Law (New Haven: Yale University Press, 1977), pp. 110-111.
From 32866.117