Framing a two car garage question.
Hello. I want to add a two car garage to my home and have a few questions on running the joists over a long span without anything midspan to support the joists from underneath.
My garage will be 26′-8″ wide by 23′-3 1/2″ deep on a slab. The joists would run parallel to the 26′-8″. It will have a hip roof 4/12 with the common rafters running parallel to the width.
If I ran a beam parallel to the depth and tied the joists to it I run into a problem. There is a two foot space between the garage doors where I could place the beam but on the opposite wall there is a door leading into the house where the opposite side of the beam would fall. If I offset the beam to one side of the door then the beam will be over a garage door on the opposite side.
Another question is if I was able to put in a beam to hang the joists off of would I have to make my hip overhang longer in order to clear the height of the beam?
I attached a crude drawing that I did on “Sketchup” for those of you who would like to take a look.
As always thanks for the help from all of you guys.
Replies
In your drawing, the door to the house is taller than the garage doors. Assuming you have an 80" door 36" wide and a 96" ceiling, you should not have an problem resting a beam on a header over that door. You'll need extra trimmers to take the load, but the door header has a very short span, so it need not be enormous.
The beam can be set flush to the ceiling, with its top sticking into the attic. Joists can be hung off either side of this beam on joist hangers. If they will double as rafter ties, there needs to be a tension tie detail at the beam to keep the roof from spreading.
You might need to increase your hip overhang to fit in a flush beam, but you can reduce the beam height by using a steel I-beam, and fill the webs with wood to accept your joist hangers.
Having said all that, what about simply using roof trusses that span the whole garage? It would be easier and cheaper than what you are proposing. They sell trusses for any shape of roof you can imagine.
Bill
Thanks Bill for the help. Sorry about the drawing, i'm not that familiar with the program I used.
Yes the door is a standard sized door.
Just a guess but what size beam would you use in this case?
Since the joists would double as rafter ties, you mentioned a tension tie. How does it work and what is a tension tie?
I can see my roof height becoming a problem on the hip side of the beam. With a 4/12 pitch there is not much height at the ends of the roof.
I will look into the trusses also. What keeps the trusses from racking back and forth? Do they have some type of ridge in between each truss?
Thanks Again.
It looks like Joe is taking good care of you now. I'd look in a table for the beam sizing, but you are on a better track to use trusses or stick frame it free-span like Joe is describing.Bill
Thanks for your help Bill.
Another question is if I was able to put in a beam to hang the joists off of would I have to make my hip overhang longer in order to clear the height of the beam?
Why would increasing the overhang clear the height of the beam?
You have to increase the height of the H.A.P. (height above plate)cut of the rafter, not increasing the overhang.
If you set the bottom of the beam on the top plate and cut the birdsmouth on the rafter and nail the birdsmouth on the top plate, increasing the overhang doesn't do anything. You have to cut an angle on the top of the beam to follow the top of the rafter so it doesn't sit above the rafter.
This is done all the time, but you have to be careful because you can't cut to much out of the top of the beam. You have to check with an Architect or Engineer first.
If you couldn't cut that much out of the beam, all you do is either nail all your ceiling joists on first and put blocks in between and sit the rafters on top of the blocks to raise the rafters up enough so that you don't cut to much out of the top of the beam, or you just sit your routers on top of the ceiling joists and be done with it.
The only problem you face is that you raise the height of the garage. We can't be any higher than 15' with a garage, so we're always close in height and adjusting pitches to make sure we're alright with the height.
Thanks Joe for your help.
Once I started thinking about it the overhang has nothing to do with the height of the roof as you mentioned. Thanks for pointing that out to me.
What about making a small column that ties into to the exterior wall and placing the beam on top of that?
Thanks again Joe.
I always stick frame roofs. I rarely use trusses. In your case, like mentioned already, you're better off with trusses for a garage this size.
Why put a beam in for no reason. Even if you don't use trusses, you still don't need a beam. I framed many 24'x 24' garages with no beams.
If you don't want to use truses, you can run 2x10's or 2x12's the 23'5" way for your ceiling joists and two rows of strongback and be done with it as long as it's code where you are.
Joe Carola
by strongback do you mean blocking? If not where do you put the strongbacks?
by strongback do you mean blocking? If not where do you put the strongbacks?
It's not blocking. I nail a 2x4 flat on top of the ceiling joists the whole length and then nail a 2x6 on edge toenailing into the top of the ceiling joists and into the side of the 2x4. In his case coming in 8' from the wall at each end.
Joe Carola
Hello Joe. If I run 2x12's the length of the 23'5" what do I use for the rafters to keep the walls from spreading? Rafter ties?
The 2x12 joists would be running perpendicular to the common rafters.
As far as code goes city I am in goes by 2003 IRC and I have not seen anything special in my local codes for framing.
The 2x12 joists would be running perpendicular to the common rafters.
No they wont. Your building is 26' 8" x 23' 3-1/2". You have to use 23' 3-1/2" as your span and divide that in half which is 11'7 -3/4" as your common rafter run(no ridge deduction for now) and that will give you a 3'4-1/2" ridge.
You'll have roughly 4 commons running front to back the 23'3-1/2" way and then two king commons on each side running the 26'8" way. Your 2x12 ceiling joists run the 23'3-1/2" way.
On each end of the 23'3-1/2" wall you will have to double up on the ceiling joist coming in enough to clear the hips and them run small(outrigger) ceiling joist perpendicular to the doubles nailing them into the doubles, top plate and the side of the king commons and jack rafters.
You could frame it the other way having two commons that run the 26'8" way and two commons running the 23' 3-1/2" way coming to a point with no ridge (diamond hip) but, that creates a bastard roof with different pitches. No need to do that and complicate things.
Here's a quick sketch.
Joe Carola
Thanks again Joe but I am adding to the side of my existing home so I will be extending the existing roof line. When I get home I am going to scan my prints and post them.
Edited 3/10/2008 4:03 pm ET by blownonfuel
I gotcha now.
If you frame it the way you drew it from front garage wall to the house you will have a 23' 3-1/2" run with a 4/12 pitch gives you a 7'9-3/16" rise(not including the rafter plumbcut).
That means your front wall is all 4/12 pitch. This makes the two side walls, the 23'3-1/2" walls a 7/12 pitch because you have a 13'4" run with a 7'9-3/16" rise.
That's up to you and you'll have to frame bastard hips. If you use the front wall of 26'8" and cut that in half giving you a 13'4" run for the rafters, you can come in on both side walls 13'4 and set two king commons and then come in from the front wall 13'4 and set one king common and put a 9' 11-1/2" ridge back to your house and have the same 4/12 pitch all the way around with both hips running at 45°.
You can bolt a ledger on the existing house wall and hang your 2x12 ceiling joists off of that and double up the two ends and run outriggers along side the commons to hold the walls in place. Then add your strong-backs.
Or, if your garage top plate are the same height as your house, you can open up the house and sit the ceiling joists on the existing top plates.
Here's another drawing of the way I just described with everything being a 4/12 pitch.Joe Carola
Thanks Joe, that is exactly the way I was supposed to draw it.I want to keep the same 4/12 pitch and not change the roof height or pitch.The plates for the garage will be the same height as the house.I need to remove one of the existing exterior walls and the joists from the current carport and adjacent master bedroom lap on the top plate of this wall. When I remove this wall I won't have any support for these joists unless I run a beam (2 2x10's tied together) from one plate to another and tie the joists to it. Then I can tie my new joists from that and start running them out to the new additions. Does this sound okay, tying the old joists to the new joist with a 2x10 beam in between?I uploaded the plans so you can take a look.So Joe it is not uncommon to run joists perpendicular to the common rafters?
Here's a drawing of the way you have it showing the 4/12 front and 7/12 sides.Joe Carola
Trusses ?
No beam reguired.
I-joists.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
Trusses, simple, easier , a lot quicker to install and less $$$ when all said and done.