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Old 04-25-2011, 08:15 AM   #1
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Carport Lean to Roof Question..


Hello everybody, I am in the process of adding an enclosed carport to my existing garage. My new structure is 18" long and 12" wide. Because the wall height of my existing garage is too low to attach the new roof to I need to attach it to my existing roof.
Many of the houses in my neighborhood have these car port additions. The only difference between mine and the other ones is mine will be enclosed with a proper garage door in front. Now.. on to the question..
My existing roof has 10 x 24" on center rafters. I bought 2 x 8 x 20 rafters to make the new roof. My question is how I should tie them in to the existing roof.
I have 2 ideas.
#1. Cut slots in my existing roof and slip the new rafters along side my existing ones and sister them up with nails. I will then built a truss above my existing garage wall to add support to the new roof.
This seems like a solid idea but it would be fairly tricky and I don't know if its the correct way to do it.
#2. Rip off a few courses of shingles and place a 2 x 10 x 18' ledger board on the surface of my existing roof and fasten it to the existing roof rafters.
Then, take my new rafters and angle cut them so that they have a fairly smooth transition when fastened to the ledger board directly above the existing roof rafters on the old roof so that when I plywood the new roof the transition is smooth. I would then toenail them into the new ledger board and install framing brackets for added strength and support. I could then flash the seam where the plywood meets the old roof, felt paper it and shingle the entire side of the roof right up to the first course under the peak.

I would like to know what you guys think. Here are 2 pictures. The 1st pic is of my garage and addition as it sits today. The other is a quick photoshop version of what my new roof is going to look like.
Thanks!

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Old 04-25-2011, 08:37 AM   #2
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Carport Lean to Roof Question..


Two thoughts...........

I don't like the low pitched roof even if everyone in town has done it this way.
But if you must....

You want to run your new rafters all the way to the peak to avoid creating a "valley" transition.

Strip the caps and a couple of courses of singles.
Check to see if the existing framing is Exactly 16 or 24" on center. If they are. set your new rafters directly on top of the existing.

If not, run a 2x12 on the flat to span the bays and set your rafters on top of that. It will act like a plate that will span the bays and allow you to lay out your new rafters at exactly 16 or 24 for your sheathing.

Option 2

You did some wonderful concrete work there.
Redo your photoshop with a pitched roof that creates a single gable
Upstairs storage, and a much better look.
It becomes a 2 car garage instead of a 1 car with carport.
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Old 04-25-2011, 09:25 AM   #3
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Carport Lean to Roof Question..


Running the rafters to the top edge of the peak sounds like a good idea.
I can just angle cut them to fit flush with the angle of the existing roof.
Should I still install a ledger board at the top edge of the peak or should I just strip the shingles off the peak and a few courses below it and toe nail the new rafters directly into the existing ones?
The existing rafters are on 24" centers. I bought 20' long 2 x 8"s for the rafters. I think they will be long enough. My new structure is 12" wide. My existing structure is 10.5' wide. Since I have to go to the peak and I need an overhang over the new outside wall I figure I need about 18' which leaves me a 2' overhang of which I only need 6" I believe for the soffit.

Does that sound about right?
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Old 04-25-2011, 03:00 PM   #4
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Carport Lean to Roof Question..


I spoke to a building inspector and he told me to use the ledger board instead of going all the way to the peak.
So, that leads me to another question.
How do I figure out the birdsmouth cut for the rafters?
I am not sure what my pitch is going to be for the new roof but I am guessing its going to be around a 3:12 pitch.
How do I figure a birdsmouth cut on a roof like this?
Do I just go by eye? I am figuring I could make the angle cut at the top of the rafter so that it sits flush on the ledger board on the existing roof. Then, I will lay the rafter on the top of my outside wall and take a pencil and a straight edge and pencil in a birdsmouth cut. The problem with that is when I make the birdsmouth cut and the rafter drops in 1-1/2" into the outside wall it will change the angle of the upper angle cut I just made.
Any ideas on how to do this? Should I not make birdsmouth cuts and use hurricane ties or those stop sign shaped brackets?
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Old 04-25-2011, 07:27 PM   #5
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Carport Lean to Roof Question..


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Originally Posted by jgcable View Post
I am figuring I could make the angle cut at the top of the rafter so that it sits flush on the ledger board on the existing roof. Then, I will lay the rafter on the top of my outside wall and take a pencil and a straight edge and pencil in a birdsmouth cut. The problem with that is when I make the birdsmouth cut and the rafter drops in 1-1/2" into the outside wall it will change the angle of the upper angle cut I just made.
Any ideas on how to do this?
As long as you have the exact angle at the top you can hold the bottom of the rafter at the plate flush to the inside of the top plate and then scribe the 3-1/2" seatcut and scribe the outside of the top plates plumbcut. That will give you your exact birdsmouth.
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Old 04-25-2011, 07:31 PM   #6
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Carport Lean to Roof Question..


An easy way to do this is to hook up a string line on the plane of the desired rafter. Then you can use a framing square or speed square off of the string to pick up the correct angles.
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Old 04-25-2011, 08:22 PM   #7
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An easy way to do this is to hook up a string line on the plane of the desired rafter. Then you can use a framing square or speed square off of the string to pick up the correct angles.
That's ok for a framer to do but a little hard for an inexperienced guy doing that. The best and easiest way to do it is to scribe it like I was saying. You can't go wrong with a scribe.
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Old 04-25-2011, 08:24 PM   #8
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That's ok for a framer to do but a little hard for an inexperienced guy doing that. The best and easiest way to do it is to scribe it like I was saying. You can't go wrong with a scribe.

But to do the scribe he will need to have the top cut already figured out. With the string in place he can figure out both. I know what you mean though Joe. I just started posting here recently. Been posting with you and the others at CT for several years though.
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Old 04-25-2011, 10:26 PM   #9
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Carport Lean to Roof Question..


jg, with the span of 17'3" and the rise of about 40" minus the meat left (HAP) above the seat cut (+-34"), you end up with close to a 2/12 cut. Not much especially if you get any snow..... Why not new trusses with storage above, as mentioned? I hope the ridge is straighter than the siding on the right.....
May want Cedar or p.t.wood next to the fresh concrete stem wall for door framing, at least put some sticky wrap or builders paper between them for a capillary break.

Gary
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Old 04-26-2011, 07:17 AM   #10
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Carport Lean to Roof Question..


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As long as you have the exact angle at the top you can hold the bottom of the rafter at the plate flush to the inside of the top plate and then scribe the 3-1/2" seatcut and scribe the outside of the top plates plumbcut. That will give you your exact birdsmouth.
Hey Joe, thanks for the response. I have a question. If I have the exact angle cut on top and I scribe the seat and plumb cut wont the angle on top change when the rafter drops into place?
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Old 04-26-2011, 07:44 AM   #11
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Originally Posted by GBR in WA View Post
jg, with the span of 17'3" and the rise of about 40" minus the meat left (HAP) above the seat cut (+-34"), you end up with close to a 2/12 cut. Not much especially if you get any snow..... Why not new trusses with storage above, as mentioned? I hope the ridge is straighter than the siding on the right.....
May want Cedar or p.t.wood next to the fresh concrete stem wall for door framing, at least put some sticky wrap or builders paper between them for a capillary break.

Gary
We get a alot of snow in CT so I definately need to invest in a roof snow rake for next winter. Many of the car ports in my neighborhood have similar pitches and none of them seem to have any problems.
I was hoping for a steeper pitch than 2-12. I was hoping to get 3-12 but it is what it is I guess.
Regarding trusses with storage on top.. I can't go higher than the original garage peak. The reason the new outside wall is tall is because I framed out the front wall to accept a 7'h by 9' wide roll up garage door. I could have went 3" shorter but that wouldn't have made much of a difference. I am going to put the ledger board up as close to the peak as I can to get the most pitch possible.
I have 20' long 2 x 8's so I am fairly sure I have enough length to go to the peak if I had to.
Is there any way for me to increase the slope (pitch) of my new roof with the situation I have?
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Old 04-26-2011, 07:51 AM   #12
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Carport Lean to Roof Question..


As you can see in the picture I posted, even though the original outside wall of my existing garage
is almost 3" off, the garage door opening is square. This is because the previous owner framed out the garage door
after the garage became twisted. Once I refinish the front of the garage you won't even be able to see the crooked wall because both of the garage door openings will be square and in
proportion to each other. I am going to open up the original garage door opening height so that it matches the height of the new door. Thats about roughly about 3 inches.
Its a fair amount of thought and planning for me but I am fairly handy with stuff like this and I do have help. We are going to make it as nice as we can but with the
understanding that its not going to be perfect. Just close and structurely sound is good enough for me. I just need a place to put my motorcycle and my lawn equipment.
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Old 04-26-2011, 11:07 PM   #13
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Carport Lean to Roof Question..


Pretty much stuck with what you have . Tell us the exact height of the existing peak garage roof and your new wall height. May want to change the gable direction to the 18' span way for a 4/12. Also can drop some of the rafter meat into the garage on hangers to get a steeper pitch.
I was talking about the siding drooping (in the center of the run) 1-2" on the car side of the old garage. Usually that is an indication of a sagging wall and/or sagging ridge line. You'll want to string-line it for straight when installing the new one or jack up the old ridge first, if sagging.

Gary
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Old 04-27-2011, 12:33 AM   #14
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Carport Lean to Roof Question..


And after all is said and done that will still be one butt-ugly garage.

I'm talking baboon butt-ugly. But what the hey, I can't see it from my house.

Andy.
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Old 04-27-2011, 08:14 AM   #15
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And after all is said and done that will still be one butt-ugly garage.

I'm talking baboon butt-ugly. But what the hey, I can't see it from my house.

Andy.
A few houses in my neighborhood have the same exact thing. Most of them have car ports. Once I install 2 new garage doors and I trim it out properly its gonna look great. I live in a very nice neighborhood with nice houses on it.
BTW... the reason you can't see it from your house is probably because the trailer park you live in is behind the landfill.
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