This isn't garage related but I didn't want to join another forum, and was hoping someone could help me out. I need to build a porch for my wife (it was part of the new garage deal) It will be a roof coming off the back of the house the rafter span will be 17' 4". I was planning on getting the lumber from HD or 84 it says it is #2 douglas fir. When I put that all into the calculator with deflection of 240 and a 20# snow load it says I can span 17' 2" on 16" spacing. Does that sound right? I just want to make sure. Thanks
Need help with "shed" roof.
- Thread starter hanly2
- Start date
pattenp
Well-known member
What dimension lumber? What's the roof pitch? You may need at least 2X8's or may be 2X10's.
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p_mori7
Well-known member
17' is a pretty long span.
You wll need to upsize your lumber and narrow the spacing.
You wll need to upsize your lumber and narrow the spacing.
Woody610nb
Banned
Double up the 2 x 8's.
I don't think your pole barn cares. Where are you?
pattenp
Well-known member
Why not use 2 X 10's on 16" centers?
Kevin54
MEMBER EMERITUS
Are you building rafters, or are you going to go with a truss?
And as far as the porch....is the porch going to be 17' across, or 34+ feet across? If the porch is only going to be something like 17' across total, then your rafter will only be half of that, plus a little more, so each rafter would only be like 9' maybe. I may be reading something wrong, but your rafter span, or what you are calling a rafter span, would be a 34' plus wide porch.
texas webb
Well-known member
Are you using 18' lumber?Where is your support beam located/ie:how far out from the house wall?And roof pitch comes into the mix also.
The roof beam will be 17' 4" from the wall of the house. That is the span from the header attached to the house to the roof beam. It is a low pitch roof, I havent measured the pitch yet maybe 4/18? Here is a picture of the back of the house the roof will be coming toward me 18'. I do not have enough room between the top of that door and the roof for anything bigger then a 2x8. plus doing 2x8's on 12's is a ton cheaper then 2x10's on 16.
<a href="http://s1190.photobucket.com/user/hanly2/media/Mobile%20Uploads/20140712_183449.jpg.html" target="_blank"><img src="http://i1190.photobucket.com/albums/z451/hanly2/Mobile%20Uploads/20140712_183449.jpg" border="0" alt=" photo 20140712_183449.jpg"/></a>
<a href="http://s1190.photobucket.com/user/hanly2/media/Mobile%20Uploads/20140712_183449.jpg.html" target="_blank"><img src="http://i1190.photobucket.com/albums/z451/hanly2/Mobile%20Uploads/20140712_183449.jpg" border="0" alt=" photo 20140712_183449.jpg"/></a>
I'd rather spend the extra cash and use 2x10s over the 2x8s. I don't care what the figures show, A 17' span seems like a helluva lot for a 2x8, even for a 20 lb snow load.
I'd rather over build it now then to have it collapse during a heavy winter storm and explain it to the wife as to why it collapsed or why it's sagging.
I'd rather over build it now then to have it collapse during a heavy winter storm and explain it to the wife as to why it collapsed or why it's sagging.
pattenp
Well-known member
You'll be fine with 2X8's on 12" centers as long as you're just using standard asphalt shingles, no slate or concrete shingles. Are you planning to leave the underside open?
p_mori7
Well-known member
You can support the rafters mid-span.
When framing your side walls, include posts to support a beam that will be perpendicular to the rafters at the midway point (about 8'6").
To span the 18' (if I am reading your prior posts correctly), I would go with a 10" x 6" beam.
Will post a sketch in a few minutes.
EDIT: Here is my quick sketch:
At a 20# snow load, your planned roof could have 6000 pounds of snow on it. You gotta build it strong enough so it won't collapse. You also gotta think about the weight of whatever roofing material you will be using.
Good luck with the build.
PS: With this type of beam, you could also use regular 10' 2x8's as they will meet up over the beam.
When framing your side walls, include posts to support a beam that will be perpendicular to the rafters at the midway point (about 8'6").
To span the 18' (if I am reading your prior posts correctly), I would go with a 10" x 6" beam.
Will post a sketch in a few minutes.
EDIT: Here is my quick sketch:
At a 20# snow load, your planned roof could have 6000 pounds of snow on it. You gotta build it strong enough so it won't collapse. You also gotta think about the weight of whatever roofing material you will be using.
Good luck with the build.
PS: With this type of beam, you could also use regular 10' 2x8's as they will meet up over the beam.
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cdestuck
Well-known member
I believing he is referring to CANTILEVERING part of the rafters.
I like that idea. But here are a few concerns. 1. I am not framing out the walls just putting screens in so it will be mostly open. 2. Footings? The slab is already poured and while i can add a footing on the outside wall. I cant add one on the side under those windows. Can I attach the beam to the house? 3. The span for that beam would be 22' I would probably have to have it made. 4. Using 2 2x8's would probably save money but how would they meet/attach at the top of that rafter? Thanks for the help.
The header on the left of the door will be lower to accomodate the windows on the side of the house. It will look like this.
I'm a little unclear of what you're doing here. I understand the header will be here (black marked area) but where will the roof be ?
If you're following the old roof line, you might want to consider putting in a shorter window to prevent any future issues.
p_mori7
Well-known member
If it will be mostly screens, then your roof & snow load need to be transferred to the ground via posts. Your posts should be in holes dug with an auger and set into concrete. Not sure about frost depth in your area, probably at least 24". If you have just a regular 3" or 4" slab, it will most likely crack where the posts rest on it if that is how you decide to go. If your slab is thicker along the perimeter (say 12" rather than 4") you would probably be OK just setting the posts onto the concrete.
The 2x8's don't **** together on top of the beam. They would actually extend past each other, then you just nail or screw them together.
Spanning 22' with a beam is a mighty task...I think you would be looking a really big LVL or steel. I was looking at some span tables yesterday, and if I read them correctly, spanning 18' would require something like 4 2x12's nailed together.
Are you planning any center support ? or do you want clear span underneath ? If you want clear span underneath, another option is going to trusses, but that would require eliminating the door on the existing addition.
The 2x8's don't **** together on top of the beam. They would actually extend past each other, then you just nail or screw them together.
Spanning 22' with a beam is a mighty task...I think you would be looking a really big LVL or steel. I was looking at some span tables yesterday, and if I read them correctly, spanning 18' would require something like 4 2x12's nailed together.
Are you planning any center support ? or do you want clear span underneath ? If you want clear span underneath, another option is going to trusses, but that would require eliminating the door on the existing addition.
The roof will be coming toward you under the existing one. I have footings under where the posts will be installed. Also just realized the beam wont work because of the step in the roof where it needs to be under the windows then over the door. Back to the drawing board.
p_mori7
Well-known member
Beam could still work, you just have to set it at the lowest point to accomodate the drop, then shim over top for the remainder.
I also would seriously look at shortening that window to get the same roof line. Easier to do that having a step in the roof line.
I also would seriously look at shortening that window to get the same roof line. Easier to do that having a step in the roof line.
pattenp
Well-known member
Before shortening the window, if it's a bedroom window, fire code sets how high the bottom of the window can be off the floor.
bob15
Well-known member
You would be better off with 2x10's. You are at the max for a 2x8, so why build like that? A freak snowstorm and it collapses......and then what? Over-build and it will last much longer and you can rest better. What happens when the "boss" wants a ceiling fan(s)? Or decides to sheetrock in the future? Now you can't because you're probably also at the max for dead load.
Build it with 2x10's and all worries will be over.
Are you pulling a permit for this? What do they want, 2x8's or 2x10's?
Build it with 2x10's and all worries will be over.
Are you pulling a permit for this? What do they want, 2x8's or 2x10's?
Hopefully you realize this is more than a simple "shed roof". You've got snow and wind load considerations, member sizing, footing calculations, flashing, siding, gutter, possible window interference, possible door interference, connecting means, a couple new electrical circuits, and the never-to-be-forgotten permitting questions.
You might want to start by verifying the existing conditions such as roof slope, dimensions, drainage paths. From that you can design the size of the new construction, plan the join methods with the existing structure, and make decisions on structural member size/spacing.
You might want to start by verifying the existing conditions such as roof slope, dimensions, drainage paths. From that you can design the size of the new construction, plan the join methods with the existing structure, and make decisions on structural member size/spacing.
I think this is my best option. So I need to look into having my truss guy make me a lvl that is 10x6x22. Can I support it at the existing window wall with a ledger board attached to the house, because a post will interfere with the windows on ground level? It is a bedroom window so shortening it probably isn't a option.
p_mori7
Well-known member
Hmm...personally, I don't think so. I would check with a more experienced framer or a structural engineer. With a ledger attached to the house, you are going to be asking it to support A LOT of dead weight + snow load.
LVL's are not made by truss manufacturers, rather; they are manufactured by companies like Weyerhauser. In looking at the Weyerhauser LVL chart, looks like you will need a 12" or 14" LVL. I don't know if you can double them up to use smaller ones.
As far as the lower windows, perhaps you could place some posts on either side and transfer the load down to the ground that way.
At this point, you planned build is getting pretty technical. I suggest you consult with the proper authorities in your area to make sure you're doing it right.
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bczygan
Well-known member
You've got a bit of a hodgepodge there.
First, where is the floor level for the new porch going to be?
How will you get from that existing door, down to the floor level?
Was that room an addition to the house?
What rooms are we dealing with here?
What is the roof slope for the existing room?
A couple of things:
I would use the existing roof slope, and simply extend it as far as practical, or until headroom is minimal at say 7'.
While the intermediate beam might not be needed or practical, if it is used, it can be essentially in the same plane as the joists by hanging joists off the side of the beam with joist hangars. This will minimize how far down the beam intrudes into the space.
The ends of an LVL that long will need support by posts on both ends rather than a ledger.
If the outside walls are basically just screen panels, then the wall at the eave, or lower edge of the roof, will need to have a beam sized to support the ends of the rafters, for whatever span it has. That span can be cut by installing one or more posts within the wall between screen panels. This beam must be below the plane of the joists if an overhang is desired.
First, where is the floor level for the new porch going to be?
How will you get from that existing door, down to the floor level?
Was that room an addition to the house?
What rooms are we dealing with here?
What is the roof slope for the existing room?
A couple of things:
I would use the existing roof slope, and simply extend it as far as practical, or until headroom is minimal at say 7'.
While the intermediate beam might not be needed or practical, if it is used, it can be essentially in the same plane as the joists by hanging joists off the side of the beam with joist hangars. This will minimize how far down the beam intrudes into the space.
The ends of an LVL that long will need support by posts on both ends rather than a ledger.
If the outside walls are basically just screen panels, then the wall at the eave, or lower edge of the roof, will need to have a beam sized to support the ends of the rafters, for whatever span it has. That span can be cut by installing one or more posts within the wall between screen panels. This beam must be below the plane of the joists if an overhang is desired.
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There is no additions to the house the wall with the door is the foyer to the right of that is the attached garage. The 2 top windows are bedrooms and the bottom is the lower level family room. I will put steps from the door down to the slab that is the floor level. The garage roof is 4/12. My neighbor around the corner has a room like this. I need to go check it out
captain14
Well-known member
Show us pictures of the neighbors house so we can get a clear idea of what you want to
do
do