I guess I’ll go ahead and attempt an answer, taking the chance that you’ll delete your original post and re-word the question in a new thread.
As I mentioned in response to your first posting of this question, a picture would help. As I now understand it, you’re wanting to add a shed-roof over a 5′ wide by 20′ long porch. But what I’m not clear about is, does it tie in to the house at the eaves, or does it tie into the gable wall?
If its the gable wall, it might be possible to maintain your 5:12 pitch, if it ties in at the eaves, it seems unlikely. Shed roofs tend to have a lower pitch when tied in at the eaves, since you’re trying to keep a reasonable beam height at the low end of the roof, and be low enough to tie-in to the existing roof at some point.
Could you offer a photo, sketch, or written clarification? Tryin’ to help you out here, but you gotta give us a little more info.
“he…never charged nothing for his preaching, and it was worth it, too” – Mark Twain
Replies
Huck,
I think he's talking about the same porch roof that you drew the picture of and I added to that with my own side view drawing here.
http://forums.taunton.com/tp-breaktime/messages?msg=71098.20
OK, got it. Thanks for the clarification. Nice pic too, by the way. Then my answer would be that he could set the beam at whatever height he wanted - but even with the top of the walls seems like a logical choice. If he'll stick around in one thread and talk to us, I'm pretty sure we could walk him through the process.
I would start with specific dimension of the existing house and porch structure and the proposed porch roof, then figure support posts, how many and how far apart. Then go to the support beam, what is the minimum size that will carry the load without sagging. On to rafter size and spacing (with your drawing, I think rafter spacing needs to match the existing roof, so the new rafters fall on top of the house rafters), and roof pitch. Building and framing details, like post footings and frieze blocking. How to tie in to the existing roof (which I think Piffin has covered in the previous thread), and suggested roofing material.
I would keep the pitch as flat as possible so that the tie-in doesn't occur at mid-span of the house rafters. The closer to the plate the better. Although a purlin wedged in lengthwise at the plate would probably accomplish the same thing. I don't see how he could envision the porch roof having the same pitch as the house roof, as that would make the two planes parallel, and they would never meet. How do you figure that?
"he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
2x10 beam 6x6 posts' 48"footings 4footings how do i cut my angles if i go with a flatter roof like a 4 or a 3 pitch. oh yea forgot 2x8 rafters but no joists because i will have a12in overhang.
T3,
Is this close to what you're talking about?
yep thats about right,but i gust neddto know a couple of things. going by that drawing, which is a better way to set the beam ,at the plate height or the soffit height.because i'm not going to use joists,i'm just going to let the rafters overhang about a foot or so.over the beam.
Edited 3/22/2006 5:22 pm ET by T3
"yep thats about right,but i gust neddto know a couple of things. going by that drawing, which is a better way to set the beam ,at the plate height or the soffit height.because i'm not going to use joists,i'm just going to let the rafters overhang about a foot or so.over the beam."
That depends on how much heght you have from the top of your grade level. If you have enough height to lower the beam that will also help increase the pitch of the porch roof if you need too. I think you said you had 8' to the top of the existing wall.
Make sure that you plan for head clearance on your soffit and fascia in your rafters and beam. Nothing like getting it all nailed together and finding out you have to duck to walk in and out of your porch.
You're entitled to sh!t.---Tony Soprano
from the porch floor to the top plate is 8ft, and i'll be using a 2x10 beam.that should be plenty of room anyone over 7ft tall i'll tell them to stay home.
I'm a little taller than average 5' 19" so I think about that kind of stuff alot.
As for cutting your rafters here's how I do it, put your beam in place, cut a scrap piece of 2x8 about four ft long stand it up on edge on your existing roof and scribe your roof pitch onto your uncut rafter then go out to your beam lay your block flat on the beam and scribe your birdsmouth on the rafter. Caveman method yes but fits everytime.You're entitled to sh!t.---Tony Soprano
i don't get the block on beam part.
When you have the block laying flat on the beam scribe along the top and edge of the block to mark the seat of the rafter on the beam.You're entitled to sh!t.---Tony Soprano
is a 2x block good enough to lay flat on the beam.
for scribing yes if you want a deeper seat use 2You're entitled to sh!t.---Tony Soprano
T3,You can start out by making a 4/12 pitch birdsmouth and since you have a 5' run for example you can measure up the rafters and mark 5'3-1/4" and scribe a 4/12 plumbcut and that will fall right at the building existing line.Then tack the rafter in on top of the beam and hold it up at the building line and plumb it up until it's plumb with the building and your 4/12 plumcut mark and tack it in place.Now at the roof line where you strip the shingles off down to the plywood you scribe the angle.Do you understand so far? It can be done easy enough with math but this is easy also to do.If the 4/12 rafter is to high at the existing ridge height you'll have to lower the beam and then put a 3/12 pitch on.Joe Carola
Nice picture, and explanation. The only thing I'd add is to wedge a purlin in at the outside wall of the house, to transfer the load to the bearing point (the wall)
View Image"he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
got it thanks. i have so much going on i forgot about this past message.
T3
I'm stupid!
My math skills are non existant.. So I simply built a template out of 1/4 inch plywood , cut and trimmed it untill it worked and then used that as a master..
I wound up with a 27/12 pitch in the billard room and a 17/12 pitch in the great room, plus a 7 1/2 /12 pitch for the attic..
Who cares what the numbers are? It looks great and it's interesting the two criteria I wanted..
In less time than you can do the math I made the template!
what does the 3-1/4 apply to and for what.also with the new rafters nailed to the existing ones and i'm installing 2x8 for rafters, do i really need a perlin.HEY you and i almost share the same D.O.B. myself 12/14/64.
You mean 5'3-1/4". You said that the porch was 5' off the house. So if you had a 5' run from the outside plate of the house to the outside of the girder and a 4/12 pitch that would give you a rafter length of 5'3-1/4". That's the mark I drew for you.
I've never installed a purlin before. In fact I've never even heard of that word until I came onto the internet. Some spans we have to break up and I would just frame a kneewall under those rafters. The kneewall would sit right on the top plate of the existing house. For most cases you don't need a kneewall, but your area might be different with snow loads and you might need one.
You old man................;-)
hey youg man thanks for the advise.