# Need help figuring out rafter lengths.



## Joe Carola (Apr 14, 2006)

CleIndiana said:


> I do not know anything about framing but I am also not scared to get in there and try it. Because of what I have read on here I will try to give as much info as I can. What i am going to attempt to build is a shed still roof attached to my existing house. The house is a single story ranch with a garage that is attached at a 90 to the left of the home. The measurements of the porch will be 31'x10'. This guy is doing the same thing I am wanting to do.http://www.diychatroom.com/f9/shed-porch-roof-tying-55967/. Can anyone help me find the common rafter length or what other info is needed to help with finding the length?
> 
> 
> I link his page because the drawing shows what I am wanting to do, but I may not be able to go all the way up to the garage ridge because I have a sky light that is siting in the front entry hall and 1/4 of it sits below the garages ridge height.


What is the pitch of the existing roof and what size rafters are they? Also, what is the length of the existing rafters and the measurement from the existing wall to the bottom of the skylight measuring up the rafters?


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## CleIndiana (Nov 8, 2009)

sorry i knew i would forgot info. its a 4/12 pitch with 2x6 rafters. from the bottom of the sky light to the edge of the facia is around ten ft and the length of one full length rafter is around 14ft. sorry only rough estimates. cant really tear anything apart while in the planing. sorry i added the over hang, so subtract that and its 8' 6"

I should also mention that I am going to tie into the side of the existing rafters, unless the ledger on the roof is a better idea. it seems to me youll be able to get sheathing to lay more flush by tting into the side of the rafters.


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## Joe Carola (Apr 14, 2006)

CleIndiana said:


> sorry i knew i would forgot info. its a 4/12 pitch with 2x6 rafters. from the bottom of the sky light to the edge of the facia is around ten ft and the length of one full length rafter is around 14ft. sorry only rough estimates. cant really tear anything apart while in the planing. sorry i added the over hang, so subtract that and its 8' 6"
> 
> I should also mention that I am going to tie into the side of the existing rafters, unless the ledger on the roof is a better idea. it seems to me youll be able to get sheathing to lay more flush by tting into the side of the rafters.


What size rafters are you using on the porch rood and will the top of the porch roof header be flush with the top of the existing top plate?

As far as the rafters running along side the existing rafters or sitting on top of the existing rafters with sleepers and getting the sheathing to lay flush, it doesn't matter, it lays flush both ways. Ledger is easier.


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## CleIndiana (Nov 8, 2009)

I was going to use the same as the house 2x6 nd i would like the new top plate match with the existing. by using the spleepers would i nail them perpendicular to the existing rafters?


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## NailedIt (Jun 19, 2009)

Sometimes it's easier (for me, at least) to put up the beam or wall that the roof will sit on at the outside edge, then put the ledger where I want it. After those 2 items are in place you can figure the rest out with strings and straight-edges. You can nail a block up on the outside edge of the beam/wall with a nail set at the desired throat height and set a tight string from that point to the top of your ledger. You can then measure exactly what length and angle you need in 3 dimensions. After you get the straight "common" section in you string/straight-edge along the top of the rafters to determine where your valley lays and measure those rafters in as well. More often than not (but not always) you find something is not exactly right when you try to calculate from an already built roof.

You can put the ledger right on top of your shingles in many cases, which helps if you can't get the whole thing built and dried-in quickly. Also, getting the sheathing down flush doesn't really make a difference, as the plane remains the same and flashing will bridge the gap, or you can just cut a bevel into the decking so it sits flat on the roof.


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## CleIndiana (Nov 8, 2009)

So your saying i can put the ledger any where i want and then figure out my rafter lengths?


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## NailedIt (Jun 19, 2009)

That's exactly what I'm saying. I'm not saying you can't figure it out with a calculator, I'm just saying you don't have to do it that way. I've built many-a-roof both ways. When building the whole thing from scratch I use a calculator to make a cutlist for the whole thing and cut 95% of the rafters before setting the first ridge, but when adding onto an existing roof I usually calculate the lengths just to get a material list, then I physically measure to make sure I get a tight fit. I believe you were referring to another post that had a picture of a string in place just as I described. 

A ledger is installed perpendicular to rafters. 

If somebody gives you a rafter length all you'll have to do is set it on top of the beam and go from there, either way it's essentially the same thing. You'd use the rafter to determine where to put the ledger, or use the ledger to determine what the rafter is.


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## CleIndiana (Nov 8, 2009)

So from what your saying I dont have to go that far up my existing roof in order to get the same pitch. I can set the ledger board say about four ft up from the top plate then figure everything out from there. i guess i see that picture of that other guys roof and just assume I have to go that far up but maybe he was doing it just for aesthetics.

That is why I;m asking all the questions because in my county i need to have a scaled drawing for them before they will issue me a building permit. and it would help me on figuring cost for wood. Also i dont care how much roof damage is done becaus ei plan on also putting new roofing on after this is completed.


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## NailedIt (Jun 19, 2009)

You won't get the same pitch. What I'm saying is if you know your general rise and run, you can place your ledger and measure an actual length for a rafter. You have to have a minimum pitch for shingles to work on a roof. The industry standard anywhere I've lived or built is 4/12, but I've seen older homes with 3/12 shingled roofs. 


Best thing to do would probably be to post a simple drawing, even a clear picture of a hand-drawn plan with dimensions of your roof and location of the skylight, etc... I've submitted plenty of hand-drawn plans for permit. A cross section of the roof/ceiling framing would be most effective.


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## Kurt1968 (Oct 15, 2009)

Joe is the man he helped me with my rafters for my porch. Do a search on porch roof I have pictures there.


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## CleIndiana (Nov 8, 2009)

Yeah I have read you post you kinda have it easy being that you can put the ledgers against a wall, I'm tying into a existing roof. Back to nailed it once I get the new top plate up for the porch would just be easier to figure out what I would need to do for a 4/12 pitch and run numbers over and over until I get the length for the rafters for that pitch. I'm afraid that I'm going to have to settle with a 3/12 or 2/12 because of the sky light. Also saw that Joe uses sketch it so might try downloading that and try to give you guys a picture to look at


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## Joe Carola (Apr 14, 2006)

CleIndiana said:


> sorry i knew i would forgot info. its a 4/12 pitch with 2x6 rafters. from the bottom of the sky light to the edge of the facia is around ten ft and the length of one full length rafter is around 14ft. sorry only rough estimates. cant really tear anything apart while in the planing. sorry i added the over hang, so subtract that and its 8' 6"
> 
> I should also mention that I am going to tie into the side of the existing rafters, unless the ledger on the roof is a better idea. it seems to me youll be able to get sheathing to lay more flush by tting into the side of the rafters.


With those dimensions keeping the shed roof top plate/girder at the existing plate height and using a 2x6 for the shed roof, your pitch will only work out to be 1-11/16:12.

Here's a quick sketch. Can you drop the girder height of the porch so that you can a least get a 3/12 pitch?


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## Joe Carola (Apr 14, 2006)

What is the height from the top of your patio to the existing top plate? What are you planning on using for the girder/headers? Is this a closed in porch or an open porch with a girder and posts?


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## CleIndiana (Nov 8, 2009)

Thanks joe for the drawing, its not going to be closed in I'm going to put in 6x6 post trying to utilize only 3 post. I plan on using 2x12 for the girders that way I get more span with less post. The porch doesnt have to be exactly the same hieght as the existing hieght but I would like to stay around 7ft for the hieght of the new porch. I'm not at home to measure but I would say the existing wall is aroung that same hieght once the pad is in place.

I believe code in my county requires a 2/12, unless I can squeeze the 1 11/16 /12 past them, hell its close enough to 2/12 to me.


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## Joe Carola (Apr 14, 2006)

CleIndiana said:


> Thanks joe for the drawing, its not going to be closed in I'm going to put in 6x6 post trying to utilize only 3 post. I plan on using 2x12 for the girders that way I get more span with less post. The porch doesnt have to be exactly the same hieght as the existing hieght but I would like to stay around 7ft for the hieght of the new porch. I'm not at home to measure *but I would say the existing wall is aroung that same hieght once the pad is in place.*
> 
> .


Your existing walls are only 7'? If so, is your house on a slab because 7' from the patio floor to the existing top plate is very low.


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## CleIndiana (Nov 8, 2009)

Joe Carola said:


> Your existing walls are only 7'? If so, is your house on a slab because 7' from the patio floor to the existing top plate is very low.



I should have mentioned I'm guessing. I'm not at home measure. My house is crawl space. I think what I meant was that when I get the patio floor powered it would be roughly 7 it maybe higher I haven't measured the height yet, I will when I get home tonight.

But from what I'm seeing all I should have to do is drop the patio girder height just 5/16 and that would get me to a 2/12?


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## Joe Carola (Apr 14, 2006)

CleIndiana said:


> I should have mentioned I'm guessing. I'm not at home measure. My house is crawl space. I think what I meant was that when I get the patio floor powered it would be roughly 7 it maybe higher I haven't measured the height yet, I will when I get home tonight.
> 
> But from what I'm seeing all I should have to do is *drop the patio girder height just 5/16 *and that would get me to a 2/12?


5/16" for every foot of run.With the 10' span, you will have to drop the girder 4-5/8" to get a 2/12. This is based on the top of the girder being even with the top of the existing plate. If you can lower the girder, that would make the pitch higher. You really don't want a 2/12 pitch and put shingles on that. It definitely voids all warranties.

Have people done that, yes. You would run snow-ice shield the whole roof and instead of going 5" to the weather, you go 4". Still voids all warranties and isn't the right way to do this.


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## CleIndiana (Nov 8, 2009)

How far would I have to drop it if I wanted to get the 3/12 so that way no warranty is voided? I can handle inches, I just have to put into consideration how much the height will affect the entry. I dont want someone that is 6'6" coming over and knocking his head on the porch roof. I would love to get rid of the sky light, but my wife says no. I guess she wants to pay for it later when it starts leaking. I think I have grasped it, I would need to drop another inch along with 5/16 every ft so it would be 1' 1 1/8" and that would only leave me with and 6' 10 7/8" height for my porch roof? if the wall height is at 8ft, which i dont build houses so I dont know. But if have you cable tv questions I am your man. haha.

I went ouside tonight and measure the wall and it is 8'. So if i have to go 6' 10" that seems a little low. so it sounds like to me the sky light goes or I dont get the porch i want.


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## Joe Carola (Apr 14, 2006)

CleIndiana said:


> How far would I have to drop it if I wanted to get the 3/12 so that way no warranty is voided? I can handle inches, I just have to put into consideration how much the height will affect the entry. I dont want someone that is 6'6" coming over and knocking his head on the porch roof. I would love to get rid of the sky light, but my wife says no. I guess she wants to pay for it later when it starts leaking. I think I have grasped it, I would need to drop another inch along with 5/16 every ft so it would be 1' 1 1/8" and that would only leave me with and 6' 10 7/8" height for my porch roof? if the wall height is at 8ft, which i dont build houses so I dont know. But if have you cable tv questions I am your man. haha.
> 
> I went ouside tonight and measure the wall and it is 8'. So if i have to go 6' 10" that seems a little low. so it sounds like to me the sky light goes or I dont get the porch i want.


I still say that the top of the girder can be lower than the existing top plate and if you can give me that height difference that would help alot. Also, you don't have to loose the skylight if you bring the new rafters to the existing ridge. You just remove the skylight and frame a new opening in the new roof above the existing opening and frame a small shaft from the top of the existing double rafters to the bottom of the new doubled up rafters for the new skylight opening.

If you can't save the skylight and flashing you might have to buy another skylight. If you give me the height difference from the top of the new girder to the top of the existing top plate, I will draw the new rafters going to the top of the existing ridge for you and tell you what pitch you will have. It might be close depending how much lower the top of the girder is from the top of the existing top p[late. Also making it a little shorter than 10' might get you to a 3/12 pitch.


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## NailedIt (Jun 19, 2009)

I'm also a framing contractor, btw. I was going to explain that you could drop the height of the beam or shorten the run, but it seemed like without some kind of visual example I would have confused you more than strictly necessary... Thankfully J.Carola is on the ball with that for you. 

You could take out the skylight, put in your new shed roof, and re-install the skylight on top of it. You'd have some drywall work to fix up inside, but it would get you up into 4/12 pitch-range and your wife keeps the skylight. Your labor is FREE, right?:thumbsup: Also, if you didn't mind a step-down onto the porch you could pick up the rise by going lower than the plate-height of the existing structure with your porch beams. I didn't catch how high up your crawlspace/stem-wall has you off the ground, I'm guessing you might have a foot or so to work with? Anyway if you pick up that much you could leave the skylight how it is and get the minimum pitch. Exceeding the minimum is better in this case, IMO.


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## CleIndiana (Nov 8, 2009)

nailedit or joe, what if i shortened the run by a foot or two and then kept the same height with the top plate and my new girder? would i still be able to stay 7" below the sky light. I dont want to drop thee girder to low because people will have to walk under it to get to the front door. I'm going to draw out a rough plan of what the front of the house looks like.

skip the drawing


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## NailedIt (Jun 19, 2009)

If you could live with an 8' porch with a few more posts... You could use smaller beams to effectively lower the tail-end of the rafters and get a steeper pitch. Going from 2x12 down to 2x8 gets you 4" more rise overall.

Leaving the same headroom under the beam, that is...


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## CleIndiana (Nov 8, 2009)

NailedIt said:


> If you could live with an 8' porch with a few more posts... You could use smaller beams to effectively lower the tail-end of the rafters and get a steeper pitch. Going from 2x12 down to 2x8 gets you 4" more rise overall.
> 
> Leaving the same headroom under the beam, that is...




I'm not sure i understand because if i use a 2x12 i will place it to the same height as the existing top plate nd i would do the same for the 2x8. So both would measure the same wall height.


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## Joe Carola (Apr 14, 2006)

CleIndiana said:


> I'm not sure i understand because if i use a 2x12 i will place it to the same height as the existing top plate nd i would do the same for the 2x8. So both would measure the same wall height.


You would gain 4" at the bottom for headroom underneath the girder. If the top of your 2x12 is 7' from the top of the patio for example, you will have 6' 1/2" to the bottom of the 2x12 for headroom. If you use a 2x8, you will have 6' 4-1/2" to the bottom.

I draw it out for you later with the rafters to the top of the existing ridge what your pitch will be. You will never get a 3/12 underneath the skylight without dropping the header down and coming in with the wall less the 10' at least 2-3'.


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## NailedIt (Jun 19, 2009)

I concur... except I was saying that you could keep the post height the same, so you'd actually be dropping the top of the beam if you switched to a double 2x8. If you did so your eaves wouldn't match up exactly(as far as overhang) if you're tying them together at an inside corner, but I'd opt for that vs. not getting the pitch I need. You'd have to add a couple posts to use 2x8, but that's your call. You don't have to have matching plate-heights where the beam ties in so long as you make the connection properly, though that's the usual way of doing these things. Joe's suggestion of going up to the ridge is actually the better looking and stronger way to do this kind of addition on your particular house, IMHO. I would draw you up a pic of what I'm saying with the beam thing, however I gotta git to the hospital, 1st baby's about to be born today... HAHA:thumbup:


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## Joe Carola (Apr 14, 2006)

Here's a drawing using the 10 span with the top of the girder that's 7' off the patio and flush with the top of the existing plate and running the roof into the existing ridge flush at the top. It only gets to around 2-1/8:12 pitch.

I also drew the roof with a 3/12 pitch with the shed rafters flush at the top of the existing ridge. You will see as the angle carries out to a girder, your span is only 8'1". This puts the top of the girder at 5' 11-1/4" off the top of the patio.

You can switch to 2x8's, but use a triple 2x8 so that you have to use less posts and drop the top down 4" as NailedIt said. that will gain a little more pitch.


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## Joe Carola (Apr 14, 2006)

NailedIt said:


> however I gotta git to the hospital, 1st baby's about to be born today... HAHA:thumbup:


Congratulations my friend!!!!!

Best thing that could ever happen for you and your wife.


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## CleIndiana (Nov 8, 2009)

Joe Carola said:


> Congratulations my friend!!!!!
> 
> Best thing that could ever happen for you and your wife.



Yes congratulations , and thansk you guys for all your in put and help. I will look over your drawings Joe. I think going all way up to the existing ridge plate would not be a bad idea and it doesnt seem there is to much work involved to raise the sky light. Thanks again guys.


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## CleIndiana (Nov 8, 2009)

Hopefully your still following this Joe, because I just came up with a new idea. I was driving around my neighbor hood and saw a house with the same style porch that i want. From what I could tell you would build up and off the existing ridge board. so the way it looked to me was that the whole front section of the roof is lifted about a couple of feet and that seemed to be how they got the right pitch. I wish I could have a drawing for you but sketch it isnt letting me open your drawing that you had fr me.


well i made a drawing on sketch it but i cant get the file name type to change.


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## Joe Carola (Apr 14, 2006)

CleIndiana said:


> Hopefully your still following this Joe, because I just came up with a new idea. I was driving around my neighbor hood and saw a house with the same style porch that i want. From what I could tell you would build up and off the existing ridge board. so the way it looked to me was that the whole front section of the roof is lifted about a couple of feet and that seemed to be how they got the right pitch. I wish I could have a drawing for you but sketch it isnt letting me open your drawing that you had fr me.


I know exactly what you're talking about. I was going to suggest that before, but I thought you have an EL shaped roof. I extend front ridges all the time when doing dormers. If you don't have to deal with another roof in the back, raising the front ridge will work fine. I will draw your roof for you so that you can have the porch girder the same height as the top plate. I will extend your front ridge to make the porch roof a 3/12.


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## CleIndiana (Nov 8, 2009)

Joe Carola said:


> I know exactly what you're talking about. I was going to suggest that before, but I thought you have an EL shaped roof. I extend front ridges all the time when doing dormers. If you don't have to deal with another roof in the back, raising the front ridge will work fine. I will draw your roof for you so that you can have the porch girder the same height as the top plate. I will extend your front ridge to make the porch roof a 3/12.



Your the man Joe, as far as the garage I would just build around it like the existing roof is correct? and also since I'm spanning farther then before do I need to switch to 2x8 or 2x10?

the main house is straight with two ridges and gable ends, and then the garage sit at a 90 to the house on the far left side and that roof has two ridges and is gabled as well.


It looks just like that guys picture I posted on the first page.


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## Joe Carola (Apr 14, 2006)

Here's the drawing.


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## CleIndiana (Nov 8, 2009)

Thanks for the drawing, I think this is the way I should go. The only thing that may give me trouble is that sky light. Also since this is pretty much a new roof system on the front should I go with a bigger rafter or just stay with the 2x6?


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## Joe Carola (Apr 14, 2006)

CleIndiana said:


> Thanks for the drawing, I think this is the way I should go. The only thing that may give me trouble is that sky light. Also since this is pretty much a new roof system on the front should I go with a bigger rafter or just stay with the 2x6?


The skylight won't give you trouble at all. It's just more framing involved. If it doesn't work out with the new roof and keeping the same opening with framing a shaft and giving you enough light, you will have to reframe the existing opening and sheetrock/tape/spackle/paint..etc.

You might have to depending on snow loads in your area. You really have to check with an Architect or Engineer about the rafters and ridge. I';m just drawing what you can do. If you would need to use 2x8's I will draw 2x8's for you. That will change things a little, but not much. You also would have to install collar ties from the existing ridge to the new shed rafters.


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## CleIndiana (Nov 8, 2009)

Thanks Joe Ill get with an engineer about the loads. Will I still need that collar if use the 2x8 or is it there for more support to the new roof?


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## Joe Carola (Apr 14, 2006)

CleIndiana said:


> Thanks Joe Ill get with an engineer about the loads. Will I still need that collar if use the 2x8 or is it there for more support to the new roof?


Maybe, maybe not. Depends on what the Engineer says. He might say you don't need the collar ties. That total length can be done on one shot. If youb use a 2x6, the kneewall might have to take the weight at that point. If so you have to make sure any headers you have in your back wall can handle the weight. You have a few options that will work for you.

You are going to have a funky spot on your roof on the other side of the perpendicular roof you have a couple options there also how to frame that. Do you have the height and distance that top ridge is coming down from the main roof?


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## CleIndiana (Nov 8, 2009)

Joe Carola said:


> Maybe, maybe not. Depends on what the Engineer says. He might say you don't need the collar ties. That total length can be done on one shot. If youb use a 2x6, the kneewall might have to take the weight at that point. If so you have to make sure any headers you have in your back wall can handle the weight. You have a few options that will work for you.
> 
> You are going to have a funky spot on your roof on the other side of the perpendicular roof you have a couple options there also how to frame that. Do you have the height and distance that top ridge is coming down from the main roof?



If you talking about were the garage ridge meets the main roof yes because the garage ridge sits below the main roof by a ft ft and half. To me it would seem that around that area i would just be building around the garage roof. Or I could stop at the garages ridge line and just flash in the side of the new roof.

If not then I'm clueless


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