Need help with a gable roof.

[Micah]

Im gonna be getting back to work on my little 8x8 cabin/shed and I have everything figured out excpet the roof. Originally I was going to go with a shed roof. After I got thinking about it I changed my mind and want to learn how to do a gable roof. I did alittle searching and I have the gist off it. I even practiced hand cutting birds mouths. Here is where I need help. Im not sure how to caculate the pitch and what angle I should cut the end where it meets ridge board. The building is 8x8 and I would like the to be around 3 to 4 foot above the wall. Is there a good how to online that goes in to detail about building gable roofs?

[MountainDon]

I have used this calculator with success.  You can input various data and it will draw a rafter, etc.


http://www.blocklayer.com/Roof/GableEng.aspx

[Micah]

Thanks Don that is a wonderful caculator. Told me everything I needed. One quick question about cutting the birds mouth. What would the foot cut be?

[Redoverfarm]

Maybe this will help

http://www.builderbill-diy-help.com/rafter-cuts.html#toc5

[MountainDon]

Well, to tell the truth I get more confused with the names that are used for all the cuts than by most anything else. It does not help that the same thing receives different names in different sources. One man's seat cut is the same as anothers foot cut or anothers level cut.    I am a visual learner  That's one thing I like very much about that calculator page. I can insert different numbers and see how it affects the output. As long as I know what I'm doing I don't care much what it is called by anyone.

One important thing to remember when planning out a rafter that has rafter tails, or an overhanging eve. That is do not make the birdsmouth cut too large. On the rafter drawing in that calculator there is a line or measurement named "HAP" which is Height Above Plate. If that line measures 9 inches, then the amount cut out along that line should never be more than 1/3. The more the overhang the more important that is as the HAP is directly proportional to the strength of the overhang; how much snow load it can hold for example.

[Micah]

Im with you MountainDon  have to physically do it in order to fully understand what it is im doing. My over hang is only going to be 8" that way I only need 3 pieces of sheeting to cover the how roof. While we are on the topic of the eve's. Is there any advantage to do the tail cut/bottom plum cut? I cannot picture what the need for it would be.

[MountainDon]

Is there any advantage to do the tail cut/bottom plum cut? I cannot picture what the need for it would be.

Gutters. It's easiest to hang gutters if you have a plumb fascia.  And some folks prefer plumb cut tails as far as aesthetics goes.

[Micah]

I probably wont be doing gutters. Only a drip edge. I think I cut them anyways. Lord knows plans NEVER change!

[MountainDon]

You need the drip edge one way or another to help preserve the roof sheathing.


I was never going to do gutters. I am now designing some angle mounts to try as a trial.  

[Redoverfarm]

Don I ran across some info on putting gutters on metal roof and not having the snow take them away.  It is sort of like a flat plate that extends halfway onto the roof and half way over the gutters.  It allows the snow to just slide over the gutters but also allows the rain water to run under it.  I will let you know when I get more info.

[NM_Shooter]

Hey Micah,

If you are unsure of how to cut the joists, get some of that brown contractor's paper at Lowe's, and tape it down on a hard surface... garage or kitchen floor... whatever.  Draw everything out to scale (starting from the top plates of the side walls) and you can make a template of you birdmouths and transfer it onto the straightest joist you have.  Cut that joist to the exact size, then use that one joist as your master for marking the other joists.

You can also measure and mark out your gable end framing components too.   

Drawing it out full size is an easy way to cheat! 

Good luck! 

Frank

[ced257]

 One of the easiest ways to do it, is set your ridge first. Figure out how high you want your ridge and what looks good to you and set it. Then set your rafter up to the outside of it and and to the side of your wall plate at the bottom and scribe the rafter. Cut one or 2 and make sure they fit at both ends. If they do then, cut your rafters to one pattern. If not, then adjust them to fit as best as you can. If everything is square and level, you shouldn't have any problems.
  To figure about what pitch you need. Take the building width, divide it in half, in feet. Figure how high the ridge is from the top plate, in inches. Divide the height of the ridge, in inches, by the width of the building, in feet.    8 foot building divided in half gives you 4 foot. You want the ridge at 4 foot, which is48 inches. 48 divided by 4 gives you 12. Your looking for a 12 pitch cut...Aka the easiest one to figure. Everything is 45 degrees.
  To figure rafter lengths on a regular calculator, remember pathagreom's theorom. A squared+B squared= Csquared. Figure everything in either feet or inches. If you did like did the first time and figure part of it with inches and part with feet...... you come up with some wild measurements. If you got the run of 4ft and the rise of 4ft. then you got 4x4+4x4=32 square root that and you got 5.6568 ft. which is 67.8823 inches, which is roughly 67 13/16 or 7/8. That is your rafter length from the long point of your rafter to the top of the plumb cut of the birdsmouth. You still have to add your overhang to that. One more thing, you'll have to take out another 3/4 inch for half your ridge width if you go with a 2x ridge.
  I'm alot better at showing then telling someone how to do something. I hope this hasn't confused you! Best of luck and once again I hope I haven't done more harm than good here!