I'm building a 1 1/2 story 20x30 camp from Johns Plans. I will be installing the rafters and ridge board soon. I'm using 2x8x16 rafters and a 2x10 or 2x12 ridge board. I will add collar ties also. I plan on using the entire 2x8x16 for the rafter and just leaving the over hang be what ever is left. Can someone do some clcualtions for me. I did them by using Wagners Framing book. I don't have the #s handy right now. I know my top cut at the ridge board is a 45* since it is a 12/12 pitch. Where should the birds mouth be and how deep? Where should the plumb cut be for the end of the rafters? How high should the ridge board be?? Thanks Pete.
I'd lay them out on the floor with a chalkline if I was doing it, Pete. I like that better than calculating it. Birds mouth about 1/3 of the board as I recall.
Others probably know better than I though.
Length per foot of run is 16.97 or about 16 15/16" x 10 (1/2 the width of your building) = 169 3/8" or 14' 1 3/8" . Now reduce for 1/2 the ridge thickness which would be 3/4" = 13' 11 7/8" or 167 7/8" .
Birds mouth depth I'd layout a seat cut that was 5 1/2" or the width of your top plates , maybe 3 1/2" but I'm assuming 2x6 walls with the 5 1/2" seat cut.
Now the important thing is to measure in a straight line either at the top or bottom , OR a imaginary line at the point of the intersections of the heel and seat cut. Just don't measure across the rafter.
You can check yourself by "stepping it off" attach square buttons at both points on the square at the 12" measurement. And step off 10 steps , the first lines you made should jive up with the step off lines.
I bet that clear as mud isn't it :-[
Your overall height will be 10' less the left over from the seat cut to the rafter top measured along the 45 deg line of the heel , commonly called the heel height.
You are way too sharp for me, PEG. I guess that's why you get the big bucks. d*
Square buttoms , not set at a 12 /12 just on the square.
(https://i21.photobucket.com/albums/b299/PEG688/Jan111.jpg)
(https://i21.photobucket.com/albums/b299/PEG688/Jan11.jpg)
I highly recommend stepping it off , also cut one pair , two rafters and tack a scrap "ridge " on one , then you temp them up on your building. This is where you find out how accurate you where in framing the place. IF your plumb and square the cuts (IF you made nice true clean cuts ) should all just "come together" .
(https://i21.photobucket.com/albums/b299/PEG688/July251.jpg)
IRRC thats a 12/ 12.
See how the seat cut intersects with the inner top plate corner , IF your finishing the ceiling which I think you will be thats a nice starting point.
(https://i21.photobucket.com/albums/b299/PEG688/July253.jpg)
Those a 2x12 rafters , on a 2x8 don't cut it down so much your tail will be weak , leave at least 3 1/2" of "meat" at the smallest point IF you can't get that intersection that way as shown get it as close as you can while not making the tail to weak.
Thanks for the info. If I'm not using any gutters would you plumb cut the ends or just leave them square?? How do you figure the birds mouth??
Quote from: peteh2833 on September 15, 2008, 04:58:11 AM
Thanks for the info.
#1: If I'm not using any gutters would you plumb cut the ends or just leave them square??
#2: How do you figure the birds mouth??
#1: Thats up to you a looks decision. Personally I'd plumb cut them I like that look . I would NOT cut them to final length until all the rafters are in place , then measure square off the building to the desired soffit width on each end and snap a line across the tops , square or plumb down then cut . Makes for a straighter fascia line.
#2: Get a book called Modern Carpentry by Willis Wagner it has pictures to show the process. It sort of simple , but hard to explain to some one who doesn't know the terms / words I'd be using.
Link to book : http://www.amazon.com/Workbook-Modern-Carpentry-Willis-Wagner/dp/1590702034
I had some photo's but deleted them :-[ , guess I need to do a thread next time I cut a roof.
Crown all your rafters , make a pattern , mark all the rafters with the pattern. If you have help cutting them the same person should cut the same end on every rafter, so don't trade places where one person cuts the tails and one cuts the peaks. Once you start the same person should cut all the birds mouths or all the peaks.
G/L PEG
Thanks for all the help. Pete
Your welcome.
Remember to check you actual width at your top plates from the point the heel of the rafter will hit which MTL is the sheeting so IF your right on (20') framing to framing our rafters will actually be 20' 1" or 10' : 1/2" of run.
My Uncle and I laid out the rafter and birds mouth cuts today. On the birds mouth we made the cut 5 1/2 inches. We made the birds mouth 5 1/2 x 5 1/2. Is that ok? I think it is a 45* at the the birds mouth. It is 2x6 walls and top plate and 12/12 pitch with 2x8 rafters. Pete
Quote from: peteh2833 on September 24, 2008, 08:02:09 PM
Is that ok?
Depends, Pete.
Depends on how much of the rafter you actually cut away AND
how much of an overhang you have AND
what your snow load is.
???
(https://i133.photobucket.com/albums/q75/djmillerbucket/construction/foot-heel-cuts.jpg)
If you have overhanging eves the critical thing is that dimension marked "W" in the drawing. Note it is not the actual width of the rafter. It is the angled width across the "heel cut" line. The cut out portion should never exceed 1/3 if there is to be much load on the eve overhang.
Got any pictures? There are worth a thousand words on things like this.
note: "foot cut" is called "seat cut" by some. possibly a regional thing. just to make it all a little more interesting.
Thanks. We made sure that it wasn't more than a 1/3 of the angled width. The 12/12 roof with no gutters and probably a metal roof will keep the snow load to a minimum. We do get snow there though. The one year I went up to camp and there was about 2 feet on the current camps roof. About a 4 or 5/12 pitch roof and shingles. I got up there and shovled it all off. I'll try to snap some pictures of the rafter we made today. Pete
I have 2 sets of square buttons but limited knowledge of the framing square!
I knew we had something here.
http://countryplans.com/smf/index.php?topic=2177.0