rafter/bird's mouth cut problems
Beau
am building. I am clearly doing something fundamentally wrong and I
am hoping someone can point out what that might be.
The shed is 120" wide and I am looking to build a shed with a 9/12
pitch with a 12" overhang. I am using a 1 by ridgeboard that is
mounted dead center, level 45" about the top of the frame (5' per
side, 9/12 pitch, 45" height ridgeboard, right??)
I then take my framing square and step off six steps using 9" on the
tongue and 12" on the body. On the sixth step I mark the angle on the
tongue as where the rafter will hit the framing. I then flip the
square putting the body at 12" on the top of the mark of the outside
edge of the wall and the tongue at 9" and then mark the angle along
the tongue to get the tail cut. I mark the underside of the body to
get the level cut of the bird's mouth cut.
I then go back up to the plumb cut, mark 3/8" off and redraw the line
to take in account the ridgeboard thickness.
What am I doing wrong? I have double checked this a million times and
when I try and mount the rafter, the bird's mouth is about 2" off.
BP
the top of the frame (5' per side, 9/12 pitch, 45" height ridgeboard,
right??)
Nope. The ridge will not be 45" high. The 45" height will occur at a point
parrellel to the top of the rafter, as it starts from the outside edge of
the wall at the top of the birdsmouth. You are using 2x6's, so you are 2"
too low. Lay everything out on the ground and take an exact measure to get
the ridge height.
"Beau" <beau_a...@hotmail.com> wrote in message
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Dan - News
news:c54f6042.02070...@posting.google.com:
You should also probably raise the top point of your ridge for the
thickness of your rafter (or what is left after you cut your birdsfoot) or
else you'll wind up with less than a 9/12 pitch. This could account for the
difference
45" at a 9/12 pitch puts the top edge of the board dead even (no wood
left for your rafter overhang) with the top of the wall at the outside edge
(a 75" board minus half the thickness of your ridge board which you say is
3/8, but you probably meant 3/4"?)
Dan
--
There are three kinds of men:
The one that learns by reading.
The few who learn by observation.
The rest of them have to pee on the electric fence for themselves.
Will Rogers
Jack
As was pointed out, the height of the ridge board is wrong. 45" is right, but 45" from where?
Not the top of the plates. You would need to start your measurement at a point above the top of
the plates that is equal to the distance from the top of the plates to a point where the top of
the rafter intersects the outside plane of the wall, in other words, the plumb cut of the
birdsmouth projected on through to the top of the rafter. Measure that distance and add it to
the 45". That will give you the very peak of the roof.
To accomodate a 3/4" ridge, drop it down a fat 1/4". That's about the drop in a 9 and 12 roof
for a 3/8" run (half the ridge board. That should be the rough height of the ridge. If this
gives you a gap between the plumb cut of the birdsmouth and the wall, simply raise the ridge til
the rafters opposite each other are tight to the wall. Careful not to pull the walls in at the
middle. They should be braced first. Conversely, if the rafters are too tight, lower the ridge.
Best way is to clamp the ridge to two temporary pieces of 2x that are toenailed to the plates at
at point that is 3/8" off of midspan of the rake walls. The you can clamp the ridge to these two
sticks and lower or raise it with ease.
Jack
Kim Whitmyre
when I try and mount the rafter, the bird's mouth is about 2" off.
The simplest way to solve the problem is to draw the rise and run to actual
scale on a sheet of plywood (or anything large enough): mark the width of
the top plate, and draw the ridge board in place. Take a piece of rafter
stock and lay it so it is in location on the plate and ridgeboard: mark
your cuts, cut this piece and use it as a pattern for the other rafters.
Your problem is probably caused by the width of the rafter. . .The
"theoretical" line is thru the center of the rafter, but you are using the
edge of the rafter as the "measuring" line. At any rate, do what I suggest
above and you will get it right.
Kim
Bripen
Strong-tie metal connectors that eliminate the need for bird-mouthing.
They work great.
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sean
sledgmb
"Beau" <beau_a...@hotmail.com> wrote in message
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koukalaka
Put the uncut rafter in place against the top of the ridgebeam and resting
on the top plate of your wall.
place a nail in the ridgebeam under the rafter so the top of the rafter is
even with the top of the ridgebeam this may mean driving the nail in the
bottom of the ridgebeam at an angle so the rafter can sit on it.
then take a scrap 2x4 and place it on the side of the ridgebeam so it covers
the rafter and scribe a line on the rafter.
now cut that line and thats your top angle
for the birdsmouth you will need to tack the rafter to the ridgebeam with a
nail as it will be for install.
dont drive the nail in all the way cuz you will be taken it down in a minute
now take a framing square and place it so its long edge is running up the
side of the exterior wall and continue that line of the wall onto the rafter
(l1). now do the same on the interior side of the wall (l2)
now turn the Framing square so its on the outside of the wall with the
inside of the inverted L running up that line l1 and the short end is
pointing into the shed. Bring the short end of the framing square down to
meet the point where the interior line (l2) starts on the rafter at the
bottom and you will have your birds mouth triangle. (l3)
you may need to adjust it an 1/8th or a degree but it will be close enough
to use as a template for the rest once you cut it.
friken ascii art
l1 l2/
| | /
/ |_ l3_|/
/ /____
/ / | |
/ | |
| |
| |
bob marencin
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