Rafter Cutting

[TheWire]

I'm hoping to be putting up rafters this weekend and have a couple questions.

1. The pitch of my 20x32 cabin roof is 9/12 and in order to get full bearing on the 2x6 knee wall plus the ½" sheeting, the bird's mouth cut will be halfway into the width of the 2x8 rafter.  I'm having a 1 foot eve over hang.  WI Code says "Bird mouth cuts may not exceed 1/3 the depth of the rafter unless the seat cut bears fully on the wall plate."  I'll have full bearing so I should meet code.  Any one see any problems with my approach?

2. I have the choice of cutting the lower rafter ends before I put the rafters up or doing them after by snapping a line and cutting them all even.  My walls are within 1/4" of perfectly straight.  Any thoughts on pre or post cutting the rafter ends?

Thanx,

Jerry

[MaineRhino]

I precut all of mine. The layout was very easy, I used a program called Easy Rafter.

It would be easier to precut at ground level than in the air.

[PEG688]

1. The pitch of my 20x32 cabin roof is 9/12 and in order to get full bearing on the 2x6 knee wall plus the ½" sheeting, the bird's mouth cut will be halfway into the width of the 2x8 rafter.  I'm having a 1 foot eve over hang.  WI Code says "Bird mouth cuts may not exceed 1/3 the depth of the rafter unless the seat cut bears fully on the wall plate."  I'll have full bearing so I should meet code.  Any one see any problems with my approach?

2. I have the choice of cutting the lower rafter ends before I put the rafters up or doing them after by snapping a line and cutting them all even.  My walls are within 1/4" of perfectly straight.  Any thoughts on pre or post cutting the rafter ends?

#1: You should have about 4 1/2" of rafter tail left with a 12" soffit you should be fine.

#2: Now on this one  within 1/4" , for me would NOT cut it. The walls need to be pulled , or pushed to within less than 1/8" , I'll give the thickness of a string line , no more on my own jobs. I pull a dry line from corner to corner using 1/2" or 7/16" OSB or CDX spacers , yes the line needs elevated about the wall plates just a bit , I string line inside the walls , the line very tight. Then use similar blocks to check your walls . It's not that  hard to get the walls straight.

That 1/4" is gonna fight you and "telegraph" itself every where and exacerbating ALL other differences , such as rafter width , they will vary  from any where to 1/8" to 3/8". All those "little " differences will add up.

  As far as cutting the tails , I Rarely ,  Rarely do. Again crowns , width differences etc all will telegraph right out to the fascia , In fact the tails are where it all "shows" the most. Sometimes I re-cut even "truss package" tails , depends on how good the truss company did thier job , BUT you know no one (except the building crew) remembers who cut the truss package , BUT they do remember who framed / built the place.

YMMV         

[JRR]

A tip for rafter pattern making: 

First, make a pattern-rafter using scrap lumber.  Make the ends of this rafter out of scrap plywood.  Cut the plywood pieces to exactly match rafter heights ... 7 1/2", 9 1/2", or etc, etc.  Use (pieced-together) 2x's to hold the end pieces apart at the correct length to match the rafter stock.

Now use this piece of cobbled-together wood to make the trial measurements and cuts.  When it exactly fits to the bearing wall and to the ridge beam ... you have your pattern. 

A lot better than crying after you have wasted an expensive piece of rafter stock making a bad cut.