Thread: How deep is the birdsmouth cut in a rafter?

The depth of the heel cut is determined by the pitch and the width of the plate the rafters will sit on. The sole of the birdsmouth should only be as wide as the plate it sits on.

The hip is usually higher than a common rafter, but the effective pitching point is the external edge of the top plate, so once you have the relevant angles just extend the sole cut to suit the diagonal of the corner.

Make sense?

Thanks Termite
Is there a maximum % of rafter depth you should go, so as not to weaken the overhanging rafter? Should I add a top plate width input, and calculate from that, but if the plate is wide, and/or the pitch steep, only up to a point ehere the heel depth does not go to far into the rafter?

OK,
THANKS A LOT YOU GUYS!!!!!

You now have me thinking;
and in the $71nk1n6 HOT Weather.

What is the angle at the end of the ORANGE one, [The HIP One ]
where it fits onto the Rafter and Ridge Meeting Point.

Is it 45* on both sides and slopes back. Or a little less than 45*?????

I know what I mean,
can someone interpret.

Originally Posted by Blocklayer

Thanks Termite
Is there a maximum % of rafter depth you should go, so as not to weaken the overhanging rafter? Should I add a top plate width input, and calculate from that, but if the plate is wide, and/or the pitch steep, only up to a point ehere the heel depth does not go to far into the rafter?

from the AS 1684.2 1999 residential timber framed construction.

7.2.11.2 Rafters may be birdsmouthed to a depth not exeeding one third of the rafter depth.

but this needs to be read in conjunction with 7.3.13.2 & 3 and refer to figure 7.28

just noticed where you live, I quoted from the non-cyclonic areas, you should refer to the cyclonic areas standard. there may be a difference

Cheers Ian

The angle is the plumb cut (sometimes pronounced plump cut) of the pitch, with each edge cut at 45 deg to suit the first common rafter and the king rafter.

The king rafter is the long rafter in the middle of the hip end. It is also half the thickness of the ridge longer than a common rafter.

Are we having fun yet?

Bloody hell lads, its been thirty years since I cut and pitched a roof.

Your doing fine Termite.
Just relax...
Breath in,............... breath out...........:eek:

Al

Originally Posted by Ian007

just noticed where you live, I quoted from the non-cyclonic areas, you should refer to the cyclonic areas standard. there may be a difference

Cheers Ian

A hell of a difference, mainly involving metal straps to tie everything down.

In the Philippines the GI sheet (What we know as corrugated iron) is held down to the rafters and purlins with a 1" wide metal strap rivetted each side to the sheet, and I mean 3/8" shaft rivets peened over with a hammer like the old days.

Thanks Ian007, I'm looking for that stuff now.
Termite, the way the calculator is set up now, the common and king rafters are the same length and the ridge is longer by its thickness, which is how its shown in my book. Whats the go?

Originally Posted by Blocklayer

Thanks Ian007, I'm looking for that stuff now.
Termite, the way the calculator is set up now, the common and king rafters are the same length and the ridge is longer by its thickness, which is how its shown in my book. Whats the go?

That's the most practical way to do it, even though you end up with a poofteenth of a degree of incorrect pitch, but I was quoting the theoretically correct way as she are taught at tech. and thats farther back than I care to remember.