When 5/12 Becomes 4 1/2 /12

katoman

We're putting a small addition on an existing home. The addition roof is a simple hip running into the existing hip roof. Well they didn't support their hip rafter, and after 40 yrs, it has sagged. It was origionaly a 5/12 pitch but now due to the sagging, it has become a 4 1/2 /12. No big problem, just slowed me down a little as I had to re calculate the cuts.

I made sure the hips were supported.

ClemS

half inch different in rise per foot would mean a 4" dip per 8 foot run. that's some mean drop

Warren

If its a 4 1/2 at the lower half, wouldn't that make the upper half a 5 1/2?

ClemS

odds are he is tying into the lower half, trying to plane out losing part of the hip.
i would still cut 2 pairs of commons to the true pitch, pinch the ridge off, then cut them down to bring the ridge to plane. un-pinch and cut the rest.
the biggest PITA about tie-ins like this is the ceiling height. older rafters are almost always undersized, so you're stuck doing the same or cutting an extra deep birdsmouth, which amounts to about the same thing.
I still prefer the deeper birdsmouth approach. I remedy that by spiking the crap out of over-notched rafters to the ceiling beams.

knucklehead

It ain't possible The ridge and the bird's mouth would have to remain the same.

How do you know it was a 5/12?

Warren

Think he is talking about the droop in the middle. Obviously the top and bottom would remain the same.

Warren

Clem is talking about using a bigger rafter, say a 2x10 wher a 2x6 was used originally. This would result in a "deeper" cut at the birds mouth. Same seat cut just more material removed

ClemS

correct. problem is, most architects don't bother peeking into the attic to see how the roof is framed, so they spec the rafters to current codes. if my plans show 2x8 rafters and the existing house has 2x6, and i'm matching plates then the 2x8's are getting hacked out at the seat.
different situations may pan out differently, and if i'm able to lose a couple of inches on the ceiling I'll frame my walls down enough to not destroy my rafters.
the worst is when they want you to tie in with a true valley, showing a double 12" lvl for the valley and the existing framing is 2x6. there's barely anything left of the poor thing

katoman

Checked the rafter tail with a short piece cut 5/12, it matched, but the existing birdsmouth was off the plate about 1/2" at the front of the plate, due to the sag. Yes, I was tying into the existing hip to match the plane in the roof. I suppose the pitch actually changed depending on which part of the sagged hip you were to measure against. But used a 4 1/2 and it matched bang on. Looks like part of the origional roof.

Side note - the architect had called for a 5/12 based on the origional.

For more entertainment read my next post which I will call "Brain Teaser",from the same job.