[Clutchcargo]

I'm tying in a new roof to an old using valley boards. Is it acceptable to attach directly through the old roof shingles or is it better to remove the shingles down to the underlayment?

 

[Gary in WA]

For the best connection, remove the old roofing. You will be weaving the old in with the new and have to remove it anyway. Some notes on valleys, use them or not. The v.b. has to be bigger (wider) than the jack rafters bearing level cut. You may have to use a 2x8 and a 2x6 next to each other as a v.b. to fully support the rafter's heel cut. (Especially low slopes). The Valley jack rafters need to be tied together (opposing pairs) at their heels, just above the old roof, to act against spreading. (Rafter ties).
The nailing at perimeter line of valley over frame is critical and always on the engineering papers. e.g. 3"o.c. row at apex of valley board and 3" o.c. at old roof sheathing. (Positive tie shear-flow nailing). Ask me if you need some tricks for valley placement. Be safe, G

 

[Clutchcargo]

Thanks GBAR, helpful as always.
I've got a book that shows the framer putting the ridge in first and then butting the v.bs. next to the ridge. Does it make more sense to put the ridge on top of the v.b. and nail the ridge to the v.b.?

The nailing at perimeter line of valley over frame is critical and always on the engineering papers. e.g. 3"o.c. row at apex of valley board and 3" o.c. at old roof sheathing. (Positive tie shear-flow nailing). Be safe, G

Let me get this right, 3" o.c. at the very highest point of both valley boards down the butt between the two valley boards into some structure in the house, correct? The ridge falls between two old rafters so I need to add a header between two old rafters so that I have something to tie into.
What does "3" o.c. at old roof sheathing" mean.

Ask me if you need some tricks for valley placement.

I was going to run a chalk line from the heal of the ridge to the inside edge of the top plate to get my placement.
Any words of wisdom are greatly appreciated.

Edit: Also how far down the roof does the v.b. go? Correct me if I'm wrong but I think that it does not need to go all the way to the top plate.

 

[Gary in WA]

Does it make more sense to put the ridge on top of the v.b. and nail the ridge to the v.b.? **** The ridge is easier to figure placement by putting in first. The simplest way is string a line over the common rafter tops at the peak from about 15' back away from the old roof. Mark the spot, clean the old roof there, check it again, mark it. Drive a nail there with head sticking up 1".
Put end of chalk line hook on nail, go to the intersecting of old roof/valley. Put a straight-edge or string across rafters as ply would lay (right angle to rafters) and mark where it hits old roof. Remove old roofing there and a little above. Snap the chalk line on old roofing for valley outline. Remove roofing there and other side for valley, 2'-3' slot. Re-snap chalk on old sheathing.

While at old roof/new valley line, lay a short 2x (1-1/2") next to the line, but lower down the old roof and under the straight edge. This is to allow for the valley material thickness and still have the tops level with the common rafters plane. 2-3" lower from the line snapped for valley to keep planes level. If you installed v.r. on the first line it would be higher than the commons by 1-1/2" vertically. Snap a new line parallel to first line for the top edge of valley board. (Dropping the valley it's thickness).

Install the ridge to the shorter apex lines, not the first line. Layout ridge from last common starting there. Install valley boards, in pieces if needed, break joint on house rafters. Check last common for straightness, or use 2nd common back. Hook tape measure on common, across the roof as ply lies, and mark layout of next valley jack on top edge of valley board. Move tape-m up about 2-1/2' and mark second v.jack, which will be 24" farther on tape-m. Then simply measure length of v.jacks and write it on ridge side, big- so read from ground. Remember as cutting if short point or long. Cut shorter (opposite sides) jacks from waste of longer jacks. Always cut heels in center of boards, to use the waste heel for opposite side, shorter jack.

After installing jacks with full support under by valley boards, install a 2x6 under the ridge, flat, sitting on v.b.'s for ridge support. Install 1x4's at every pair of jacks, to tie opposites.

Sheath commons in stair-step pattern, as many full sheets as possible, right to the ridge, starting from end away from valleys. Then sheath over the valleys, using the first caulk line for measurements. I find it way easier to fill in the valley sheathing starting with the ridge ply first. Always write the measurement of the width first, like in window sizes, so not to get confused. eg. Square right, 54"x7-1/4" = Ply is 48" on right side (up and down the rafter), 54" across the top (8'way), and 7-1/4" across the bottom (8'way). Your strength grain of ply or osb will never get installed wrong.

The 3" is ply nailing, along the valley board and along the old roof sheathing. The v.b.'s just nail 3-16d's into old rafters every time they cross over one.

Be safe, G

 

[Clutchcargo]

Thanks GBAR,
Lots of detail here and took some concentration to picture it all.
One thing I can't wrap my head around is the flat 2x6 under the ridge. Could you explain?

After installing jacks with full support under by valley boards, install a 2x6 under the ridge, flat, sitting on v.b.'s for ridge support. Install 1x4's at every pair of jacks, to tie opposites.

The 1x4's are rafter ties, correct?

 

[Gary in WA]

The 1x4's are rafter ties, correct? Yes.

the flat 2x6 under the ridge. Picture the ridge installed, the v.b. running up next to it, on both sides, nailed. The ridge needs support as it's only bearing on the old roof's sheathing.Install a cross support, at right angles to the ridge. Shove a 2x under the ridge, across and bearing on the v.b.'s, like a +. With the vert.. part being the ridge, the horz. being a 2-1/2' or 3' 2x4.
This carries the weight of the tip of the ridge, transferring load to the v.b.s., as the 1x4 tied rafters carry themselves.
Be safe, G