Hello,
I read the archives on valley flashing and got thoroughly confused, so I thought I’d post my specific questions.
Redoing a 4:12 roof at 7,600 feet in snow country. Back (no valley) done with new decking, 100% ice & water shield, 15# paper for lay lines, 50 year composite shingles.
Front has two valleys at the California addition. A friend in the trade helped with installing a new girder truss and rebuilding the California, but he put the valley directly on the decking, nailed it through, and put the ice & water shield over the valley to about 6 inches from the W ridge. I’m tempted to tear off his flashing, lay the ice & water shield down the valley, and overlay some of the existing ice & water shield so everything sheds correctly.
[Edit: Turned out my friend did it pretty much the way described below. However, I had to replace flashing on one side anyhow, so the discussion was very helpful.]
My questions have to do with the flashing installation.
1. I gather that I should lay the flashing on top of the ice & water shield and 15# paper, and side nail or clip it, with only the shingles on top of the flashing. Is this correct?
2. For the top where the two valleys meet, should I have a sheet metal shop make a cap (the California’s ridgeline ends about 20″ from the main ridgeline)? Or, is there some trick for setting the shingles over the W ridge without it looking like crap?
Thanks,
Curtis
Edited 7/31/2004 7:01 pm ET by BADDOGLT
Edited 7/31/2004 7:01 pm ET by BADDOGLT
Edited 8/7/2004 10:32 pm ET by BADDOGLT
Replies
Yep. The way you propose is the best way to do it. Or another modification would be to run the ice and water shield over all, then a 15# slip sheet down the valley, then the copper W, than run your 15# paper on the rest of the roof, overlapping the W.
One question is on the edges of your W - is there a return hem? or a bare edge that is nailed down. I've used both. With the return lipped up along the edge, there should never be any nails driven into the metal. That way, any water that backs up in the valley will be caught on the hem and return to run down the valley metal. a hole from a nail there is a possible leak.
But that is a practice from wood, tile, and slate roofing. When you do it that way with asphalt shingles, the hump will telegraph through the shingles to look a bit ungly or uneven. Some people don't like it. So then, we make the W with no retrun along the edge, nail it right down along that edge, and seal it in to the undrelayment in one of several ways. For you, it would probably be easiest to cut six inch strips if the ice and water shield, or if Vycor is available there, buy it that size and lay it on the nailed edge with half on and half over.
The way your buddy did it has two probnlems. First - it depends entirely on the seal between the bituthene and the copper to stop all leaks if water backs up. Since no seal is perfect when it is under water - or ice - it would probably find a way to leak in the next fifty years.
second - Assuming that the nails in the sheathing are steel of some sort other than stainless, there is a chance for galvanic reaction to weaken the copper at points where the copper and steel are in contact or near-contact, depending on a few other variables .
BTW, what sort of ventilation, insulation, moisture control system do you have designed?
For the ridge cap, you can have a piece made, buy lead sheet and pound it in, make one yourself from scrap of copper valley, or shingle it over.
To do the latter, I start my ridge at the valley intersects byt slitting a ridge cap halfway on the break line. The twin wings that flare out get slipped up under the shingles on the main roof. Then the next ridge gets only about a two inch slit and flare. Then the next piece is normallon out to the gable end, where a couple fine heads are used to tack the top piece in and caulk over the nail haeds. Thios way, the flaps of the ridge are facing solid roof and they are less prone to catch wind and blow off.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
"One question is on the edges of your W - is there a return hem? or a bare edge that is nailed down."
The one that is there now has a return hem. I was concerned about the bare edge cutting the underlayment, but if I use your idea of a slip sheet, I may switch to a bare edge. It's not copper, so switching will be cheap.
"...and seal it in to the undrelayment..."
So, basically seal it to the slip sheet or the 15# if I skip the slip sheet?
"...what sort of ventilation, insulation, moisture control system do you have designed?"
Continuous soffit vents, durovents between each rafter pair, oversize gable vents (California and one gable on main house, garage is its own airspace), and the California has a lot of air flow to the main house. The living room (where we put the girder truss) now has R-30 between (and above) the 2x6 joists with a oversize chunk of R-30 above each IC canned light. The rest of the house has an assortment ranging from bare sheetrock (where there was wet R-13) to R-19. As the remodel progresses, everything gets R-30.
If the attic is still too warm when the insulating is done, I'll put an exhaust fan over the main gable vent. Ruled out a ridge vent as we have several feet of snow on the roof for months but being in the Sierra can get rain on top of the snow, and I was paranoid about leaks or blockage.
Thanks for your help. I'll be removing the old flashing and laying bituthene in the valleys today.
- Curtis
Edited 8/1/2004 12:51 pm ET by BADDOGLT
If you are going to reseal the edges of the 'W' with I&W-shield, you do not need the slip sheet between it and the underlying I&W. Or, you would need to slice the protruding portion of it off so that the 6" tie-in is sticking directly to the underlying I&W.
sounds like a decent vent and insulation pachage. The reason I asked is that it is important to vent and or seal since the I&W will stop breathing at the sheathing level entirely.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!