Underlayment on Overlay

I see a lot of contractors past work and notice that they often install an underlayment when doing an overlay. I kind of feel like it’s not necessary when there’ll be a layer of shingles down already. I was thinking that if I use 30lb the new shingles will lay flatter. This upcoming roof is 3-tab so it will lay flat anyway. Codes don’t really apply here because we’re doing this on an Indian reservation. Do you guys use an underlayment when adding a second layer?

Underlayment on an roof over is a waste of time/money. No it won’t help your new shingles lay any flatter.

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Second that, and unless you cap nailed it would just make the job more dangerous because staples will not hold to shingles.

Thanks. I felt like it was unnecessary. I’d say most people do that though here in the North West. I bet my guys are going to want to put it down when they do this job.

I’ve seen people cut the old shingles back to the barge boards and remove the old metal. Then paper on top, install new metal and then new shingles. That way the old layer isn’t visible. (but omit the paper)

Cut back 7" minus overhang which should be the old starter course and 12" of the exposed shingles. Eliminates the 4 layer hump from the old starter/old roof. The 1st course of new shingles will have a 3" exposure, but will lay smooth.

I personally don’t believe in taking any extra steps if I’m doing a shingle over. I usually do maybe 5 a year tops (yeah yeah, i know they aren’t ideal) and the conditions need to be about perfect (laying flat/no less then 6/12 /very little flashing details/no signs of any bad wood/ect) but even then I make it clear to the homeowner its still not my preferred method.

If that’s what they choose I am not going out of my way to hide the fact that its a roof over. I’m not gonna be removing an old drip edge and replacing it with new. I’m not gonna be cutting any old shingles from the edge so you can’t tell is now double layer. You won’t be getting any I+w anywhere. I will add new flashing so I can guarantee things won’t leak but that’s the only upgrade you get. If you want a better job then don’t choose a roof over (I tell people this upfront).