I replaced a damaged shingle. I damaged a few more trying to loosen the one above the damage. So I ended up replacing 3 rows.

Starting from the bottom I nailed the sheets. When I got to the last one, there was not enough room to lift and hammer nails. I slit that shingle so I could lift the smaller portion to get a nail in there. After driving the nails under each flap, I covered those nail heads with cement and smeared more under each to press each flap down.

The alternative would have been not to nail that top row and just use cement.

What is the proper technique when you get to that last row?

Also

Laying side by side, are the sheets supposed to overlap on the sides? Or just lay flush with each other?

The section I had to replace was slightly larger than a full sheet... instead of removing another full sheet next to it I cut a smaller piece to cover that difference. Was I supposed to replace them in full sheets or is cutting one small (in this case about 6-8" width) acceptable?

And finally,

I am concerned that when I was done the new installed shingles could be lifted by hand where the rest of the shingles on the roof where tightly sealed down. I assume that it needs the heat of the sun to "glue" them to each other. I wasn't sure so I smeared some roofing cement under each over lapping layer.... Is that the proper technique?

Im a little nervous after attempting this for the first time.

 

The shingles lose their flexibility over the years. That's one of the reasons why it might have split when you lifted the last row. I had a boss who described that as "turning to cornflakes". That & the other problems that you described are common during patch work.

 

Under the right conditions, shingles will seal down by themselves, provided enough sunlight/heat are present to melt the applied sealant on the underside of each shingle. It never hurts to hand-dab roofing cement to hasten the process along. For the last row, some people will nail through a few overlying shingles to ensure nails are holding them, followed by dabbing the nail heads with roofing cement. Best to nail between gaps if at all possible, using a drift pin for the last few blows to avoid damaging adjacent shingles. And no, adjacent tabs aren't supposed to overlap--the overlapping part is accomplished by the course(s) above.

 

The biggest mistake I made I am realizing now. My eyes were playing tricks and when I put the new sheet it appeared to not be as thick as the rest of the roof. I doubled up on one of the sheets in my repair... so there is two layers of shingle on my repair. The repair spot looks a bit bulged to the rest of the roof.

Is adding that extra sheet on top of another going to cause a leak?

Also, I didn't realize I had to pull the clear strip off on the shingle before installing.... I installed them with this strip in place. How bad is that?

 

The clear strips don't have to be manually removed. The sun's heat causes them to disintegrate. If you can live with the appearance of the doubled-thickness of your repair, good for you. I know I couldn't, and would redo it correctly.

Another reason for perusing this or other DIY sites before tackling something you've never done before, instead of after.

 

When trying to push shingle up into the overlapped one above..... if the shingle will not insert all the way to the white line(half way exposure point) is it acceptable to trim the shingle?

If I were to redo this, or just in general, what do you do with the old nail holes? Im not exposing the wood (the tar paper is below) are you supposed to cover the holes with roof cement on top of the tar paper?

and finally, if the area you need to reshingle is say the width of an entire shingle sheet and say a quarter of a shingle sheet more... is it proper to cut a full sheet to that quarter or are you supposed to remove a whole another panel and keep them all full sheets?

 

Since you went with double-thickness on the replacement shingles, I can't tell you what to do to enable full penetration under the above courses. Trying to slide 2 shingles where just 1 will fit (and is needed) doesn't make any sense. You could also be hitting nails when sliding the shingles. It's your roof, so feel free to cut and trim as you see fit, both vertically and horizontally. And fill any nail holes with roofing cement too.

Keep in mind if you wind up with a real butcher job, come time to sell the place could cost you. A buyer's home inspector is likely to spot abnormalities that don't belong on a roof. Especially if it looks like someone is trying to hide something.

 

My question remains. Is it not standard to cut vertically or horizontally or fill nail holes?

 

Let's go back to the beginning. Did you have a water leak or did you happen to notice a few damaged shingles & decided to replace them? How old is the current roof?