Old school calls them "books" or "starter books". The shingles that create the step pattern.
MOST typical architectural laminates have some cut off pattern like full, full less 10-1/2", full less 19" , etc. Honestly I have found that as long as each cut butt seam is offset by 6" or more, it's go time. Stray from the wrapper directions at your own risk :whistling
I have done pre-cut "books" and I've cut them in place as well. We have done apartments where I cut through whole bundles at a time with a powered cut off saw to make "books"
One needs the right blade, but it's really fast,
really fast. But that was a situation where we had enormous runs, and lot's of them.
And we start a full shingle, cut off about 6"(save), cut off about 12"(save), cut shingle in half (nail on half, save half), nail on 12" piece, nail on 6" piece, drop to bottom of run. Shingle up to rake and repeat the cut process using the left over half every other time. Or just have a book at the rake edge every time you hit it.
Sometimes I cut these books in advance. It is actually faster this way if you work it into the routine. The guy running the step never has to get out his knife and just stays down shingling. Like I said if you work it into the routine. You don't want the crew standing around waiting the for the "books" to be cut. In practice, typical residential roof, they are more likely to be cut as you go.
As far as making straight cuts for the rake, well each guy handles a knife a little differently and sloppy edge cuts are unacceptable so it's usually a better mechanic starting on a rake.
If they get cut in advance I use a straight blade and cut the back of the shingle using another shingle as a straight edge guide. Usually I try and do enough "books" to complete the whole rake before the guns start bangin'. In warmer weather a hook blade from the front of the shingle works fine.
Following the exact measurements for the cut offs given on the wrapper might make some feel better. If they are followed, the cut offs can be saved to fill in the opposite rake as the side is completed. Since I have already 'splained how I do it, filling in the opposite side is, full shingle cut to fit (save cut off), full shingle cut to fit (save cut off),etc. As soon as a cut off fits to finish a row it's used. Then follow with the exact same procedure. I can do the side of a gable roof with almost zero waste, I mean
almost zero.
You can step off a valley too, but usually the step off runs differently than the actual valley angle. Following the valley exactly doesn't allow enough offset.
Recently did a metal roof on a job where the shingle crew (not mine) installed an IKO Royal Estate. This is a laminate, but has a pattern that has irregularly spaced cut outs. On a shingle like this it's best to follow the exact layout specs from the manufacturer. The shingler did not. There were a lot of stacked lines going up the roof and it looked awful. Well when I looked at the product on the IKO website, I found they look like crap on their promo pics as well :laughing: Never liked IKO anyway.
So know your product and its limitations.
