couple things i would like to point out.
@Photo 1+2 with the low slope/rooted wood and the dip in the roof
For a pitch this low (2/12) you can get low slope shingles which have a seal strip on the bottom of the shingle and in the middle on the back of the shingle.
the purpose of the seal strip in the middle is a crucial factor when it comes to low slope, we need to think about water flow here that is all roofing is guys, so in order for your roof to leak what has to happen is where the seams of your shingles are "2 shingles butt together" the water has 2-3 inches of coverage from the seam to the top of the shingle underneath those 2 butt shingles before it will leak. there fore those middle seal strips prevent the water from back tracking up those 2-3 inches and helps cover nails that can cause slow leaks ICE AND WATER THE WHOLE LOW SLOPE so the ice and water metals around the perimeter of the nail sealing it off"BUT,! this is very important part" just because it has those seals you are not 100% in the right, what needs to be done is put tar manually across each row on the top part of the shingle in a solid line so the water has no way of back up! its water flow were dealing with people, lets pretend we are the water. low slope shingles u can ge away with just taring the seam area on the top but, would give it a hell of a job if you did a solid bead across the whole top.
Please ask a question if that explanation was confuses or didnt get the point out, i understand it can be confusing and i might not be the greatest at wording this stuff but, imma do my best for you.
@photo 1+2 still, the dips in the roof should be fixed (tear shingles up and replace boards/plywood so you got a flat surface to deal with)
@photo1+2 Inspect your attic insulation, the smallest bit that is exposed/ not insulated can actually cause problems and for low slope this is something that should be gone to a "T" poor insulation will have hot/heat spot sdin your attic causing ice dams "snow melts then refreezes and repeats causes back ups)
@photo 3 Yes you can see the Nail line "ALMOST" this isnt a serious factor though. it is more of a LOOKS issue when its so small such as the photo shown (1/4 in / 1/2in) yes it takes that small amount away from its coverage and area that the water needs to back up but, if everything is done properly that will not cause your leak that is out of the question in this situation
@photo4 Ice and water shield should be places up the wall of the chimney and to take extreme caution while shingling this chimney due to its low slope this is going to seem like a over kill but this is going to do the job and make a low slope roof with shingles effective, Each shingle going up towards the wall needs to be Tar'd on the bottom from the top to the bottom of the shingle then placed down, the bead then goes across the top of the shingle, step flashing over that bead then so the water wont back under the step flashing area, then a bit on that piece of step flashing in the same zone "top of the shingle but across the flashing.
@photo4 the backpan of the chimney
once you reach the back pan this is the most common spot to get leaks, to the same steps as stated before with the taring, for the last pieice of step flashing that will get cut at the corner of the back pan YOU WILL NOT USE METAL step flashing! you will get a small peice of lead and make a peice of step flashing the same size but mold it around the corner once again using tar in the same areas as stated before,
using this method you can shingle a 1/12 and sleep without worries, trust me this is one of the only ways to shingle a 1/12 a chimney / roof and get away with it.
@photo5 for this part you will have to take off the fascia board and make sure there is step flashing up those walls all the way up and make sure those shingles go under that fasica board and not butt next to it, you will need to cut a slit in the low slope to get that last shingle up there
if you dont like this method then hey go with the torch down roofing that is another way to go about this, i dont like torching to brick though, years down the road the torch on will break away from the brick, use counter flashing over the top/bead of the torch on aswell, and throw a bead of sealant over the top of the torch on bead as well "winter worries"
going to the extreme haha