i am removing a wall air conditioner and need to know to install new cedar
shingles to match existing. this includes sheathing and type of underlayment. do i remove some surrounding shingles in order to install
underlayment? do i need to remove existing shinges to top of wall to make
If you want the repair to look unobtrusive, you will need to take off enough shingles to install the sheathing underneath. Then you must integrate a tarpaper cover so it's water shedding from top to bottom and side to side, just like the original tarpaper.
You don't mention the exposure you have on the shingles. The smaller the exposure, the harder it is to slide the shingles into the rows above due to the nails in the upper rows. You might be able to do it with a 14" exposure. Forget about it with a 5-6" one.