First I just want to say hello and thanks to all who participate and provide great advice on these forums. I've been going through many different forums and websites and this one definitely seems to one of the most civil and useful.
I am in the planning/preparation phase of a siding and window reaplacement project on my first home. I've been doing quite a bit of research on the window installation as that seems like the trickiest and most critical element of my project.
I will be installing vinyl replacement windows and hardiplank lap siding directly over existing T1-11 siding. I've already cutback the siding around the windows to get accurate R.O. measurements and inspect the old sills/framing. I plan to cut strips of 5/8" ply or OSB to put back in around the R.O. so I will basically have a coherent sheathing layer, with a small gap around the back edge of the strips.
First question, do I need to worry about that small gap? I could fill it with caulk but I don't have a good feel if that is necessary. The T1-11 siding will be covered with Tyvek.
On to windows...I really like the detail and clarity of this installation guide from Pella,
which I plan to use in conjunction with some other materials. My only point of confusion is top of page 3, section 1H (Rough Opening Preparation cont). The guide says to install and level sill by putting shims in place before placing the window. Is this just so the window is placed on top of the shims? I feel like I'm either over thinking this step or I'm missing something.
....The guide says to install and level sill by putting shims in place before placing the window. Is this just so the window is placed on top of the shims? I feel like I'm either over thinking this step or I'm missing something?
Yes, the window is placed on top of the shims.
The instructions are stating that you should install a "set" of shims on each side, 18" apart prior to the actual window installation. Then install the window on top of the shims. Then, using the shims (by sliding either inward, or outward), to adjust the sides to get the window level. If you install the window onto the shims, check it, and it is already level, then don't adjust the shims.
The point they are stating is to have the shims there already, so that you have the ability to adjust for level.