Installing windows in a new house is pretty easy. You have the rough opening already there. If it’s the wrong size (as it can often be), you can fix that with a wrecking bar, a saw, and a new 2×6. Otherwise, it’s straightforward: put the window in, shim it all around, check it for plumb, level, and square, drive a couple of nails. Simple.

In a renovation, though, it can be more annoying. I have replaced 8 windows in my house, installed 7 new ones, and there are still 6 old windows to go. This isn’t a big house, either. Anyway, I saw some windows at a good price. They were four-feet square sliders and they looked right to replace all the windows down one side of my house. So, I bought them.

I thought, rather stupidly, that the windows that were already installed were 48 inches wide and a bit taller than that. But when I got the new windows home, I discovered the old windows were actually 46 inches wide. Now, you ask, who makes 46 inch windows? Apparently, aluminum window manufacturers from 1968 did. Or perhaps the inch has grown slightly over the last 40 years. I can imagine a situation where you would need a custom window, where you need a width two inches less than a nice round number, but this house has windows in the middle of walls and has 16 inch stud spacing. It was inconvenient in 1970 to put these windows in.

And it was inconvenient to put the bigger windows in, too. You can imagine the mess I had to make to get them installed. I had to remake the opening using a wrecking bar, a saw, and some new wood. Then I had to patch the drywall. I was already replacing the siding, so that part didn’t matter. But I had messed up wall from floor to ceiling.

One of the first times I replaced a window was on a job where the house was occupied by what seemed like two or three dozen college-aged girls. The majority of that job was to remove the old fibre-based siding (I can’t remember what it was called, but it soaked up water like a sponge) and install new pale-green vinyl. That looked as bad as it sounds.
There were two or three windows to replace. The old were nicely made double-hung, but single-glazed. They were the last original windows in the house (the terrible siding was not original, there was clapboard under it). In one of the girls’ rooms, a new casement window was put in. It fit the existing opening perfectly. So, it was shimmed, plumbed, nailed. Pink insulation was stuffed into the space between the window and the framing (no sprayfoam at hand). The gap between the old window and the framing was not filled with insulation when originally done, but it did become completely filled with dead houseflies over the years (a bit of a sight upon removal).

The moulding that had been carefully removed was reinstalled and the new window looked pretty complete. Even the wood was painted.
The next day, however, we were told that something went wrong with the installation because the window was broken. And sure enough, the glass was cracked diagonally from the bottom of one side to the top of the other.
Not-exactly-close examination revealed that the likely cause was an attempt to open the window using the crank while leaving the lock engaged. No matter, we replaced it. We made sure to leave the replacement window unlocked.

Incidentally, the house next to mine had all its windows replaced in one day. It was an impressive task, because when they left, it looked like the new windows had always been there. I’m not sure about how good it is, though. They brought windows that could be installed in the frames of the old sliding windows. So, they removed the sliding glass and foamed the new windows into the aluminum frame. But in my house, the wind was blowing in around the aluminum frame. Wind tends to not blow through glass. So, I imagine they gained almost no energy savings by that replacement. But at least the new windows were clean for a while, if a few inches smaller than the old ones.