Title is pretty much everything!
I have these high up windows that I'd like to clean and maybe in the future install curtains on. I guestimate the wall being 20ft (6m) tall.
For other rooms in the house I typically use an A-Frame, but it's impossible to find an A-Frame to reach that high where I am.
I plan on draping a towel over the top of the ladder to prevent scratches and scuffs on the wall, as well as getting a rubber mat or something if the floor seems slippery. I am just not sure if drywall would support a ladder? Especially near the frame of the windows. Maybe there's something else I'm not considering as well?
It's not a dumb question. Ladders are one of the most dangerous things people keep in their house, and making sure you're using one correctly is important. As to your situation, I think it would be fine to use an extension ladder. My only experience with extension ladder is using 28'-32' ladders to get into tree for trimming. I am not an expert on indoor use.
Yeah, I'd consider myself comfortable with ladders and with heights. I've climbed higher things than this. But you're right, they can be dangerous. I know how to respect them outside the house, but inside the house just feels more sketchy because I have to be aware of myself and any potential damage to the house. Don't want to make the wife mad ๐ .