Thanks for the page of links! Now I know what to Google. I'd been unfamiliar with the term "rubblestone." I'll check out those links. There's no sign of the foundation changing in the past 40 years--no changes in the way doors close or other differences in the 1st and 2nd floors with its post-and-beam construction. It's reasonably water-tight (some water has always leaked in at the base of one corner; it follows a trench to a sandy spot where it sinks away). I'm not so much trying to "fix" our cellar's foundation walls as to plug up air leaks and make it a bit more challenging for rodents to get in. Basically we hope to patch it up more or less the way the previous generations did. We just heard from the guys who haul in our firewood each fall--suddenly our cellar work has to be done within the next 5 days due to their schedule. Looks like we'll be stuffing fiberglass into the cracks again. I did note in some article links (just started reading them) that there's a danger in repairing only from the inside--I can see there's more to this than I'd imagined. Sadly, we can't afford a major (or minor) engineering project. The house needs to stay intact about 15-20 years (our maximum expected lifespan), which I think it will do. Thanks again!

"As I understand it, there is to be a 1/4" nailing strip installed on each side, for a total of 1/2" for each dimension, which is why the rough dimension is quoted as 1/2" larger." That is not the reason for the rough opening being 1/2" larger. You need to look at a window. The nailing strip is actually a 1 1/2" +/- flange that overlaps the rough opening and is nailed to the sheathing so the gap between the window frame and the framing does not have to be exact or perfect. The framer will treat the specified R.O. as a minimum and try to make it as square and level as possible. A slightly larger opening is not a problem. You only need to tell the framer the R.O.'s and the only reason to modify them is if you wanted to use a sill pan or another kind of sill flashing that required more space. A long span over a set of windows might require a larger gap at the head for future deflection. Adding to the specified manufacturers R.O.'s can result in redundant increases in the final opening size so such increases are better shown in a note in the window schedule with an asterisk at the R.O. for the appropriate window. Many designers have gotten into the habit of showing a frame size on the elevation drawings. That is OK for vinyl and fiberglass windows and perhaps clad wood casements and awning windows but for many double-hung windows the frame size is not an even dimension (windows sizes are a function of standard glass sizes) and varies a lot between manufacturers. The solution is to pick a manufacturer and put everything into a window schedule. If the manufacturer is changed all of the R.O.'s will have to be changed.

Having a gap between a structural header and a window casing (or door) is actually a desirable thing, It means any sag in the header will not immediately affect the window, The trim on the inside should easily cover the gap. You did install flashing on the outside, right? The siding will cover that.

Simply great said “technically they aren’t fiberglass”, not that they are another material with simialr features tht competes directly with Fiberglass. By that logic there are vinyl and even wood windows that are similar and “technically not fiberglass“ as well. I guess all window materials are similar then, although in that case no “technical” clarification would have been needed here Between these two. Fibrex is technically not fecal matter, but both are made by Andersen employees, both have a component of being swept up off the floor, both are earthtone hues in their natural state, both have a pungent odor when produced, and i desire to have them make up the material of windows that I install equally. This is a facetious comparison of course (or is it fecetious?)