Every window covering hangs one of two ways, and picking the wrong one is the most common reason a finished job looks slightly off. In older Kentucky homes the choice is a real decision, not a formality.
What each mount means
Inside mount puts the headrail inside the window opening. The treatment sits within the frame, tucked back into the casing, and your woodwork stays visible around it. It is the cleaner look, and it is what most people picture.
Outside mount puts the headrail on the wall above the opening, or on the flat face of the trim. The treatment covers the opening from outside it and overlaps the edges.
That is the whole vocabulary. The hard part is knowing which one a given window can take.
Depth is the first thing I measure
Before width or height, I measure depth. From the front edge of the frame back to the glass. It decides what is even possible.
Every product has a minimum. A slim roller shade headrail needs the least. A wood or faux wood blind headrail needs more. A plantation shutter frame needs the most, because the frame itself has real thickness. A motorized roller needs room for the battery tube inside the roll.
Older housing stock is a mixed bag on this. Plenty of older homes around Lexington and Corbin have deep, generous wood casings that are ideal for inside mount, and the treatments end up looking built in. Then two rooms later there is a window that got replaced at some point with a vinyl insert, and that insert ate two or three inches of the original depth. Same house, opposite answer.
Hardware steals depth too. Window locks, crank handles on casements, and older storm window tracks all sit in the path of a lowered treatment. Better to find that with a tape measure than after the order ships.
When the frame is out of square
Houses settle. Foundations shift, framing moves, sills sag, and decades of paint build up unevenly. Openings that are out of square by a quarter inch or more are normal in older homes, not unusual.
Here is how I find it. I measure width at three heights, top, middle, and bottom. I measure height at three widths, left, center, and right. On a square opening those numbers match. On a settled opening they do not, and the spread tells me what I am working with.
A small variance, up to about an eighth of an inch, is workable for inside mount. The product gets cut to the narrowest width and the resulting gap is small enough that nobody notices it.
A larger variance is a different situation. The treatment will be built perfectly square, because that is how factories build. The opening is not square. Put a square object in a crooked hole and you get a visible wedge of daylight that widens toward one end. No amount of build quality fixes that.
Out of level sills cause their own trouble. If the sill runs downhill, a blind bottom rail will touch on one side and gap on the other. On a shutter it is worse, because the frame is rigid and the mismatch is obvious.
When outside mount is the honest answer
Outside mount is often the correct choice, not a fallback.
Use it when the opening is too shallow for the product you want. Use it when the frame is meaningfully out of square, because the wall surface around a window is usually flatter and more consistent than the opening itself. Use it when a window is small and you want it to read larger, since mounting wide and high visually enlarges the opening. Use it when you need serious light control, because the overlap closes light gaps that an inside mount structurally cannot.
It has its own requirements. You need enough flat wall or flat trim face above the opening to land brackets solidly, and you need clearance on each side for the overlap. On a window tight to a corner, tight under crown molding, or crowded by a door casing, that room may not exist.
When outside mount is hiding a problem
Now the part people do not enjoy hearing.
Outside mount is forgiving, which makes it the easy default for anyone who does not want to do careful measuring. If someone recommends outside mount on every window in a house without checking depth or square, that is a shortcut dressed up as a design choice.
It also covers things up. A rotted sill, a chipped casing, a gap where the trim pulled away from the wall. A headrail hides all of it. I would rather point at a soft sill and let you decide what to do than bury it behind a shade and let you discover it in three years.
If a window needs repair before treatment, you should hear about it while you can still act on it.
Light gaps and privacy
This is where the two mounts genuinely differ in how the room feels.
An inside mount treatment is built slightly narrower than the opening so it can raise and lower without binding. That deduction leaves a small gap on each side by design. On a light filtering shade in a living room, nobody notices. In a bedroom where you want real darkness, that gap becomes a bright stripe on the wall at sunrise.
Outside mount overlaps the opening on all four sides and closes most of that light. For bedrooms, nurseries, media rooms, and anyone who sleeps during daylight hours, it is usually the better call. Side channels are the other route, and they seal the edges of an inside mount without going to a full outside mount.
Privacy follows the same rule. A gap that lets light out at night is a gap that lets a sightline in.
Why this gets decided in person
You cannot settle this over the phone or from a photo. It takes a tape measure, a level, and somebody standing in the room.
On a free in-home consultation I measure every opening at three points in each direction, check depth against the specific product you are considering, check square and level, look at hardware clearance, and note anything about the sill or casing that changes the plan. Then I tell you what each window should be and why.
Often one house ends up with both mounts, and that is the right outcome. Shutters inside mount in the deep front room, roller shades outside mount on the shallow replacement windows in back. It should be decided window by window, not by a blanket rule.
If you are weighing products, our plantation shutters page covers the option with the strictest depth requirements, and our installation page explains how we handle fit and mounting. When you want your own windows looked at, book a free consultation and we will walk the house together.