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The mount type determines what will fit, how it looks and whether drilling is required. It is decided by the window rather than by preference, and the choice is usually made for you.
Inside Mount
The shade sits within the window recess, gripping the frame from inside. It gives a clean built-in appearance, does not intrude into the room, and leaves the surrounding wall untouched.
It requires a recess of adequate depth, typically at least an inch and a half, and a frame in sound condition.
No-Drill Options Are Inside Only
This is a genuine limitation worth understanding before buying. Spring-rod and tension mounts work by pushing against the inside faces of a recess. There is nothing for them to grip on a flat wall.
Ranges built entirely around inside mounting, of the kind at lazblinds.net, state this plainly among their limitations rather than implying they suit every window, which is the honest position: no recess means no tension mount.
Outside Mount
The shade mounts on the wall or the frame face, above and beyond the opening. It covers the whole window and some of the wall around it.
It suits shallow recesses, windows with obstructions, and situations where blocking light at the edges matters. It almost always requires drilling into the wall.
Which Situation You Have
- Deep recess, sound frame, no obstructions: inside mount
- Recess shallower than about 1.5 inches: outside mount or curtains
- Handles or catches in the way: outside mount
- Inward-opening windows: outside mount, or a shade on the sash itself
- Renting, no drilling permitted: inside mount with a tension fixing
The Light Gap
Inside mounts leave a small gap at each side by necessity, since the shade must be narrower than the opening to fit inside it.
For most rooms this is irrelevant. For a bedroom where genuine darkness matters, that gap is where light comes in, and it is the reason a blackout blind can still leave a bright outline.
The usual answers are an outside mount, or layering: a fitted blind inside with a curtain over it.
Appearance
Inside mounts look neat and show the frame, which suits period windows and rooms where the joinery is attractive.
Outside mounts make a window look larger, which is useful for small windows, and they hide an unattractive frame entirely.
Measuring Differs
Inside mount: measure the opening at three points and take the narrowest. Outside mount: measure the opening and add overlap, typically two or three inches each side and above.
Confusing the two produces either a shade that will not fit or one that leaves the window half exposed.
When Neither Works
Some windows resist both: no recess, no wall above, or a mechanism in the way. Curtains on a tension rod, or a shade fixed to the sash itself, are the remaining options.
