Custom blinds are cut to your opening, so the wrong mount is not something you can send back. We work it out when we measure, before anyone picks a fabric. Three things decide it, and any one of them can rule out an inside mount on its own:
- Usable depth behind the casing
- How square the opening is
- What hardware is already sitting inside it
Depth Decides First
An inside mount puts the headrail inside the window casing, so the treatment sits recessed and the trim stays visible. An outside mount puts the headrail on the trim or the wall above the opening, so the treatment covers the frame entirely. Inside mount blinds need enough room between the glass and the front edge of the casing for the entire headrail to sit back where you cannot see it.
Exact depth requirements shift by manufacturer and product line, but the pattern holds, because what drives the number is the mechanism inside the headrail. A motorized roller shade carries a motor and a battery tube, so it needs roughly twice the depth of the same shade with a manual chain. That is worth knowing before you commit to motorization, because on a shallow opening the upgrade forces an outside mount whether you wanted one or not.
| Treatment | Minimum depth for a flush inside mount | What happens when the depth is short |
|---|---|---|
| 2 inch faux wood blinds | About 2 inches | The headrail sits proud of the trim and the valance will not close against the frame |
| Manual roller shades | About 1.5 to 2 inches | The fabric roll clears the frame but the brackets show from the side |
| Motorized roller shades | About 3 to 3.5 inches | The battery tube or motor housing will not fit at all |
| Plantation shutters | About 2.5 to 3.5 inches, depending on louver size | Louvers strike the glass or the sash when they rotate |
| Cellular shades | About 1 inch | The headrail can be face mounted inside, but the stack sits low |
A partial inside mount is the middle option when depth is close but short. The headrail sits inside the casing and protrudes slightly, which reads as intentional on a 2 inch cordless faux wood blind with a valance and reads as a mistake on almost everything else.
A Lot of Openings Here Are Not Square
The clay under North Texas swells when it rains and shrinks when it does not, and the foundation rides along with it. Windows get pulled slightly out of square. Older houses in East Dallas and Oak Cliff show it the most.
A shade cut to fit an opening that is a quarter inch wider at the bottom than the top will show a visible wedge of daylight down one side. The shade is not defective and the measurement was not wrong. The opening is not a rectangle. We measure width at the top, middle, and bottom of every opening and take the narrowest of the three, which is why a treatment that fits perfectly at the sill can still leave a gap at the header.
Once an opening is off by more than a quarter inch or so, outside mount is the way to go. Mounting on the trim hides it. The blind becomes the straight line, and nobody sees what is behind it.
Hardware Already in the opening
Casement crank handles are the most common obstruction we find. A crank sitting an inch and a half off the sash will foul an inside mounted blind every time it is lowered. Sliding window latches, alarm contacts wired into the frame, and tilt-in sash hardware on newer double hungs all do the same thing on a smaller scale.
Tile and stone returns are the other one, and they show up constantly in bathrooms and kitchen windows. A tiled return takes up the depth the headrail needed, and drilling brackets into tile is a bad idea to begin with. Outside mount is usually the only workable answer, and it has the side benefit of protecting the tile edge from drill holes. The same logic applies to plantation shutters, except shutters carry a frame of their own, so the frame style becomes part of the decision rather than a separate mount question.
Why Room Darkening Shades Leak Light on an Inside Mount
An inside mounted roller shade is cut narrower than the opening so the fabric can travel without binding, typically by a quarter to half an inch total. That clearance becomes a permanent strip of daylight down both sides. On light filtering roller shades nobody notices, because diffused light is the point.
On room darkening roller shades, an inside mount works against the whole point. A west facing bedroom in Plano at seven in the evening will throw a bright vertical line across the wall no matter what the fabric is rated at. If the goal is genuine darkness, the shade needs to mount outside the opening with roughly two inches of overlap on each side and three inches above, or it needs side channels. We ask which bedrooms are meant to go dark before we quote, because the answer changes the mount and the mount changes the size.
When Outside Mount Is Out
Outside mount needs flat, fastenable wall or trim above and beside the opening. Crown molding running tight to the header removes it. So do transom windows, arched tops, and openings that sit close enough to a corner that the overlap would run into the adjoining wall. Two windows set close together on the same wall create the same problem, since the overlaps collide.
Those openings usually get an inside mount with the light gap accepted, or a drapery treatment mounted well above and outside the whole assembly. That second approach is why so many tall windows in newer Frisco and Prosper builds end up with a hard treatment inside the frame and a soft treatment outside it.
Sliding glass doors sit outside all of this. A door opening is almost always treated above and beyond the frame regardless of depth, because the panel has to clear the handle and the traffic path, so the mount question is settled before it gets asked. The decisions that actually matter there are stack position and clearance, which we work through in what actually works on sliding glass doors.
Where This Leaves the Decision
Inside vs outside mount blinds comes down to what the opening will physically accept, then what the room needs from the treatment, and only then to how you want it to look. Depth rules out inside mount on shallow openings, movement in the foundation rules it out on racked ones, hardware rules it out where a crank or a tile return is in the way, and room darkening requirements rule it out in bedrooms. What remains after those four filters is where preference gets a say.
We Will Handle the Measuring
We measure every opening in your home, check depth and squareness at each one, and tell you which openings need an outside mount before anything gets ordered. Our own crew handles the measure and the install, so nobody is guessing and nobody is passing the job to a subcontractor. Schedule a free in-home measure and we will bring samples with us.
