Mounting curtains inside window frame is the cleanest looking option for double-hung windows, casements, and any opening with detailed trim worth showing off. The challenge is that an inside mount has zero forgiveness on measurement, rod selection, or panel width. After hanging hundreds of inside-mount window treatments in everything from 1920s bungalows to new construction, I can walk you through the specifics that separate a tailored installation from a sloppy one.
When Inside Mount Works Best
Choose inside mount when the window has at least 2 inches of depth from the front edge of the casing to the glass, when you want to showcase the existing trim or molding, and when light gap is acceptable (a small sliver of light will always escape around the panels). Inside mount also works well when there is no wall space above or beside the window for an outside-mount rod.
Skip inside mount on shallow windows under 1.5 inches deep, on windows that need full light blockout for sleep, or when the existing casing is damaged and best hidden. In those cases, a standard outside mount above the casing performs better.
Measure the Window Correctly
Measure the inside width of the window opening at the top, middle, and bottom. Use the smallest number minus 1/4 inch for your rod length. Measure the inside height from the top of the opening to the sill for full-length panels, or to your desired length for cafe curtains.
Check the depth from the front of the trim to the window glass. You need at least 2 inches of clearance for a standard rod with rings, or 1.5 inches for a tension rod or recessed track. Less than 1.5 inches and the panels rub the glass every time they close.
Rod Options That Fit Inside
Tension Rods
The simplest choice. Spring-loaded tension rods from Kenney, Umbra, or InterDesign install in seconds without screws and work in openings from 18 to 96 inches wide. Budget $8 to $35 per rod. They support light fabrics like sheer linen or cotton voile but sag under blackout panels heavier than 4 pounds per linear foot.
Recessed Mount Rods
Standard rod and bracket sets mounted to the inside top of the window frame. Use small projection brackets (1.5 to 2 inches) so the rod sits flush within the opening. Restoration Hardware, Pottery Barn, and Levolor all sell suitable hardware in the $40 to $120 range.
Track Systems
For tailored panels that operate like draperies, a ceiling-mount or recessed track from Silent Gliss or Forest Drapery Hardware lets panels slide smoothly without rod sag. Track installs run $80 to $250 plus custom panels at $90 to $300 each. This is the highest-end option and suits formal rooms.
Choosing Panel Size for Inside Mount
Width should equal 1.5 to 2 times the rod length for proper fullness. A 36-inch window opening calls for two panels that are each 36 inches wide (1 times) for stationary side panels, or 54 to 72 inches wide combined (1.5 to 2 times) for functional operating panels.
Length should hit the sill exactly or end 1/2 inch above it. Measure from the rod to the sill, then subtract the ring-and-clip drop (usually 1 inch) to get the finished panel length. Order custom or hem ready-made panels to that exact dimension. A floor-puddled curtain inside a window frame looks like a mistake; precise length is the entire point of inside mount.
Hardware Details That Matter
Use return brackets if your rod is more than 1 inch deep. The return wraps the panel back to the wall and eliminates side light gap. For tighter installations, use a wraparound rod from Kirsch or Umbra that integrates the return into the rod profile.
Rings should be 1.5 to 2 inches in diameter and matched to the rod diameter. A 5/8 inch rod takes 1 inch inner-diameter rings. Heavier 1 inch rods take 1.5 inch rings. Mismatched proportions look amateur even when the rest of the install is correct.
Installation Step by Step
Mark bracket positions on the inside of the window frame at the top corners. Pre-drill pilot holes sized to your screws (typically 1/16 inch for #8 screws into wood casing). Use 1.25 inch screws to anchor brackets to the casing, not the drywall return. The casing is solid wood; the return is hollow.
Mount brackets 1/2 to 1 inch down from the top of the opening so the rod and rings sit fully inside the frame. Test fit the rod and rings, then hang panels temporarily before final tightening to confirm operation. Adjust bracket position if rings catch on the top of the frame.
Combining With Other Treatments
Inside mount curtains layer beautifully with outside mount Roman shades, roller shades, or wood blinds. Mount the rod first inside the frame, then add the outside treatment above and beside the casing. This combination delivers full privacy and light control without sacrificing the trim showcase that inside mount provides.
Alternatively, layer two inside mount treatments: a privacy sheer panel on one rod and an opaque panel on a second rod. Use a double-track ceiling-mount system or two parallel rods at different depths. This is common in master bedrooms where light control and daytime privacy both matter.
Common Mistakes
The biggest mistake is forcing a panel that is too wide into a narrow opening. The fabric bunches at the rings and never stacks neatly. Calculate fullness based on the actual rod length, not the window dimension. Ready-made panels sold as 50 inches wide are usually 1.5 times that as fullness; check the actual flat width before ordering.
The second mistake is mounting brackets too far forward in the frame. Bracket positions should sit at the back third of the casing depth so panels clear sash hardware and locks. Test the window operation with the rod and panels in place before final installation; a curtain that blocks the lock or limits the sash from opening defeats the purpose.
Budget Realistic Numbers
A standard inside-mount installation for a typical 36-by-60 inch window with ready-made panels and a basic rod runs:
- Tension rod plus ready-made panels: $40 to $90 total
- Standard rod, brackets, rings, and ready-made panels: $90 to $220 total
- Custom panels, premium hardware, professional install: $400 to $900 total per window
A clean install of curtains inside window frame elevates the room and showcases the trim that wraps the opening. Measure carefully, match rod and ring proportions to the panel weight, and the result reads custom rather than catalog. Inside mount rewards precision; an extra 15 minutes of careful measuring saves an hour of rework.
