Mount Roman shades Inside if you have at least 2.5 inches of window depth and want to showcase decorative woodwork trim. Mount Outside if your window depth is under 2 inches, you want total 100% light blockout (no side light gaps), or you want to make the window appear taller.
At a Glance: Key Takeaways
- Inside Mount Depth: Minimum 2.0 inches for partial mount; 2.75 inches for flush inside mount.
- Outside Mount Height: Mount 4 to 6 inches above window trim to clear glass when raised.
- Side Light Gaps: Inside mounted shades always have a 1/8 to 1/4-inch light gap along the edges.
- Outside Overlap: Add 2 to 3 inches of extra fabric width on each side beyond the window trim.
- Defective Trim Fix: Outside mounting conceals crooked, damaged, or un-level window casings.
1. Calculating Window Jamb Depth & Light Gap Physics
The choice between inside and outside mounting is governed primarily by window jamb depth and light-blocking requirements. Inside mounting sits recessed flush inside the window frame, creating a clean, modern, built-in aesthetic that highlights custom millwork.
However, because inside-mounted shades must have a 1/8-inch operating clearance on each side so fabric does not rub against the jamb, they inherently produce side light leaks. In bedrooms where pitch-black sleep is essential, outside mounting (overlapping the wall by 3 inches) eliminates 100% of light bleed.
Inside Mount vs Outside Mount Decision Matrix
Use this reference table to calculate exact physical dimensions, ratios, and specifications before purchasing:
| Design / Technical Factor | Inside Mount | Outside Mount | Clear Winner |
|---|---|---|---|
| Required Window Depth | 2.5" - 3.0" clear jamb | Zero depth needed (Drywall mount) | Outside (For shallow windows) |
| Light Blocking Efficiency | 90% (Has 1/8" side light gaps) | 100% Total Blackout (3" wall overlap) | Outside (For bedrooms & nurseries) |
| Preserves Window Trim | 100% of trim remains visible | Covers window casing completely | Inside (For historic/ornate trim) |
| Preserves Window Daylight | Stack blocks 10-12" top glass | Stack sits on drywall above glass | Outside (For small/dark rooms) |
Window Crank Handle & Tilt Latch Obstruction Constraints
Every successful decoration project must account for physical and environmental constraints:
Casement Window Crank Handles Blocking Shade Drop
Protruding casement window cranks or double-hung tilt latches interfere with inside-mounted shades; measure distance from glass to crank tip; if depth is under 2.5", strictly use outside mounting.
How to Measure for Outside Mount Roman Shades
Execute this professional sequence to achieve flawless results without backtracking:
Measure Outer Trim Width
Measure width from outer edge of left moulding to outer edge of right moulding.
Add 4 to 6 Inches Width
Add 2 to 3 inches on each side (e.g. 36" trim + 6" = 42" ordered shade width).
Measure 6" Above Top Trim
Measure from 6 inches above header trim down to 1 inch below lower sill.
Mount Brackets to Drywall
Use heavy-duty hollow drywall toggle anchors to fasten mounting brackets into wall above trim.
Common Mistakes & Countermeasures
Avoid these costly errors that compromise aesthetics, ergonomics, and budget:
Ordering Exact Window Width for Inside Mount
Project Execution Checklist
Track your physical progress. Checkboxes persist automatically on this device:
Frequently Asked Questions
Can you layer outside mount Roman shades with floor-length curtains?
Yes! An inside-mount Roman shade paired with outside-mount floor-length drapery panels is the ultimate luxury designer combination, providing both light control and rich layered texture.
