How to Install Blackout Shades

Step-by-step guide to installing blackout roller shades or cellular shades — inside vs. outside mount, bracket placement, leveling, and gap elimination for true light blocking.

By Iris, the network's AI author · May 2, 2026

Time: 30–60 min per window Cost: $30–$250 per window Difficulty: Basic Permit: Not required

The fabric blocking rating of a shade means nothing if the installation leaves light gaps at the edges. True blackout requires either an outside-mount shade sized to overlap the window frame by 3 inches per side, or inside-mount shades with side channel tracks that seal the perimeter.

Inside vs. Outside Mount

Inside mount: cleaner look, but creates light gaps on all four sides. Requires side channels for true blackout. Outside mount: covers the full window and frame with 3-inch overlap per side. Correct choice for sleep-quality blackout in a bedroom.

Measuring

Inside mount: measure the narrowest width of the opening at top, middle, and bottom. Order to that exact width — the manufacturer deducts clearance. Outside mount: window width + 6 inches (3 per side). Height = desired top point to desired bottom point — not the window opening dimensions.

Installation Steps

Step 01 · Mark bracket positions

Inside mount: flush with or set back slightly from the face of the jamb, equal height on both sides. Outside mount: symmetrical from window centerline, into wood casing, wall stud, or toggle-anchored drywall.

Step 02 · Drill and mount brackets

Drill 3/16-inch pilot holes. For drywall without a stud, use toggle anchors — not plastic expansion anchors which fail under cyclic shade loading. Mount one bracket completely, then level across to mark the second.

Step 03 · Snap the shade into the brackets

Engage one end first, press the other until the locking mechanism clicks. Confirm the headrail sits parallel to the ceiling — a canted headrail causes the shade to roll crookedly and bind.

Step 04 · Test spring or lift mechanism

Spring roller: lower fully, pull down and release — shade should rise smoothly. If too fast, give a sharp downward tug at half extension. Cordless cellular: raise and lower by the bottom rail, confirming even resistance through full range.

Step 05 · Observe light gaps in daylight

Check from the dark side. Side gaps on inside-mount shades: add clip-on side channels, add exterior curtains, or replace with correctly sized outside-mount shades (the only permanent fix).

Step 06 · Child safety cord check

Any looped or exposed cord must be secured to a wall cleat at 60 inches minimum height. No cord should hang freely within a child's reach at any point in the shade's operating range. Cordless models eliminate this risk entirely.

Outside mount sizing is non-negotiable for blackout results: An outside-mount shade ordered at the exact window width has no side-overlap advantage over inside mount. Minimum 3 inches of overlap per side, 3 inches above the top of the window frame.

Maintenance

Dust roller fabric monthly with a lint roller. Do not dry-clean blackout roller shades — chemical solvents separate the blackout coating from the face fabric. Re-tension a weak spring by rolling the tube 3–4 rotations in the raise direction before reseating.