Will a total blackout shade fit your window?
Total darkness depends on side channels, and a channel is a rigid track with real limits. Two minutes here saves a shade that does not fit.
1. Is your window the right size?
Measure the opening at its widest and tallest points.
Width
12" – 96"
Wider openings are covered with two shades side by side, which also keeps each one light enough to run smoothly.
Drop, with channels
12" – 110"
The channel is one cut length of aluminium, and 110" is the most we can supply. The shade itself can go to 120" without channels.
2. Is the recess deep enough?
Only matters for an inside mount, where the shade sits inside the opening. Measure from the face of the glass to the front edge of the frame.
Cellular shades
1½"
The slimmest headrail we make.
Everything else
2½"
Roller, zebra, sheer and blackout rollers.
Less than that
Outside mount
Mount on the wall above the opening instead — and it blocks light better anyway.
If you want the darkest possible room, choose an outside mount. The shade overlaps the opening instead of sitting inside it, so there is no recess gap to seal in the first place.
3. What kind of window is it?
A side channel is a straight rigid track, so the shape of the opening decides what is possible.
- Suits it well
Standard square or rectangular
The ideal case. Flat jambs on both sides give the channel a straight run.
- Suits it well
Double-hung / sash
Fine inside or outside mount, as long as the recess is deep enough.
- Suits it well
Picture window
No moving parts to clear. Check the width against the 96" maximum.
- Suits it well
Sliding window
Works well. Mount outside if the sash track eats the recess depth.
- Suits it well
Patio / sliding door
Outside mount, and measure the handle projection before ordering.
- Usually workable
Casement (crank)
The crank handle usually fouls an inside mount. Outside mount clears it.
- Usually workable
Awning
Opens inwards at the bottom, so an inside-mounted channel can block it.
- Usually workable
Bay window
Each pane is treated as its own window. The angled corner posts are the problem.
- Usually workable
Tilt-and-turn
The sash swings into the room. Outside mount only, with clearance.
- Usually workable
Shallow recess under 1½"
Too shallow for an inside mount. Outside mount instead.
- Not suitable
Arched or round-top
A channel is a straight extrusion. It cannot follow a curve.
- Not suitable
Skylight / sloped
Needs a purpose-built skylight system, not a side-channel roller.
- Not suitable
Over 96" wide
Past our maximum width. Two shades side by side is the answer.
- Not suitable
Over 110" drop
The channel is cut to the drop and 110" is the limit. The shade alone can go taller.
4. Anything in the way?
A channel runs the full drop down both sides of the opening. Anything projecting into that line has to be cleared, usually by mounting outside.
Not sure? Send us a photo.
Unusual shape, shallow recess, or something in the way — send a photo of the window with a tape measure in shot and we will tell you what will work before you order anything.
Measuring first? Read the measuring guide.
Quick answers
What is the maximum size for a blackout shade with side channels?
Widths run from 12 to 96 inches. The side channel is a single cut length of aluminium and 110 inches is the longest we can supply, so 110 inches is the maximum drop with channels. The shade on its own can go to 120 inches without them. Openings wider than 96 inches are covered with two shades side by side, which also keeps each shade light enough to run smoothly.
How much recess depth do I need for an inside mount?
2.5 inches of flat depth for most ranges, and 1.5 inches for cellular shades. If your recess is shallower than that, mount outside the opening instead — and if you want the darkest possible room, an outside mount is the better choice anyway because it covers the gap around the whole opening.
Which types of window suit side channels?
Standard square and rectangular openings are ideal, along with double-hung and sash, picture, and sliding windows, and patio doors on an outside mount. Casement windows with crank handles and awning windows that open inwards usually need an outside mount so the channel clears the moving parts. Arched, circular and bay corners cannot take a straight rigid channel.
What gets in the way of a side channel?
Crank handles on casement windows, window locks and latches, deep or ornate trim around the opening, a sill that projects into the opening, and alarm sensors or wiring. A channel needs a straight flat run down both jambs, so anything standing proud of that surface either forces an outside mount or has to be worked around. If you are not sure, send us a photo of the window and we will tell you.