Window blinds are one of the highest-frequency hardware installations in any home and one of the most-commonly botched. The brackets ship in unmarked plastic bags, the screws are too short to hit anything structural, and the included instructions assume the installer knows the difference between an inside-mount and an outside-mount. Done wrong, the blinds tilt within weeks, the brackets pull free of the casing or drywall, and the slats jam at one end of the head rail.
This guide covers vinyl, faux wood, and aluminum blinds for standard residential windows. Cellular shades and roller blinds use similar mounting principles. Heavy plantation shutters or motorized blinds are different installations covered in their own guides.
Before you start
Three things to settle:
1. Inside or outside mount. Inside-mount blinds sit inside the window casing — cleaner look, but the window must have at least 1.5 inches of casing depth for the brackets to fit. Outside-mount blinds sit on the wall above and beside the window — easier install, more flexibility on size, but read as bulkier visually. Measure your casing depth before deciding.
2. Width and length measurements. Inside-mount: measure the inside opening width at top, middle, and bottom. Use the smallest of the three measurements (windows aren't always square). Subtract 1/4 inch for clearance. Length is from the top of the casing to the sill. Outside-mount: measure the casing's outside dimensions plus 2-3 inches of overlap on each side and 2-3 inches above the casing for the head rail. Length covers the casing or extends below to your preference.
3. Mounting surface. Window casings are solid wood — screws drive directly without anchors. Drywall above or beside the window needs anchors (snaptoggles or self-drilling threaded anchors) unless the screws hit a stud. Plan the bracket positions with this in mind.
What you'll need
Tools
- Cordless drill with adjustable clutch
- Drill bits: 1/16" pilot, 1/8" wood pilot, 3/16" for anchor holes
- Phillips driver
- Tape measure
- Pencil
- 9-inch torpedo level
- Stud finder (for outside-mount on drywall)
- Step ladder for upper windows
Materials
- Window blind unit (sized to your measurements)
- Mounting brackets (included with the blind)
- Screws #6 × 1" wood screws (included; replace with 1.5" if into drywall over framing)
- Snaptoggles or E-Z Ancor (for outside-mount on drywall, not included)
- Painter's tape (for marking)
Measure twice; the wrong size is non-returnable on custom blinds
Stock blinds at Home Depot or Lowe's are returnable; custom-sized blinds from window-treatment specialists are not. A measurement error on a custom cellular shade means the whole blind is wasted.
Always measure inside dimensions at three points (top, middle, bottom) and use the smallest. Windows settle and aren't always rectangular. Order to the smallest dimension; the small gap left at wider points is invisible.
Step-by-step instructions
Confirm inside vs outside mount
Open the blind packaging and read the bracket type. Inside-mount brackets attach to the inner faces of the window casing. Outside-mount brackets attach to the wall surface above and beside the casing.
Some blinds support both — the bracket has a flange on top for outside mount and on the side for inside mount. Confirm which orientation matches your install before drilling.
Position the brackets and mark screw holes
For inside mount: place each bracket against the casing's top inside corner (one bracket on each end of the head rail). The bracket's mounting holes should align with where the screws will drive.
For outside mount: hold the bracket above and outside the window casing at the planned position. Mark each screw hole with a pencil through the bracket holes.
Verify the brackets are level relative to each other. Lay a torpedo level across the planned positions and adjust if needed.
Pre-drill into wood casing or anchor into drywall
For wood casing (inside mount): drill a 1/16-inch or 1/8-inch pilot hole at each marked position. The pilot prevents the casing from splitting when the screw drives in.
For drywall (outside mount): if a stud finder shows a stud at the bracket position, use a 1/8-inch wood pilot bit. If no stud, drill a 1/4-inch hole for a self-drilling threaded anchor or 1/2-inch for a snaptoggle.
Mount the brackets
Drive the screws through the bracket into the pre-drilled holes. Snug only — over-driving strips the wood or anchor.
Verify the brackets are secure by pressing with your hand. They should not flex, rotate, or pull out.
Snap or slide the head rail into the brackets
Most modern blinds have brackets with hinged covers that snap closed over the head rail. Position the head rail so it engages with the bracket's clip, then close the bracket cover until it clicks.
Some older designs use a slide-in motion — the head rail slides into a track on each bracket from one end.
Test operation
Lower and raise the blind through its full travel. The slats should lift smoothly without binding.
Tilt the slats with the wand or chain. The mechanism should rotate the slats fully open and fully closed without resistance.
If anything binds, the head rail is twisted (one bracket higher than the other) — re-mount the brackets to align them.
Install the wand or cord safety devices
Most modern blinds include cord cleats (small hooks that mount to the wall, allowing the user to wrap excess cord out of children's reach) for safety compliance. Install the cleat at least 4 feet above the floor.
Some newer blinds use cordless lift mechanisms — these have no exposed cords and skip this step entirely.
Install the valance (if applicable)
Decorative valances cover the head rail and brackets. They typically clip to the front of the head rail.
Snap the valance onto the head rail's clips. The valance should sit flush against the top of the blind.
Adjust slat tilt and final positioning
Open and close the slats a few times to confirm smooth operation. The blinds should sit straight in the window opening.
If the bottom rail isn't level when the blind is fully lowered, the head rail is tilted — adjust by shimming behind one of the brackets or re-mounting.
Pro tip: if installing multiple windows in the same room, ensure all blinds are at the same height and project the same amount from the wall. Inconsistencies between windows are immediately visible from the room and harder to fix after install.
Common mistakes that cost you
- Measuring outside opening for inside-mount blinds. Always measure the inside dimension for inside-mount, including at three points to find the smallest. Wrong measurement means returns or wasted custom orders.
- Single bracket on a wide blind. Anything over 36 inches wide needs at least one centre bracket between the ends. Otherwise the head rail sags.
- Skipping the level check across brackets. Brackets at slightly different heights mean the head rail tilts and the slats jam. Always level the brackets relative to each other before mounting.
- No anchor on drywall outside-mount. Wood screws into bare drywall hold nothing. Use snaptoggles or E-Z Ancor unless the screws hit studs.
- Installing without cord safety devices. Cord cleats are required for child safety in Canada. Cordless lift mechanisms eliminate the need entirely; otherwise install the cleat at 4+ feet.
- Over-tightening bracket screws. Strips the wood casing or drywall anchor. Snug only — the bracket's contact with the surface plus the screws is the holding force.
Frequently asked questions
How do I measure for blinds?
Inside-mount: measure inside the window opening at three points (top, middle, bottom). Use the smallest measurement minus 1/4 inch for clearance. Length is from the top of the casing to the sill (or longer if you want them to extend past).
Outside-mount: measure the outside of the window casing plus 2-3 inches of overlap on each side and 2-3 inches above. Length is your preference — to the sill, just past the sill, or to the floor for full coverage.
What's the difference between vinyl, faux wood, and real wood blinds?
Vinyl is cheapest, lightest, suitable for high-humidity rooms (bathrooms, kitchens). Aluminum is similar to vinyl but slightly more durable.
Faux wood looks like real wood but is made from PVC or composite — handles humidity better than real wood, weighs less, costs less. Real wood is heaviest, most expensive, requires more careful installation, and warps in high-humidity environments.
Should I get cordless blinds?
Yes if there are kids in the household. Loose cords are a strangulation hazard and several Canadian regulators have restricted corded blinds. Cordless lift mechanisms cost a little more per blind but eliminate the safety concern entirely.
Cordless blinds use a spring-loaded lift mechanism — pull down on the bottom rail to lower, push up to raise. They lock in position automatically.
Why do my blinds tilt when raised?
The head rail isn't level. Either the brackets were mounted at slightly different heights, or one bracket has worked loose over time.
Take the blind down, check the bracket positions with a torpedo level. Re-mount the brackets at identical heights, then re-install.
When to call us instead
If you're installing motorized blinds, smart home integrated treatments, or custom plantation shutters, this becomes a different job involving electrical or precision millwork. We handle window-treatment installation as part of larger renovation work or as a single-visit service.
Book a free 60-minute site visit →Related Ottawa services
If you're updating window treatments as part of a room refresh, our residential renovation team handles trim, lighting, and window dressings as fixed-price line items. Book a free 60-minute consultation.