We have seen every blind installation mistake there is. Here are the ones that come up again and again, and how to keep them from happening in your home.
Most blind problems are installation problems
A good blind installed badly looks and performs worse than a mediocre blind installed well. We see this constantly: customers call about a blind that will not stay up, hangs crooked, or has light gaps, and when we show up, the blind itself is fine. The installation is the problem.
Some of these mistakes are easy to avoid if you know what to look for. Others are why professional installation exists.
Mistake 1: Wrong measurements
This is the big one. It causes more problems than everything else on this list combined.
Common measurement errors:
Measuring width at only one point (windows are rarely perfectly square)Rounding up instead of recording exact measurementsConfusing inside mount and outside mount dimensionsMeasuring the window frame instead of the opening (or vice versa)Using a cloth tape measure that stretchesHow to avoid it:
Measure width at three points: top, middle, and bottom. Use the narrowest measurement for inside mount.Measure height at three points: left, centre, and right. Use the longest measurement for inside mount.Always record to the nearest 1/8 inch. Never round.Confirm whether you are measuring for inside mount or outside mount before you start.Use a steel tape measure. Cloth tapes can be off by 1/4 inch or more.The stakes: Custom blinds are built to your measurements and cannot be returned for sizing errors. A blind that is 1/2 inch too wide for inside mount will not fit. A blind that is 1/2 inch too narrow will have visible light gaps on both sides.
Mistake 2: Choosing the wrong mount type
Inside mount (the blind sits inside the window frame) looks cleaner, but it is not always possible or practical.
When inside mount does not work:
The window frame is too shallow for the blind type. Roller blinds need at least 1.5 inches. Zebra blinds need 2.5 inches. Motorized blinds need 3.5 inches.The window frame is out of square. If your width measurements differ by more than 1/4 inch across the three points, outside mount will look better.There are obstructions inside the frame (window handles, cranks, latches) that interfere with the blind.How to avoid it:
Measure the depth of your window frame before deciding on mount type.Check for obstructions that would block the blind when it moves.If in doubt, outside mount is the safer choice. It hides imperfections and provides better light blocking.Mistake 3: Not checking for level
Just because your window frame looks straight does not mean it is. Houses settle, frames warp, and walls shift over time. Installing a blind that is perfectly level on a frame that is not perfectly level creates a visible gap on one side.
How to avoid it:
Use a spirit level on the top of the window frame before installing.If the frame is off-level, adjust the bracket positions to split the difference rather than following the frame exactly.For outside mount, use the level to mark your bracket positions on the wall, not the window trim.Mistake 4: Using the wrong fasteners
This one mostly affects outside-mount installations and condos with concrete walls or ceilings.
Common fastener mistakes:
Using drywall anchors that cannot support the blind weightScrewing into drywall without hitting a stud (the bracket pulls out under load)Using wood screws in concrete or masonryUsing screws that are too short to grip properlyUsing screws that are too long and penetrating through to the other sideHow to avoid it:
For drywall: Find the studs with a stud finder and screw into them. If you must mount between studs, use toggle bolts rated for the weight of your blind.For concrete: Use Tapcon screws or sleeve anchors with a hammer drill. Standard drill bits and screws will not hold.For wood frames: Standard wood screws are fine, but pre-drill to prevent splitting.Match the screw gauge and length to what the blind manufacturer specifies.Mistake 5: Mounting brackets unevenly
If your left bracket is 1/4 inch higher than your right bracket, the blind will hang crooked. It is one of those things that looks small on paper but bothers you every time you see it.
How to avoid it:
Measure both bracket positions from the same reference point (top of the window frame, or ceiling for ceiling mount).Use a level between the two bracket positions.For three-bracket installations (wider blinds), the centre bracket must be at the same height as the end brackets. Sagging in the middle is a telltale sign of a low centre bracket.Mistake 6: Ignoring clearance
Blinds need room to operate. A roller blind needs clearance above the window to roll up. Vertical blinds need clearance to the side for the vanes to stack. A motorized blind needs room for the motor housing.
Common clearance problems:
The blind hits the window handle when loweredThe roller cannot fully retract because it hits the top of the frameVertical blind vanes bunch up because there is not enough stacking spaceThe blind interferes with curtains or another blind on the same windowHow to avoid it:
Open and close your window before installing to check for handle clearance.Measure the total space needed for the blind when fully retracted (the manufacturer's specs will tell you).For vertical blinds, add 4 inches to the window width for proper stacking space.If layering blinds and curtains, plan the depth order (blind closest to the glass, curtain in front).Mistake 7: Skipping the pilot holes
Driving a screw straight into a wood frame without a pilot hole can split the wood, especially near the edges. It can also cause the screw to go in at an angle, which means the bracket sits crooked.
How to avoid it:
Pre-drill a pilot hole that is slightly smaller than the screw diameter.This takes 30 seconds per hole and prevents problems that are much harder to fix after the fact.For hardwood frames, pilot holes are not optional.Mistake 8: Not accounting for child and pet safety
Cord loops that hang within reach of children or pets are a strangulation hazard. This is not just a best practice; it is a serious safety issue.
How to avoid it:
Choose cordless or motorized blinds for any room where children or pets are present.If you have corded blinds, install cord cleats high on the wall and wrap excess cord tightly.Cut loop cords and add individual cord stops so there is no loop to get caught in.Consider cord-free retrofit kits for existing blinds.When to call a professional
DIY blind installation is straightforward for simple jobs: a single roller blind on a wood window frame in a standard window. Beyond that, the complexity rises quickly.
Call a professional when:
You have multiple windows that need to match perfectlyYour walls are concrete, brick, or plasterThe windows are tall or hard to reachYou are installing motorized blinds (wiring and programming are involved)Your windows are non-standard shapes (bay, arched, angled)You have already tried and it is not going wellWhy Blinds Planet?
Professional installation comes included with every Blinds Planet order. No extra charge, no cutting corners.
We measure, we install, and we take responsibility for the fitProper fasteners for every wall type (drywall, concrete, wood, plaster)Level, aligned, and tested before we leaveOld blind removal and disposal included30+ years of family expertise and 5,200+ installations across the GTAGet it right the first time
A bad installation is frustrating to live with and expensive to fix. Professional measurement and installation is included with your Blinds Planet order.
Call (416) 890-4554 or request a free quote online. We will take care of the details so your blinds fit, operate, and look the way they should.
