Measurement errors are the single biggest cause of blind installation problems. I have seen brand new blinds that had to be returned because they were ordered 20mm too wide for an inside mount, or curtain rods that were cut too short because someone measured the glass instead of the full window opening. Getting the measurements right before you order is critical, and it is trickier than most people expect, especially in older Northern Rivers homes where nothing is perfectly square or level.
How to Measure for Inside Mount Blinds
Inside mount means the blind sits within the window recess, flush with the wall. For this to work well, you need accurate measurements of the recess width, height, and depth. Here is how I do it.
For the width, I measure the inside of the window recess at three points: the top, the middle, and the bottom. In a perfect world all three measurements are the same. In reality, especially in homes around Bangalow, Mullumbimby, and the older parts of Byron Bay, they can vary by 5mm or more. I take the narrowest measurement and that becomes the ordering width. Most blind manufacturers will then deduct a further 2 to 3mm from each side to allow for installation clearance, so the blind operates smoothly without rubbing against the frame.
For the height, I measure the inside of the recess at the left, centre, and right. Again, I take the shortest measurement to make sure the blind does not end up too long for the recess. If the height variation is more than about 5mm across the window width, I flag this because it means the bottom of the blind will not sit evenly against the sill. In severe cases, outside mount is a better option.
For the depth, I measure how deep the recess is from the wall surface to the window glass. Different blind types need different minimum depths. Roller blinds typically need 60mm or more. Venetian blinds need 75 to 80mm. If the recess is too shallow, the blind will stick out past the wall surface and look awkward, or worse, interfere with the curtain or other window treatments. If the depth is borderline, I always recommend outside mount instead.
How to Measure for Outside Mount Blinds
Outside mount is more forgiving on measurements because the blind overlaps the window opening rather than sitting inside it. But you still need to measure carefully to get a good result. I measure the full width of the area I want the blind to cover, which is usually the window opening plus 50 to 100mm overlap on each side. This overlap ensures no light leaks around the edges and gives the installation a clean, finished look.
For the height, I measure from where the top of the bracket will sit down to where I want the bottom of the blind to reach. For most windows, that is 100mm above the window opening down to the window sill or slightly below it. For floor-length blinds or curtains, I measure down to 10 to 15mm above the floor to allow for clearance.
The mounting surface above the window also matters. I need solid material to screw the brackets into, whether that is timber framing above the window, a concrete lintel, or plasterboard with studs behind it. If the area above the window is just plasterboard with no framing, I need to use heavy-duty anchors or install a timber batten across the top of the window to create a solid fixing point.
Common Measurement Mistakes
The mistakes I see most often on measurement are straightforward but costly. Measuring the glass size instead of the recess or opening size is a common one, and it always results in blinds that are too small. Measuring only once at one point instead of at three points across the width and height is another one, and it causes problems in older homes where the openings are out of square. Confusing inside mount and outside mount measurements when ordering is surprisingly common too, and it means the blind arrives completely the wrong size for the intended installation method.
Another frequent mistake is not accounting for obstructions inside the recess. Window winders, security stays, tilt-and-turn handles, and even window sensors can all interfere with an inside-mounted blind. I check for these obstructions during my measurement visit and factor them into the recommendation. Sometimes a simple bracket spacer solves the problem. Other times, outside mount is the only practical option. Either way, it is much better to discover this before you have ordered and paid for the blinds.
Stacking Clearances for Curtains and Dual Blinds
If you are installing curtains, the rod or track needs to extend beyond the window opening on each side so the curtains can stack clear of the glass when open. This is called the stacking allowance, and it is typically 150 to 250mm on each side depending on the curtain fabric weight and fullness. Heavy blockout curtains need more stacking room than lightweight sheers. If you skip the stacking allowance, your curtains will permanently cover part of the window even when open, which blocks natural light and makes the window look smaller.
For dual blind systems, like a sheer roller blind behind a blockout roller blind, you need enough depth in the recess or enough clearance from the wall to fit both brackets without the blinds touching each other. Dual brackets are typically 80 to 100mm deep in total. I check the recess depth and wall clearance before recommending a dual system, and if space is tight, I can use low-profile brackets or offset the front blind to an outside mount position while keeping the rear blind as an inside mount.
Motorised Blind Wiring Considerations
Motorised blinds are becoming increasingly popular across the Northern Rivers, especially in homes with hard-to-reach windows or for people who want smart home integration. Most modern motorised roller blinds are battery-powered, which means no wiring at all. I install the blind, fit the motor, pair the remote or connect it to your wifi bridge, and you are good to go. Battery-powered motors typically last one to two years between charges depending on usage, and they recharge via USB.
For hardwired motorised systems, which are common in new builds and higher-end installations, a power supply needs to be available at or near the window head. This usually means a power point inside the pelmet or a low-voltage cable run from a central transformer. I do not do electrical wiring myself as that requires a licensed electrician, but I coordinate with local sparkies in Byron Bay and the Northern Rivers regularly for these jobs. I install the blind and the mounting hardware, and the electrician runs the power. We can usually do both in the same visit to keep things simple for the customer.
