The Sash Lock Bulge: Finding Blinds Double Hung Windows Won't Ruin

I remember standing in my first apartment—a drafty 1920s brick walk-up with gorgeous original moldings—holding a set of custom-ordered wood blinds and feeling my heart sink. I’d spent three weeks’ worth of grocery money on them, only to realize that the chunky brass sash lock in the center of my window was pushing the blinds out at a hideous 15-degree angle. It looked broken, cheap, and completely amateur. I had measured the width perfectly, but I hadn't accounted for the physics of the hardware.

Finding blinds double hung windows won't absolutely mangle is a rite of passage for any decorator. It’s a battle against architectural anatomy. You want that clean, recessed look, but the very mechanism that keeps your home secure—the meeting rail and its lock—is actively working against your aesthetic goals. If you've ever felt the frustration of a shade that won't close flush, you know exactly what I'm talking about.

• Prioritize slim profiles like honeycomb or roller shades to clear the middle hardware.
• Always measure the depth from the face of the sash lock, not just the outer frame.
• Use a 'reverse roll' on roller shades to bypass the lock bulge naturally.
• Avoid 2-inch faux wood slats unless you have at least 3.5 inches of casing depth.

The Elephant in the Room (Or, The Sash Lock)

The double-hung window is an American classic, but it is a nightmare for window treatments. The problem lies in the 'meeting rail'—the horizontal bar where the top and bottom sashes meet. Usually, there is a cam lock or a sweep lock sitting right in the center. If you install standard The Awkward Middle Lock: Why Blinds Double Hung Windows Always Bulge, you’ll notice the fabric or slats hit that lock and bow outward toward the room.

It’s not just a visual quirk; it’s a functional failure. When your blinds for double hung windows are pushed out by the lock, they leave light gaps on the sides and put unnecessary tension on the mounting brackets. I've seen brackets pull right out of the drywall because the shade was constantly under pressure from that middle lock. You lose that crisp, tailored finish that makes a room feel finished, and instead, you get a silhouette that looks like it's trying to hide a secret behind the fabric.

The anatomy of these windows means the top sash is usually recessed further back than the bottom sash. This creates an uneven plane. When you drop a straight blind over an uneven surface, the blind will always lose. To fix this, you have to stop thinking about the window frame as a flat box and start thinking about it as a series of obstacles to be cleared.

Inside vs. Outside Mount: Which Actually Works Here?

Designers usually prefer an inside mount because it shows off the window trim and keeps the profile of the room tight. However, double-hung window shades require more depth than most people realize. To get a flush mount, you need enough space for the headrail plus the distance the sash lock sticks out from the glass. In many older homes, that depth simply doesn't exist.

Grab your metal tape measure. Measure from the very front edge of the window casing back to the face of the sash lock. If you have less than 2 inches of clearance, a standard 2-inch blind will never sit right. It will hang over the edge of the trim like a shelf. This is the moment where you have to be honest with yourself: do you force a shallow inside mount and live with the bulge, or do you embrace an outside mount? An outside mount covers the trim but hides the hardware entirely, providing a much cleaner fabric line.

If you're stuck in the middle, look for 'partial inside mounts.' This is where the headrail sticks out slightly, but the fabric drops just behind the trim. It’s a compromise, but it requires precise math. You’ll need to account for about a 1/8-inch deduction on each side to ensure the shade doesn't scrape the paint off your casing every time you pull the cord.

The Best Blinds for Double Hung Windows (That Clear the Hardware)

If you are dead-set on an inside mount, you need to think thin. Roller Shades are my absolute go-to here. They have a tiny footprint and a flat profile. Since the fabric is thin—often a 300-series polyester or a light-filtering weave—it can usually slide right past the lock without a noticeable bump. I recently styled a sunroom with 5% openness solar shades, and they cleared the hardware with just a hair of room to spare.

For ground-floor rooms where you need light but crave privacy, Day Night Shades are a brilliant alternative. These double-hung window shades allow you to keep the bottom half opaque while the top stays sheer. Because they use cellular fabric, they are flexible enough to gently skim over hardware rather than fighting against it like a rigid wooden board would. The 3/4-inch cell size is usually the sweet spot for clearing standard cam locks.

Another option is the pleated shade. Unlike cellular shades, which have a double layer of fabric, pleated shades are a single layer. They take up almost zero depth when fully raised, which is a massive win if you want to maximize your view during the day. Just be sure to choose a high-quality fabric; cheap pleated shades can lose their 'memory' and start to sag after a summer of humidity.

What to Avoid: Slats and Rigid Materials

I’ve seen too many people try to force 2-inch faux wood double hung blinds into a shallow window frame. It never ends well. The rigid bottom rail of a wood blind will sit precariously on top of the lock, leaving a two-inch gap at the bottom of the window where light pours in at 6 AM. It’s the opposite of the cozy, darkened bedroom vibe most of us are after.

When you use slats, the 'jagged' look is emphasized. Every time the blind hits the lock, it tilts the entire stack of slats below it. This ruins the visual weight and horizontal lines of the room. Instead of a calm, structured window, you get a messy, uneven distraction. You can find better options in The Only Blinds Double Hung Windows Wont Ruin With Their Sash Locks, which focuses on materials that actually behave under pressure.

Avoid heavy vertical blinds as well. While they don't have the same sash lock issues as horizontal slats, the vanes tend to rattle against the meeting rail every time a breeze comes through the screen. It’s a constant 'clack-clack-clack' that will drive you crazy during a peaceful afternoon nap.

The Designer Trick: Reverse Roll and Layering

Here is the secret I tell all my clients: order your shades with a 'reverse roll.' Normally, the fabric hangs off the back of the tube, close to the glass. A reverse roll makes the fabric fall off the front of the roller, giving you an extra inch of clearance. It effectively 'jumps' over the sash lock. It’s a simple mechanical change that solves 90% of your window treatments for double hung windows problems without requiring any extra hardware.

If you want the ultimate high-end look, I recommend Canisteo Motorized Dual Roller Shades Cordless Custom Double Roller Blinds. This allows you to layer a solar screen for daytime glare and a blackout shade for sleep. Because they are custom-engineered, you can specify the roll direction to ensure both layers clear your hardware without the dreaded 'sash lock hump.' Plus, motorization means no messy cords tangling with your window cranks or locks.

I once tried to 'hack' a set of bamboo shades in a rental by carving a small notch out of the bamboo to fit around a particularly aggressive window lock. It was a disaster. The bamboo started unravelling within a week, and I ended up losing my security deposit over a $40 shade. Lesson learned: don't fight the hardware. Buy the right profile from the start, or go with an outside mount and a beautiful valance to hide the transition.

Can I use Roman shades on double-hung windows?

Yes, but stick to a 'flat' or 'European' fold. These use less fabric depth than a 'hobbled' style, meaning they are less likely to get caught on the lock when you raise and lower them.

What is the minimum depth for an inside mount?

Most honeycomb shades need about 1.5 inches for a partial mount, but for a truly flush look that clears a sash lock, you really want 2.5 to 3 inches of depth from the face of the lock to the edge of the trim.

Do I need to replace my sash locks?

Sometimes! If you have an old, bulky cam lock, switching to a modern 'slimline' sash lock can buy you an extra half-inch of clearance, which is often the difference between a blind fitting or bowing out.