My Window Frames Are Crooked: How to Hang Shades Inside Mount Anyway

I live in a house built in 1912, which means I live in a house that is slowly trying to return to the earth. Every time I pick up a level, I regret it. The floors slope toward the center of the building, and the window casings look more like trapezoids than rectangles. Last spring, I spent three hours wrestling with a set of custom romans, only to realize my header was nearly half an inch off from left to right. Learning how to hang shades inside mount in a house that refuses to be straight is a rite of passage for any old-home owner who values a clean aesthetic over easy labor.

• Trust your bubble level, never your window frame.
• Plastic shims are the secret to a horizontal roller tube.
• Always pre-drill to save your original century-old wood trim.
• Toss the screws that come in the box; they are usually junk.

The Old House Dilemma: When Nothing is Plumb

In a perfect world, your window frame is a perfect 90-degree box. In my world, and likely yours if you have original plaster and lath, that box has settled into a parallelogram. Decades of the foundation shifting and the wood drying out mean that the top of your window—the header—is almost certainly sloping. If you just screw your brackets directly into that crooked wood, your shade will hang crooked. It is a mathematical certainty.

The frustration is real. You spend weeks picking the perfect fabric, only to hold it up and see a glaring, wedge-shaped gap at the bottom because the top isn't level. It’s enough to make you want to give up and just throw some cheap curtains over the whole mess. But don’t. The architectural detail of those old frames is worth seeing, even if they aren't perfect. We just have to trick the eye into thinking they are.

Why We Still Fight for the Inside Mount

Despite the headache, the inside mount is the gold standard for a reason. It keeps the profile of the window clean and allows your beautiful moldings to actually breathe. When you tuck a treatment inside the frame, you're highlighting the architecture rather than hiding it. I’ve seen stunning day night shades that look like they were built into the house simply because the owner took the time to recess them properly into a deep wood casing.

An inside mount also offers better light control if you get the fit right. By keeping the fabric close to the glass, you minimize that halo effect around the edges. It’s a minimalist look that works even in maximalist homes because it stays out of the way of your art and furniture. It feels intentional. An outside mount often feels like a bandage; an inside mount feels like a design choice.

The Tools You Actually Need (Throw Away the Cheap Screws)

Before you even touch a bracket, look at the hardware that came in the box. Those silver, zinc-coated screws are garbage. They are soft, the heads strip the moment they meet resistance, and they will snap off inside your 100-year-old oak trim, leaving you with a permanent, unfixable problem. Go to the hardware store and buy some high-quality, 1.5-inch hardened wood screws with a Torx or Robertson head.

You will also need a solid cordless drill, a set of sharp wood bits, and—most importantly—a pack of plastic or cedar shims. A small 12-inch level is better than a long one for this job because it actually fits inside the window frame. I also keep a roll of blue painter’s tape handy for marking my bracket locations without leaving pencil marks on my freshly painted trim.

The Shim Strategy: How to Install Shades Inside Mount Level

The secret to a straight shade in a crooked house is the shim. You aren't going to fix the house, so you have to fix the bracket. First, use your level to find the high side of the window header. Hold your bracket up and see how much space exists between the bracket and the wood when the bracket itself is level. This is where you’ll be placing your shims.

Follow the standard instructions for how to install shades inside mount, but with one modification: you are going to sandwich those shims between the bracket and the top of the frame. This ensures the roller tube or headrail is perfectly horizontal. If the roller isn't level, the fabric will 'telescope'—it will track to one side as you roll it up, eventually fraying the edges of the fabric against the brackets. It’s not just about looks; it’s about the life of the shade.

How to Hang Shades Inside Mount Without Splintering the Wood

Old wood is brittle. If you try to drive a screw directly into century-old pine or oak, it will split like a dry twig. This is where pre-drilling becomes your best friend. Choose a drill bit that is slightly smaller than the shank of your screw. You want the threads to bite into the wood, but you don't want the screw itself to force the wood fibers apart with raw pressure.

Before you drill, check your window depth clearance. You need to make sure your drill bit isn't going to go straight through the casing and hit the weights or the brick behind it. Once you've cleared the path, drill a clean, straight pilot hole. This is the only way to ensure your brackets stay secure for the next twenty years without ruining the historical integrity of your home.

Hiding the Evidence: Making the Gaps Disappear

So, you’ve done it. Your shade is perfectly level, the roller tracks straight, and the brackets are secure. But because your windowsill is crooked, there’s now a half-inch gap on the left side when the shade is closed. It’s the curse of the old house. Don’t panic. Most people will never notice the gap if you manage the light correctly.

If the gap is truly driving you crazy, you can use small 'light blocks'—L-shaped plastic strips that stick to the inside of the frame. But honestly? My favorite trick is to just let it be. A little bit of 'wonk' is part of the charm of an old home. If the shade itself is level, the eye tends to ignore the sloping sill. It’s only when the shade is crooked that the whole room feels off-balance.

My Midnight Measurement Meltdown

I once spent four hundred dollars on a custom linen shade for my primary bedroom. I measured the top of the frame, the middle, and the bottom, just like the guides say. What I didn't do was check if the frame was square. When the shade arrived, it was a perfect fit for the top, but it got stuck halfway down because the window frame narrowed by a quarter inch in the middle. I had to spend a whole Saturday sanding down the inside of my window casing just to get the shade to drop. I learned the hard way: always measure the narrowest point, and always, always use a level before you order.

FAQ

Do I really need to use a level if the window looks straight?

Yes. Your eyes will lie to you, especially in a room where the floor or ceiling is also sloped. A bubble level is the only objective truth in home renovation.

What if my window casing is too shallow for the brackets?

If you don't have at least two inches of depth, you might have to look at a partial inside mount where the bracket sticks out slightly, or switch to an outside mount. Forcing it usually leads to a shade that hits the glass or the handle.

Can I use Command strips instead of drilling?

Absolutely not. Shades are heavy and the constant pulling and tugging will rip a Command strip right off the paint, likely taking a chunk of your wall with it. Do it right the first time and use screws.