What Window Coverings Work Best for Windows with Deep Sills or Wide Trim?

TLDR;

The best window coverings for deep sills or wide trim are cellular shades, roller shades, Roman shades, and café curtains, which can be mounted inside or outside the frame depending on trim depth and aesthetic preference. These options offer versatility, style, and function while accommodating non-standard window dimensions.

Why Deep Window Sills and Wide Trim Need Specialized Solutions

Windows with deep sills or wide trim require tailored treatments because traditional options often don’t fit correctly or clash with the architectural design.

A deep sill is typically anything over 3 inches, while wide trim can be 2.5 inches or more in projection. These dimensions can interfere with how blinds or shades mount and operate, particularly for inside mounts.

Challenges include:

• Obstructed operation of standard blinds
  
• Gaps from poor mounting
  
• Visual imbalance with bulky trim
  
• Limited bracket compatibility
  
  

Custom solutions or flexible coverings are essential to preserve both function and aesthetics.

Measuring Your Window: Sill Depth, Trim Width, and Mounting Options

Choosing the right covering starts with accurate measurements.

Inside Mount vs Outside Mount:

• Inside Mount offers a cleaner look but needs sufficient depth (typically at least 1.5–2 inches for roller shades, more for cellular).
  
• Outside Mount is more forgiving and ideal when trim or sill restricts internal space.
  
  

Steps to Measure:

• Measure window recess depth at three points (top, middle, bottom)
  
• Measure width from edge to edge across the trim
  
• Note any obstructions like handles or locks
  
  

Key considerations:

• Anything under 1.75 inches of sill depth likely won’t support an inside mount.
  
• Wide trim can require projection brackets or spacers for an outside mount to clear the casing.

Best Window Covering Options for Deep Window Sills

Cellular Shades (Honeycomb Shades)

• Perfect for deep sills because of compact stacking and clean fit
  
• Provide excellent insulation
  
• Work well with inside mount if sill depth is 2" or more
  
• Cordless or top-down-bottom-up designs offer both safety and flexibility
  
  

Roller and Solar Shades

• Sleek and minimal, making them ideal for deep or recessed window frames
  
• Can be inside or outside mounted
  
• Solar fabrics protect against UV rays while preserving light
  
• Great in modern homes and office spaces
  
  

Roman Shades

• Excellent for windows with decorative or thick trim
  
• Soft, fabric folds complement classic or traditional interiors
  
• Options for inside mount in deeper frames or outside mount to highlight elegant trim—making them a great choice for double hung window treatments that require both flexibility and style
  
• Relaxed or flat fold styles enhance design without bulk
  
  

Café Curtains and Sheer Panels

• Best suited for kitchens, bathrooms, and farmhouse-style interiors
  
• Half-height coverage lets light in while maintaining privacy
  
• Hang from tension rods or small brackets on the frame or wall
  
• Especially useful in spaces with deep lower sills
  
  

Vertical and Panel Track Shades

• Ideal for deep or large-scale windows like sliders or bay windows
  
• Vertical blinds work well with high-trim walls or multi-pane frames
  
• Panel track systems are easy to operate and mount externally

Can You Mount Shades Inside Deep Window Frames with Wide Trim?

Yes, but you need to assess trim projection and sill clearance.

Inside Mount Tips:

• Use low-profile brackets that allow flush mounting
  
• Consider brands that make specialty brackets for deep window casings (e.g., Shop Love Is Blinds’ Fenstermann-style bracket solutions)
  
• Allow space for shade stack height so it doesn't block sunlight when raised
  
  

Outside Mount Tips:

• Mount above the window frame to avoid interference with trim
  
• Use spacer blocks or projection brackets to clear molding
  
• Use valances or decorative cornices to hide brackets and hardware

Styling Tips: Combining Treatments with Design-Heavy Trim

Trim doesn’t have to clash with coverings. With the right style choices, they can complement each other beautifully.

Design Ideas:

• Layer sheer curtains over roller shades for added depth
  
• Match metal rods and hardware finishes to your window trim color
  
• Use Roman shades in prints that echo the architectural period of your trim
  
• Add a cornice box to bridge between deep sills and high trim for a polished look
  
  

Blending texture, color, and mounting height makes the overall appearance cohesive and elegant.

Comparison Table: Best Window Coverings by Function

Installation Tips: Make it Fit Without Sacrificing Style

Tools to Use:

• Level
  
• Tape measure
  
• Power drill with appropriate bits
  
• Anchors for drywall if no studs
  
• Bracket extenders if trim is especially wide
  
  

Mistakes to Avoid:

• Mounting brackets too close to trim edges
  
• Forcing inside mount with insufficient sill depth
  
• Choosing heavy drapes for light framing
  
  

Trusted Brands to Explore:

• Shop Love Is Blinds
  
• Hunter Douglas
  
• Levolor
  
• Fenstermann
  
• Bali

Product Recommendations and DIY Options

Best Off-the-Shelf Blinds:

• Cellular Shades: Shop Love Is Blinds custom honeycomb options
  
• Roller Shades: IKEA's smart shades or Home Depot's Bali line
  
• Roman Shades: Pottery Barn’s cord-free linen selections
  
• Café Curtains: Target’s Hearth & Hand collection
  
  

DIY Hacks:

• Use copper piping or conduit as curtain rods for wide trim spacing
  
• Combine adhesive mounting brackets with lightweight shades for no-drill installs
  
• Add custom cut-to-size valances to cover unsightly brackets

FAQs About Window Treatments for Deep Sills and Wide Trim

Can I do inside mount with a 3-inch sill depth?

Yes. Most cellular and roller shades only need 1.5 to 2.5 inches to mount flush.

What’s the easiest to install shade for a thick window frame?

Roller shades with outside mount brackets are the most forgiving and simple to install.

Can you combine inside and outside mounts?

Absolutely. Many designers layer an inside-mounted blind with an outside-mounted curtain or valance for function and flair.

What style works best in bathrooms or kitchens with deep windows?

Café curtains or inside-mounted solar shades offer light control without sacrificing space.