Creating a cornice board valance is a rewarding window treatment project that adds architectural definition and a polished finish to any room. Unlike soft fabric valances, a cornice is a rigid, tailored box that sits atop the window, concealing the curtain hardware and framing the glass with clean lines. This guide provides a detailed, step-by-step process for constructing a professional-looking cornice board valance using medium-density fiberboard (MDF) or plywood.
Understanding the Cornice Board Valance
A cornice board valance serves both functional and aesthetic purposes. Functionally, it hides the curtain rod, finials, and the header of the drapery panels, creating a seamless look. Aesthetically, it acts as a design statement, adding height and visual weight to the window. The structure is typically built in a workshop and then painted on-site for a flawless finish, allowing for crisp lines and perfect symmetry that is difficult to achieve with fabric alone.
Tools and Material Necessities
Before beginning, gathering the correct materials ensures a smooth construction process. You will need MDF or plywood for the main body, which provides a solid and paintable surface. For assembly, wood glue and a pin nailer are essential for creating strong, immediate bonds. You will also require wood filler to hide any nail holes, sandpaper in various grits for a smooth surface, a sturdy saw for cutting precise angles, and measuring tools to guarantee accuracy.
| Material/Tool | Purpose |
|---|---|
| 3/4" MDF or Plywood | Main structure of the valance |
| Wood Glue & Pin Nailer | Assembly and initial fixation |
| Wood Filler & Sandpaper | Surface preparation and finishing |
| Miter Saw or Circular Saw | Cutting precise 45-degree angles |
Taking Accurate Measurements
Precision begins with measurement. Use a tape measure to determine the exact width of the window frame where the valance will sit. Decide on the desired depth of the cornice; standard depths range from four to six inches, which provides enough volume to look substantial without overwhelming the window. Transfer these measurements to the MDF board, marking the top, bottom, and sides with a pencil and a straightedge to ensure every cut is deliberate and accurate.
Cutting the Boards to Size
With the measurements transferred, cut the MDF to create the top piece and the two side pieces. The top piece should match the width of the window, while the side pieces should match the chosen depth. To achieve a professional, finished corner, set your saw to a 45-degree angle. Cut the ends of the side pieces at this angle so they will meet the top piece to form a neat, mitered corner. Dry-fit the pieces together to confirm the angles align perfectly before proceeding to assembly.
Assembly and Structure Building
Apply a generous bead of wood glue to the mitered edge of one side piece and attach it to the underside of the top piece. Secure the joint immediately using a pin nailer, driving nails through the top into the side piece to lock the angle in place. Repeat this process for the second side piece, ensuring the corners are square and the structure resembles a shallow box. Wipe away any excess glue with a damp cloth to prevent it from interfering with the finishing process later.
Finishing and Installation Techniques
Once the glue is dry, fill the nail holes and any imperfections with wood filler, allowing it to dry completely. Sand the entire cornice board with progressively finer grits of sandpaper until the surface is perfectly smooth to the touch. This step is critical for achieving a high-gloss paint finish. To install, attach the valance directly to the wall or to a front-facing board mounted above the window frame using construction adhesive and screws, ensuring it is level before the adhesive sets.
Fabricating the Fabric Cover
After the cornice board is installed, it is time to cover it with fabric. Cut a piece of decorator fabric that is wide enough to wrap over the front and deep enough to fold neatly into the interior. Stretch the fabric tightly over the board, securing it with staples along the back edges. For a tailored liner look, you may line the fabric with batting or a thin foam to add body and prevent sagging. Finally, fold and staple the corners as if wrapping a gift, creating a crisp, professional appearance that elevates the entire window treatment.
