What Is a Window Board?
A window board (also called a window sill board) is the horizontal shelf fitted at the base of a window frame on the interior side. It provides a clean, finished look to your window reveal while protecting the wall below from moisture and condensation.
Why Choose MDF?
MDF (Medium Density Fibreboard) is the most popular choice for interior window boards in UK homes because it:
- Is moisture-resistant when primed and painted
- Offers a perfectly smooth, paint-ready surface
- Is more affordable than solid timber
- Won't warp, split, or knot over time
- Comes pre-primed, saving you preparation time
What Sizes Are Available?
MDF window boards are typically available in a range of widths (150mm–400mm) and thicknesses (18mm–25mm), with lengths cut to suit your window reveal. Always measure your window reveal depth before ordering — add 15–20mm overhang on each side for a neat finish.
How to Choose the Right Window Board
- Width: Measure the full depth of your window reveal from the frame to the plaster line
- Thickness: 18mm is standard for most domestic windows; 25mm gives a more substantial, premium feel
- Length: Measure the internal width of the window opening and add your desired overhang
- Finish: Our boards come pre-primed and ready to paint in any colour
Installation Tips
- Use grab adhesive and panel pins for a secure fix
- Seal the back edge with decorator's caulk to prevent moisture ingress
- Fill any pin holes before painting for a flawless finish
- Always prime cut edges before painting
Shop MDF Window Boards
Browse our full range of pre-primed MDF window boards — cut to size, delivered across the UK.