NotchLoading plan…
Loading plan…
Wood window boxes rot from the inside out — they hold damp soil against end grain for months at a stretch, and even a good finish eventually loses that fight. Building the box from PVC trim board instead removes the problem entirely: PVC doesn't absorb water, so there's no rot risk to manage with paint or sealant in the first place.
Joinery here is PVC cement, not glue — a solvent weld that actually fuses the pieces together at the surface, backed up with finish nails for immediate positioning while the weld cures.
Measure your window's width before cutting anything. That single measurement sets the length of every long piece in the box; the plan scales directly to whatever window you're building for.
| Item | Qty |
|---|---|
| PVC trim board, 1x8, 10 ft | 1 each |
| PVC trim board, 1x3, 8 ft | 1 each |
| PVC trim board, 1x2, 8 ft | 1 each |
| PVC cove moulding | 1 each |
| PVC cement | 1 can |
| Exterior caulk | 1 tube |
| Finish nails, 1-1/4" | 1 box |
| Mounting screws (Tapcon for brick, wood screws for siding) | 10 each |
Overall cost: $$. Lumber prices vary by region, species, and season, so we give a band rather than a figure we would only be pretending to know.
| Part | Qty | T × W × L |
|---|---|---|
| Front/back panels1x8 PVCAdjust length to match your window's width. | 2 | 3/4" × 7 1/4" × 32" |
| Bottom1x8 PVC, ripped | 1 | 3/4" × 6 1/2" × 32" |
| End panels1x8 PVC | 2 | 3/4" × 7 1/4" × 8" |
| Front trim1x2 PVCMitered both ends. | 1 | 3/4" × 1 1/2" × 33 1/2" |
| Side trim1x2 PVCMitered one end. | 2 | 3/4" × 1 1/2" × 8 1/2" |
| Mounting cleats1x3 PVCMitered lengthwise along the top edge. | 2 | 3/4" × 2 1/2" × 30 1/2" |
Buy 4 boards at 8 ft.
1 board
1 board
1 board
1 board
Assumes 8 ft stock, a 1/8" saw kerf, and buying each part at its own width. Change the board size or kerf on the full board plan →
Measure the window's width — this sets the box's overall length. Cut all PVC pieces per the cut list, mitering the trim pieces as noted.
Glue the ripped bottom panel to one of the long side panels with PVC cement and finish nails, set in 3/4in from the edge.
Attach the two end panels with PVC cement and finish nails to close up the box.
Attach the mitered trim pieces around the top edge, and the cleat pieces to the back for mounting.
Caulk any remaining seams, then mount to the house with Tapcon screws on brick or wood screws on siding.
No reviews yet
Sign in to review this plan or share your build.
No reviews yet. Be the first to build this.