How to Build a Window Bench | Custom Seat Plans

A custom window bench is built by framing a level base from 2x4s or stock cabinets, adding a plywood top, then trimming and painting the assembly for a built-in look with optional storage.

Building a window bench turns an empty nook or bay window into usable seating and storage. The project takes a weekend for most DIYers and costs far less than a custom-built unit. The key is getting the framing level, the height comfortable, and the finish clean enough that the bench looks like it was always part of the room.

Planning the Dimensions

The seat height that works for most adults is about 18 inches, matching standard chair height. Depth varies with how you plan to use the bench. The pros at Fine Homebuilding suggest roughly 16 inches for upright seated reading, 24 inches if you want to sit sideways with your feet up, and up to 30 inches for a loungeable perch where you recline against cushions. Lowe’s recommends staying between 16 and 20 inches deep for a bay-window bench with storage underneath. Measure your nook’s width at both the front and back walls — bay windows often taper — and subtract the thickness of the plywood and trim from your final plan.

Framing the Base

This Old House describes two solid base methods: build a frame from 2x4s and plywood, or use stock kitchen cabinets as drop-in base modules. Either approach works — cabinets save cutting time, while custom framing lets you match odd angles exactly. Start by removing any baseboards or moulding from the walls where the bench will sit. Use a stud finder to locate wall studs and mark their positions on the floor and sill. Draw a level line on the wall at your chosen seat height (minus the top’s plywood thickness). Frame the front span with 2x4s screwed into the studs using 2.5-inch screws, then add corner blocks and interior supports. Drive 3.5-inch screws into the studs through the wall-side battens for a rock-solid anchor. If you are building a bench for a bay window, measure the corner angle where two walls meet — a 135-degree angle takes 45-degree miter cuts on the frame ends, while a 120-degree corner uses 60-degree cuts. When you are ready to buy, see our recommendations for bench seating options that fit different room layouts.

Sheathing, Finishing, and Common Mistakes

Once the frame is level and secured, sheath the front and top with 3/4-inch plywood or MDF. Drill pilot holes for all screws and use double-countersunk screws so the heads sit below the surface. Fill every screw hole with wood filler, caulk all seams where the bench meets the wall, and let the caulk dry for about 30 minutes to an hour before sanding and painting. Prime first, then apply two coats of paint in a satin or semi-gloss finish — those sheens wipe clean easily. For storage lids on a bench with lifting seat sections, Lowe’s recommends drilling finger-access holes so lids are easy to lift. The biggest mistakes that trip up first-time builders are skipping stud location, forgetting to subtract plywood thickness from measurements, and assuming the floor is level — always shim the frame so the top sits level even if the floor slopes. Lowe’s bay window bench guide shows the full sequence with diagrams and material lists.

FAQs

Can I build a window bench without removing baseboards?

You can leave baseboards in place, but the bench will sit proud of the wall and may leave a gap. Removing the baseboards first lets you fit the bench flush against the wall, then reinstall the trim or add new skirting for a seamless built-in look.

What plywood thickness should I use for the seat top?

Three-quarter-inch plywood or MDF is the standard choice for the seat top — thick enough to support an adult’s weight without sagging between supports. Use exterior-grade plywood if the bench sits near a window that sees moisture or direct sun.

How do I make a window bench with angled bay corners?

Measure the inside angle where the two walls meet, then divide by two to find your miter cut. A 135-degree corner takes two 67.5-degree cuts on the frame pieces, and a 120-degree corner takes two 60-degree cuts. Always test-fit the mitered frame pieces before cutting the plywood top.