Build a Window Seat With IKEA BESTA Frames in 8 Steps for 30% More Storage

Start with the 38cm frame, not the taller one

The BESTA range includes 20cm and 40cm depths, with common frame heights of 38cm, 64cm, and 128cm. For a bench under a window, the useful carcass is the 40cm-deep, 38cm-high frame, listed on IKEA as BESTA frame 60x40x38. Once you add an 18mm plywood capping board, small feet or a recessed plinth, and a 50mm cushion, the finished seat falls in the 42cm to 48cm band that reads like normal bench height.

The 64cm frame belongs in a different build. Add a 5cm pad to that carcass and the sitting surface is already about 69cm before any plywood cap is counted, so it becomes a high perch rather than a window seat.

The particleboard box still needs restraint. With its back panel fitted and the frame fixed to the wall, the carcass can take a static seated load far better than it can resist side racking from the open front. A freestanding BESTA unit loaded along the top front edge will work loose over time. Two wall anchor points per frame, into studs or masonry where available, remove that wobble, and the metal wall bracket and anti-tip fitting supplied with the unit are there for that job.

Steps 1 to 4: measure, assemble, level, and anchor

Measure the bay or recess in three places: down at the floor, around seat height, and near the top of the intended run. Plastered reveals are rarely parallel, and walls can be 15mm to 20mm out over a two-metre span in older houses. Use the smallest width as the working dimension. Three 60cm frames need 180cm of clear width plus a little tolerance; in a 184cm recess, the spare 4cm can disappear into end fillers cut from 18mm plywood.

Build each BESTA frame flat on the floor, following the instruction sheet, and slide the back panel in before standing the box upright. That thin back is the part that squares the frame. Skipping it during the dry fit makes every later measurement less reliable.

Set the frames in their final positions and check each one with a spirit level from front to back and from side to side. Shim under the feet with the plastic packers from the bracket bag or small pieces of 3mm hardboard until the top edges lie in one plane. Even a 2mm step between neighbouring boxes can show through the plywood cap, especially along the cushion front.

Clamp adjacent frames through their side panels and fit two M6 connecting bolts at each joint. These are the same style of connectors used to gang BESTA or KALLAX units in a run. The row should behave as one long carcass before the wall brackets go in.

Now deal with the wall. Mark the bracket positions through the back panel, find studs with a detector, or drill for an 8mm frame fixing in masonry. Put one bracket near the top of each frame and drive it into solid backing. Where plasterboard leaves no stud in the right place, use a metal cavity fixing rated for at least 25kg per anchor. The bracket matters most when someone sits on the front edge and pushes down to stand, because that action tries to tip the bench forward.

Storage figures should be tied to the frame actually used. A 60x40x38 BESTA box holds close to 60 litres before shelves, doors, or drawers reduce the clear space. The taller 60x40x64 version is closer to 120 litres, which is useful for cabinets, but it is the wrong starting height for this seat. Three of the 38cm-high frames give roughly 180 litres gross under the cushion.

Against an open-front bench of the same footprint, the closed BESTA boxes can come out about 30 percent ahead in usable stowage when the open design gives up the lower 12cm to 15cm to a face rail and leaves the rear zone awkward to reach. The comparison depends on that bench construction, not on any hidden capacity in the BESTA frame.

With the frames bolted together and fixed to the wall, choose the front access. BESTA doors on soft-close hinges keep the face simple. Internal drawer runners make the back of a 40cm-deep box easier to use, since the contents come forward instead of being reached from above through the cushion line.

Steps 5 to 7: cap the boxes and make the cushion

Cut one continuous capping board from 18mm birch plywood. Let it overhang the front of the carcass by about 30mm and run tight to the wall at the back. A single board across all three frames hides the joints and gives the cushion a clean front edge.

Soften the front edge with a 6mm roundover bit or careful sanding. A square plywood arris will press into the back of the knee, especially through thinner upholstery fabric. Fix the board from inside the frames with 30mm screws driven upward through existing top-panel fixing holes, leaving the seat surface free of screw heads.

For the cushion, use 50mm high-density upholstery foam at around 35kg per cubic metre. It keeps its shape under repeated sitting better than the softer reflex foam sold for backrests. Cut the foam 5mm smaller than the board all round so the fabric cover pulls tight at the edges.

A removable cover with a zip on the back edge is easier to wash. Add a thin layer of polyester wadding over the foam and hold it with spray adhesive, which stops the foam corners showing as hard lines through the fabric.

If the bay takes direct afternoon sun, hang thermal curtain lining so it falls just to the seat lip. That protects the exposed cushion face from fading and reduces the heat the glass sends into the storage below during summer.

Closed storage against a cold external wall has one awkward trait. Under single glazing, the space behind a closed door can become a still-air pocket against cold plaster, and stored fabrics may pick up damp over winter. A 25mm air gap behind the back panel and a few drilled vent holes in the doors can help the cavity breathe, though the wall construction still decides how dry that pocket stays.

Step 8: fit the fronts after the cushion

Install the BESTA doors or drawer fronts once the cushion is in place. Foam thickness, fabric tension, and shims can move the visual line by a few millimetres, so final hinge adjustment is best done against the finished seat.

Push-open catches keep the face flush with no visible handle. They also avoid handle projections under the front overhang, where knees and vacuum cleaners catch them.

A 196cm bay worked through

Suppose the bay measures 196cm at the narrowest of the three readings. Three 60cm frames occupy 180cm and leave 16cm. Split evenly, that gives an 8cm filler at each end. Cut the fillers from the same 18mm birch plywood as the cap, screw them to the outer frame sides, and run the top board across the full 196cm so the filler line disappears beneath the cushion.

Storage in that layout is straightforward. Three boxes at roughly 60 litres each give 180 litres gross. Add one 30mm fixed shelf in each box and the clear stowage comes down to about 165 litres, reached through three soft-close doors. An open bench across the same bay with a 15cm front rail and an awkward hollow zone at the back gives up a noticeable share of that usable depth.

On a splayed bay, the end fillers are doing cosmetic work. They carry no seated load, so two screws into each outer frame side are enough; the wall brackets and inter-frame bolts take the working forces. Wedge-shaped fillers keep the front face parallel to the room while the awkward gap retreats to the wall. After the doors are adjusted and the cushion drops on top, the only unfinished-looking place is the shadow line where the filler meets an old, uneven reveal.