Inspired by a helpful YouTube guide. We based this walk-through on the popular UK video "How to make a window seat with storage, Part 1 of 2 #007" by Peter Millard of 10 Minute Workshop, a West London-based carpenter whose channel has over 300,000 subscribers.
1. Plan and measure the space
Before you cut anything, spend time measuring and drawing out the space. The seat height will usually be somewhere between 400mm and 450mm from floor to lid - check what is comfortable for your household. The depth from front to back should ideally match the window sill depth or sit just below it. Width is whatever the alcove or bay gives you.
Think about what the storage will hold - blankets and cushions are fine with a simple box; toys or books may be better served by a divided interior or shelves instead of a lid. Sketch it out and note all dimensions before buying any sheet material.
2. Choose your materials
18mm MDF is the most common choice for painted window seats - it takes paint well, is easy to work with, and is inexpensive. Plywood (birch ply or structural ply) is stronger and holds screws better, which matters if the lid gets a lot of use. Avoid chipboard for anything structural.
For a painted finish, MDF is fine and the grain-free surface is easier to get smooth. For a stained or varnished finish, use ply. If the seat has to span a long distance, consider adding a mid-span support leg or using thicker material for the lid to stop it sagging when someone sits on it.
3. Cut the box sides and base
Cut the two side panels, the front panel, and the base from your sheet material. The back of the box is usually the wall, so you will not need a back panel - the box sits against the wall directly. Cut everything square and check measurements again before cutting - sheet materials are not free.
If the alcove walls are slightly out of square, scribe the side panels to the wall rather than cutting a perfect rectangle and hoping it fits. Hold the panel in position, run a compass along the wall, and cut to the scribed line. This takes longer but gives a much neater result.
4. Assemble the main box
Join the sides to the base with PVA wood glue and 50mm screws. Drill pilot holes first to avoid splitting the material, and countersink the screws so the heads sit below the surface. Clamp each joint while the glue sets if you have clamps, or hold it firm while the first few screws go in.
Check the box is square by measuring diagonally corner to corner - both diagonals should be the same length. If they are not, clamp across the longer diagonal to pull it into square before the glue sets. This matters for the lid to fit properly.
5. Fix the box in position
Offer the box up to the alcove and check it sits level. If the floor is uneven - and most older houses have floors that are not perfectly flat - pack under the base with folded cardboard or thin plywood shims until the top of the box is level. Secure the box to the wall using angle brackets screwed into the sides and wall plugged into the plaster.
If the seat spans a long bay window, a central support leg or a mid-span fixed shelf keeps the lid from flexing. Trim any excess front panel to sit flush with the front of the lid once fitted.
6. Cut and fit the lid
The lid is the face of the whole thing, so cut it carefully. It should overhang the front of the box by about 20-25mm (this becomes the front edge you lift by) and sit flush at the sides and back. Cut from the good face down to reduce chipping if using a circular saw, or score the cut line with a knife first.
Sand the edges smooth and, if using MDF, seal the edges with diluted PVA or an MDF primer before painting - bare MDF edges absorb paint and go fuzzy otherwise. Round over the front edge with 120-grit paper for a comfortable finished feel.
7. Fit the piano hinge
A piano hinge (continuous hinge) spread along the full width of the back edge of the lid gives the smoothest action and shares the load evenly. Mark the hinge centreline along the back of the lid and along the top of the back panel, then screw it down with the lid held in position. Start with a screw at each end and in the middle, check the lid opens and closes cleanly, then add the remaining screws.
A lid stay - the small hinged arm that holds the lid open without it falling back - is worth fitting if children will be using the seat. They are inexpensive and straightforward to install. Fit one at each end for a long lid.
8. Fill, prime, and paint
Fill screw holes and any gaps with a flexible filler (not interior filler, which cracks with movement). Sand flush once dry. Prime the whole piece before applying topcoat - two coats of a good acrylic eggshell or satin in the same colour as the room's woodwork will tie the seat in nicely. Sand lightly between coats with 240-grit paper.
Caulk the joint where the seat meets the walls and skirting with a flexible decorators caulk rather than rigid filler - this allows for the movement that happens in a lived-in house. Once the paint is fully dry, add a cushion and the job is done.
When to call a handyman
This is a manageable DIY project if you are comfortable using a circular saw and working to accurate measurements. That said, a few situations make it worth calling someone in. If the alcove walls are very uneven, if there is a radiator or pipework to work around, or if you want the seat to match existing built-in furniture precisely, getting the fit right takes more experience than a typical DIY job. A seat that is slightly wonky or has visible gaps at the walls will always look like a DIY seat.
If you would rather have it built properly than attempt it yourself, Richard covers carpentry and fitting work around Sandwich and nearby East Kent villages. Describe the space and what you have in mind and he can give you an honest steer.
Need help building a window seat?
Richard covers fitted carpentry and handyman jobs around Sandwich and East Kent. Happy to take a look at the space and talk through options before committing to anything.
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