From a helpful YouTube guide. This walk-through draws on the popular UK DIY video "DIY Garden Outdoor Storage Box/Unit - Waterproof with Felted Hinged Lid!". It shows the full build including the framing, assembly, and felting the lid to keep the rain out, which is useful to watch alongside this written guide before you start cutting.
1. Plan the size and sketch a cutting list
Decide what the box needs to hold. A standard garden cushion storage box tends to be around 120 by 60 centimetres and 50 to 60 centimetres tall. For tools and bags, you might want something taller and narrower. Sketch out your dimensions and work out a cutting list from standard sheet timber sizes to minimise waste.
Most timber merchants and DIY sheds stock exterior-grade plywood in sheets of 2440 by 1220 millimetres. 18-millimetre ply is sturdy enough for a garden box without being excessively heavy. Write out the panel sizes you need before ordering.
2. Choose the right timber
For a box that will live outside year-round, use either pressure-treated or exterior-grade plywood for the carcass, or a naturally durable hardwood such as cedar or oak. Avoid untreated softwood: it will rot within a couple of seasons in the UK climate, especially in a wet corner of the garden.
For the lid frame, 44 by 44 millimetre treated structural timber is solid and gives you enough surface area to staple the felt down properly. Check the timber for any significant warps before you buy it.
3. Cut the panels accurately
Mark out each panel with a pencil and straightedge before cutting. A track saw or a circular saw with a guide rail gives a straighter cut than a jigsaw on large panels. Clamp the sheet firmly to a pair of sawhorses before cutting.
Cut the base first. This sets the reference dimensions for the sides. The front and back panels sit on top of the base; the side panels fill in between them, or you can run it the other way, but stay consistent across the build so the joints line up properly.
4. Assemble the box with exterior screws and waterproof adhesive
Use stainless steel or galvanised exterior screws throughout. Ordinary steel screws will rust through in a year or two and the heads will stain the timber. Pre-drill and countersink each hole before driving the screw to avoid splitting the ply edges.
Apply a bead of waterproof wood adhesive (PVA or a polyurethane glue such as Gorilla Glue) along each joint before screwing. The combination of glue and screws is stronger than either on its own. Clamp the joints while the glue cures if you can.
5. Add corner reinforcement on the inside
Cut short lengths of 44 by 44 millimetre timber to fit inside each vertical corner. Screw and glue them in place from both panels. This significantly stiffens the box and reduces the chance of the corners working loose over time. It also gives you something solid to screw the lid hinges into.
If the box is large or will carry heavy contents, add a central cross-member across the base from side to side. This stops the base flexing under load.
6. Build the lid frame
The lid needs a frame to hold its shape and to give the felt something to fasten to. Cut four pieces of 44 by 44 millimetre treated timber to form a rectangle that matches the top of the box, with a small overhang on three sides to help shed rain. Halve-joint or butt-join the corners, gluing and screwing them together.
Cut a panel of 12-millimetre exterior ply to fit inside the frame, or use the frame alone if you are felting directly onto the timber. Screw the panel in from the underside of the frame. The finished lid should sit flat and firm without any flex.
7. Felt the lid to make it waterproof
Roll out a piece of shed felt (or torch-on felt if you prefer a more robust finish) over the lid with a generous overhang on all sides. Staple it firmly along the top surface, pulling it taut as you go to avoid creases. Fold and tack the corners neatly like a wrapped parcel, cutting away the excess to avoid bulky build-up at the corners.
Bring the felt down over the sides of the lid frame and staple along the underside. Apply a bead of exterior silicone sealant along the felt edges where they meet the timber to seal them. This stops water tracking in along the staple line.
8. Fit the hinges and treat the timber
Fit two heavy-duty stainless or galvanised butt hinges to the rear of the box and lid. Position them so the lid opens and stays open without falling backwards. A lid stay is useful if the box is large: it stops the lid slamming down unexpectedly and damaging whatever is stored inside.
Treat the outside of the timber with an exterior wood preserver or stain. Two coats is the minimum. Get into all the end grain carefully as this is where moisture penetrates most readily. Touch up every year or two to keep it protected.
When to call a handyman
If the box needs to match a specific space, or if you want a larger built-in storage solution rather than a freestanding box, that is a job where having someone experienced helps. Richard builds garden storage boxes and log stores across Sandwich and the East Kent area to fit whatever space is available.
Need a garden storage box built?
The Sandwich Handyman can design and build garden storage boxes, log stores, and outdoor timber structures across Sandwich, Deal, Ramsgate, and nearby East Kent villages.
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