Almost every chimney breast has two alcoves sitting either side of it, and in most houses they're doing nothing but gathering a lamp and a tangle of charger cables. Fill them with proper fitted shelving and you get bookcase-grade storage that looks built-in, costs a fraction of made-to-measure joinery, and takes a single weekend. The catch is that those recesses are almost never square — older walls lean, splay and bow — so the real skill isn't cutting shelves, it's making imperfect shelves look perfect.
Measure the alcove at several heights
Never trust a single measurement. Take the width at the top, the middle and the bottom of each alcove, and do the same for the depth front and back. You'll usually find a centimetre or more of difference, and the two alcoves either side of the same breast often aren't the same size as each other. Write every figure down on a rough sketch. The widest measurement is the one that matters for fitting — a board cut to the narrowest point will leave a gap, but one cut a hair over the widest can be eased and scribed in.
Decide your shelf spacing while you're at it. Around 280–320mm between shelves suits most paperbacks and ornaments; leave one taller bay near the bottom for box files, a record player or larger books. There's no rule that says the gaps have to be identical, and varying them slightly actually looks more deliberate.
Choose your material
For painted shelving, 18mm MDF is the sensible default — it's flat, stable, cheap at around £25–35 a sheet, and cuts cleanly. If you want a natural timber finish, go for furniture-grade plywood with a lipping on the front edge, or solid pine if you don't mind a bit more movement. Avoid anything thinner than 18mm for shelf boards longer than about 700mm, or they'll bow under a row of books within a year. For the support battens, 25mm x 25mm (1" x 1") softwood is plenty.
Fix the battens — the part that does the work
The shelves sit on a frame of battens screwed to the back and side walls, hidden once the boards go on. This is where the strength comes from, so get the fixings right for what you're screwing into.
Into masonry
A chimney breast is usually solid brick, so the side battens screw straight into it with 50–60mm screws and brown wall plugs. Drill with a masonry bit, and keep clear of the flue if the chimney is still live. Use a long spirit level — ideally a 1.2m one — to set each batten dead level, and check across the alcove from side batten to back batten so the whole shelf will sit flat, not just level left-to-right.
Into plasterboard
The back wall of an alcove is often a stud or dry-lined wall rather than solid brick. Find the timber studs with a detector and screw into those wherever you can; where you can't hit a stud, use proper plasterboard fixings rated for the load, not the flimsy plastic ones that came free with a flat-pack. A shelf carrying a metre of hardback books is holding 15–20kg, and a failed back fixing is what makes a shelf sag in the middle.
Cut and scribe the shelves to fit
Here's the trick that separates a fitted shelf from a wobbly board on a bracket. Cut each shelf about 2–3mm under the widest width so it drops in, then hold it in place and use a small block of wood and a pencil to scribe the wall profile onto the board — run the block along the wall with the pencil against it, and it traces every bump and lean. Plane or sand down to that line and the shelf will sit tight against the wall with no gap, even though the wall is anything but straight. Do this for both ends and, if the back wall bows, the back edge too.
Rest each shelf on its battens and check it with the level front-to-back; a shelf that tips forward looks fine but slides everything off over time. Once you're happy, fix the boards down to the battens with a couple of countersunk screws or panel pins into each bearer so they can't lift.
Fill, caulk and paint for the built-in look
The illusion of joinery comes almost entirely from the finishing. Fill the screw heads with two-part wood filler, sand flush, and — this is the important bit — run a bead of decorator's caulk along every join where shelf meets wall, then smooth it with a wet finger. That caulk line erases the last hairline gaps and makes the shelving read as one solid unit rather than separate boards. Prime any bare MDF edges (they drink paint otherwise), then finish in the same colour as the wall for a seamless recess, or a contrasting tone if you want the shelving to stand out. Two coats of a durable eggshell or satinwood will wipe clean and won't scuff like matt emulsion.
A weekend well spent
Set against the £400–800 a joiner would quote for the same thing, a pair of fitted alcoves costs you a sheet or two of MDF, a handful of battens and screws, and a couple of days. The measuring and scribing are fiddly the first time and quick the second, so do the simpler alcove first to find your rhythm. Get the battens level and the scribing tight, and nobody who sees the finished room will believe you didn't pay someone.