Building in shelving, units and a dog pen

A wall of built-in shelving, a run of units with a worktop on top and a pen for the dog all come down to the same thing: boxes made from sheet board, fixed together and to the wall. What goes wrong is rarely the joinery. It is a shelf that sags because the bay is too wide, a board short because the parts were never laid out, or a tall case that is not fixed to the wall.

This planner follows the order of work: measure, decide how wide each bay can be, size the units, draw up the cut list and buy the boards, then build, fix and finish. It is for carcasses made from plywood, MDF or chipboard, and it gives a starting list rather than a structural design. A surveyor or a joiner will want to check fixings into old walls, so do ask.

Step 1: Measure the room and decide what goes where

Measure each wall at the top, the middle and the bottom, because rooms are rarely square, and check the floor and the ceiling for level. Note the position of sockets, radiators, windows and the skirting, and find the studs or the type of masonry. Sketch the plan: shelving along one wall, units with a worktop along another, and the pen in a corner or an alcove where fewer sides need fencing.

Step 2: Find how wide a bay can be before the shelves sag

Shelves sag, and then stay sagging. How far a shelf can span depends on the board, its thickness and what it carries. As a guide, 18 mm plywood with books on it spans about 730 mm, MDF about 620 mm and chipboard about 540 mm. A strip of hardwood glued under the front edge, or a thicker board, stretches the span.

Step 3: Plan the bookcase or shelving wall

Divide the wall into equal bays, each no wider than the shelf span. Leave a plinth at the bottom to clear the skirting and a gap at the top for a scribing strip, since ceilings are not level. The calculator counts the bays, the shelves, the boards for the case and the back, the shelf pins and the wall fixings.

Step 4: Size the units and the worktop

A base unit carcass is usually 720 mm high and 560 mm deep, on legs about 150 mm tall, and with a 40 mm worktop it reaches about 910 mm. A wall unit is 300 mm deep. Check the size of any sink, hob or dishwasher before you set the widths. The worktop calculator works out the lengths and joints; the cabinet calculator lists every part, the doors and the hinges.

Step 5: Plan the dog pen

Size the pen to the dog: a floor area that lets it lie out and turn round, a fence tall enough that it will not hop over, and bars close enough that a head cannot get through. A pen in a corner or an alcove needs less fencing. The pen calculator gives the floor area to aim for, the fence height and the panels or timber to buy.

Step 6: Draw up the cut list and buy the boards

List every part with its size and quantity, and the calculator packs them onto 2440 × 1220 mm sheets so you buy the right number rather than guessing. Rip the sheets into strips first, then cut to length with a track saw or a panel saw. Add a few per cent for mistakes, and order the back panels and edging at the same time.

Step 7: Build, fix to the wall and finish

Build the cases as boxes, check them for square, then fix them to the wall through a rail into studs or masonry with fixings that suit the wall. Scribe the end panels to the wall, add the scribing strip and the skirting, then fill, sand and paint. Fit the doors last so they are not damaged while you work.

Before you start

• Measure each wall in three places and check the ceiling and floor for level.
• Find the studs or the type of masonry, and check for cables and pipes before drilling.
• Decide the bay width from the shelf span for your board and load.
• Check the size of appliances, a sink and a hob before setting unit widths.
• Work out the cut list and the number of boards before you buy.
• Plan how the case will be fixed to the wall, and fix every tall unit.

Mistakes that cost people money

• Making bays too wide, so that the shelves sag within a year or two.
• Not fixing a tall case to the wall, which makes it a tipping hazard.
• Buying boards without a cut list, then being one short.
• Building to a wall measurement taken in one place, when the wall is not square.
• Leaving no gap for a scribing strip, then having to cut the case to fit.
• A dog pen too small for the dog, or with bars wide enough for a head to get stuck.

Frequently asked questions