A two-car garage that still fits two cars

A double garage is two single garages with the tight bit in the middle

A double garage loses a car the same way a single one does: a shelf goes along one wall, then a bike, then a workbench, and one car lives on the drive. The reason it happens is that nobody measured with the doors open. Two cars side by side create one walkway down the middle that has to take both inside doors, one walkway along each outer wall that takes one door, and an end wall that takes nothing but the bonnets. Each of those walls can carry a different depth of storage, and the middle can carry none.

The premise is the same as every garage project. The floor is the scarce resource — here it is spoken for twice over — and the walls are the free one. A double garage that still holds two cars is a garage where everything except the cars has gone up the walls, above the height a car door swings, or onto the one wall nothing swings into.

Measure with the doors open, not with the cars parked

Park both cars where they normally sit. Open every door to its first stop, the position it holds itself at, and the boot or tailgate at the back. Now chalk the floor at the furthest edge of every door and the widest point of every mirror. Those chalk lines are the real footprint of the cars. The gap between a chalk line and the wall is the depth you can use on that wall below door height, and on most side walls it is nothing.

Do it with the cars you have and the way you park them. A car reversed in puts the driver's door on the other side; a bigger car next year moves every line; a child's door opened to the second stop reaches further than yours. The numbers are yours, which is why this guide does not give them. What it can say is that the up-and-over door adds its own line: the panel and track occupy the ceiling and the first metre of wall when the door is open, and nothing fixed lives there.

What each wall can take

The measured gaps sort the walls into four kinds. A side wall beside a door is limited by the door swing below the height of the door top, and above that height it is free. The end wall in front of the bonnets is never swung into, so it takes the deepest storage in the garage, minus the bonnet overhang and a margin for the day you park a foot further in. The wall by the up-and-over door is dead along its first stretch. And the middle takes nothing but people.

Depth is the word that matters in that table. A shallow steel shelf sits above a car door on a side wall and takes tins and the middling things; a boltless shelving unit stands against the end wall to the depth the bonnets leave. Check the depth of any shelving before it goes on a side wall; a unit that is fine against the end wall is a door dent against the side, and you find that out with the door.

The wall behind the bonnet is different, and it is the one to use

The end wall is where a double garage keeps its storage, because it is the only wall a door never swings into. Both bonnets stop short of it, and the gap between bumper and wall is the depth of shelving you can have, less a margin. Set the margin with something you can see from the driver's seat: a mark on the wall at eye level, or a ball hung on a string that touches the windscreen where you stop. Nobody parks to a tape measure in the dark.

Which end faces the wall matters. A car nosed in puts the bonnet against it; reversed in, it is the boot, and a tailgate needs room to lift, which a bonnet does not. If one car is reversed and one nosed, the end wall gets two different depths and the shelving follows suit. Bikes belong here too, on a rotating mount that swings out when the car is on the drive and folds flat when it is not, at a height above the bonnet line.

The end wall is also where the order of work bites. Test the slab and the wall for damp before the shelving goes against it, because the back wall of a garage is the one that gets least air and shows damp first, and a loaded unit against a wet wall is a unit you will not want to move to find out. Then the wall fixings go in, then the shelving is built where it stands, and the floor is swept and covered last, because building shelving drops washers and grit on whatever is underneath.

Above the cars

Above door height every wall is free, and the ceiling nearly is, apart from the door track. Steel hooks fixed into masonry take ladders, the hose and the folding chairs above the line a door reaches; a pair of gridwall panels above the bonnets takes baskets for the things too small for a hook. Hang high enough that a wet car door does not meet a hook, and remember that a hook above a car is a hook above paint: nothing goes up there that could come down.

What this guide does not cover is a ceiling rack over the bonnets, because the safe load of one over a car is a question for the maker of that rack and for the joists it hangs from, and it is not something to guess at. Walls first. A double garage that has put its hooks, shelves and bikes on the walls at the right heights usually finds it did not need the ceiling at all.