ARCHITECTURAL INCHES: No Skimping Allowed

Nice try—but illegal. The treads need to be at least 9" deep,
and the risers can't be higher than 8".

I often get calls from nice folks who’ve drawn up their own plans and want me to check them for problems. Some of these designs are wonderfully creative, yet virtually all of them are sabotaged by the same basic shortcomings: people never allow enough space for hallways, staircases, kitchens, or baths. 

This is what a four-foot kitchen aisle looks like.
It sounds wide, but it isn't.

Stairs are undoubtedly the biggest booby trap for neophyte planners. Even a relatively steep, straight stair climbing your basic nine-foot-high story requires a bare minimum floor area of three by ten feet--and this doesn’t include the top and bottom landings or the thickness of the enclosing walls. L- or U-shaped stairs need even more room. Yet people routinely show me designs for second-story additions in which the entire staircase is miraculously packed into a linen closet. They’re usually crestfallen to learn that, in fact, the new second-floor bedroom they thought they were adding will only be replacing the one wiped out by the stairs. 

No less than 36" wide, please.
That's the code minimum.

Kitchens are typically overcrowded as well. The absolute minimum aisle width between facing countertops—even those on islands—is four feet. Although this may seem excessive on paper, it won’t be once you’ve got doors, drawers, and dishwasher racks projecting into the aisle, not to mention a few bystanders “helping” you cook. Nor should sinks and cooktops have less than eighteen inches of counter space on either side—and again, this includes islands.  

A double-loaded walk in closet (one with
clothes rods on two sides) requires a minimum
width of 7 feet. Period.

Even when they know there really isn’t enough room to accommodate everything they want, amateur planners will often try to cheat their way out of the problem by cannibalizing other spaces. Clothes closets are a common victim: although they need to be at least two feet deep, people are always trying to whittle a few inches off  them to buy space somewhere else.  Forget it—jacket sleeves cannot be fooled by this strategy.    

Other immutable rock-bottom minimums:

•  Foyers need to be at least six by six feet.

 •  Hallways, like stairs, can be no less than three feet wide.

Sorry, not kosher. By code, a toilet has to sit in a space
that's no less than 30 inches wide.

•  Walk-in closets need to be at least five feet wide for a single-loaded arrangement, and seven feet wide for a double-loaded one. 

•  Double lavatory sinks require a countertop at least six feet wide.  Never mind those dinky five-foot examples you find at the big-box store--that’s just wishful thinking. 

•  Toilets should occupy a space at least 30 inches wide when between a wall and a counter, and at least 36 inches wide when between two walls.

•  Stall showers require a space no less that three feet square; tubs and tub/showers need at least 2 foot 8 inches by 5 feet.

•  Garages must be at least 19 feet deep inside.  And don’t dream of trying to squeeze a furnace, water heater, or washer and dryer into that minimum, either; if you do, only a Smart car will ever fit in there.

Lavatory sinks: Make them round or make them square,
but for heaven's sake, make the counter at least six feet wide.

When space is tight, both architects and amateurs can be tempted to fudge minimum dimensions by a few inches here or there. Don’t.  In fact, it’s good practice to allow a few inches more than you need, since finishes, trim, and unexpected errors or obstructions often conspire to nibble away preciousroom from a space that’s already squeezed. If you can’t accomodate the above minimums, you may need to rethink your wish list. Better to throw a few things overboard than to sink the whole ship.