Bathrooms cost more than you’d think.

“What surprises my clients is how labor-intensive bathrooms are: They’re the most expensive rooms to renovate per square foot,” says Dee David. “That’s because it can take 20-plus people to create a bathroom—the designer, the person you picked the tile from, the guy who cuts the mirror, the guy who does the light.”

Lesson seven: Although a bathroom is a small space, you may have many strangers in and out of your house, from the plumber to the tile setter to the painter.

Don’t dwell just on design—consider function.

Before my husband and I embarked on our project, we gave a lot of thought to what we liked and didn’t about our bathrooms. It’s one reason we tore out the tub upstairs—we never used it. We also installed extra lighting in both dark bathrooms.

In my bath, I weighed a jetted tub versus non-jetted, a shower door versus a curtain. I changed the mirror placement so it was easier for me to get ready in the morning.

But I admit that I gave more thought overall to looks than to function. I had fallen in love with a particular Kohler pedestal sink, and I had the bathroom built around it. I spent hours poring over the sink faucet and the tile but only minutes picking a showerhead and the heated floor—decisions that later mattered when the showerhead was too low and had to be raised and the heated floor didn’t work as well as I thought it would.

“There’s a natural tendency on the part of homeowners to immediately go to a showroom and choose product instead of taking an inventory of their needs,” says Case’s Mark Richardson.

My husband and I had also debated whether to gut both baths or simply do cosmetic touchups. Why not tile over the chipped floor and refinish the tub? One contractor pushed us in that direction—but the price wasn’t that big a savings.

Valery Tessier-Leon, a project designer at Case Design/Remodeling, says that when clients ask her that—“Should I just tile over?”—she counters with “How long do you plan to stay in your home?” If a bathroom is more than 20 years old—a typical lifespan, she says—and you expect to be in the house another decade or more, you might save money by gutting a bathroom in which problems, such as a cracked shower pan, could surface later.

Lesson eight: Before you go shopping, think about how you use your bathroom, what you’d change, and how long you plan to be in your house.

Your contractor will make decisions you may not like or understand.

Anyone who has had renovation done knows that you may come home at some point, look at the work that’s been done that day, and think, “Why did they do that?”

We had a number of those moments, as with a light fixture that wasn’t centered over the medicine cabinet, an oddly cut windowsill, and a shower seat much larger than we’d discussed. Some things were done for a reason; others were not but weren’t worth changing. For example, we had told our contractor three times to use ivory grout on the stone tile. We came home to sand-colored grout—which I ended up liking better.

We talked to or e-mailed our contractor almost every day and met with him weekly, trying to avoid surprises. For the most part, our contractor had no problem when we asked to have something fixed.

Lesson nine: If a contractor does something you don’t like, point it out. But if you’re a perfectionist, you’ll need to let go of some things or you’ll go mad. No one but you is going to notice sand-colored versus ivory grout.

Try to keep the project in perspective.

For many people, bathrooms are a sanctuary—and if they’re spending all this money on renovating their sanctuary, they want to sweat the details and get it right.

Like many a homeowner who has done renovation, I became obsessed with it. I’m sure I drove my contractor crazy. It was sometimes all I could talk about with friends, family, and colleagues—sorry about that, guys—because it was front and center in my mind. It’s stressful: When you come home to chaos and dust and strange men with power tools, your home is no longer a haven. The Friday we came home to the poorly laid tile, I barely slept.