American homeowners spend upward of $30 billion per year renovating kitchens and bathrooms, ­according to a 2013 survey from Harvard University’s Joint Center for Housing Studies. That’s more than all the other rooms in the house combined. The outsized investment in these rooms tends to pay off: Per the National Association of Realtors, remodelers report the biggest boost to satisfaction and happiness with their homes after wrapping up a kitchen or bath overhaul.

More on Remodeling

But it takes some doing to get there. These are complex rooms outfitted with fixtures and appliances that can get expensive, put together by the most skilled pros in the indus­try. Given the stakes, in 2016 Consumer Reports conducted a nation­ally representative survey of 1,012 homeowners who had tackled a kitchen or bath project in the previous four years, to learn what they did right and what they wish they’d done differently.

The secret to getting the space that works perfectly for you­ without blowing your budget? Plan ahead before you spend serious money. Work on the room’s design until it’s exactly right and do enough research to know when it’s smart to splurge on materials and appliances—and when you should save.

How to Stay on Schedule

In our survey, 29 percent of remodelers acknowledged that their renovations took longer than they anticipated. Don’t expect a consensus on who shoulders the blame. Homeowners might quickly point the finger at their contractors, but in a nationwide survey Consumer Reports conducted in late 2015, 60 percent of general contractors said the biggest mistake they saw clients make was changing their mind midconstruction. That can easily ­derail your ­project, as can structural concerns, permit problems, and materials that arrive damaged or broken, all of which were cited by contractors as primary reasons for delays. Anticipate these common problem ­areas and help keep your project on track. Here's how:

1. Look for Structural Problems

Forty-two percent of contractors we surveyed called out unforeseen structural damage as the leading reason they fall behind schedule. But these problems don’t need to be a surprise. Contractors can view your project through its narrow lens, but a home inspector will look at the bigger picture and shed light on how changes might affect complex household systems.

“Most people only think of having an inspection when they buy or sell a home,” says Frank Lesh of the American Society of Home Inspectors. “But inspectors can actually be helpful throughout the remodeling process.” You could find out if, for example, low water pressure means you won't be thrilled with a pricey multijet rain shower or if you’ll have to upgrade a kitchen circuit to power an induction range.

2. Come Up With a Plan for Permits

News flash: As a homeowner, it’s your job to secure the proper paperwork. Plenty of contractors will get permits on your behalf, but the trick is to make clear, from day one, who will take on the responsibility. If your contractor charges you for obtaining permits, consider a DIY approach—you don’t want to spend $100 per hour for him to wait in line. (And regardless of who takes charge, mark important inspection dates on a calendar at your work site so that everyone’s aware.)

In certain urban areas, obtaining permits is so cumbersome that specialists called permit expediters have emerged to tackle the process for a fee. Certain cities keep lists of approved expediters at the building department. And hiring one brings a serious advantage: Their sole focus is to keep clients’ projects moving along.

3. Shop Locally

Almost one-third of contractors ­reported that they’d been delayed on a job because materials arrived damaged (or manufacturers shipped the wrong stuff). Avoid this common pitfall by shopping locally, even from a chain retailer, whenever possible. “Paying a little more to buy materials and finishes in your area is like adding a layer of insurance to your project,” says Courtney Ludeman, whose design-build firm, based in Richmond, Va., has faced countless problems with floor tile, sinks, and the like ordered on the internet.

“It’s fine to snag a light fixture or door pulls in an online flash sale, but for cabinetry I use a local cabinetmaker. If there’s an issue, he’s back at the house in a few days finishing the job,” Ludeman says. Though custom cabinets might sound wildly expensive, Ludeman says that’s ­becoming an outdated notion. Some independent pros now use computer programs to generate a cut list after they’ve measured. “That lets them keep costs competitive with premium mass-market brands and outfit a large kitchen in two weeks,” she says.

Editor's Note: This article also appeared in the July 2017 issue of Consumer Reports magazine.