When Sara Kate Gillingham decided to install an outdoor pizza oven at her upstate New York house, she didn’t call a specialist.

Gillingham, co-founder of the Brooklyn cooking school the Dynamite Shop, “nerded out” on wood-burning ovens, reading books and watching YouTube videos. “There’s so much information online," she says, "it’s kind of dizzying.”

A few sites suggested that with the help of a few friends, an oven could be built in a weekend from a “put this in quotes,” she says, “kit.” The components, including fire brick, perlite, and the oven dome in four pieces, would be delivered on a pallet, ready for assembly.

If only it had been that easy. She discovered the oven needed a two-foot-deep foundation, and putting the pieces together was so difficult that she had to bring in a mason.

“I had all these dreams of an outdoor kitchen," Gillingham says. "Eventually, we’ll do that, but this thing stopped me in my tracks.”

The internet, and cable television, increasingly make DIY seem like NBD — no big deal. YouTube is packed with videos on everything from tiling a backsplash to building a tiny house for less than $2,000.

Little wonder that Americans are increasingly finding DIY appealing. With some time and sweat, homeowners think, they can save money, learn new skills and (theoretically) ensure their project turns out exactly the way they want it.

But there’s a reason that some say DIY really stands for “destroy it yourself.” Countless homeowners spent much more time or money than they anticipated, or had to hire someone to take over. Worse, some have unwittingly caused major damage to their homes, made modifications that violated building codes, or put their safety at risk.

Professionals to the rescue

Professionals around the country are seeing an uptick in requests to help with — or repair — DIY projects.

One reason for the DIY surge, says Greg Antonioli, president of Out of the Woods Construction & Cabinetry in Waltham, Mass., is high real estate prices: Home buyers are trying to save money.

You might assume that pros are keen for bigger, more complex jobs, but the reverse can actually be true. “It’s a nightmare when ... now it’s at the point where they call you,” says Marco Radocaj, general manager at HVAC service company Temp Control in Vero Beach, Fla. When a licensed professional has done the work, you can assume that everything was done correctly, he says. There are no such assurances when a homeowner digs in.

“YouTube is great for what it is; I even use it for a resource when I get in a bind,” says Kelley Williamson, owner and operator of She Fixed It, a San Diego-based handywoman company. “But I think a lot of people see the shows and videos and they have this super, hyper-confidence that they’ve got this down.”

Williamson thinks HGTV is more to blame for DIY mishaps: “All of the remodeling shows — or even when they do it on Queer Eye — it’s like, they have these ideas, and boom it’s done and it looks amazing. But you don’t even see all the workers that have to do it in a day.”

Get a permit

Michael Byrne, director of inspectional services for Arlington, Va., says his office is getting more requests for DIY permits — and seeing more problems as a result of unpermitted work. One local engineer removed the main support post for his house, causing the roof to start to cave in.

“Undersized lumber, it’s almost a given on DIYers, because a two-by-three is cheaper than a two-by-four,” Byrne says. “People think they’re saving all this money by not taking out a permit,” but they may be chancing major damage to their home.

Projects to avoid

Experts say amateurs should avoid several kinds of projects.

“Electrical or plumbing should not be done without somebody that has a license,” Williamson says. Electrical mistakes can be deadly, and plumbing errors can lead to leaks and floods.

Andrew Helling, a Nebraska real estate agent and owner of REthority.com, an online resource for real estate professionals and their clients, says roofs can cause falls, and even a tiny hole can cause a destructive leak.

Kitchen remodeling is popular but often requires a building permit — and is a project that can easily violate local building codes, Helling says.

Aaron Bowman, a real estate investor in Windsor, Conn., has relied on YouTube for several DIY projects, but “one time I had a gas furnace with a pilot light that would not stay on,” he says. "So I figured out what needed to be replaced and ended up having the wrong settings and almost blew myself up.”

He no longer messes with gas.

How to decide

Experts offer a few tips for deciding whether to undertake a DIY project. First, consider the worst that can happen.

Consider whether special tools are needed, and whether you're willing to invest in them.

Look into whether a building permit is required: If it is, think twice.

Finally, DIY for realistic reasons.

“I wouldn’t say DIY saves you a ton of money; it depends how you value your own time,” says Laura Sampson, a DIYer in Alaska. “A lot of times you have a project that takes four or five weeks longer than if you had just hired someone.”