Specifically, they’ll guide you to Porch.com, accessing the site either on their own phone, or on yours, or on in-store computers at designated kiosks. Lowe’s has had a quiet partnership with the Seattle-based startup since January, testing it out in 139 stores (most of them in North Carolina), but beginning on May 5 the retail giant will push Porch to customers in all 1,707 Lowe’s stores in the country.

It represents a gamble by a big Fortune 500 company (No. 56 on our 2013 list, with $50.52 billion in revenue) on a tiny, still unknown web startup. (Porch would not share financial data.) The new national partnership will be anything but quiet, with hard-to-miss banners and signage all over Lowe’s stores, and Lowe’s associates talking up the website to anyone who asks for a professional recommendation. “Need a landscaper?” or “Need an electrician?” the colorful posters read. Below that text: “Meet Porch.com, where you’ll find the right professional for your project.”

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Porch isn’t just a listing of home-improvement professionals, though that core element of it is what most interests Lowe’s (LOW). The site also has detailed listings of homes in your area, with sales history and deeper data on renovations and the associated costs.

Porch CEO Matt Ehrlichman, who sought to fill a need he and his wife discovered when they were building a new home and struggled to find recommendations for local professionals, says his site is “tackling a problem for the real people across the country, in normal America.” That is: not so much in big cities, as you could have guessed. Those living in apartments may not have a searing need to find carpenters, roofers, or plumbers for hire. Porch.com sees most of its traffic from suburbia, in areas, Ehrlichman says, “where there is true home ownership, vs. renters and condo owners.”

Of course, those homeowners have some other options if they want to get information on local homes. Zillow and Trulia both show nearby addresses and can tell you facts like a home’s most recent selling price. And on the find-a-professional side, websites like Angie’s List and, to an extent, Craigslist, can aid with your search. But Porch does both, while also attempting to be something of a social network. (Ehrlichman compares Porch to Pinterest, since people like to post photos of their completed projects, as well as to LinkedIn.) That latter function is perhaps a distraction, though it is one that these days many websites, even those with the most all-business focuses, seem to feel is a required effort.

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Ehrlichman says he views sites like Zillow and Trulia more as partners than competitors. Professional listing sites like Angie’s List are the competitors (though not Yelp, which lists brick-and-mortar businesses). In addition to the listings and social photo-sharing aspect, Porch also posts editorial content under the section “Get Advice,” such as “Five ways to update your bathroom for under $200.” And it recently leveraged its data to create a Porch Home Report released exclusively on realtor.com.

Lowe’s devotees might wonder why the national chain would so wholly endorse a young startup, rather than trying to build its own similar listings site. Richard Maltsbarger, who runs business development for Lowe’s, says it’s because there has been a sea change, across many industries, in the way that we ask for an expert: “The way that we access expertise has evolved.”

Speaking exclusively to Fortune about the national partnership, Maltsbarger explains that there are services for hire that Lowe’s offers through Lowes.com, like installation of flooring or cabinets, but there are more jobs that Lowe’s does not offer (plumbing, for example) and it was looking for a way to cater to in-store customers that seek those services. Of course, many Lowe’s customers in stores are also professionals themselves, who come to buy supplies. Thus, says Maltsbarger, “The other upside for us is it’s a continued value-add for professionals that shop with us.”

One might wonder if it makes business sense for Lowe’s to be directing people to a website other than its own, but Maltsbarger says the company wants to aid customers “whenever and wherever they choose to interact with us.” This is the first partnership of its type that Lowe’s has ever done.

In fact, Lowe’s took a look at a wide range of companies for this partnership and settled on Porch after an extensive search. “A core reason for Porch’s interest to us was their data-based approach,” says Maltsbarger. “They’re bringing to the services marketplace a much more advanced use of actual project data, and they have project profiles of the pros that are in your local market.”

Porch has grown quickly. In six months, it has gone from 25 to 140 full-time employees. It has data on over 100 million home projects. One and a half million professionals, meanwhile, have listed themselves on the site. As Zillow and Trulia do, Porch offers a premium service for professionals — they pay a fee to get targeted promotion in local areas.

Sal Giangrande, the New York Couch Doctor, is one of those professionals, though he does not yet pay for the premium service. Look up “carpentry” on Porch.com in midtown Manhattan and, curiously, his couch-repair business pops up. The site tells you he’s done five projects nearby and gives you the chance to “endorse this pro” if you’ve used him. Giangrande, who operates out of Hyde Park, N.Y., says he hasn’t been able to tell whether he’s getting new business from Porch, but that when he received a call about it he didn’t hesitate to sign up. After all, “you can never have enough business,” he says. That’s why he’s also on Angie’s List, though he says he stays away from Craigslist because he believes people on there are “just looking for a deal.”

Here’s the key — for Porch, anyway: After the company offered to help Giangrande set up a free listing, and after he spoke to a rep for 10 minutes, he says he called everyone in his circle of friends that also have their own businesses and recommended they list on the site. That word of mouth is how Porch has grown, up until now. “The web has definitely changed everything for the better,” he says. “My biggest tool is the Internet.”

Porch is already on the radar of many home professionals that use the Internet; now it hopes the big backing of Lowe’s will introduce it to those who still like the smell of old-fashioned hardware stores.