In an industry — window replacement — known for “one and run” installations, Energy Swing Windows boasts that 76% of its business comes from previous customers, mostly referrals.

Roofing, a recent addition to the company’s product line and now accounting for a quarter of its sales, came about, says founder Steve Rennekamp, because “our customers were beating us over the head” looking for a quality roofer. Every roofing job involves an attic inspection and aerial estimating.

The most difficult part of entering that business was finding the right people. “Any business is a people business,” says Rennekamp, who created and patented the company’s unique “swing out” vinyl window. “The hardest part is finding the right people to deliver the right kind of things to customers.”

Last year the company’s annual Customer Appreciation Day drew hundreds of satisfied clients and featured an on-site videographer and a video testimonial contest. Energy Swing Windows has 400 testimonials on its website.