Treehouses occupy a big space in our childhood memories. They provided not just play spaces but also adventure, fun and excitement.

But a recent housing trend has made treehouses not just for kids alone, but for adults too. Catherine Sherman, a real estate writer for the Zillow Blog, describes that treehouses nowadays have provided adults spaces for relaxation, for their hobbies, and even for primary residence. According to her also, there are 15 companies that are into the "treehouse business," with a complete set of teams of engineers and interior designers, specializing in custom-designed treehouses, and providing kits and tools for homeowners who wish to construct their own. Sherman continues to give a clear picture of how treehouses are constructed.

Nelson and Treehouse and Supply (a firm which has been building treehouses for the past 25 years and was featured on Animal Planet's "Treehouse Masters") for one, has built everything possible suspended in trees -- from breweries, recording studios, to spas with steam showers. Its team foreman, Daryl McDonald, said: "A lot of people think of treehouses and children, but 9 out of 10 treehouses we build are for adults. People want an escape pod - a way to get out of the busyness of being in a home."

Owner Pete Nelson attributes the cause of the people's desire to have an alternative living spaces to stress. "Trees are healing. They're a meditative retreat from the stress zone. It takes about 10 minutes of breathing in the rich oxygen of the forest before your cares melt away," he explained.

Linda Federico-O'Murchu of CNBC adds that in 2013, a survey on Stress in America conducted by the American Psychological Association (APA), concluded that stress, especially work-related, is a major factor that leads to long-term health problems.

As for its cost, Nelson says there is a wide range of costs: "A simple platform in a tree with a deck costs $120-150 a square foot, but fitting kitchens and baths into a small space can throw your budget out. I'd be lucky to hit $120 a square foot (if a kitchen or a bath is installed)."

"A fully appointed treehouse with kitchen, bathroom, heat and air conditioning costs about $350-500 a square foot. We're building those around $200,000," he added.

The length of time for the consultation, construction and installation also varies, between two days to nine months, depending on the size and difficulty of the project. McDonald shares that the most complex they have completed was a 1,000-square-foot treehouse with a 500-square-foot deck.