From the book A-Frame by Chad Randl

WHAT IS AN A-FRAME?
An A-frame is a triangular structure with a series of rafters or trusses that are joined at the peak and descend outward to a main floor level, with no intervening vertical walls. Most have horizontal collar beams that strengthen the frame and function as floor joists for a second-level loft. These cross ties, combined with the angled roof rafters, give the A-frame its name.

EARLY BEGINNINGS
Triangular “roof huts” turned up in ancient China, on South Pacific islands, and throughout Europe, where they functioned as cooking houses, farm storage sheds, animal shelters, peasant cottages, and ceremonial structures. In the United States, the A-frame was a utilitarian form until after World War II. After the war, a succession of architects found the A-frame to be an appropriately whimsical and informal stage on which to play out the growing leisure lifestyle.

MID-CENTURY MODERN?
Starting in the 1950s, the A-frame gained prominence as a popular vacation home type. Its appeal transcended geography and class in part because its form defied categorization. Was it the embodiment of contemporary geometric invention, or a steadfast, timeless form, suggesting rustic survival? Perhaps its greatest appeal was that it was different, an expression of individuality that meant relaxation and escape from the everyday, workaday world. From the glazed gable walls and open plans to the easy flow from interior to spacious integrated decks, A-frames were an up-to-date alternative to traditional cabins with small windows and big fireplaces.

By the early 1960s, the A-frame became a cultural icon, a geometric representation of the good life. A variety of companies made A-frames the centerpiece of their advertising and promotional campaigns. Restaurants, gas stations, liquor stores, and a range of other businesses set up shop in triangular buildings, relying on the prominent shape to lure customers.

LASTING IMPACT
Some of the most provocative postwar architecture was designed for leisure living. Small size, low cost, and freedom from the requirements of a permanent home encouraged a spirit of experimentation and a willingness to explore the unorthodox. The A-frame was a catalyst for this trend, as well as one of its best examples. The triangular vacation home broadened the thinking of postwar leisure seekers. It blended into the landscape in which it was built and opened the door to an anything goes attitute toward recreational design, the repercussions of which were felt beyond the beach and mountainside. The A-frame building boom has come and gone, yet tens of thousands of A-frames still dot the landscape, and they still attract attention.