For the past 26 years, he has been a principal in San Luis Sustainability Group (SLSG). Known as a pioneer in passive solar design, Haggard has designed numerous residential and commercial projects with an emphasis on making the best use of the energy and materials available on-site. In 1972, he served as architect and senior researcher for the first passive solar house in California. In 1978, he co-wrote "Passive Solar Handbook for California," a guide for architects interested in the passive solar design. With colleague Polly Cooper, Haggard helped renew serious interest in straw bale construction in California by designing the first-permitted straw bale house in the state.