(Please note that in certain situations,  what ,  when , and  where  can function as relative pronouns.) Relative pronouns introduce relative clauses, which are a type of dependent clause. Relative clauses modify a word, phrase, or idea in the main clause.
The 2014 Survey of Construction (SOC) from the Census Bureau shows that the average completion time of a single-family house is around 7 months, which usually includes around 25 days from authorization to start and another 6 months to finish the construction.
New home construction in the United States is on the upswing. Six of the top 10 fastest-growing industries in the country are related to home construction. The U.S. Department of Housing and Urban Development and the U.S. Census Bureau report that there were 930,000 new homes completed in January 2015.