(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.
The Census Bureau conducts its survey every year. And by the same token, the question, âHow long does it take to build a house?â is a recurring one. The Wall Street Journal reported on the 2013 Census findings back in January, looking for some meaning in the figures (see: âAverage Time to Build a House: 6 Months,â by Adam Bonislawski. The numbers fluctuate from year to year, the Journal observes: âIn 1973 it took, on average, six months to build a single-family home.