(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.
1 A finished basement typically includes all of that plus flooring, walls, ceilings, drywall, windows, and additional waterproofing and more in order to provide the desired living space. 2  Overall, a basement adds about 3-4 weeks to the new-house construction schedule. However, house-moving companies like Klier Structural Movers in Ohio assert that adding a basement to an existing house is a cost-effective addition. 2  A basement alone does not guarantee safety during a tornado.