Masonry chimneys are the most common type of chimney when you think of a standard chimney. They are constructed with non-combustible masonry materials, which include standard brick, mortar, vitrified clay flue liners, and firebrick. Masonry chimneys have detailed design requirements regarding fireplace openings in relation to flue size. Other construction building code requirements must be followed to ensure that the clearances to combustibles will not cause a fire hazard and that the design does not restrict draft and cause the chimney smoke back into the house or cause excessive creosote formation.