Original sentence: An Illustrated glossary of roofs and roofing terms
Edited sentence: Box gutters are essentially placed between parallel surfaces, as in a valley between parallel roofs or at the junction of a roof and a parapet wall.Provision is made in the design of the gutter to have a rain flow to the outlet with a maximum slope of 1:200 and a minimum of 1:400.They should not be confused with so-called valley gutters or valley flashings which occur at the non-parallel intersection of roof surfaces, typically at right angled internal corners of pitched roofs