Experiences with external drainage systems from compact roofs in Norwegian climates

Abstract

To reduce loads on urban drainage systems and facilitate local infiltration of stormwater, it is desired to lead runoff water from roofs through external drains and into the local soil. However, in cold climates, situations often arise where water freezes in external drainpipes, damaging the pipes and preventing drainage. This article investigates the perceived feasibility of external drainage when compared against the risk of freezing damage. A literature study investigates mechanics of ice formation in drains and gutters, and under which conditions ice formation poses a risk to the building. Actors in the Norwegian building sector are interviewed about the challenges related to external drainage from compact roofs in several locations in Norway. Findings suggest that external drainage is considered feasible, but many challenges exist. Suggested solutions may conflict with building regulations, either due to risk of damages or through an unreasonably high energy consumption. Passive solutions without heating elements may, however, be feasible in certain climates in Norway. It is suggested that further research follows up the feasibility of using external drainage in relation to local climate and building concepts.