How Does the Snow Melt?

Insulation and Insolation:

Dr. David Schnerch, Ph.D., PE
Associate Principal, Wiss Janney Elstner Associates, Inc.

Improving the energy efficiency of buildings has been a significant goal for many decades and has provided significant cost savings to building owners and reduces our reliance on non-renewable energy. Melting of snow on roofs is sensitive to changes in temperature at the membrane surface and the amount of solar radiation. Structural failures due to excessive snow load frequently occur due to the accumulation of snow from multiple events rather than a single snow event. Reduced heat loss due to building energy efficiency improvements mandated by energy codes reduces the duration when snow melt may occur and snow from subsequent events is more likely to accumulate before it completely melts. Low-slope roofs have traditionally consisted of ballasted systems, built-up membranes, and other dark colored membranes sometimes with little underlying insulation. For new construction, energy code changes have increased the require thermal resistance of roof insulation and more frequently, roofs are light colored even in Northern climates. Similarly, existing buildings subject to roof membrane replacement are often required to add insulation prior to installing the new roof membrane. The effect of the building code changes for roof insulation requirements on design snow loads are discussed.

Learning Objectives:

• Learn the effects of greater hear transfer resistance on the amount of snow accumulation on low slope roof assemblies.
• Learn about the code requirements for roof insulation materials and how they differ from past requirements.
• Learn the effect of these new requirements on the snow loads that re-roofed assemblies must now assume due to the effects of the greater heat transfer resistance required by the latest building codes.
• Learn how to deal with these issues in the design of both new roofs and re-roofing of existing buildings.

Speaker:

Dr. David Schnerch, Ph.D., PE
Associate Principal, Wiss Janney Elstner Associates, Inc.

Since joining WJE in 2005, Dr. David Schnerch has completed a wide range of failure investigations, structural evaluations, load tests, and repair designs of buildings, bridges, parking garages, and other structures. This work has included evaluation of reinforced, prestressed, and post-tensioned concrete as well as masonry, steel, and wood structures.
Before joining WJE, Dr. Schnerch studied the repair of concrete and steel structures using ultra-high modulus fiber reinforced polymer (FRP) materials. This work focused on the repair and strengthening of existing structures and has been published in the Journal of Bridge Engineering, Transportation Research Record: Journal of the Transportation Research Board, and other publications.

Kara Kea
EIT, Wiss Janney Elstner Associates, Inc.

Kara Kea has performed a wide range of investigations, repair and rehabilitation projects, failure investigations, and instrumentation and monitoring projects. These structures primarily consist of reinforced concrete, prestressed concrete, steel, and wood. Prior to joining WJE, Ms. Kea was involved in multiple research projects during her collegiate career. At ASCE’s Structures Congress 2014, she presented her research of a three-dimensional model of a base isolated cooling tower created in Sap2000, which correlated numerical model data with experimental data. As part of her master’s degree thesis, Ms. Kea researched, designed, and modeled a Bio-Inspired Self Centering Rocking Frame in Sap2000.