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Building Science Digests
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Building Science Digests provide building industry professionals from different disciplinary backgrounds with a concise overview of fundamental building science topics. They were inspired by the Canadian Building Digests produced by the National Research Council of Canada starting in 1960, which in turn drew on a long history of other practice-oriented publications.
BSC Building Science Digests focus on translating theory into practical, usable information. Some address a broad topic such as building enclosure design, while others illustrate the applicability of building science to more specific or specialized issues such as strawbale construction. Building Science Digests are keystone BSC documents, exemplifying the ideas and research approaches that we view as critical to our work
There has been a recent surge of interest in Ground Source Heat Pump (GSHP or “geothermal” or GeoExchange™) systems for residential projects. Outrageous claims and misunderstandings about how they work are common. This digest provides some basic information and definitions, offers advice on how to compare the carbon emissions, and defines the climate regions and operating conditions for which GSHP systems are best suited.
This digest reviews the moisture control principles that must be followed for a successful insulated retrofit of a solid load-bearing masonry wall. Two possible approaches to retrofitting such walls are presented and compared.
Pitched roofs of either wood rafter and joist or truss construction are used in the construction of literally millions of homes and small commercial buildings each year. There are variations in these roofs, but there are relatively few primary options. The following digest describes the most common types of wood pitched roofs, their enclosure functions, and common modes of failure.
Ice rinks and arenas are a common building type in many communities. The trend over the last 25 years has been to operate these arenas for greater periods of the year, often throughout the summer. Also, an increasing number of such buildings are being built in areas with warm, humid summer weather. The result has been an increase in the number of reported moisture problems, most of which revolve around summer condensation.
This digest will describe the causes and discuss potential retrofit solutions for summer condensation in ice arenas.
Ice dams are a common roof performance problem in buildings that experience snowfall and at least a month of below freezing temperatures. The combination of sufficient roof pitch, adequate insulation just above the exterior wall, and air sealing at the wall-roof assemblies transition are all essential to prevent ice dams. But ice dams can occur even in properly detailed roof assemblies from differential solar snow melt. This digest outlines both the causes and solutions to ice dam problems.
Moisture is involved in most building problems. The most serious tend to be structural damage due to wood decay, unhealthy fungal growth, corrosion, freeze-thaw, and damage to moisture sensitive interior finishes. Avoiding these problems requires an understanding of moisture, the nature of materials, and how it interacts with materials. This digest deals with these fundamentals.
The American Foursquare, a Sears, Roebuck & Co. kit home, was a staple of small American towns between 1908 and 1940. More than 100,000 of them were built in America. Homes built prior to 1980 make up 80% of the housing stock in the United States, and are responsible for a majority of the residential energy use in the country. All of the renovations used systems engineering principles to ensure good indoor air quality and longterm durability while providing deep energy reductions. This posting is permission of ASHRAE. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission.
The current building industry focus on durability is in part a reaction to the current perceived lack of it. Warranty claims and callbacks are viewed as increasing. Litigation and insurance costs are felt to be rising as a result. Another reason for the current focus on durability is the recognition that sustainability is not possible without durability. If you double the life of a building and you use the same amount of resources to construct it, the building is twice as resource efficient. Therefore durability is a key component of sustainability.
It seems that one thing that both the development community and the environmental community can agree on is that durability is a good thing.
What do we know about durability and how do we know it? The lessons of durability have come principally out of failure. Engineering is an iterative process of design by failure. Buildings are constructed. Problems are experienced. Designs and processes are changed. Better buildings are constructed.
The building industry is in essence a reactive industry, not a proactive industry. It can be argued that the industry continues to do things until they become intolerably bad and then the industry changes. Examining failures gives us guidance on increasing the durability of building constructions.
Stucco and EIFS are common cladding systems that appear similar from the exterior. These systems have very different attributes however. This Digest explains the reasons why face-sealed EIFS are fundamentally flawed as cladding systems for most applications, and describes how drained EIFS can be used successfully in almost all climate zones and exposures. Cracks, lamina deterioration, and movement joints are also discussed.
Driving rain on building facades is on of the largest sources of moisture that impacts durability of enclosures. Several approaches to predicting driving rain on buildings have been developed over the last 50 years. Field measurements have been collected on more than a dozen buildings in several different countries. Based on this research, and some CFD modeling studies, simplified approaches have been standardized in a British Standard and German guidelines. This digest consolidates and summarizes this research to provide a practical method for predicting driving rain deposition for a wide range of purposes, but particularly to aid in WUFI modelling and ASHRAE 160P analysis.
A brief description of different types of unvented roof assemblies and the benefits of unvented roof construction.
This digest offers a detailed explanation of the causes of carpet discoloration, particulate deposits on surfaces and "ghosting" of wood stud members on the interior gypsum board surfaces of exterior walls.
The difference between site and source energy is a vital concept to understand when looking at the energy performance of buildings—failing to account for the difference will result in an apples-to-oranges comparison that does not give the true picture of a building’s energy consumption. This document explains how these two types of energy are accounted for differently and why.
Putting metrics on building energy performance is a required step to make any progress on low-energy use and/or “green” buildings. However, there are many confusing and contradictory metrics available; to speak a common language, it is necessary to understand the topics that are behind these measurements. These topics include site vs. source energy, modeled results vs. reality, US average energy use figures, and methods of normalizing energy use. The normalization of energy use intensity (EUI), or dividing by square footage is examined; several significant problems in applying this metric to residential use are demonstrated. Various other metrics are presented, as well as a proposed method to provide all of the useful building energy information in a format that allows normalization by any chosen metric.
Condensation within walls during cold weather is a common performance problem. Most such condensation is due to air leakage, not diffusion. Although air barrier and vapor control layers can reduce the quantity and occurrence of condensation due to both mechanisms, the use of exterior insulation (even if that insulation is a vapor barrier and/or air barrier) can warm sensitive surfaces within a wall and thereby eliminate or reduce condensation risks. This digest provides the background for designers to select the insulation levels need to reach specific levels of condensation control.
