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climates

Very Cold - A very cold climate is defined as a region with approximately 9,000 heating degree days or greater (65°F basis) or greater and less than 12,600 heating degree days (65°F basis).

Cold - A cold climate is defined as a region with approximately 5,400 heating degree days (65°F basis) or greater and less than approximately 9,000 heating degree days (65°F basis).

Mixed-Humid - A mixed-humid and warm-humid climate is defined as a region that receives more than 20 inches of annual precipitation with approximately 4,500 cooling degree days (50°F basis) or greater and less than approximately 6,300 cooling degree days (50°F basis) and less than approximately 5,400 heating degree days (65°F basis) and where the average monthly outdoor temperature drops below 45°F during the winter months.

Hot-Humid - A hot-humid climate is defined as a region that receives more than 20 inches of annual precipitation with approximately 6,300 cooling degree days (50°F basis) or greater and where the monthly average outdoor temperature remains above 45°F throughout the year. This definition characterizes a region that is similar to the ASHRAE definition of hot-humid climates where one or both of the following occur:

  • a 67°F r higher wet bulb temperature for 3,000 or more hours during the warmest six consecutive months of the year; or
  • a 73°F or higher wet bulb temperature for 1,500 or more hours during the warmest six consecutive months of the year.

Hot-Dry/Mixed-Dry - A hot-dry climate is defined as region that receives less than 20 inches of annual precipitation with approximately 6,300 cooling degree days (50°F basis)or greater and where the monthly average outdoor temperature remains above 45°F throughout the year.

A warm-dry and mixed-dry climate is defined as a region that receives less than 20 inches of annual precipitation with approximately 4,500 cooling degree days (50°F basis) or greater and less than approximately 6,300 cooling degree days (50°F basis) and less than approximately 5,400 heating degree days (65°F basis) and where the average monthly outdoor temperature drops below 45°F during the winter months.

Marine - A marine climate meets is defined as a region where all of the following occur:

  • a mean temperature of the coldest month between 27°F and 65°F;
  • a mean temperature of the warmest month below 72°F;
  • at least four months with mean temperatures over 50°F; and
  • a dry season in the summer, the month with the heaviest precipitation in the cold season has at least three times as much precipitation as the month with the least precipitation.

information

Building Science Insights are short discussions on a particular topic of general interest. They are intended to highlight one or more building science principles. The discussion is informal and sometimes irreverent but never irrelevant.

Building Science Digests provide building professionals from different disciplinary backgrounds with concise overview of important building science topics. Digests explain the theory behind each topic and then translate this theory into practical information.

Published Articles aare a selected set of articles written by BSC personnel and published in professional and trade magazines that address building science topics. For example, our work has appeared in Fine Homebuilding, Home Energy, ASHRAE's High Performance Buildings, The Journal of Building Enclosure Design and The Journal of Building Physics. We thank these publications for their gracious permission to republish.

Conference Papers are peer-reviewed papers published in conference proceedings.

Research Reports are technical reports written for researchers but accessible to design professionals and builders. These reports typically provide an in-depth study of a particular topic or describe the results of a research project. They are often peer reviewed and also provide support for advice given in our Building Science Digests.

Building America Reports are technical reports funded by the U.S. Department of Energy (DOE) Building America research program.

Designs That Work are residential Case Studies and House Plans developed by BSC to be appropriate for residential construction in specific climate zones. Case Studies provide a summary of results for homes built in partnership with BSC’s Building America team. The case study typically includes enclosure and mechanical details, testing performed, builder profile, and unique project highlights. House Plans are fully integrated construction drawing sets that include floor plans, framing plans and wall framing elevations, exterior elevations, building and wall sections, and mechanical and electrical plans.

Enclosures That Work are Building Profiles and High R-Value Assemblies developed by BSC to be appropriate for residential construction in specific climate zones. Building Profiles are residential building cross sections that include enclosure and mechanical design recommendations. Most profiles also include field expertise notes, material compatibility analysis, and climate challenges. High R-Value Assemblies are summaries of the results of BSC's ongoing High R-Value Enclosure research — a study that BSC has undertaken for the U.S. Department of Energy (DOE) Building America research program to identify and evaluate residential assemblies that cost-effectively provide 50 percent improvement in thermal resistance.

Guides and Manuals are "how-to" documents, giving advice and instructions on specific building techniques and methods. Longer guides and manuals include background information to help facilitate a strong understanding of the building science behind the hands-on advice. This section also contains two quick, easy-to-read series. The IRC FAQ series answers common questions about the building science approach to specific building tasks (for example, insulating a basement). The READ THIS: Before... series offers guidelines and recommendations for everyday situations such as moving into a new home or deciding to renovate.

Information Sheets are short, descriptive overviews of basic building science topics and are useful both as an introduction to building science and as a handy reference that can be easily printed for use in the field, in a design meeting, or at the building permit counter. Through illustrations, photographs, and straightforward explanations, each Information Sheet covers the essential aspects of a single topic. Common, avoidable mistakes are also examined in the What's Wrong with this Project? and What's Wrong with this Practice? mini-series.

Building Science Insights
Joseph Lstiburek

Of course the crazy way we speak about the Second Law does not help: “In an isolated system, a process can occur only if it increases the total entropy of the system.” Huh? It makes you want to hate...
Building Science Insights
Joseph Lstiburek

Crawlspaces stink, they rot, and are just plain icky. Photograph 1 shows the modern crawlspace, which is a forest of water droplets on the underside of fiberglass batt insulation. The exposed wood...
Mixed-HumidHot-Humid
Building Science Insights
Joseph Lstiburek

Here is a pop quiz for you folks that are bored of Jeopardy. California is desert. Florida is a swamp. We build concrete slab-on-grade in both places. Which place has more slab moisture problems?...
Building Science Digests
John Straube

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.

Very ColdCold
Building Science Digests
John Straube

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.

Building Science Digests
Joseph Lstiburek

Water comes in four forms: solid, liquid, vapor and adsorbed. All four forms can cause grief to building owners, designers and contractors. When water causes building problems investigating and diagnosing the problem can be challenging because water constantly changes its form inside a building and within its materials. The investigator must hunt down the water thinking like water.

Building Science Digests
Joseph Lstiburek

The function of a vapor barrier is to retard the migration of water vapor. Where it is located in an assembly and its permeability is a function of climate, the characteristics of the materials that comprise the assembly and the interior conditions. Vapor barriers are not typically intended to retard the migration of air. That is the function of air barriers.

Building Science Digests
Joseph Lstiburek

Controlling rain is the single most important factor in the design and construction of durable buildings and in the control of mold. Drainage planes are used in the design and construction of building enclosures to control rain. All exterior claddings pass some rainwater. Siding leaks, brick leaks, stucco leaks, stone leaks, etc. As such, some control of this penetrating rainwater is required. In most walls, this penetrating rainwater is controlled by the drainage plane that directs the penetrating water downwards and outwards.

Building Science Digests
Joseph Lstiburek

Controlling heat flow, airflow, moisture flow and solar and other radiation will control the interactions among the physical elements of the building, its occupants and the environment. Of these four, airflow “merits major consideration mainly because of its influence on heat and moisture flow” (Hutcheon, 1953). Airflow carries moisture that impacts a materials long-term performance (serviceability) and structural integrity (durability). Airflow also affects building behavior in a fire (spread of smoke and other toxic gases, supply of oxygen), indoor air quality (distribution of pollutants and location of microbial reservoirs) and thermal energy use. One of the key strategies in the control of airflow is the use of air barriers. 

Very ColdCold
Building Science Digests
Joseph Lstiburek

Buildings used to be constructed over cellars. Cellars were dank, dark places where coal was stored. People never intended to live in cellars. Now we have things called basements that have pool tables, media centers and play rooms. Cellars were easy to construct – rubble, stone, bricks and sometimes block. If they got wet or were damp so what? Basements are different. They are not easy to construct if we intend to live in them. They need to be dry, comfortable and keep contaminants out. Basements are viewed by many as cheap space that can easily be incorporated into a home. Keeping basements dry, comfortable and contaminant free is proving to be anything but simple.

Building Science Digests
Joseph Lstiburek

Attics or roofs can be designed and constructed to be either vented or unvented in any hygro-thermal zone (Map 1). The choice of venting or not venting is a design and construction choice not a requirement determined by the physics or by the building code. The model building codes allow both vented and unvented roof assemblies. The applicable physics impacts the design of attic or roof systems as does the applicable building code but neither limit the choice.

Building Science Digests
John Straube

The control of air flow is important for several reasons: to control moisture damage, reduce energy losses, and to ensure occupant comfort and health. Airflow across the building enclosure is driven by wind pressures, stack effect, and mechanical air handling equipment like fans and furnaces. A continuous, strong, stiff, durable and air impermeable air barrier system is required between the exterior and conditioned space to control airflow driven by these forces.

Building Science Digests
Joseph Lstiburek

Moisture accumulates when the rate of moisture entry into an assembly exceeds the rate of moisture removal. When moisture accumulation exceeds the ability of the assembly materials to store the moisture without significantly degrading performance or long-term service life, moisture problems result.

Building America Reports
Kohta Ueno, Joseph Lstiburek

This research is a test implementation of an unvented tile roof assembly in a hot-humid climate (Orlando, FL; Zone 2A), insulated with air permeable insulation (netted and blown fiberglass). Given the localized moisture accumulation and failures seen in previous unvented roof field work, it was theorized that a “diffusion vent” (water vapor open, but air barrier “closed”) at the highest points in the roof assembly might allow for the wintertime release of moisture, to safe levels. The “diffusion vent” is an open slot at the ridge and hips, covered with a water-resistant but vapor open (500+ perm) air barrier membrane. As a control comparison, one portion of the roof was constructed as a typical unvented roof (self-adhered membrane at ridge).

Hot-Humid
Building America Reports
Joseph Lstiburek, Kohta Ueno

This Technical Report describes the modeling of typical wall assemblies that have performed well historically in various climate zones. The provided information can be generalized for application to a broad population of houses, within the limits of existing experience. WUFI software model was calibrated or “tuned” using wall assemblies with historically successful performance. Running the rainwater and airflow “tuned” WUFI software model generated the library of input data and results presented. The results agree with historical experience of these assemblies constructed in the climate zones modeled. The files present various custom settings that will help avoid results that will require overly conservative enclosure assemblies.

Building America Reports
Joseph Lstiburek, Kohta Ueno

This Measure Guideline describes how to model and interpret results of models for above grade walls. It analyzes the failure thresholds and criteria for above grade walls. A library of above-grade walls with historically successful performance was used to calibrate WUFI (Wärme und Feuchte instationär) software models. The information is generalized for application to a broad population of houses within the limits of existing experience.

Building America Reports
Kohta Ueno

Double-stud walls insulated with cellulose or low-density spray foam can have high R-values; compared to approaches using exterior insulating sheathing, double-stud walls are typically less expensive, and have exterior details similar to typical construction. However, double stud walls have higher risks of interior-sourced wintertime condensation damage. Field monitoring was installed in a Zone 5A climate house with 12” thick double stud walls; assemblies included 12” open cell polyurethane spray foam, 12” netted and blown cellulose, and 5-½” open cell spray foam at the exterior of the stud bay. Data were collected for three winters.

Cold
Building America Reports
Kohta Ueno, Joseph Lstiburek

In cold climates, a common practice of the weatherization industry is to retrofit compact roof/ceiling assemblies with blown-in dense-pack cellulose. However, this assembly has high moisture and durability risks (due to wintertime interior-sourced condensation) and violates building code. Developing methods to retrofit dense pack insulation into compact roof assemblies while controlling moisture risks would allow for widespread application of this lowcost technique without potentially compromising building durability. In hot-humid climates, HVAC equipment is typically located in vented, unconditioned attics, with associated energy penalties; one method of moving the ductwork inside the conditioned space is to insulate at the roof deck. However, market penetration of this method has been slow, due to the expense of insulating at the roof line, typically using polyurethane spray foam. If roof assemblies with fibrous insulation could be developed that control moisture risks, this would likely reduce the first cost of unvented roofs, potentially increasing their adoption.

ColdHot-Humid
Building America Reports
Kohta Ueno, Joseph Lstiburek

Hygrothermal simulations such as WUFI are coming into increasingly common use among building science researchers and practitioners, architects and designers, and energy analysts. Such simulations have been shown to be powerful and validated tools. However, with increasing dissemination of these types of modeling tools–most notable WUFI–less-experienced or less-informed practitioners have run models that provide unrealistic results. Therefore, Building Science Corporation led a Building America Expert Meeting where presenters from national laboratories, consulting firms, and building material manufacturers presented on their research, followed by a group discussion on various topics.

Building America Reports
Robert LePage, Christopher Schumacher, Alex Lukachko

This report explains the moisture-related concerns for high R-value wall assemblies and discusses past Building America research work that informs this study. Hygrothermal simulations were prepared for several common approaches to high R-value wall construction in six U.S. cities (Houston, Atlanta, Seattle, St. Louis, Chicago, and International Falls) representing a range of climate zones (2, 3, 4C, 4, 5A, and 7, respectively). The simulations are informed by experience gained from past research in this area and validated by field measurement and forensic experience.

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