Building Science

OK, the title here may be a little extreme, but if you've taken a look at the new chapter on performance testing and scope of work in the HERS Standards, you know what I'm talking about. RESNET just adopted this as the new chapter 8 in August of this year, and it goes into effect on 3 January 2012.

One of the most frustrating parts of my job as a Home Energy Rating (HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5.) provider is dealing with the size of air conditioners installed in Energy Star homesA U.S. Environmental Protection Agency (EPA) program to promote the construction of new homes that are at least 15% more energy-efficient than homes that minimally comply with the 2004 International Residential Code. Energy Star Home requirements vary by climate..

Building Science Fundamentals: Roof, Part 1: Ventilation

By Dr. Joseph Lstiburek

Dr. Joseph Lstiburek talks about the not-so-controversial ways to maximize the efficiency and airflow of your roof and attic.

Video Transcript:
There’s been so much stuff said about roofs that you sometimes lose perspective. I’m going to start off by saying what might seem controversial but really shouldn’t be.

If your attic is going to have 50 bags of insulation blown into it, does it make much of a difference if it goes in flat or lumpy?

One reason that I'm interested in the question is that my dissertation in grad school was called “Flat or Lumpy.” (Of course, it had the requisite incomprehensibility in the subtitle, with words like “heteroepitaxy.”) Those two words in the title, which cut to the heart of what my surface physics research was all about, also describe a property of insulation that's important in building science.

In our last episode, Dr. John talked about How Heat Moves Through Homes and why radiant barriers work better in outer space than on earth.

In this episode, Dr. John talks about the history of insulation, how different materials work, and where they make sense.

TRANSCRIPT
The history of insulation comes about because of the history of structural engineering. Now, I’m a recovering structural engineer, which is probably why I like to think of it that way.

Today’s walls, roofs, and floors are better insulated, tighter, and made with a much greater variety of components than they used to be, making them a lot more susceptible to moisture problems when they get wet. Compared to the old days, today's walls and ceilings are more complicated and can be very slow to dry.

The weathering of wood is very different from decay; weathering is breakdown at the surface only. While there are a number of forces that contribute to weathering of wood—moisture, temperature, abrasion by wind-borne particles, air pollution—it’s the narrow band of high-energy ultraviolet light in sunlight that is the dominant force (see Image #1).

What bare wood looks like when cut or milled

In our last episode, Dr. Joe Lstiburek talked about efflorescence and the serious damage that water and salt can do to masonry. This week, Dr. John Straube explains how the three forms of heat flow work, and debunks the claims of a few common insulating materials.

Comfort is the Primary Purpose of Buildings

This podcast series is excerpted from a two-day class called "Building Science Fundamentals" taught by Dr. Joe Lstiburek and Dr. John Straube of Building Science Corporation.

This podcast series is excerpted from a two-day class called "Building Science Fundamentals" taught by Dr. Joe Lstiburek and Dr. John Straube, of Building Science Corporation.