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Home Performance

By Holehouse Construction Company on Jan 19, 2017 at 10:12 PM in Current News

Home Performance

What is it?  Why do I want it?

written by Jon Heffner, LEED AP

Perhaps you have heard the terms lately; "home performance", "high performance home", "zero net energy home" or perhaps "smart home"?

All of them have come from the same roots; evaluating the house as a complex interactive system, designing, building, remodeling, and retrofitting to maximize efficiency and occupant health, while minimizing energy usage and indoor air pollutants.

In this information age, there are plenty of experts and sources for in-depth studies on any of these topics.  I have listed a few of the major, reputable organizations web pages at the end of the blog for those who want to dig deep into the data and science.

Science is the key word here.  Building Science to be exact.  There are three inescapable laws of physics/thermodynamics that apply to building science and everything relates back to them:

1. Hot moves to Cold

2. Wet moves to Dry

3. High pressure moves to Low pressure

While seemingly simple and basic these three rules dictate how healthy and efficient your home is and/or could become.

1. Hot>Cold. Think of your home as an Igloo ice chest.  When it is cold outside you want to be warm inside and vice versa.  This will work if all four sides are both air sealed and insulated from the outdoor conditions.  It is only when insulation and air sealing are combined that they function properly.  A great analogy is skiing down a mountain; with only a windbreaker shell or only a down vest.  One will stop the breeze (pressure) but not retain your body heat, and one will retain your body heat until the wind blows through and transfers the heat from your body (the heater) to the environment via convection.  By working together, the system will work to keep you warm.  The same applies to your home, especially in areas like the attic where there is a large exposed surface area (the ceiling) between your living space and essentially the outdoors (ventilated attic).  Thus, the condition, quality and installatio of what is called the assembly (drywall, framing, air sealing at pentrations and insulation) is critical to maintaining a healthy and comfortable indoor condition.  Nature wants to equilibrate at all times and the only thing preventing or "resisting this heat transfer is the assemply.  That funny term you always hear "R-value"... R is simply resistance to heat transfer.  The same happens in the summer, but the direction is reversed and the hot attic energy is "moving" into the cool indoor space making you uncomfortable or your air conditioner run harder to remove the heat energy and throw it back outside (how an air conditioner really functions.. it does not "add cold", it removes heat.)

2. Wet>Dry. Everyone has probably seen or performed the crimpled straw wrapper snake trick for an amazed child.  By putting a small drop of water on the extremely dry and compressed cellulose material, it expands quickly and the "snake" grows.  This process is known as wicking and can wreak havoc on building structures and walls, when conditions exist for water to go the wrong way.  One classic example would be when landscapers end up burying the termination line of stucco where it ends at the foundation.  Those who know building, realize that there is a "weep screed" at that location designed to allow moisture to escape from the wall before it builds up and causes framing rot, mold or other issues.  When this pathway is blocked, or closed off with other moist material, performance problems are only a matter of time.

3. High Pressure>Low Pressure.  Where do we want our indoor air to come from?  I would bet that everyone would agree that we wnt it to come from a clean and controlled location.  Unless you already live in a recently constructed, performance built and verified home, or have recently undergone a deep energy retrofit, chances are that your indoor air is most likely up to 2-3 times more polluted than outdoor air.  Let's review an average day inside your home.  We wake up and turn on the bath fan, which begins to exhaust indoor air, at the same time, someone starts cooking and turns on the kitchen hood, removing more conditioned air.  At this point the interior is under a slightly negative pressure since air is being forced out without a designated make up location (unless a mechanical or passive air exchange system exists).  If your home is like many, someone in the recent past was swayed by a window salesperson with the sales pitch of replacing windows and saving energy.  While in many cases, replacing windows can lead to energy savings, usually this is only the case when the entire home is viewed as a system and action is also taken in other areas, like the attic and crawlspace (if existing).  Back to our example:  as air is removed from the interior, it is replaced in the same volume from the outdoors, and this is the dirty, and potentially fecal or other particulate laden crawlspace or attics.  You can see that you are concentrating toxins indoors while at the same time allowing unconditioned (cold or hot) air from outdoors in, causing the conditioning (HVAC) equipment to engage in order to maintain the indoor temperature.  Based on blower door tests, the average California home built before 2010, will have a combined leakage of a basketball sized hole in the side of the home.  A performance audit and retrofit can address this issue.

Summary

While easily taken for granted, our houses are quite complex.  Although some generalities exist, no one knows what will make your house more comfortable or safer, without looking at it first.  The updated and recently released California Energy Code and State Building Codes are very stringent and contain efficiency targets for all new homes being permitted today.  The code requires all new homes permitted as of 2020 will be net zero energy (producing the same amount or more as consumed).  There is no way to achieve that goal without application of building science principles and designs into the building plans.  Addressing the subject of performance improvements in existing buildings is the focus of many contractors in the market, confirming that the personnel of those firms are trained and certified in building science before hiring them to evaluate or do work is certainly suggested.  Occupant health, comfort, indoor air quality, affordability, energy use and the durability of the house itself is what "house as a system" building science delivers. 

Below are a few of the organizations whose mission is to educate the public and the professionals on these topics.

http://bpi.org/home_pros.aspx

http://www.usgbc.org

http://www.homeperformance.org

http://energyupgradeca.org

Please post any questions and I'll be happy to try and help!!