I would like to welcome guest blogger Ben Broughton to you today. I hired Ben as a new Project Manager for Risinger Homes last month and as part of his training he attended an all day EEBA Building Science session in Houston. I’m super blessed to have Ben on my staff as he has an amazing background. He got his Masters in Construction Science & Management from Texas State and worked previously for SpawGlass doing super complicated commercial projects. Ben’s experience, education, and sharp problem solving skills will be a huge benefit to me as I continue towards my goal of being the best Builder in Austin, TX.
Ben wrote today’s post which is his notes and thoughts from the “Houses that Work” training. As an aside, I first attended this same program 11 years ago in Portland, OR and that was one of my first introductions to Building Science taught by Mark LaLiberte at that time. Here’s Ben’s notes:
Anyone who regularly reads Matt’s blog will know how highly he regards the science taught by the folks at the Energy and Environmental Building Alliance (EEBA). If you ever get the chance to attend one of their seminars, especially the one entitled “Houses that Work,” you will begin to understand Matt’s passion for EEBA. I was fortunate enough to participate in the Houses That Work seminar recently held in Houston and want to share some of the high points that made their way into my notebook.
Three Critical things to pay attention to as we build increasingly airtight homes:
-Combustion dangers (burning gas in airtight house)
-Water infiltration (houses can’t handle it like they used to because they don’t dry well.)
-Indoor Air Quality (chemical fumes, etc…)
Ergo: ‘Build tight but ventilate right”
HERS Scores (Home Energy Rating) – Scale of 100-0.
100 = Energy consumption of a standard American Building built to current “code”. 0 = no net purchased energy, a netzero home.
-A great goal to shoot for as a builder is HERS score of 40 by 2020 and 0 by 2030.
(SIDE NOTE: The remodel Risinger Homes just finished scored a HERS 45 with no renewables)
Average house expenditures on energy:
Appliances 25% (including lighting and general)
Hot water 20%
Energy waste in a HERS 100 House
Ducts in unconditioned space 23%
Internal (lights, body heat) 22%
Air Leakage 5%
Edge of foundation 5%
Start with the big sources first. Move ducts to conditioned space and go to a HERS 80.
1 ton of A/c removes 12,000 BTU of heat per hour.
Heat flow (BTUs) = (Exposed area x Temperature difference)/R-value
Ex: R20 insulation in attic, 1000 sqft of ceiling, 115 degrees outside, 75 degrees inside home
[1000 x (115-75)]/20 = 2,000 BTUs lost per hour which is almost 1/5 th of a ton of A/C every hour.
Duct work run in unconditioned space: 300 sqft of duct surface, R6 insulation on ducts, 135 degrees in attic, 70 degrees in house. = 1/3 of a ton of a/c loss just to heat flow not counting duct leakage.
Cubic Feet per Minute of airflow needed:
CFM = (# of bedrooms) x 7.5 x (0.01 x Conditioned sqft).
Radiant Barriers need an airspace to work. If you spray foam onto the bottom of roof deck with a radiant barrier plywood you would need air space between roof deck and the foam in order for that radiant barrier to work.
EEBA research: Houses don’t dry well b/c they are so tight. If 1% of water from a rain event gets behind weather barrier we are ok. If 3% gets behind weather barrier the house molds in 90 hours and falls apart in 1 year. That is why rain screens are so crucial behind cladding.
Capillary action in wood can lift water 300 ft, in concrete 1000 ft. that is why capillary breaks are so important.
When tackling water infiltration, air flow is much more important than diffusion if you have to attack only one. With an air leak in your home, 1 ¾ gallons of water can enter in two weeks as vapor. By diffusion, only 11 oz of water will enter in 6 summer months.
A home with 70 degree F air with a relative humidity of 55% with not feel as comfortable as a house with 75 degree F air at 40% relative humidity. Everyone thinks they want more HVAC tonnage to get the air colder but what we need is dehumidifiers. (Matt loves to talk about this!)
Roof slope must shed water first and foremost. With the trend toward very cut up roofs we need to be sure to understand the path of water so we aren’t dumping onto windows, penetrations, etc…
Slope grade away from house at 5%
Venting a house’s cladding is important if it is in an environment that sees > 20” of rain per year. Austin’s annual rainfall is 32.15” over the last 30 years.
Fiberglass Insulation: We want all six sides of batt material to be against airtight material such as framing or gypsum wall board. (This is why we don’t use or recommend batt insulation. Install needs to be “perfect” to achieve stated R Value)
2012 Energy codes on windows in Texas:
U-value = .40 (Many windows sold today don’t make this number)
SHGC = .25 (specify Cardinal LoE 366 glass and you’ll make this no problem)
Normal 2×4 wall with R13 insulation installed perfectly is R10 (considering the whole wall)
A 2×6 wall no windows and no doors has a cavity R value of 21. Studs have an R value of 8, so the wall unit has an R value of 14.4 when installed perfectly
A 2×6 wall with R-21 Blown cavity and R5 continuous rigid foam on the exterior is R 20.05
A 2×6 wall with R-21 Blown cavity and R10 continuous rigid foam on the exterior is R 25.05
Low e windows example:
House #1: U=.65 AND SHGC = .65
You will need a 4 ton A/C unit in the house
Same House Different Windows: U=.32 AND SHGC = .32
You will need a 2.5 ton A/C unit
84% of high SEER units set up wrong. Refrigerant charge verification very important.
Measure airflow at all registers, put it in contract that HVAC sub will balance system based on third party duct flow test of installed system.
If a Manual J is done right an HVAC sub could say “most HVAC contractors would put in two 4 ton units, I’ll put in a 3 and a 2 and guarantee comfort and throw in a dehumidifier for free with the cost savings.”
One of the most exciting lessons I took away from the seminar is the vast array of tools at our disposal to increase comfort in our homes. A comfortable house is a healthy and happy house. Modern architecture has provided sublime structures that take one’s breath away but one complaint against this school of design is it tends to come off as uninviting, cold, uncomfortable. The result of this has been a backlash against Modern architecture because home owners don’t want to give up comfort even in the pursuit of beauty. Comfort is crucial. As a quick aside, the concept of Modern architecture has unfairly received the criticism of uncomfortable. We have built and seen many homes classified as Modern that are warm, inviting and comfortable. We have the privilege to work with architects in Austin, Tx who are gifted at achieving both ends, continually proving that one does not have to sacrifice comfort for architectural splendor.
Comforts is key to our homes and as a society our tolerances for comfort are narrowing. As our ability to control the internal environment of a house improves, our expectations for comfort grow alongside. There was a time in the 1800s when a “comfortable” house meant one that kept the animals out, the rain off and provided some shade in the middle of a sweltering summer day. I doubt any of us would consider such accommodations as “comfortable” today.
The question then arises, “What will ‘comfortable’ mean in twenty years?” First let’s talk about one aspect of how the average home in the US is currently made “comfortable.” In a hot and humid climate like we have in Austin, large HVAC systems are the name of the game. It is not unusual to see two 5 ton units on a house. These units will have single speed condensers and the result is, for most of the year the units will come on, blow full speed for a minute or two and then shut off. Such activity equals vast swings from too cold (as a blizzard of air hits us) to too humid and hot as we wait for the unit to blow again. Instead of this setup, a variable speed or even two speed condenser alongside a dehumidifier would keep the conditioned space much more comfortable and especially more consistently comfortable. A house at 70 F with 65% humidity will never feel as comfortable to the occupants as a house that is 75 F at 45% humidity. Despite this fact, current setups see the temperature of the conditioned air as the most important metric for design. It reminds me of my high school days when I measured the power of a motor by cubic inches alone. I didn’t care about other performance contributors such as exhaust capacity as long as it had a big number by the motor. Now I am a more sophisticated consumer and analyze my vehicles on across multiple dimensions resulting in much better performance. In the same way we must expand our matrix to evaluate HVAC criteria.
Matt has been on the forefront of building homes that utilize the innovative science that EEBA and other pioneering groups have developed.
Constructing high performing envelopes is a trademark of Matt’s company but where Matt really gets excited is when he is detailing HVAC systems.
After attending this EEBA seminar I better understand why.
“Comfort” as the average home owner defines it is only called such because he has not experienced what a well designed, innovative system can offer.
I predict it will not be too long before we look at current home environments with a similar head shake to when
we look at an 1800’s definition.
|Ben Broughton with his unofficial Risinger Homes uniform “Black Shirt w a Logo”