Is the Pretty Good House the Next Big Thing?
And what might one look like in a mixed-humid climate?
I love the Pretty Good House concept! The folks up in Maine who've been developing this idea in their monthly green building discussion group (Steve's Garage) have struck a chord with a lot of us who design, build, or verify green homes. The growing complexity and expense of green building and energy programs has ledLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. to growing frustration. Wouldn't it be great if we could list just a handful of measures that a home builder has to achieve to build a Pretty Good House?
Especially since ENERGY STARLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. Version 3 started kicking in last year, I've been thinking about new ways to achieve good results, and the Pretty Good House idea is a great way to get this going. One way I've proposed to simplify HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. requirements, for example, is with a new benchmark for sizing air conditioning systems. Also, even in the performance path for verification, the prescriptive requirements have become a burden. So where can we take this idea?
What's the question again?
Even after just seeing the title of the first Pretty Good House article, I started thinking about what a Pretty Good House might look like. Since I'm in International Energy Conservation Code (IECC International Energy Conservation Code.) Climate Zone 3, my thoughts naturally gravitated to elements that would work well in our mixed-humid climate. I began imagining lists of building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. details, HVAC system specifications, distribution system requirements, mechanical ventilation, ceiling fans...
But then I took a step back and asked the question, Whose Pretty Good House are we talking about here? Since I'm on the training, consulting, and design side of this business, my Pretty Good House would probably look different from the Pretty Good House of someone who's in the trenches building custom homes. The disparity would be even greater between my Pretty Good Home and that of a production home builder.
Since we're talking about the Pretty Good House—not the Damn Good House—I'm going to take the view that even production builders should be able to achieve it...if they really want to and they work hard to do it. Because it's voluntary, it should be better than the worst house allowed by law, i.e., the code-built house. With the code getting so much tougher in the 2012 and 2015 IECC versions, that latter objective gets harder and harder to do, but we have to start somewhere.
The essential elements
To keep this simple, we need to start with the essentials. I'm a fan of performance goals because they allow the project team to figure out how best to meet the goals, but some of the items are best left as prescriptive (e.g., no atmospheric combustion inside).
Pretty Good Design. The Pretty Good House must begin with design. This is where you have to start to make sure that the building envelope, water management systems, and mechanical systems get integrated properly. By the end of the design phase, everyone would know where all the ducts, wires, plumbing pipes, insulation, air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both., and flashing details are going to go, what materials they'll use, and when they're getting done.
- Design review. All the critical team members review the plan and strive to minimize surprises once construction starts.
- Complete HVAC design. Before the foundation is built, the HVAC contractor knows what the heating and cooling loads are, which systems (including ventilation) are going in, and all of the distribution details.
- Projected Home Energy Rating. Along with the HVAC design, a HERS rater works up the preliminary HERS rating. I think the target should be 70 or lower for a Pretty Good House.
Pretty Good Building Envelope and Weather Shell. In this part of the Pretty Good House, it's going to be hard to improve upon the 2012 IECC, so I'd go with their insulation and air-sealing levels. The building envelope also must be complete and continuous, of course. The insulation and air barrier must be in contact with each other and use materials that will stay in contact with each other for the life of the assemblies (i.e.,no batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. in framed floors).
Other envelope and shell goodies:
Grade I insulation installation. No exceptions. It's got to be done right. ENERGY STAR may have backed off of this a bit since I wrote about it earlier, but that doesn't mean we should.
Reduced thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. . Foam board or rigid mineral wool on the outside, structural insulated panels, insulated concrete forms, double wall construction, Mooney Walls, or some other method that would produce a nice, uniform color when someone looks at the house with a thermal imaging cameraA camera that provides an image showing radiation in the infrared range of the electromagnetic spectrum. Since the amount of infrared radiation emitted from a surface varies with temperature, a thermal imaging camera is a useful tool for detecting hot or cold areas on walls, ceilings, roofs, and duct systems. When used to scan a building envelope, a thermal imaging camera can detect missing insulation or locations with high levels of infiltration. Thermal imaging cameras can provide useful information when the difference in temperature (delta T) between the indoors and the outdoors is as low as 18F°; however, the higher the delta T, the easier it is to see building defects..
No big or medium holes in air barrier or insulation. The Blower Door test will catch the air barrier holes. Thermal imaging and third-party inspections will catch the insulation holes. Some places to watch out for are attic access holes, slab perimeters (must be insulated for CZ 3), and ceiling insulation above exterior walls.
Pretty Good Water management. I like ENERGY STAR's approach here. Create a checklist that the home builder is responsible for completing. The rater collects it, but the builder is the one who signs it and is responsible if something goes wrong.
I'm thinking that the shift in the IECC from R-values to U-values, as Wes Riley pointed out in the second Pretty Good House article by Michael Maines, can lead to better ways to view the house. In fact, since size matters so much, let's go even further and look at levels of performance based on the UA values, with a table showing the acceptable numbers for each climate zone. That would complete the transition from materials to assemblies to enclosures. I also like the Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. approach regarding thermal bridging.
Pretty Good Mechanical Systems. As I said above, each Pretty Good House would get complete HVAC design up front. I'd also want:
> 1000 square feet per ton of air conditioning capacity. This is my rule of thumb, and I think it would be a nice way to make it easy to check. If it were my house, I'd want no less than 2000 sf/ton, but remember, this is the Pretty Good House, and that's a pretty good benchmark.
All distribution inside the envelope. No ducts in attics especially. Crawl spaces get encapsulated. With good design, doing this isn't a problem.
No atmospheric combustion. If it's not electric (e.g., heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump.), it's got to be sealed combustionCombustion system for space heating or water heating in which outside combustion air is fed directly into the combustion chamber and flue gasses are exhausted directly outside.. Period. You can't call it a pretty good house otherwise. If you're in a hot climate where sealed combustion heating equipment is too expensive, I'd say combustion equipment doesn't make sense. Use a heat pump. They're actually good for more climates than you might think, especially when combined with a hydronic coil for supplemental heat.
Mechanical ventilation. Since the house is going to be tight, it must have a mechanical ventilation system. It will be able to meet the ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant. requirements with a controller that allows the homeowner to dial it back when necessary.
That's a pretty good start
I'm sure I didn't get everything related to those topics in there that should be there. I'll post again about this topic and cover the items below that didn't make it into this already-long article.
In Part 2, I'll cover:
- Pretty Good Water Conservation
- Pretty Good Verification
- Pretty Good Homeowner Package
- Pretty Good Performance
I'm sure I'll have some clarifications and refinements based on the comments you're going to leave me, too, so go ahead and start typing now.
Allison Bailes of Decatur, Georgia, is a RESNET-accredited energy consultant, trainer, and the author of the Energy Vanguard blog.
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