Image Credit: Energy Vanguard
Image Credit: Energy Vanguard A Pretty Good House must have a blower-door test and come in below 0.25 cfm per square foot of building envelope at 50 Pascals (or 3 ACH50 if you want to normalize with the wrong quantity, volume).
Image Credit: Energy Vanguard
More Building Science
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 led 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 STAR 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 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) Climate Zone 3, my thoughts naturally gravitated to elements that would work well in our mixed-humid climate. I began imagining lists of building envelope 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 barrier, 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 insulation in framed floors).
Other envelope and shell goodies:
Blower Door testing. 0.25 cfm per square foot of building envelope (or 3 air changes per hour, if you must) at 50 Pascals. Joe Lstiburek says this is a pretty good air leakage threshold for homes.
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 bridging. 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 camera.
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 House 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 pump), it’s got to be sealed combustion. 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 62.2 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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22 Comments
I guess I'm learning something
You really wouldn't want me doing a lot more to a building than paying the bills, but it's funny how close this is to the PGH I'd like to build in CZ 3 for myself. My head has been shaping it for a long time, but especially since Dan and Mike's initial posts. I really think the PGH concept is better than ideal -- it's useful!
Looking forward to Part 2, Allison. Thanks for this.
Design perspective
Allison,
Since you mentioned the importance of begining the process at the design stage...
I have lately been thinking that resiliency should be a primary requirement for a "pretty good" house in any climate/region.
A house should not become "unlivable" under conditions that (though infrequent) are predictable.
For example, a house that is to be built on a flood plain should be built on high ground, or a house that is to be built in a hot climate should not have to rely on A/C to maintain a "livable" interior temperature.
I'm not sure what "resilient design" means specifically for your climate/region.
Regional specifics are maybe not-so-important for such a generalized conversation...
But maybe you could provide some good climate specific ideas (ie: zone 3, mixed/humid)?
Edit to say:
Just trying to think outside my "climate box"...
Strive for perfection, work
Strive for perfection, work with what you actually wind up with---the pretty good house in my opinion...as long as we don't mess with ideas that have NO leeway, or ZERO error tolerance, success is in the works. Let's face it, nobody can build a perfectly airtight house (except maybe NASA in a clean lab somewhere), and even if it were to be done, sizing the exactly right air and pressure exchanges would be just as challenging. So, we may as well learn to build a close-enough to airtight house with escape passages for moisture and vapors.
Building the pretty good house is the way to go, as it's all we as human contractors and skilled builders can do. To first understand how and why a perfect building could be, then to understand the inevitable failures and weaknesses, and finally to design a building which encompasses all this will ultimately be the best of all worlds---a cost effective building that serves the need it was intended to .....the sweet spot on the curve between the most cost effective and the most high performing building.....
No atmospheric combustion.
Does that include gas stoves with up to 100,000 Btu worth of cooktop burners? Certainly hope so.
Response to Lucas Durand
I've read a bit of Alex Wilson's writing on resilient design, but to do justice to your question, I'd need to go back and read more. Here in the Atlanta area, we have floods, tornadoes, droughts, wind, hail...the usual stuff. Hurricanes are usually muted by the time they reach us. Designing a house to survive a direct hit by a tornado would be difficult and expensive, I think. A Pretty Good House ought to be able to withstand high wind, floods, and droughts, though.
Response to deniz bilge
Actually, even NASA can't build anything perfectly airtight. I used to do research with ultra-high vacuum chambers, and we had to keep the various stages of pumping going continuously because of tiny leaks and even because of hydrogen diffusing through the walls of the stainless steel chambers.
Response to James Morgan
Good question, James! Actually, a regular gas cooktop isn't so bad if the (reasonably sized) range hood is on whenever it's on, but if someone put a high capacity commercial range in the kitchen and did a lot of cooking with it, that could be a problem. If they tried to solve that problem by putting in a commercial range hood that exhausted air from the house at the rate of 2000 cubic feet per minute, now they have another problem.
What's worse than gas cooktops, however, are gas ovens. They can produce a lot of carbon monoxide, so they should be on the list of things to exclude. I know I wouldn't want one in my house.
Pretty good overview, Allison -
and I'd plug in a few additional thoughts:
On pretty good design - yes, wholeheartedly to early engineering integration etc. I know your focus here is on mechanicals but if we're starting with design basics I feel like you've left out pretty good solar orientation, pretty good daylighting and pretty damn good space planning. If we're talking of a general standard of performance for the average builder and homeowner I really don't feel we can take these (to me) essential attributes for granted, and I don't see where they fit in your outline for future articles. And let's not ignore esthetics either. A house is no damn good at all unless someone loves it.
Meanwhile on the purely mechanical side I have a concern about the mechanical ventilation requirement. I don't believe all climates require the degree of airtightness that demands this - we've completed many pretty darn good houses without them, and I feel we should be really careful of over-engineering a PGH spec. Engineering tells me I should expect my water heater to use $500 of electricity a year. As the total annual energy bill for my fifty-year-old only somewhat-upgraded house and studio is little more than twice that I somehow doubt it's true. Many of my clients are rightly skeptical of similarly over-calculated energy nerd numbers. Let's take a look from outside the bubble.
Response to Allison
Allison,
I agree.
Many of the hazards you mentioned are regional in nature so the risks would have to be evaluated on an individual basis.
Maybe zone 3 mixed/humid is not so extreme that it could be designed to achieve "passive livability" - as in that the house, though uncomfortable, could remain liveable year round without any HVAC...
Do you think is possible with a "pretty good" design?
Along the lines of what James Morgan was suggesting...
With respect to your climate, maybe all that is required in terms resilient design is to have a "pretty good" envelope and ensure that the principals of passive solar design are adhered to...
Then add in the resilient design considerations for regional risks.
A "pretty good" house design should not create its own HVAC challenges.
Edit to say:
I made some edits to my earlier post...
Sorry, Allison. Just thinking out loud.
Responses to James Morgan & Lucas Durand
James, I actually did include info about the site when I posted a version of this article in the Energy Vanguard Blog because, like you, I believe strongly that the house isn't isolated from the site. I decided to leave it out here, though, and the reason is that houses get built on less than ideal sites all the time. If someone is building on a lot that they have no control over or they're building on a lake and really want those big west-facing windows for the views, I think we'd agree that they can still put a Pretty Good House on that lot.
Regarding ventilation, I see where you're coming from, but if the climate requires the house to be closed up for heating or cooling at all, why shouldn't it be tight and have ventilation? Relying on random leaks for ventilation isn't a good idea. I do agree that if the house is in a climate where they don't have to put in any kind of heating or cooling system (parts of Hawaii?), they certainly wouldn't need a mechanical ventilation system.
Lucas, we could certainly live without cooling here. My grandparents in Louisiana didn't get air conditioning until about 1970. Here in Atlanta, we get about 3000 heating degree days and have a winter design temperature of 23° F, so we do need a heating system. The house I built had a woodstove because it was on 66 mostly-wooded acres, and we wanted to have heat even when the power went out. That turned out to be useful during one ice storm in particular.
Response to Allison
In the first case maybe but in the second case definitely no, I can't agree. I'm with Lucas on his excellent graphic. Architects took full advantage of spectacular views for centuries before the giant window wall came into vogue. They used terraces, porches and loggias to full advantage, with carefully-framed view windows designed to entice the occupant outward, not to supplant the outside experience with an ersatz interiorized version. (Even without the energy penalty those giant walls of glass have many other drawbacks such as glare and maintenance issues. And they're so..... cliche, no? Aren't we over the 1980's yet?)
I can think of several reasons, one that it's not (in my climate) necessary in a house that's sealed to a pretty good but not Passivhaus standard, two that the opportunity cost of the system and its maintenance might be better spent elsewhere, and three, that the idea of a house sealed up so tight you need to blow air in and out of it would give the heebie-jeebies to a lot of worthy customers for a Pretty Good House. People want energy efficiency for sure, and for sure I've done my share of talking up the virtues of Pretty Good Airsealing, but that doesn't have to mean a hermetically-sealed box. At least not in these parts.
You got me...
James, you're right, of course, that giant windows are a liability. Unless they're being used for passive solar purposes (and many overdo it for that), I would recommend limiting window area. I'm a fan of tradeoffs, though, and we are talking about the Pretty Good House here, so I think it could work to have large windows on one side to take advantage of views.
Why should sealing up a house as tight as possible and adding ventilation give anyone the heebie-jeebies? Those of us who work in the world of building science know better than that and should be able to convince squeamish clients that it's much better to bring in outside air in a controlled manner rather than relying on random leaks, which tend to bring in the worst air -- with pesticides, exhaust, and paint fumes from the garage; with mold and other nasties from the crawl space; and sucked through the dead squirrel in the attic. Give me a hermetically sealed house with ventilation any day.
What are 'these parts' that you're talking about anyway?
North Carolina Piedmont.
Somehow we manage to get good air quality in low-energy homes without benefit of HRV or ERV. What are we doing wrong?
Re: tradeoffs - It's true that there are few self-imposed liabilities that you can't fix by throwing enough money at them. Wouldn't it be smarter though to use a better design in the first place, one where you could still enjoy your view, maybe enjoy it even more, especially knowing you're treading a little lighter on the earth?
Further thoughts on window walls
Maybe we need a subcategory, PGHUC - a Pretty Good House Under the Circumstances - for the times when we have insistent clients with problematic programs.
Pretty good for the occupants
One again I am going to shamelessly advocate here for smaller reasonably sized homes as the number one goal of the PGH. Smaller house, smaller energy use, smaller bills, smaller maintenance, smaller pile of construction debris, smaller thing to take apart someday. Smaller mortgage, smaller amount of furniture and possessions. Fewer corners, less trim, fewer windows. Less concrete. Less roof runoff, less landscaping at the periphery. More homes per acre. Smaller liability when one earner loses a job. More contact with family members.
I have read in other places, Allison where you have come to the aid of HERS under fire. I am not sure why. It is my mathematical contention that the pretty good house needs another method of measuring energy "efficiency" especially if it is small, because even with ES3 the size factor does not equalize scores and cover the additional energy use of a large home, removing the great marketing opportunity of a small house, small bills and a small carbon footprint. That seems to be the one subject all of the HERS raters shy away from...carbon equivalent. The HERS Index has nothing to do with a carbon footprint of the home, or of the occupants.
As the climate changes, I for one think its important to be able to identify the homes that are larger contributors to the problem, versus those that are smaller ones, for buyers, builders and others. And HERS just can't give me that, since the index is based on a metric that boils down to BTU/ft2.
Comparison to a reference house is just bad logic (unless one is in a higher economic bracket and needs to feel good about thatr "energy efficient" behemoth). People or bedrooms belong in the denominator of energy efficiency ratios. How many BTU's does it take to condition the shelter for 3 people in your climate? Depends on the house you say...of course it does. And we should score that house, without dividing by its largest energy using determinant, its size.
I'll start and propose 1800 BTU/bedroom/HDD65 as a benchmark (100) of an energy efficient PGH for heating. Score me from there. We can leave ACH50 out. We can forget the Index. Let's let everyone be scored for what they choose to live in and use. Let's let folks with small budgets live more modestly and still call them green for what they don't use. Let's have those with the resources to build 6000 ft2 homes build much better and put PV or solar thermal on their roof and whatever they can to produce all the BTU's over the benchmark. Or maybe they need to face the fact that their housing indulgences just aren't green and there's no denominator to divide up their use into more conveneint parts to make it seem so.
Not to be draconian, but I'd like to imagine for one humorous moment that everyone has the total energy their home uses per year painted on the front door, like the scarlet letter. Maybe then houses would shrink, shells would thicken and tighten, and we could forget the silly HERS index. Especially on those unusual weather days where we look up and wonder how this happened.
if we are ever going to know how efficient our structures are we need to make them efficient in their use (housing three people) not in their manifestation (3200 ft2).
Michael, you are on a roll...
Michael, you are on a roll... a pretty good one.
Simple is the key all of you.
Size,,, and birthrates
If you have no offspring, you are doing more than any 100 other supergreen Platinum HERS -10 types period.
Smoke that and let me know how ya feel greenies.
Nice concept for an article
Pretty good is what we all seem to be pushing for these days. But we still need a shift in mentality, Most of our thinking when it comes to owning a home or designing one is that a house is something that lasts for at most a few decades. A house is really for generations and should be designed and lived in as such. Keeping a house durable and low maintenance is really the building block of green building.
Daniel Glickman
SVP Sustainable Construction Services, Sherborn MA
AJ - careful!
And I thought I was treading on thin ice questioning the American way of "by golly, if you can afford it you deserve it" (and with the right rating to endorse your indulgence, you get to call it green to boot). But you AJ, you are questioning the impact of procreation. Shhhh. Someone might hear.
My mother told me the one with the best manners was the one who made the fewest people in the room uncomfortable. I know my small house talk is being mentioned in "mixed" (economic) company. As for your comment: What if architect Mike Brady is lurking?
mixed economic company
You have to give us slow learners some credit....my husband and I built MY dream house in 1994...afterall I was working my butt off in the bio-tech industry and DESERVED it!!!!! Now my 3500 sq ft dream ( not counting the 2600 ft2 walk-out basement) is my nightmare. I have learned that as we aged & the kids grew up and moved out of state, the maintenance, fuel bills, etc are more than hassels. The good news is that our 17 year old home is close to 2009 code....so we were smart back then, just not smart enough.
Still looking for a Michigan referral for an architect/builder for our PG(new-dream)H---we have nixed passivhaus---after all, we need room for improvement over the next 20 years. Our no so big (read very small---1200 ft2 footprint) needs to be built in Suttons Bay near Traverse City. I do believe we have had a loss of building professionals in this state due to the auto fiasco.....there has to be somebody out there.
Please send me your recommendations----we are quick studies and do learn from our mistakes.
thanks and love this site
Diana
Response to Diana, a.k.a "Jim White"
Diana,
Readers are more likely to read your question if you post it on the Q&A page:
https://www.greenbuildingadvisor.com/node/add/forum
I have one...
Diana,
There are many architects and designers who frequent this site, so you'll probably get many to choose from by posting in the forum, as suggested by Martin. Let me throw my pitch out there for our company, since we do design as well and have an architect who spends a lot of time doing HVAC design and building science consulting, too. See our page on integrated design for more info:
http://www.energyvanguard.com/architecture/integrated-design.
thanks, Martin and Allison
will do
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