More Guest Blogs
You may already know about the Pretty Good House concept, the result of a question that moderator Dan Kolbert asked back in 2011, partly as a joke, at the long-running building science discussion group at Performance Building Supply in Portland, Maine. Fed up with other building standards, from the wimpy and under-enforced building code to the nit-picky Passivhaus, Dan asked, essentially, what you should include in a house that does right for its inhabitants and the planet, but that does not go beyond reasonable environmental or financial payback.
We developed a list, which I shared in a blog post on Green Building Advisor, and since then the idea has taken on a life of its own. (A list of GBA articles discussing the “pretty good house” concept can be found on the “Pretty Good House” category page.) A lot has changed since 2011, and — unfortunately, perhaps — the time has come to revisit the Pretty Good House, also known as PGH.
Reducing embodied carbon in buildings — especially in Pretty Good Houses — was the topic at the last two building science discussion groups in Portland, then at one of the BS + Beer events I moderate in Liberty, Maine. (“BS” for Building Science, of course.) Right now is the worst time in the history of our species to dump a lot of carbon into the atmosphere, but that’s exactly the result of many construction practices. Even builders concerned with energy efficiency often front-load enormous amounts of carbon-intensive materials with the expectation of saving over the life of the building. But if we only have one or two decades to mitigate the worst impacts of climate change, what should we do instead? The following ideas are a summary of our discussions.
Like everything PGH, the 2.0/Low Carbon Edition is meant for thought, discussion, and action, not for check boxes, awards, or membership dues. As always, however, if you feel that you deserve a plaque, feel free to buy yourself one.
Include these features
In no particular order, a PGH 2.0/Low Carbon Home should:
• Be as small as possible. Ideally with multi-family or multi-generational occupants.
• Be PV-ready or include photovoltaic panels. PV-ready means designed, built, and sited in such a way that a reasonably sized photovoltaic array can handle all of the home’s energy needs on an annual basis. (PV panels pay their carbon debt in 2 to 4 years.)
• Be simple and durable. Simple shapes are easier to air seal and insulate, perform better in harsh weather, and require fewer materials and less maintenance than more complicated buildings. If you need to bring in a structural engineer, your design might be too complicated. Invest in the parts that are hard to change later.
• Use wood and wood-derived products as construction materials. Just make sure that the wood is sustainably harvested, locally if possible. Otherwise the trees are better left to remove CO2 through photosynthesis. The more materials are processed, in general, the higher their carbon footprint.
• Use air-source heat pumps. Minisplits can be efficient to -15°F or below, affordable (especially for the sizes needed in a PGH), and relatively simple to install. For those who can’t stand the look of an appliance on the wall, there are slim-duct, ceiling cassette, and floor-mounted versions. But the wall-mounted units are the most efficient, so learn to love them. Heat-pump water heaters are a no-brainer for most homes.
• Invest in the envelope. Insulation and air-sealing should be good enough that heating and cooling systems can be minimal, with indoor air quality and comfort levels that are very high.
• Be affordable, healthy, responsible, and resilient.
• KISS: Keep It Simple + Safe — easy to operate and understand. Use owner-proof systems to get around operator influence.
• Consider traditional, non-flashy approaches: deciduous trees shading south and west walls; cooling via fans and natural convection instead of air conditioners; use biomass secondary water heating (i.e., let your wood stove heat your water); air-dry your clothes.
• Be part of a sustainable community: have access to community solar, jobs, and services nearby that minimize driving and provide shared infrastructure costs, to name a few advantages. A one-hit wonder in the middle of the woods often comes with a bigger carbon footprint than a community-based home.
Minimize or avoid these features
A PGH 2.0/Low Carbon Home should minimize or avoid:
• Concrete, which contributes 10% of man-made global warming emissions, partly through fuel to heat and move minerals, but 60% from release of carbon dioxide (CO2) from limestone (CaCO3) to get calcium oxide (CaO) for Portland cement. One concrete-reducing technology that is gaining ground is the use of helical metal piers, which are screwed into the soil to support decks, houses, and more. Some engineers and builders have doubts, but with many thousands of installations, they have a proven track record.
• Foam, especially HFC (hydrofluorocarbon)-blown closed-cell spray foam and XPS (extruded polystyrene) rigid insulation. When building a new house, there should be no need to use foam above grade. (For more information on this topic, see “Building a Foam-Free House.”)
• Combustion appliances, especially those that burn fossil fuels. You can have a wood stove in a PGH, but make sure it’s EPA-certified and includes dedicated makeup air.
• Unhealthy materials.
Worth considering
Some bigger ideas to consider:
- Straw bale construction. Although straw bale construction is dismissed by many as low-tech, low-R, and prone to moisture damage, experienced straw bale builders have developed effective ways to use this carbon-sequestering approach to building.
- Phenolic rigid foam. Zero greenhouse-gas emissions, extremely high R-value — what’s not to love? The fact that it’s impossible to get.
- Mycelium insulation. (Cue “fungus among us” jokes.) But seriously — it sequesters carbon and traps air, so why not use it to insulate homes?
- “Smart” materials. Variable-permeance membranes have made many of us more confident about simple but theoretically risky assemblies like double stud walls and building without foam. Glazing has come a long way in the last 10-20 years, but we could benefit from more glazing and other materials that respond passively to changes in conditions.
- Offsite fabrication. There is a lot of carbon burned getting workers and materials to job sites, and a lot of efficiency and quality control possible in a factory setting.
Prescriptive guidelines
The original PGH had simple rules for insulation and airtightness, borrowed from Dr. Joe Lstiburek of Building Science Corporation as his recommendations for efficient homes in a cold climate. For PGH 2.0, we need to update the rules a bit to account for easy access to better windows and a better understanding of embodied carbon.
In a cold climate, DOE climate zone 5 or 6, use:
- R-5 to R-8 windows (U-0.20 to U-0.13); the higher the glazing-to-wall-area ratio, the more important it is for the windows to have a low U-factor. Even the best windows make lousy walls, so don’t over-glaze.
- R-10 sub-slab insulation (either EPS — that is, expanded polystyrene — or mineral wool or recycled XPS).
- R-20 foundation wall, frost wall or slab perimeter insulation (or build on piers).
- R-40 above-grade walls.
- R-60 roof.
- The wall and roof values should be lower if you’re using foam, due to its long carbon payback, but in a PGH 2.0 there is no reason to use foam above grade.
- Airtightness: 1.0 ACH50 (air changes per hour at ±50 Pascals pressure) is the maximum air leakage target many of us are using, but others say 1.5 or 2.0 ACH50 is tight enough. Definitely stay well below code-minimum requirement of 3.0 ACH50. Going tighter than 1.0 ACH50 gets you cool-kid points but may not add significantly to your home’s performance.
Performance-based approach (optional)
Use energy modeling to optimize designs, especially for fine-tuning window performance values. (BeOpt is a good, simple, free program for this.)
Should there be a standard PGH energy-use target, such as xx% better than code-minimum, xx% of Passive House levels, xx Btu/ft² or xx BTU/occupant?
Want to learn more about building a pretty good house? Sign up for the Sustainable Building Accelerator and learn directly from author and architect Emily Mottram.
Additional thoughts
Our generation is the only one who can fix the climate change problem. We can’t opt out; this is our only chance.
Aim for the biggest targets; don’t get lost in the weeds.
If you’re a designer or builder, sell the comfort aspect of a PGH; many clients do not understand or want to hear about technical details or climate change.
We need a carrot-and-stick approach: improve building codes and enforce them.
We need affordable and effective PGH 2.0 retrofits.
Read the Project Drawdown website or book for 100 more ways to reach carbon-neutral emissions.
Read Bruce King’s The New Carbon Architecture to learn more about reducing embodied carbon in buildings.
What would you include (or avoid) in a Pretty Good House 2.0/Low Carbon Home?
Michael Maines designs Pretty Good (and better) homes and renovations throughout New England, and also builds them in central- and midcoast-Maine. He writes the “Building Matters” column for Fine Homebuilding magazine, and the “Building Science 101” column for Green and Healthy Maine Homes. Email him through michaelmaines.com to join the BS + Beer discussion group mailing list, or join facebook.com/groups/BSandBeer. To join the mailing list for the Portland discussion group, send an email to [email protected]
Weekly Newsletter
Get building science and energy efficiency advice, plus special offers, in your inbox.
74 Comments
The Mycelium insulation link goes to a speculative article, which further links to a page not found, plus a page that indicates this stuff is an engineered to order material. They list a bunch of theoretical applications, but no way to order any material.
So to answer your question of why not to use it to insulate homes, because you can't. It looks even more difficult to obtain than the "impossible to get" phenolic foam, which at least has an actual commercial product and an office and manufacturing facility in North America.
Trevor, the mycelium insulation is more in a "maybe this should happen" category. One of our regular members has been trying to get phenolic foam for quite a while with no luck. I'm glad that others have been able to buy some.
Michael,
Very well thought out, I agree with all of this. Building durable, energy efficient and planet conscious buildings is a skill and should be considered as such. What a great community you have going there in New England, would love to sit in on those meetings.
There is a cold climate item one might consider to be a bit more heating degree day specific for wall and ceiling R-value. I like Harold Orr's definition of superinsulation as Hdd divided by 180 for walls and 120 for ceiling r-value.
Doug, thank you; we do have a great community of forward-thinking builders and designers up here. Come up anytime! Harold Orr's rule works well, pretty close to what we are using for cold climates. Part of PGH 2.0, though, is that what the materials are matter greatly--so if you are using a material with high embodied carbon, you should consider using less insulation than you would if you were only worried about energy efficiency.
I will be using Phenolic Foam on my house this spring. I found a local supplier in upstate NY.
That's great! Have you actually made plans to purchase it from them? That seems to be the missing link up here--we know it exists; we just can't buy it.
I just heard from a Kingspan rep, as far as I know the only supplier of phenolic foam in the US. He said they are currently in the process of setting up distribution, but that in smaller quantities they would be competitive with a flame-retardant polyiso (aka Thermax) on a cost per R-value basis. He said that if they had to go through an intermediate distributor, which may be the case, it could add 15-18%. He's sending me a sample and more information. But as of today, I can't buy it.
Who's the supplier? What's the brand? Thanks
Great read! So cozy feeling when we share what we know, but how can we get this into the press where it's needed? We're all surrounded by thousands of homes that so desperately need our help. Think of all that work waiting to be had! Deep energy retrofits should not be expensive. Anytime of year, I can get 2" used polyiso for less than 15 cents/sq.ft. from mostly roofers who need to dump it. 4-6" EPS the same. Most of them even separate good from abused. Zero embodied carbon at that point.
Paul,
You wrote, "Deep energy retrofits should not be expensive." I hear that a lot. The implication seems to be that builders who are performing deep energy retrofits are overcharging -- and that's really not the case. People who want to see deep reductions in greenhouse gas emissions often promote deep energy retrofits -- and they often seem to have a feeling in their gut that deep energy retrofits should be cheap. But they're not.
Substituting used rigid foam for new rigid foam will bring down the cost of a $120,000 deep energy retrofit to $100,000 or $110,000, perhaps, but it won't solve the basic problem of affordability.
We don't need deep energy retrofits. We need cost-effective weatherization work.
But if you think I'm wrong, you should get into the deep energy retrofit business. You might offer to install exterior rigid foam (using used foam, of course) along with new windows for a bargain price -- like, I don't know, $20,000 or $30,000 per house. Do a few jobs and tell me whether it's a good business plan.
What Martin said!
Deep Energy Retrofits are usually only "reasonable" when dealing with a house that needs massive renovation in the first place, and has a low purchase price. When a house is in bad enough shape that the interior needs to be gutted, the siding, roofing, & windows all need replacing the cost of even doing a basic cosmetic rehab will usually run more than half the cost of a DER. If it's a house that you plan on living in (as opposed to flipping at a profit) spending the extra can still make sense.
If any of the upgrades can be subsidized by state/local/utility programs it can be even more palatable, but it's never going to be cheap, even using reclaimed materials.
I'd pay $50k for full frame replacement windows and exterior rigid foam!!
One approach is to start with a scope of work based on fixing problems that need to be addressed regardless of energy considerations, and a wish list of upgrades: aesthetic and functional. Prioritize the upgrades that allow energy upgrades to be rolled into the project, and include energy retrofits in the repairs where possible.
The problem of course is that any of the above is so expensive that many homeowners will run out of money before getting as far as one might hope.
A $100k DER is hard to justify, but a $120k comprehensive renovation project is easier to get used to. At least until the cost doubles to $240k and then to $480k by the time it's done.
For some clarification:
Since the material cost of the insulation on an exterior insulation retrofit wouldn't differ from the insulation cost on new construction, (notice i'm saying insulation, not installation) I assume it is primarily in labor that a DER becomes non-viable. I.e. the integration of the new layer with existing openings/trims etc.
Well, of course if good siding is being removed and tossed for new siding to be added, that would be another added material expense (in comparison to new)
And if new windows are added, that would be another added expense (compared to new).
What I'm getting at here is that if siding is in need of replacement anyways, the material cost of a DER (if new windows aren't included) wouldn't really be significantly different than the cost of adding exterior insulation during new construction, correct?
This is just to clarify the expense breakdown, not to imply that we can ignore labor costs (obviously that's a huge part of the equation).
Paul, thank you. Unfortunately I have to agree with the others who say that deep energy retrofits virtually never make financial sense as a stand-alone project, but if you are doing other work, definitely work in improved efficiency.
I would also disagree (mildly) that recycled foam has zero embodied carbon, since embodied carbon includes what happens to the product at the end of its life. But for retrofits I agree that if recycled foam makes the job easier, and still safe and healthy, then go for it.
Genius
Adding exterior insulation to walls, new siding and windows are a major part of the energy retrofit expense, with the lowest return on investment. Concentrate on air sealing, attic insulation, insulating where there is none and foundation insulation where accessible, especially rim joists. When the time is right, upgrade to a high efficiency heating system and you will see a substantial reduction in energy use and increased comfort.
I've done exactly that, air sealing, increased attic insulation, more energy efficient appliances as the old ones aged, reduced hot water usage, DWHR, reduced standby loads, drying clothes with a clothes line when possible, and air source heat pumps. Though I still haven't gotten to the uninsulated slab yet. Doing the majority of the work myself, I've reduced my homes energy usage by 62% for $17500 CAD. I'm not sure if adding exterior insulation or better windows would make financial sense at this point. I might add good insulating blinds to the windows to get a portion of the effect of new windows for a more reasonable price, but that's still a sizeable chunk of money for the effect.
Adding cellular blinds to our old house made a huge difference to summertime overheating. Less so for winter, but still noticeable.
Good to hear, thanks.
The window and insulation reconditions do make since in Maine but are silly for Miami.
If PGH is going to have hard numbers for windows and R values they should vary by climate zone or just recommend using the lowest cost option from your BEopt model.
To me Passive house seemed to be the best house regardless of its cost or climate zone.
I thought PGH was the green home that considered return on investment.
A pretty good house should make financial since give its climate zone and today’s fuel prices
Walta
Walter- please note those prescriptive values were predicated on "In a cold climate, DOE climate zone 5 or 6... ", which would include most of Maine, but not Miami...
I always fall back on the 2009 classic BA-1005, table 2, page 10 as the starting point for "pretty good house" performance levels, zone by zone:
https://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf
With improvements in performance/lower cost PV and heat pumps that have occurred in the intervening decade, backing off by one full climate zone might be closer to the current financial sweet spot, but the table as-is would still be a reasonable starting point to work from.
You say to "minimize concrete which contributes 10% of man-made global warming emissions, partly through fuel to heat and move minerals, but 60% from release of carbon dioxide (CO2) from limestone (CaCO3) to get calcium oxide (CaO) for Portland cement."
Just about every building site uses some concrete, so why not use Carboncure concrete (which injects carbon dioxide into the concrete, trapping it forever)? The process of injecting CO2 into the mix also strengthens the concrete as well.
https://money.cnn.com/2018/06/12/technology/concrete-carboncure/index.html
Since its introduction it is becoming even more common to find a producer in the US.
https://www.carboncure.com/producers/
Scott, I agree that CarbonCure is a great concept, enough that I mentioned it a recent Fine Homebuilding article I wrote about climate change (https://www.finehomebuilding.com/2018/11/02/climate-change-builders-biggest-opportunity). Chemically speaking, it essentially changes cement back to limestone. It was mentioned at our discussion, but it's not currently available at ready-mix plants near us. I probably should have put that on the "big ideas" list, though--thanks for bringing it up!
What about LC3 cement?
LC3 cement is great! One of several "blended cements" coming soon to market, it uses lightly calcined (baked) clay to augment Portland, resulting in equal quality cement with half the carbon footprint. I know the inventor, Fernando Martirena of Cuba, but don't know when it will be available to us Yanks.
Hey Bruce - was just reading the LC3 part in your book a couple of days ago. Exciting stuff. And fantastic book. Thanks!
How do they address the problem of carbonic acid corroding rebar?
John,
Some reading. Granted, this first study is not from a 3rd party:
https://www.emcoblock.com/pdf/divisions/bay-ready-mix/CarbonCure-Technical-Note-CarbonCure-and-pore-solution-pH.pdf
"Research conducted by CarbonCure Technologies (at right) has shown that an carbon dioxide utilization process has a minimal effect on the pH of the pore solution of mature concrete. Paste samples were created with varying levels of carbonation (expressed as CO2 content by weight of cement) that were achieved through a carbon dioxide injection during
mixing. The paste was then cast into cylindrical specimens and moist cured. The pore solution was extracted at 28 days and the pH was measured. The impact was minimal and suggests no risk of depassivation of ferrous reinforcement."
Might be worth emailing their VP of tech:
Sean Monkman, PhD PEng
VP of Technology Development
[email protected]
Other works referencing the ph issue I believe you're referring to (see references at the end):
http://www.parkerblock.com/pdf/divisions/bay-ready-mix/CarbonCure-Technical-Note-Chemistry-of-Fresh-Concrete-Carbonation.pdf
Recent study from Civil Eng. dept. of U of T on the increased strength of similar mixtures, but no word on acidity:
http://downloads.calmetrix.com/Downloads/Monkman-MacDonald-Hooton-NRMCA-2015.pdf
This research should address your question (no idea if it's out yet):
http://thomasbetong.se/images/articles-images/student/Master-thesis-proposal_Carbon-Curing.pdf
I, too, would be interested to see if they've addressed it. The unfortunate fact of a new product is that we won't know the long-term effects until someone takes the plunge.
"As always, however, if you feel that you deserve a plaque, feel free to buy yourself one."
I love this. Don't ever change!
"In a cold climate, DOE climate zone 5 or 6, use"
As Dana referenced above, is it worth being more explicit about other climate zones? Only ever mentioning zone 5/6 might put a lot of people off.
John, I suppose I could have been more clear, but anyone who is familiar with the original PGH concept knows that a house in southern Maine will have different requirements than one in Texas, or even in northern Maine. This is an "open-source" idea, so everyone should feel encouraged to add what they feel makes sense for their location. The key difference in PGH 2.0, compared to the original, is placing emphasis on the fact that embodied carbon needs to pay for itself in 10-20 years.
John,
Several GBA readers have proposed PGH targets for climates other than Maine. You can read some of these proposals here: "Regional Variations on the ‘Pretty Good House.’"
"Heat-pump water heaters are a no-brainer for most homes."
Do they make sense in cold climates when they're taking heat from the building while another source is adding heat most of the year? I thought they weren't a good idea in heating dominate climates.
Heat pump water heaters still make sense in heating dominated climates, even more so zones the "-A" climate zones ( 5A, 6A etc) where dehumidification is needed to keep indoor humidity in the optimal human-healthy range in summer, even when there is little to no sensible cooling load.
During the heating season the advantage is a bit less, but if heating the house with cold climate heat pumps the ~2/3 of the heat being drawn from the house to heat the water is still being leveraged by the space heating heat pump, making it more efficient than a plain old electric tank.
Thanks Dana.
Michael, thanks for a really well done article (and the book plug!). Thanks also to Martin Holladay for his ever-sensible comments. A few minor notes:
1) Portland cement (not concrete) accounts for 8% of anthropogenic greenhouse gas emissions. We've all seen various numbers from 5 to 8% or more, but I take this from LaFarge-Holcim, the biggest cement company in the world.
2) CarbonCure is definitely a cool new thing, and will hopefully be available soon at readymix plants. But its use reduces but doesn't nearly remove concrete's footprint. And I believe they have worked out any corrosion problems due to changed pH levels.
3) Borrowing from Michael Pollan: Build, but not too big, and mostly with plants.
Nuff said.
Bruce, thanks for your comment, and for being a major part of the inspiration for PGH 2.0. I like the Michael Pollan reference, too--for anyone who doesn't get it, author Michael Pollan said the ideal diet is to "eat (real) food, not too much, mostly plants." The Dilbert clip sums up the situation pretty well.
As for concrete vs. cement, good point, and with a degree in structural engineering it's one I should have caught. As for the percentage, I know in your book you cite 8%, and that's what I used in another article recently, but I've also heard 10% and 12% from reasonably reliable sources, so I rounded/averaged to 10%. I'll double check my other sources.
Read "The New Carbon Architecture" by Bruce King. Great read. Very useful.
Also read ASTM E2392 Standard Guide for Design of Earthen Wall Building Systems. Great standard.
Along with Bruce King's book, I'd say the biggest inspiration for this topic was a talk at least year's NESEA Building Energy conference in Boston, where Ace McCarleton, Jacob Racusin and Chris Magwood blew the minds of most attendees in a packed room when they presented their research on embodied carbon vs. operating carbon in buildings. They are presenting again this year, as the keynote address: http://nesea.org/session/carbon-drawdown-now-turning-buildings-carbon-sinks.
Has anyone thought of / analyzed /developed a potential geothermal heating/cooling system which circulates liquid in the poured concrete floor slabs and foundations which are typically part of building construction? If so and the information is available on the interwebs, please share link. Thanks
Seth,
A geothermal heating system is more accurately called a "ground-source heat pump."
The usual phrase to describe "a system which circulates liquid in the poured concrete floor slab" is "radiant floor" (a type of hydronic heating system).
If you search for "ground-source heat pump" and "radiant floor" on the GBA site, you'll find dozens of articles.
"Heat-pump water heaters are a no-brainer for most homes."
What makes me think twice is the horror stories I've read about them. I don't recall any horror stories about any other energy-saving technology. I wish I could have as much confidence in HPWH's as I do in straight resistance heaters.
In comment #28, Michael Maines says: "a house in southern Maine will have different requirements than one in Texas, or even in northern Maine", and in comment #25 Dana talks about the "-A" climate zones ( 5A, 6A etc) where dehumidification is needed to keep indoor humidity in the optimal human-healthy range in summer, even when there is little to no sensible cooling load"
All these zones and sub-zones gets confusing. Is there a map for North America (USA and Canada) that shows these sub-zones? The average homeowner may do the research to discover whether they are in a "cold or very cold" zone, or maybe whether they are in a zone 4 or 5, but what about zone 5A? Where do you find out what the difference is between a 5A and 5B zone, or where they are located?
“[Deleted]”
Scott, great question. This is the map that has the most information for the continental US: https://www.greenbuildingadvisor.com/question/new-improved-iecc-climate-zone-map. (Coincidentally, posted by a contributor at our BS + Beer discussion; KISS was one of his suggestions.)
Here's one that included Canada, though it's lacking other information: https://www.greenbuildingadvisor.com/article/climate-zone-map-including-canada.
And here's one that shows more of a general categorization: https://www.greenbuildingadvisor.com/article/all-about-climate-zones.
You mention that people should plant deciduous trees on the south and west sides. I thought a study some years ago found that there should be no trees on the south side, because it cuts back quite a bit on the radiant heat gains in the winter. The deciduous trees still have a lot of branches that block the sun in the winter. As I recall it was up to 70% reduction (or was that 30%?). The summer sun on the south should be shaded with overhangs and shades instead. Also, it some places, like here in Colorado, it would be 10 to 15 years (or more) before a planted tree would create any appreciable shade.
Then there is also the problem of shading PV arrays. And there was an article on this site a few years ago that west-facing arrays in cooling climates are important.
Lawrence, I was careful to say "consider" items like that because clearly they won't be right for every situation. My own house is an under-insulated 1830 farmhouse, and I have a large pear tree on the southwest side that helps a lot with summer heat gains, and I'd like to add a grape arbor to protect the south-facing windows, which are not very good but still not bad enough to justify the expense of new ones. Every situation is different, and a low-carbon approach requires a different decision process than simply focusing on lowest energy use.
Lets make a plaque out of old chunk of foam or something.
This makes me wish we had an upvote button on this site.
I was thinking the same thing. We had one in the early days, before they were popular elsewhere.
Or an old empty foam pak container. I have one left before Mike cured me of my wickedness.
Was there any mention of low carbon roofing products? I just realized that I don't think I've read anything on the embodied carbon of metal roofing vs tar based shingles.
Calum, no, we did not discuss roofing. I would be interested in seeing hard data, but in general, I believe that both steel and asphalt-based roofing are readily and generally recycled at the end of their lifespans, though I could be wrong. I'm not sure about membrane roofs such as EPDM, PVC and TPO, but doubt they are easily recycled. Slate is probably has the lowest embodied carbon but also the most expensive installation costs.
Yes, asphalt, that's the word I was looking for.
Thanks for responding. I suspect your right, but I'd like to see some hard data on it as well.
Ahh... the old woodstove makeup air debate smolders on...
https://www.woodheat.org/the-outdoor-air-myth-exposed.html
> Use air-source heat pumps.
Be careful with this one. For example, in N Dakota, it's better to use a natural gas furnace.
>"...Use air-source heat pumps"
Better how?
Operating cost-wise gas is dirt cheap in ND. The ND grid is currently pretty cheap but high-carb, but with the change over to combined cycle gas and a booming wind power development it's greening-up more rapidly than most state grids.
https://www.eia.gov/state/?sid=ND#tabs-4
As of 2017 nearly 27% of all power generated in ND was generated from wind, making it into the top five states on a percentage basis:
https://upload.wikimedia.org/wikipedia/commons/7/7d/WindPowrPctg.svg
It takes a crystal ball clearer than mine to say with certainty that over the lifecycle of the equipement a gas furnace would be lower-carb than an air source heat pump.
It's currently much less carbon beneficial to use a heat pump + utility power vs burning nat gas in ND. Sure, one can always argue that the ND coal plants are going to be shut down soon - I doubt it. It would be a big step forward if people would at least run the numbers based on some assumptions vs blindly following generic advice.
It may be that installing nat gas and a heat pump (a small price increase over central AC) and switching based on the weather (which effects COP) and the current utility situation is much better than R8 windows.
What methods are PGH 2.0 builders using to achieve r40 for above grade walls without the use of foam? Is it mostly double stud construction with blown in cellulose? If you're doing double stud construction and have r5-r8 triple pane windows and are air sealing enough to get down to 1.0 ach (which I would guess already requires taping sheathing seems?) is it really that much more expensive to expand the wall cavity a few inches, put in some more blown in cellulose, air seal a little extra to get down to 0.6 ach and meet passive house standards? It seems like PGH 3.0 is going to be a Passive House. Am I just under estimating the additional costs of going from PGH 2.0 to Passive House?
User-7625234,
You could expand the gap between double-stud walls some as you described (as well as add more slab edge/sub-slab foam and attic insulation, etc), but those steps alone still wouldn't get you to the the passive house standard.
The passive house standard is more than an energy conservation standard. It also has certain requirements for durability. PHIUS uses a German software called WUFI to model the durability of the enclosure for moisture transfer. A simple double-stud wall will fail WUFI in a cold-ish climate. To use a double stud wall, you would likely need to add about 5-7 inches of closed cell spray foam within the wall. This leads to another challenge with Passive House; it's more than a standard for energy conservation and durability. They also look at embodied energy. They will need to run separate calculations to determine if the added spray foam exceeds certain thresholds needed to comply with the standard. This is why most PHIUS homes use Larson trusses or exterior rigid foam. Double-stud walls feature spray foam or a mid-wall air barrier/vapor retarder. You can read more about this in the PHIUS Guidebook which is free to download.
There are other elements as well, including shading, peak loads, etc. You can achieve the same or lower energy usage figures with a pretty good house but it will not comply with a standard. (That is the whole point behind PGH.) Given that there are have been few, if any recorded failures from double stud walls, most people avoid the complexity of PHIUS and just build a DGH.
Rick Evans,
Thanks for the clarification. As far as passive house durability standards regarding double stud walls, is airtight drywall sealed at the top and bottom and all penetrations and a vapor impermeable primer not a viable option for an interior air and vapor barrier?
I think an air tight dry wall approach will work in terms of durability. (It would still fail WUFI though.) I would avoid a vapor impermeable primer however unless you are building in Zone 7 or higher or live in a very dry climate.
Martin Holliday has written a lot about moisture concerns in double stud walls on GBA. He recommends including a smart vapor retarder behind your drywall for added protection. ( I did this with my own double stud wall). A best practice might be to protect that membrane with some 2x strapping and then add your drywall.
user THX-1138,
Check out Lstiburek’s Ideal Double-Stud Wall Design if you want to see... well, Lstiburek's Ideal Double-Stud Wall Design.
Having a 'smart' vapor retarder (sheet good or something like intello) and having it protected from likely damages (future homeowners) are two key points. A vapor open exterior and a rainscreen are also key points.
I find that using helical metal piers to reduce concrete usage to be an interesting idea. I'm wondering why some doubt it? Why isn't it a good idea? I'm also wondering if anyone has had success building a PGH using them?
Hey Adam - I built a small house entirely on helical piers, and a bathroom addition as well. Both worked great. You need to figure out a way to get water in and waste out without freezing, and a good insulation/air sealing strategy for the underside. But otherwise all went well.
Hi Dan,
I'll be building a pier and beam house in the next couple years, what strategy did you use for the water supply and waste lines entering and leaving the house? What did you use for insulation underneath?
Most contractors are leery of change, often for good reasons. Everyone I know who has tried helical piers is a fan, for at least some situations.
I was involved with designing and building a Passive House on helical piers, and I'm currently working on a PGH addition for my mother in law that is on helical piers. The one thing they lack is lateral resistance, so you need a plan for that or you'll get uncomfortable shaking (or worse). It's not hard to do, but should be planned for and not an afterthought.
In our beach communities, our soils can't support spread footings and there are scouring concerns near the water, so construction with helical piers and grade beams is becoming more common. Granted, this doesn't decrease concrete use much, but it is making our local contractors more comfortable with the technology. The alternative here to helical piers and grade beams is foundations raised on wood piles. These don't use any concrete and they are a mature technology.
I just received a couple window quotes and they're quoting U values in two different units: metric and US. So I just need to be sure of something. When the article suggests striving for U values of 0.2, that's US units, right?
Adam, yes, PGH numbers are in IP units, not metric. If you are getting metric U-factors you should also see if they are NFRC values; NFRC is a US institution that calculates the whole-window U-factor somewhat differently from European manufacturers.
Adam,
See this article: "All About U-factor."
Are there any specific resources for conducting a PGH retrofit? I am considering doing a retrofit (historic property, so it'd be an interior retrofit) in Indianapolis and haven't had a lot of luck finding contractors familiar with these techniques.
I have looked over the 475 high performance wood retrofit details, but was wondering if there is anything else out there. Especially with regard to the rest of the building systems not just the enclosure.
Thanks,
Max
Thanks for a great article about "carbon"! I also recommend to view this video https://youtu.be/DeKUlEOJ0p0
Log in or create an account to post a comment.
Sign up Log in