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Things I would do differently…

Not to be a downer, as the house is really AMAZING, appears to be performing right in line with estimates we made for heat load and UA and the more detailed PHPP workup. But I can’t help it, there are definitely things I would do a little differently if I were to build a house again.

  1. Our property has a 2-bedroom deed restriction, which we knew going in, and it’s totally fine, but if I were to do it again, I would have been in communication with the town’s building inspector (who is also the zoning enforcement person) early on in deciding — show him our rough plans, what we were going to build — instead of waiting until submitting formal plans. Novice mistake. Luckily things turned out fine.
  2. Don’t be afraid of stock plans. I don’t think one necessarily needs custom home plans to build a superinsulated house. Certainly if you are trying to do passivhaus then you probably do since it will mean really messing with window sizes and placement, but otherwise, I would advise that, if you already have a plan that you really like, just go with it, and ask your builder to build 12″ or so double walls, rather than the 2×6 walls shown in the plans. Spend that money you save on something else!
  3. If I were to do it again, I might not be quite so enamored of strict strategies for reaching/approaching passivhaus in New England. A passivhaus would use 2.5x less energy than our house, approximately (assuming the same TFA) but we’re talking maybe $200 in heating PER YEAR vs $600 PER YEAR. I am not at the moment convinced it is worth the substantial extra effort/expense due to slightly unusual methods needed and products. It’s still tricky to do this stuff and so it means having a team — a builder and architect — who are obsessed I would say. Correct me if I’m wrong! So, do all of the items on the passivhaus checklist that are low-hanging fruit, but pass on items that are stretches. Might as well do 6″ of foam under the slab and edge, for instance. But have nice views on the North, East or West of your house? I would say not to feel bad about putting in nice windows there! That’s me. (I would aim for R40 walls including basement, R80 roof, R5 windows, R20 slab)
  4. On the other hand, I would also ENCOURAGE everyone to VERY EARLY in the project to seek out a Certified Passivhaus Consultant (such as ours in the Boston, Massachusetts area: DEAP GROUP) and have them model your house plans in PHPP. Even if you don’t follow all the Passive House advice, you will be very well informed!
  5. On Solar PV panels: I really like the Enphase microinverter approach we took, but I can’t help but think that the grass-is-greener — IOW, a central inverter. I like that a central inverter approach would have 1) been a little cheaper, and 2) allowed for a “hybrid” grid-tie AND small battery approach, and 3) w/ battery, allowed for some degree of “off-grid” use in case the grid goes down during storms and such. Ah well, I probably would be wishing we had microinverters had we gone with a central inverter approach! I am remembering that I think part of my decision for microinverters had to do with worrying about shade. I should have trusted the solar survey more! We are pretty much totally shade free except at the beginning and end of the day. Which microinverters don’t help much with I don’t believe.
  6. I would probably try to use as little foam as possible. Cellulose all the way! And generally, vapor-open envelope assemblies seem like a Good Idea. I now like this thinking better than the Lstiburek “perfect wall” approach which is closer to what we have. Ah well, grass is greener…
  7. I would use bigger windows in some spots and remove them in others. I guess trying to be a bit more site-aware. Where are neighboring houses… where are views, etc. We did this to some extent, but there are a few misses where I wish there was a double bank of windows. That sort of thing.
  8. I would have looked into unusual choices IN PERSON a bit more. I think it would have helped, for instance, to visit a house with had the Thermotech windows we were considered upgrading too. We were feeling stuck on using double hung (which we love) vs casement (which we do not). But maybe we would have been swayed seeing them in person?
  9. Sorta related to that… I would have in some cases gone with the experience of the subcontractors (on paint brand choice) but in other cases, considered using a different contractor who had specific experience using an uncommon but greener product (OSMO Poly-X floor finish). So there are 2 alternate sides to the same issue of trying too hard to use a product that is maybe greener, but if it also gets installed wrong might mean expensive undoing or redoing. And “wasting” green ($) is not green! :-)
  10. I said not to worry about custom house plans, but on the other hand, I will admit that it is a Very Good Idea to have it worked out ahead of time exactly where the HVAC ductwork will go. I think it is wrong to leave it to the contractors. Better to have it worked out ahead of time.
  11. I might have considered more seriously a “backwards saltbox” approach (we face south, so the long roof would be in front) since it would give more room for panels.
  12. I think everyone who builds a house feels this way, but there are definitely a few spots where I wish a light-switch or outlet was in a different spot. Our electrician did a great job helping us with this, but maybe there is a way to get this even MORE right. Not sure how without living in it first.
  13. OK, that’s a pretty short list actually. More as I think of it…

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Net zero in New England seems easy now…

Net zero in new england seems easy to me now… and here’s a little about why…

First some qualifications:
– I am talking about new construction since that is what I am familiar with.
– By easy I mean “not that expensive” by which I mean, it is doable for the same (net cash flow) as a typical new house.

The reason it seems easy is because we seem pretty close to on target to be net zero for the year, and we don’t even have:
– solar hot water heating
– and more importantly… solar air heating
– the house isn’t all that small. I mean, it’s smaller than a typical new house with 4 people living in it, but in retrospect, I think a different design might have been more efficient. I will talk more about that in the future.*

Solar Air Heating
What I realize now, more than ever, is that it is not difficult or expensive to design an inexpensive solar air heater for a house that gives 100% of your heating on a sunny day, even if it is 0F outside. That’s because you don’t need all that much (even in New England) if you have insulated enough. The method that I am most interested in at the moment is Aluminum Downspout Hot Air Solar Collector–which is quite unobtrusive… (youtube) Read more here at

You want in?
1. calculate how large a collector one would need, you need to first estimate your house’s “heat load” using PHPP (if you are building a new Passive House) or get a pretty good estimate using this form or the excel file here as an example.
2. build it! With your kids!

Here’s what I would do if I were to do it again:
– double stud walls 12″ with dense packed cellulose by an installer who knows what they are doing and has the right equipment
– air barrier at the exterior — taped Zip system walls perhaps. Meaning… applied eaves. Search on Marc Rosenbaum applied eaves, etc.
– ventilated/cold roof with insulation on attic floor, no ceiling cans on 2nd floor, etc. and a hatch on exterior of the house to access this space if need be.
– Don’t worry about the roof angle being 45 degrees (near your latitude) or being exactly solar south. Maybe even a shed roof so there is even MORE roof for solar panels.
– heat with a wood stove or pellet stove, looking to Rachel Wagner for any advice on best practices for heating with wood in a tight house
– Use an HRV
– I like having a basement to put mechanicals in, but if I were to do it again, I would probably build only 2 bigger above ground floors and keep the attic level outside the envelope. For a number of reasons. I will write more on this in the future.

Basically, I would follow the rules of building a superinsulated house, even Passive House, but not go too crazy with expensive closed-cell** spray foam insulation or very expensive windows. Pretty much what we did, but I would try to spend even less, and if anything, spend the difference on solar heating!

What’s my point?
The point is… even in a superinsulated house, heating is a big part of the overall energy use (if looking at heating, cooling, hot-water heating, cooking, lighting and appliance use in a household that is reasonably considerate of their usage.) So if you can cut this, even by 25% due to solar, you are going to be in much better shape. Some will argue that is better to spend solar dollars on PVs that can be used year-round, but in cold climates with very efficient solar-thermal heating done on the cheap with the help of and “simplysolar” and “solarheat” yahoo group participants, the cost per KWh of energy saved is going to be much lower.

*A neat book on small houses is Little House on a Small Planet: Simple Homes, Cozy Retreats, and Energy Efficient Possibilities

**Some closed-cell foam is still going to be useful in certain spots — like the rim joists. Just be sure to use a brand with water as the blowing agent so you aren’t adding to the greenhouse effect due to HFC-134a. (article discussing foam insulation and GWP)

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Erik on insulation: like everything in life, the more you know, the more you realize you don’t know. Until…

(Erik on insulation: like everything in life, the more you know, the more you realize you don’t know. Until…)

Until… you have clarity and you think finally know it all. But then later you realize you don’t.

Ok, so here is my overview of the tradeoffs associated with insulation… specifically the pros and cons of using spray foam and rigid foam in insulating your new or used/retrofit house project. I know at least a bit of what I speak because we just built a house which uses a number of different insulating products:

1. XPS (blue Dow Styrofoam) — under and side slab and 2″ in attic ceiling/roof
2. closed-cell foam and open cell foam — walls and roof
3. foil faced polyiso — also in walls
4. dense-packed cellulose — also in walls and roof

The issues with insulation choices. The generally fall in to one or more overarching principles.
a) Reduce energy use (name your favorite reason: global warming, energy independence, $ savings, etc)
b) KISS (“Keep it simple, stupid”)
c) Local economy

OK, so finally… here they are:

1. embodied energy
2. global warming potential
3. vapor barrier — permeance
4. air barrier
5. dew points
6. drying potential — “keep the water out, but let it get out if it DOES get in”
7. cost
8. r-value per inch
9. longevity
10. full-life-cycle — recycle-ability
11. ease for installer to do a good job
12. “insulate local”
13. “heat with wood” LINK

OK, so just listing those issues just tired me out without even writing
about them.! Perhaps I will discuss them one at a time in separate posts.

But let me for now, jump right to the conclusion after factoring in all the above issues as I see it:

1) Do not:
Do not use XPS or Closed-Cell Foam (unless it is the type using water as a blowing agent)

2) If building new:
insulation: 12-inch double stud walls (not staggered — no need) with dense packed
cellulose behind mesh from a local installer with the heavy duty blowing
equipment that I will figure out the proper name for.

air barrier: external taped “zip system”

roof: cellulose in 2×8 or 2×10 with OSB-gussets holding 2x4s to provide thermal break.
probably do a vented roof so maybe use 2×4 on edge with another layer of OSB on top.

3) old houses — deep energy retrofit
insulation: add cellulose to the walls. Maybe hang cellulose-filled larsen truss or EPS SIPs on the outside.
roof: if there is an attic, either do deep cellulose on the floor (seal holes first!) or if a used
attic… water-blown (not HFC-245fa) closed-cell foam in the rafter bays. Or maybe open-cell

4) aside: solar for everyone (if you have sun)
4.1 electricity: PVs actually pay off pretty quickly in MA even without factoring in tax credits

4.2 hot water: if DIY: follow and oversize collector and storage if possible. Otherwise
consider heating water with geyser hot water heat pump and more PVs

4.3 space heating:
4.31 Make thermosiphon air-collectors (see, solar siding (ala Nick Pine) or a thermally isolated
low-mass sunspace (ala Nick Pine and Laren Corie) with water storage for cloudy days
4.32 Join the solarheat Yahoo group.
4.33 This almost has to be a DIY job, unless you use the small Solarsheat collectors like those at

4.4 the basic idea with solar is that it is at some point going to be cheaper to add solar electricity and/or
solar heating than more insulation to your home, especially after a certain point if it is a retrofit job. It is
pretty simple math to figure out what that point is by using Ohm’s Law for Heatflow (ala Nick Pine) — basically
calculating the thermal resistance of your home by factoring in all the different walls/windows/etc.

5) aside: employment
if you are unemployed…. this seems like a great field to go into with endless work to do!
This is probably what I would do if I were out of work! You could either get in on consulting people what to do …
like Passivhaus consultants. Or be a construction contractor specializing in deep energy retrofits or solar projects.

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Out of sight out of mind

Ya know how if you have junk food in the house… you eat it? So best to not buy it in the first place? Well, we’re going to try the same thing with our house in two aspects — no exterior venting of our (electric) stove. And no clothes dryer (we’ll see how that works out! We’ll probably have our old one, just not plugged in, and we’ll sell it if all works out…). Health first obviously. Saving energy is a distant second…. so first and foremost this has to make sense from a health stand point. No internal combustion in the kitchen (electric range), so no need to vent out carbon monoxide (CO) from combustion. And clothes drying… no health issues there, except that we obviously need to keep humidity levels in check.

Well so the problem with both of these types of holes/vents in a house in the first place is that there would need to be an equal amount of make-up air coming IN to the house from another source, and since our house is quite tight, that might be kinda tough to get it via leakage as in most houses. (Our house tested at just above Passivhaus tightness levels, and this was the first blower door test before drywall… so we will be even a little tighter probably.) And the basic point that you are venting out conditioned air, and bringing in cold (or hot in summer) air in exchange. So that’s a waste.

On the other hand… it’s also a bit of a waste to be cooking with electricity (vs propane or natural gas) as it takes 3 times the amount of fossil fuels at the power plant. But I believe I’ve done the calculations, and given the fairly low efficiency of gas ranges, the numbers don’t work out to be quite so bad. And some money savings, since no need for “dual fuel” to get an electric oven out of the deal.

Anyway, back to clothes drying. Our clothes already come out of our washer almost dry actually (front loader) so hanging them on a drying rack, even right in the house, should dry them out rather quickly. If need be, a space dehumidifier can help with moisture levels. Or we will stop being lazy and hang clothes outside. Imagine that! See this building science article on latent vs sensible loads. Basically the issue of “how do you dehumidify when you don’t need cooling?” BSI-028: Energy Flow Across Enclosures especially “Photograph 6: Hotel Room Fix—The through-wall unit controls the temperature (the “sensible” system). The dehumidifier controls the humidity (the “latent” system).”

Others will say that this (0.6 ACH) is excessive tightness, and something more like (2.0 ACH) is still plenty tight but would alleviate issues with make-up air. And maybe at that level an “exhaust only” ventilation system would work with no need for a HRV or ERV. Maybe. I think there are smart people on both sides of this issue. Let’s check back in 10 years and see what people think? My current thinking is KISS — keep it simple stupid — so if there is a way to do this with less complicated and more local methods (less complicated HVAC equipment, cellulose-only insulation instead of spray foam) etc, then that’s a more sustainable gameplan ultimately. Better for the environment and the local economy. Another way to put it is I’d rather spend money on people doing work than on expensive equipment. That said, I also prefer negawatts to megawatts. So let’s aim for both of these… local and negawatts!

Good night.

[Update: I should have explained one thing better... There IS a range hood with some fancy grease filters, but it does recirculate. And there IS also an exhaust duct for the HRV in the kitchen. And an operable window right behind the range. We are basically following the approach used in Passivhaus construction to use a recirculating hood and a HRV exhaust duct nearby but not directly connected. We'll see how it goes. We can always add an outside vented range hood but thought it would be good to at least try this since it apparently works fine for 1000s of passivhauses in Europe.]

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We can heat our house with a hair dryer. Is that inexpensive?

The house we are building here in lovely Massachusetts, USA… almost a Passive House, but not quite certifiable… well, we can heat it with a hair dryer (1500 W of heat). And two on a very cold day (6F design temperature). Does this mean our heating bills will be low? Pretty low, I imagine, yes. But not zero.

Let’s do some math… And first let’s simplify things… the HDD (heating degree days) for Stow, MA is somewhere around 7200 (base 68F) meaning that if you multiply the days of the year we need heat times the temperature differential between the inside and outside temperature on these days, you’ll get 7200. It’s a little more exact than this (think “area under the curve” from calculus — using hour by hour measurements), but that’s the basic idea.

So let’s simplify it even more. Let’s call every winter day exactly 32F outside vs 68F inside and assume our 1500 W can keep up with that (which from my back-of-the-envelope calculations seems about right…) So that’s a delta of 36F. Now how many days is that? 7200 F*days / 36 F = 200 days = 6.66 months. Let’s go crazy and call it 7 months.

OK, so let’s say one really did run a hair dryer for 7 months, 24 hours a day. What would that cost to run 1500 W (1.5kW) that whole time? Well, we pay $0.20/KWh. So using the factor-label method to keep track of our units… making sure numerators and denominators cancel out, that’s:

7 months * 30 days/month * 24 h / day * 1.5 KW * $0.20 / KWh = $1,512.00 per year

In other words, kinda a lot!!!!

But that’s why people don’t typically use electric heat, it’s expensive. (It’s also not a great idea because fossil-fuel power plants are roughly 33% efficient in converting the fuel to electricity… I imagine that’s exactly why it’s expensive! So… it’s better to use it in direct form at your house…) That’s where the heat pump comes in. If we factor in the 2.7 COP (coefficient of performance) of our Mitsubishi “Mr Slim” air-source heat pumps that’s:

$ 1512 / 2.7 = $560

OK, now we’re talking! This also happens to be almost exactly the number you would get if you calculated the cost of delivering 1500W of heat via propane or natural gas. That would be fine and dandy too. So the 2.7 COP mainly serves to green up the electricity use, getting back to parity with using propane directly. 2.7 * 0.33 = 0.8991 (probably about the efficiency of a Rinnai propane direct-vent heater)

Now, the reality is that I hope most of this heat comes from active solar heating. But more on that later!

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Passive Houses and other tight houses — When the power fails

OK, so we know that passivhaus homes are superinsulated and built tight. That’s good right? Less heat (or coolth) flying out the cracks and thru the walls. But one needs fresh air! I think it’s a valid concern people have. I mean, day to day things are hunky dory… the HRV or ERV (heat recovery ventilation system) in a PH is bringing in fresh air at a rate that is quite excellent… by design, instead of just hoping that it leaks in. But… what about when there’s a power failure / power cut that lasts a while?

Open 2 windows a little.

The total “effective leakage” area of the house will still be minuscule compared to most homes. In fact, this is the same idea as the approach that some think is superior to an HRV/ERV for day to day living — usually called “exhaust only / passive inlet” ventilation I believe. So instead of 2 windows cracked, you have a super efficient and quiet bathroom fan (Panasonic WhisperGreen one used to be called?) that runs on a timer and you poke a hole with a damper in another spot in the house. Instant ventilation. But harder to direct to individual rooms and no heat-exchange. Some still think this is a better way. The K. I. S. S. approach.

Anyway, back to window opening. This again might be seen by some as a disadvantage. With most houses, one could maybe claim that the owner/user doesn’t to know a single thing except to pay the bills. (Passive House folks say that their is evidence to the contrary… that many of our buildings are inadequately ventilated. Interesting.)

But back to passivehouses and power failures. Such an house might be lacking in fresh air during this time. But it doesn’t seem like it’s asking too much to open windows. Especially since this is a rare occurrence in most places, and meanwhile, for 95% of the rest of the time, their air quality is probably better with active ventilation. I am open to hearing otherwise, but my guess is the case.

People are used to having to make sure that they have oil or propane (or wood!) delivered in many parts of the world to avoid freezing in the winter. And to make sure their AC is working if they’re in a warm place. So is opening the windows asking too much?

I suppose a parallel analogy is seat belts vs air-bags. I believe as early as 1959 Ralph Nader thought air-bags were important in cars because one could never expect that people would use seat-belts. And remember those automatic seat belts on tracks? Gone! We now understand that good old normal 3-point seat-belts are WAY effective AND people will use them. Airbags are an excellent addition, but they can’t replace belts. OK, so I am trying to equate the active participation in home-operation with the active step of putting on a seat belt. Seems reasonable. People can be expected to know to open their windows if need be. One can install CO2 monitors for that matter…


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To Passive House or not Passive House – That is the Question

OK, so building a Passive House is not such a big deal, right?
– PHPP modelling? check
– lots of insulation? check (R70 walls, R90 roof)
– very good air tightness? check (We’re around 0.70 ACH50 before drywall)
– minimize thermal breaks? check (4″ rigid polyiso on outside)
– fancy windows? check (Paradigm triple pane)
– heat recovery ventilation (HRV or ERV) system? check (Lifebreath 155 ECM)
– passive solar? check. (well, kinda. active solar coming soon…)

OK, but in the US at the moment it’s a bit harder. As Mark Siddall writes over here, to be a true passivhaus — a certified passivehouse / passivhaus — one really has to go the extra extra mile on the items above. And well… we haven’t exactly. Part of it is that, from what I can tell, even if we do 50% or 100% worse than the Passive House standard, this is still really really really good. And in the process we have saved many thousands of dollars.

But let’s take a closer look. Let’s say our house ends up costing $700/year to heat vs a certified passive house which maybe would be $350 for a house of our size. So that’s $350 a year more. (One edit… I think the numbers are probably more like $250 vs $500, so I suppose that’s an even tougher sell. As John Straube put it… that’s less than a Starbucks coffee a day… LINK Valid point. But there are good reasons to do this stuff money aside!)

But this means the owner now just has to buy 25
MMBtu/year or about $300 at todays gas prices. Even for a motivated
homeowner, it is hard to spend too much time, money, give up
convenience and aesthetics to reduce the cost of home heating below the
“annual cost of a Starbucks Venti latte per week”.

First of all, the “net zero homes” and some superinsulation people say it’s cheaper to make up for that $350 using PVs rather than spending more on further improvements in the envelope. example discussion… The basic problem with some net-zero thinking I think is that PVs eventually break or wear-out. And insulation doesn’t. So comparing their cost is difficult. So we did go pretty crazy with insulation (R70 walls, R90 roof). But on the other hand, passivhaus-level windows and HRVs will eventually break too. So these are areas we didn’t go quite as far on. Also, we were selfish and wanted double hung windows. That’s a no-no with certified passive house windows as far as I know. But we got the best ones we could find on the east coast (Paradigm Premium Double Hung — triple pane, warm edge spacers, foam insulated frames, R5). And we’ll get cellular / honeycomb shades for night, since I want them anyway. Better than looking out black holes.

Second of all… just for curiosity’s sake, what is the simple payoff for (let’s say it would have been $10,000 additional spent on fancier windows and heat recovery, etc?) vs that extra $350 a year in heat. BTW, that $350 is assuming you/we have “GreenUp” energy from your utility — National Grid or NStar. (We don’t, since we have a municipal electric company, but we do pay into the Mass Wind program, so I guess you could say we do…) Anyway, so whether it’s PVs or green electricity from the grid, we’re supposedly on pretty equal footing.

So that’s $10,000 / $350 = 28.57 years

Really… simple payoff is misleading and one should figure out what it costs to borrow that $10k, since maybe it is most realistic that it’s in a mortgage. Either that, or if it’s $ spent in cash, then theoretically it would be earning some interest over 30 years. So you have to include opportunity cost. So maybe you could double the number of years for the payoff in either scenario.

In any case, you can see it’s probably a fairly close tradeoff, assuming my numbers are somewhere near right.

Third of all… what we are *really* planning to do is install a much fancier *active* solar heating (and hot water) system for the house which I think will reduce our “primary” or “source” energy use by more than the fancier windows or HRV would have. Thermosyphon air collector … based on the proven principles here at

And heck, we can always put in a fancier HRV. Apparently they make them in a different/better way in Europe. Ours is still pretty fancy. It’s a Lifebreath 155 ECM.

OK, and just a little more on windows… the “even better windows” we were considering are from Thermotech, in Canada. The increase in cost (for doors and windows) would have been substantial over the Paradigm. Almost double… maybe more like 70% more to be roughly precise from the numbers I crunched last night looking at old quotes. They would have been awesome, no doubt. Even Thermotech windows I don’t think(?) are technically “certified” Passivhaus windows, which are maybe only available from Europe at this point. But it seems like the company is at least obsessed enough that one could get the calculations and measurements one would need to fill in the blanks in the PHPP modelling software. Versus many other companies are not willing to do that for you, even if they have pretty darn good windows. That’s my understanding anyway. Here’s a discussion about the differences between European and North American window calculations.

Just for completeness I should mention 5 other ways (besides house insulation, etc.) to use substantially less energy. Specifically fossil fuels:
1. Don’t live in New England!
2. Live in a smaller house! Or in an apartment building with shared walls. (*)
3. Heat with wood. From locally, sustainably forested forests. (**)
4. Don’t drive. Or drive less. (*)
5. Don’t eat meat.

* Number 2 and 4: It’s green living in a city. Thank goodness for New York City, etc, etc!

** Number 3 is tricky with a passive house because it is SO tight, that even with direct-vent pellet stoves or masonry stoves like Tulikivi, etc. (where the make-up air comes from outside) one has to worry about the tightness of the firebox itself. You don’t want to be breathing smoke. So there is maybe some argument for building a little less tight and burning wood if you want to be fossil fuel free. But that’s not possible everywhere because of local laws or non-availability of local wood. And I’d have to find a recent study, but I’m not sure it’s sustainable for everyone in the northeast to burn wood. Let me know if you know the answer to this!
Here’s a recent discussion of heating a passivhaus with wood

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