I have been aware of PAHS designs for several years now. The idea seemed like a stroke of genius when I first read about that underground umbrella. But when I read Paul's wofati article, where he describes the evolution of the idea, I thought I saw a major flaw. Since then I've continued reading these forums hoping to see someone else catching, and possibly correcting the problem. Nobody has, and I am plagued with self-doubt now, but it seems that a wofati project on Paul's land is not to far off, so now is the time to address the issue.

I have indicated what I see as the problem area in red in this modified version of Paul's drawing.



There appears to be no barrier to heat loss along this part of the building's perimeter. It's like a wofati only includes half of the underground umbrella, so fails to isolate the enormous mass of earth under and around the house from the cold of winter. I don't care how good the umbrella is on the other side. A bucket that only leaks on one side is still going to empty quickly.

Am I missing something, or have I just saved everybody from embarking on a doomed project? Somebody, please tell me I'm crazy.

the solution is simple and well explained in John Hait's PAHS e-book:
you need a second umbrella under the front of the house
see here:
http://www.norishouse.com/PAHS/UmbrellaHouse.html
John Hait’s book, PASSIVE ANNUAL HEAT STORAGE, Improving the Design of Earth Shelters, is still the best available book on PAHS.
You are cheating yourself if you don’t read it before building ANY earth sheltered home.
Frank

Frank, the solution shown in the umbrella house would be prohibitively expensive (excavation costs) in Paul's hillside wofati design. I would suggest that simply putting in a thermal barrier in the red area in Micky's drawing, to at least the footings/frost line, would be sufficient.

The PAHS article also mentions the importance of keeping the earth surrounding the house dry, hence the name, "umbrella house." A water barrier, as well as a thermal barrier, may be necessary to keep the earth under the house dry to a sufficient depth.

one can not hope to build up solar energy that is in contact with the water table:
the earth must be dry, which can take several months to two years to achieve under the umbrellas
a first layer of coarse sand or gravel or pebbles will avoid capilarity, this could be the water barrier
moving the house up 1 m in height against the hill will allow for the second umbrella,
which is the thermal barrier you suggest
this umbrella doesn't need to be large at all,
as long as the solar heat is contained in dry sand or soil
there is no flaw in the concept, it just may not be applicable everywhere
Frank

I think deserts would be the only place capable of controlling the ground moisture levels under a home with the umbrella techniques. Especially in wet years like the Eastern US is experiencing right now.. Someone make it stop for one freaking week please..

Brian, the term "desert" is relative, but I see what you mean. Missoula, where the PAHS was developed, is the Garden of Eden, compared to most of the West (minus the Cascades to the coast), but it is still drier than in the Mid-West, South and East of the US. Where I live is semi-arid and we get a little testy when someone describes it as desert. The desert starts thirty miles west.

Frank mentioned, it may take up to a couple of years for the mound of dirt to dry out, once the umbrella is up.

If a gravel barrier is not enough to break the capillary action, you could always put down a layer of plastic.

In wet areas or in the absence of a hillside, you would want to build a wofati on a berm (an earth-berm house on a berm) to isolate it from a shallow water table and possible flooding (Don't worry about where all that dirt will come from. You need a pond anyway -- right?).

Frank, you're right that building the other side of the umbrella would address my concern, but one of the points of wofati is to build something freaky-cheap (that's the 'f', remember?) that works well. As Andrew points out, adding the umbrella on this side increases cost significantly. Also, because this umbrella would be a water barrier sloping toward the house, you would end up channeling water from 20' or more out right to the base of your wall, which is a recipe for trouble. Furthermore, any excavation on the uphill side will require a lot of careful engineering to ensure you don't end up buried under that hillside in the first big rainfall.

Andrew, I disagree with your suggestion that a water/thermal barrier down to the frost line would be sufficient. The earth under Hait's umbrella is more than just a thermal flywheel; it is also the insulative barrier. That's why it needs to stay dry. But even dry, earth is a poor insulator, which is why you need 20' or more of it to make an effective barrier to heat loss. Even going down 10' with a water/thermal barrier (for a down/up distance of 20' to the outside air) would not be sufficient because the earth outside the barrier would not stay dry. Again, it seems fixing the problem this way would be prohibitively expensive.

While I'm poking holes in the wofati thing (and PAHS in general), I would like to point out to that some of the favorite techniques in the permaculture world -- keyline plowing, swales, ponds & dams -- may cause the hydrology of a landscape to be in flux for many years. Even if you thoroughly check your groundwater situation before you build your PAHS house, you may be unpleasantly surprised down the road to find that the water table below your house has risen 10'. Oops.

Micky, we will just have to disagree. While reducing the coverage of the umbrella would reduce efficiency, compared to a full umbrella, it would still provide a large thermal flywheel on the downslope side of the house. I don't really see any point in agonizing over not being able to build a full umbrella due to site selection. The Oehler design has shown itself to be thermally efficient, without any umbrella. Adding a thermal flyhweel to one side should have some benefit. I suppose we won't know until Paul finishes his first wofati.

I appreciate your criticism Andrew. I get the impression that you are more conversant with this technology than I am, so your assurances allay some of my concern. I admit that us arguing over some thought experiment is not the best way to prove anything. Certainly a finite element simulation would be preferable, but I'm afraid I can't offer that. Still, I'm glad I aired my thoughts on the subject, and perhaps provoked others to give this part of the design some extra scrutiny. I would really like to see some successful wofati houses go up. And it would feel very bad to see Paul's efforts flop while I sat on my hands.

just a simple question: how many of you have bought and read in depth and after that reread John Hiat's book ?

Frank De Block-Burij wrote:just a simple question: how many of you have bought and read in depth and after that reread John Hiat's book ?

Not me. Perhaps you guessed as much from my naive arguments? That's part of why I sat on this question so long before actually asking it. I'd like to think I'm still eligible to participate in a discussion on the topic though. It's been said that the only stupid question is the one you don't ask.

Frank, I am reflexively cheap. I have not purchased Hait's book or Oehler's, nor do I plan to unless I intend on building a house using their design concepts. I have followed Hait's work since the early '80's. I read the early articles and there is now an abundant amount of information on the web (some of which surpasses Hait's expertise).

I tend not to get married to any particular idea and I don't think that Hait's PAHS is the do all and end all of energy efficient house designs. I do find the concept intriguing and may apply it, or adapt it, if the occasion arises.

Getting all orthodox about things kills innovation. Sometimes you have to think outside the box. Sometimes it works out, sometimes it doesn't. The umbrella house itself was a happy accident, a solution to a not particularly well thought out design for an earth sheltered dome.

Micky voiced some legitimate concerns. Replying with "have you read the book?" was unhelpful, and certainly ought not to kill the discussion.

Agreed. I would much rather hear about successful real world examples with temperature, humidity, energy and IAQ data logging. I think real world success is lacking so far but hopefully everyone can contribute to repeatable, meaningful results. Its a cool concept but one with a lot of risk that the inexperienced shouldn't take too lightly when investing large amounts of time and effort even if it is done on the cheap. And no, I haven't read it either.

one way of avoiding to waste money is to buy this book and read it
whichever way your decision goes afterwards:
whether you decide to apply the principles or not,
you will at least know why or why not
what I read is a lot of speculation

looking back at the drawing,
at first sight it seems to me an earth sheltered house built on the wrong slope of a hill
in the northern hemisphere you should have a slope from north (highest) to south (lowest)
only then can you in summer hope to catch the most possible sunlight during the largest part of the day to stack it in the earth for annual storage
only then can you hope to catch all possible sunlight in winter too, stack that too
this goes for any concept meant for solar heating: if your plot slopes from south (highest) to north (lowest) in the northern hemisphere,
don't even bother
sell the plot, buy another one that does have the right inclination
or buy flatland:
you don't need a slope, as you can cover your building (that stands above the water table) with a moat
much simpler, much cheaper,
plus you get a free pond downhill, where you excavated the necessary dirt for the moat

if you are stuck with a plot with the wrong inclination,
better forget solar heating alltogether

the second umbrella in front of the house, to avoid stored heat loss can be very small, as long as it is adequate

I guess I have answererd all quetions so far, after all

greets,

Frank

I also tend to agree with Micky that ground moisture is the biggest design obstacle. The insulation, ventilation and ability to resist becoming a cave relies on water and ground moisture behaving like you tell it to in a diagram. I think most of the population is building in non-arid climates where it actually rains once in a while. Yes, all of Utah is in a desert to me. But that makes me wonder about the average anual precip in the wettest part of UT or even MT for that matter?

Water and moisture movement through the ground is extremely variable and regularly ignores the laws of gravity. If it takes several years to dry and you then have a very wet season that raises the ground moisture again I guess you have to wait another couple years to be comfortable or have healthy mold free air coming in the ground tubes?

In any other place thats not a desert, I think the safest way to do it is how Andrew describes starting with a sealed, capillary broken flat (slightly pitched) ground service and adding the dry dirt (and building envelope) on top of that. Even if you could protect that much ground surface and volume from the relentless persistence of moisture Iam not at all convinced that a 20' perimeter of excavated, protected dry earth can perform as well or be as cost effective as a more typical net-zero home. Even if one does own excavation equipment and has a lot of time to spare (and is extremely detail oriented), I bet there would be better performance by putting the insulation against the building. At any rate, people that are doing it should be measuring and sharing their results with lessons learned.

There are a few, well maybe a couple, of PAHS and related forums that address most, if not all, of Brian's concerns. One I found while researching this thread was the PACCS Forum through the PACCS site at Fuga de Ideas. Be warned that many of the offsite references are obsolete, but with a little sleuthing most of them can be found. The forum is somewhat dormant, which indicates that either there is a lack of interest in building PAHS, or there is another more active forum. Most of the posts are by builders so it is well worth going through the archives.

Frank, I appreciate your input. I think that you misunderstand the Oehler design. If you investigated it more thoroughly you would better understand the concept and why Paul is adapting PAHS to it.

Sometimes, more often than not, it is easier to adapt a design to the site than to find a site ideal for the design. Oehler people seem to find it difficult to conceive of building on a flat site and PAHS people seem equally flummoxed by a steep site. Perhaps it is the illustrations?

Do not concern yourself with our losing money, as long as the conversation remains speculative. I agree, if anyone is making the decision to actually build a PAHS or WOFATI structure, please purchase or borrow the appropriate books, do a thorough internet search for the most up-to-date information and communicate with builders.

Brian, it appears that many PAHS builders do not use earth tubes at all, as it introduces a higher level of complexity beyond the risk of airborne illness. I saw mention of "earth boxes" being used under slabs in some homes. This could alleviate, to en extent, the issue of a high water table, as well as negate the issue of soil moisture, at least in the earth box. One could take it a step further and isolate the entire "ball". I am not saying you should dig down 20', but going down one or two meters would not be difficult (unless you are digging by hand) and if you compacted the dirt, it would have greater thermal storage capacity. The trick would be using an inexpensive thermal barrier over the water barrier. Foam is very expensive and the bubble insulations are not effective in reducing convective heat transfer. Here are some candidates: clay slip and/or MgO concrete and straw or wood-chip or expanded clay/slate/shale or perlite, or foamed concrete.


There is great diversity of microclimates and physiography in this "desert". There are many areas with high water tables where basements are problematic. Most water wells here, away from valley bottoms and perennial streams, go down hundreds of feet. There is usually a layer of moist soil near the surface which may go down a few inches to several feet. In the real desert, the soil tends to keep rainwater and snowmelt at the surface, sending it quickly into washes and canyons, where it either joins a creek or river, empties into a marsh or salt pan or percolates into an aquifer. Mountains and high plateaus receive a lot of water during the year, mostly in Winter in the form of snow. You will notice on a map that we have a lot of mountains. There are desert mountain ranges here whose creeks empty into salt pans, but that have native Bonneville Cutthroat Trout left over from ancient Lake Bonneville, when the mountains were islands.

These are the kinds of questions and issues I've wanted to see talked about: I posted a question asking if anyone had built an oehler type structure east of the mississippi because i have doubts about keeping it dry. Mold, bacteria/rot and termites go after wood here in Illinois, even above ground! I've known about Oehler since the early 80s but I have doubts about his structures where annual rainfall is above, say, 25 inches and we got over 35 the first 6 months of this year. I'd like to experiment with a small structure but I think I'd have to keep it warm in the winter to give it a chance to stay dry so I probably won't given my long list of things I want to do.

I think if i built below ground in Illinois I would go with concrete, maybe include urbanite stonework if I could get a source. Concrete, metal roofing, epdm rolls, machines such as excavators, skid steers and tractors, etc. pose challenges to the depth of our commitment to sustainable building and lifestyles and I struggle with those choices like others who are trying to do better than we have in the past. I keep telling myself to "go small" but the devil inside says I need that special piece of equipment or building material, then i'll be fine...

Michael,

How about starting with testing if the "umbrella" will work at your site? Start with a sheet of plastic and a well packed mound of dirt. See if the dirt dries out under the plastic after a year or two. You could try putting a layer of gravel under the mound, or even a layer of plastic, to isolate it from the water table moisture. Next add some type of inexpensive insulation, perhaps even a layer of hay entombed in plastic sheeting. If you keep it dry inside the plastic, it should last the length of the experiment. If you want to get a little fancy in the next step, you could go for an earth sheltered cold frame -- a mini walipini or Oehler greenhouse. My maternal grandfather built something like it back in the '40's, but without the moisture barriers and insulation, so more like a walipini. He used urbanite and salvaged windows.

You shouldn't need to heat the test structure. If you feel you must add heat, how about building a trombe wall with a used window and some urbanite painted black? You could even get fancy and put in an earth tube.

If you are leery of using wood, by all means use something else. I recently traveled through a corner of the vast pine forests of the Northwest. I can see why Mike and Paul are fixated on wood. I live in a more arid region and "free" timber is hard find (we are no longer given access to National Forest timber, as federal land managers are steadfast in their determination to protect the pine beetle and promote catastrophic wildfires) so I would be more inclined to use an alternative.

As far as wood lasting underground, I will speculate that wood under an "umbrella" will last significantly longer than wood exposed to soil moisture -- if you can keep the termites and carpenter ants away. To test, throw some salvaged lumber into your dirt pile.

Great ideas Andrew. Thank you

indeed excellent ideas, Andrew:
the proof of the cake is in it's eating
and I am convinced that the PAHS theories, if well studied and applied
show no fundamental flaws
Frank

I agree with Frank, the PAHS system is genius!! You don't have to worry so about the soil being wet for a while. it will still do it's job to capture and retain heat through the summer months and release it through the winter. You don't want water running thur the soil. This washes away heat with every rain. The umbrella serves to isolate the soil so it can store heat. You don't need all the fancy heat sinks and to turn flips to store the heat inside the house. The heat will transfer into the soil via the earth tubes and natural convection, so the temperature in the house is warm in the winter and cool in the summer. This system eliminates the need to insulate the house from the soil. In fact , you want to facilitate the heat exchange from house to soil to maximize the amount of heat you can store. However, you do need to use that insulation in the umbrella. to keep the heat trapped in the soil as well as keeping the water from running through this soil. This system is so simple , but elegant. And very inexpensive. I am planning to build a walipini, using the PAHS methods. Facing south,I'm in Virginia, Dirt walls slanting out or stepping up bermed on the northside. The north berm will allow a gentle slope down into a trench 20 feet out from the base. Add 4 inch pvc tubing snaking through this soil entering at the front base and exiting near the roof for natural ventilation; covering all around with a layer of plastic and insulation 20 feet out from all sides. And a layer of soil on top of the umbrella to protect it and add to the insulation. I haven't got the roof down yet, since the angle for the roof must be 52 degrees here. It will be rather steep, mostly glass or polycarbonate.
It will take one summer to capture the heat it needs for the winter. Planning to put an aquaponics system inside, with an in ground fish tank , that will serve to hold heat also.
If it does well, I may move in with my plants and fish.

I am brand new to Permies, having been a lurker for awhile! Following the Wofati discussions avidly, and this is my very first post

I have not read Johh's book, but found it online for free here:

http://www.scribd.com/doc/131641374/passive-annual-heat-storage-john-hait

As I looked at the illustration on pg 13, I noticed that there IS a watershed umbrella at the base of the structure, and not just overhead....., which seems to address Micky's original question. Also, John's illustration does indicate a different slope than the Wofati is located on.

I have zero building experience, but I've been interested in green building solutions for a long time. Looking forward to reading/understanding John's book now. and I also look forward to hearing from Paul and his "on the ground" experience on this issue....

Yes, I am thinking that the earth lodges of the natives to the eastern plains/western woodlands were something like this. They built them partially below grade (scraping down through several feet of topsoil to get to inorganic dirt). They used materials that would shed water away from the lodge, extending out beyond. I think this probably kept the earth immediately around their living space relatively dry. They used cottonwood bolts for their main posts, which would rot out after a few years regardless, but I think they probably lasted twice as long as they would have if they were wet.

I have another, similar concern:

And, our earliest tests have raised some concerns about the amount of heat loss through the two conventional walls.

So here is something that we are currently considering.

The eave is extended. A straw bale wall is embedded in the ground a wee bit (yes, there are complications with rot there - but let's set those aside for a moment). The concern is that the pole needs the strong structure of the earth. If we dig too near the poles, that would be problematic.

One more tiny enhancement.

Data logger: $300-$4k
Thermocouples $10 each
I don't know these brands/technology, the links are just to offer scale to data gathering.

For <$5K the next WOFATI could be temperature instrumented at dozens of points.
Do a Kickstarter, I'm in for $100.

Yes I realize that the data would cost multiples of the build cost. Data is worth paying for.

ETA: put some radon sensors in there too. Someone will ask. Moisture? What else?

[Just saw the recent posts, but I think the comments are still relevant]

Paul,

Did you insulate to below the frostline on the "uphill" side of Wofati 0.7? You could use foam panels or a trench filled with perlite (maybe add a water barrier to the uphill side of the trench). Rather than covering the overhang with dirt, extend your insulated wall all the way up. If you want to preserve the aesthetic, you could put additional, uninsulated dirt, over the overhang. To keep it permaculture, you might put in a straw bale or light clay straw or wood chip exterior wall. Whatever you do, those exterior walls need to be very well insulated (superinsulated), and make some insulating window coverings.

I am pretty sure you will discover a few more heat "leaks" as you progress with your prototyping.

One of the things that I am currently considering is adding an insulated "porch" a few feet out from each conventional wall. The idea is that if it is, say, zero, outside and the thermal mass is at 75 degrees, then the "porch space" might be at, say, 40. So the indoor temp might be at, say, 68.

But basically, I agree with the current analysis - the exterior walls are a major heat leak.

I'm glad to see you on this thread Paul, though I guess it's too late to prevent a few mistakes.

I have to agree that your current concern is valid. In fact, the exterior walls are a much more serious heat leak, if they are not super-insulated, than the area I originally flagged. I had always just assumed that they would be. Annual heat storage just can't achieve a comfortable temperature range in a temperate climate without serious insulation. That big mass gives you temperature stability but it doesn't give you warmth. What warmth you accumulate, you have to hold onto like a miser.

There's more bad news, I'm afraid. The roof will also be a big heat leak if it is not insulated as thoroughly as the walls. Every part of the umbrella has to be a barrier to heat loss or you just won't achieve the performance you are shooting for.

I must now confess that all of this is from a guy with very little building experience and none with PAHS. All my assertions above are based on theory and my mental model. I do have a math degree and a good grasp of physics but the real world can sometimes be surprising.