Storing heat beneath our feet - the umbrella challenge

Hi everyone.

I am rewriting this for the 3rd time in hope i get it right and not boringly long.

The earth has a huge heat capacity, so much that only the first 2m (6ft) of the soil is subject to any temperature variation, be it daily or seasonal.
We are each and every day benefiting from this planetary system even if we don't realize it.

But we can benefit from it even more.
Some have put up ideas like AGS and PAHS.
They all use ways to restrict heat flow in one direction, mostly out of the ground.
The use of an "umbrella" to restrict heat flow is very good in theory.
The practical side has issues since materials used are not natural and they're use in other fields (plastic foil underground) has shown they don't really work.

So, i am trying to find ways that this naturally working system can be tweaked in one direction or another by using natural materials and techniques.

So let's take it piece by piece.

If the ground receives more heat than it loses, we will achieve a multiannual increase in the subsoil temperature.
This is very good for a house or greenhouse situated in a cold climate.

If the ground loses more heat than it gains, we will achieve a multiannual decrease in the subsoil temperature.
This is very good for a house in warmer climates or for an icehouse.

I have uses for both of these cases.

I will make another post about the elements that take part in this heat transfer and ways to control them.

The elements are part of 2 groups:

1. Heat gain : here we have solar radiation.

2. Heat loss :
a) conductive loss to the ground beneath;
b) convective loss to the air above;
c) radiative loss to the sky;
d) conductive loss thru infiltrated rain/groundwater from the high watertable.


For 1, we can not increase solar gain beyond it's natural irradiance except we make use of mirrors ...
But we can reach the maximum solar exposure by proper positioning, stuff well known.
However, we can decrease it by using shade (used alot in warm climates).

For 2.a, we need not worry.
The annual/multi annual balance is negligible.

For 2.b, we can use different forms of insulation to protect the ground from the air/wind.
These can be of the solid type like sand, pumice, LECA, aerated concrete block, something else ?
Or they can be just a trapped air space.
If anyone knows of more natural-ish insulative materials that are good in ground contact, please share.

For 2.c we can use the same solution as for 2.b

For 2.d the problem gets challenging.
If we have a high water table, we stop now.
Otherwise we only need to protect from rain.
If we don't need to walk upon the ground, we could cover it roof style, at a height above the ground.
Or maybe even make some form of structure to double as storage in addition to rain protection function.
This might work very well for a icehouse, especially if underground.

If we need to walk on the ground above the umbrella i don't know any solution ...
Use of plastic PE foil even in layers is prone to punctures which lets the water in.
Possible substitutes would be EPDM or even dimpled foundation film but they are still unnatural materials.
Use of a clay as waterprofing layer is ok for a pond but in this situation the soil will be pretty dry, cracking the clay.
Perhaps a layer of cob or rammed earth would suffice...
Any ideas are welcomed.

I will attach some drawings for some scenarios.

Here are the drawings.

The challenge are the materials/methods, especially for rain protecting the underground.

I vote for dry sand and or dawdust as insulation. I like the idea of keeping the insulation and water proofing separate.
A pavilion style roof is easier to inspect and maintain than is a membrane on or in the ground.
For storing "coolth" like a pavilaion style roof,white washed, perforated clay pipe "earth tubes" leading to a black solar chimney. The floor in the pavilion in sand , with pavers, and beneath that is the root cellar. Put the cellar in the side of a hill, and the pavilion on top.
Grow shade around it .
If you can come up with a good natural matirial water tank, put that on top of the cellar , underneath and fed by the pavilion roof.
Maybe even have an impermeable portion of the "earth tube" pass through the tank itself.
The tank should be stocked with fish, to keep the skeeters down, but there should be no lid, to allow for evaporation and freezing.
A bucket or hand powered pump could be employed to pour near freezing water into the "earth tube"' thus delivering "coolth" to the soil under the root cellar.
The reason I put " earth tubes " in quotes is that earth tubes are traditionally sealed away from the earth aroun them.
This allows condensate to collecting makes an inviting enviroment for mold and mildew.
The Subterranean Heating and Cooling System (SHCS)for greenhouses uses perforated pipes and a fan to drive heated air from the peak of a greenhouses interior down into the soil beneath it. Condensation is expected and desired, as that phase change from vapor to liquid transfers a lot of heat.
The liquid soaks into the ground via the perforations, and the mold and mildew is kept in check by the soil biology.
To use this to capture "coolth" (a useful if unscientific concept) we inject cold air and pull out warmer, wetter air,reversing the heating process.
The fan is replaced by a solar chimney, with questionable results...
Dumping ice cold water down there is perhaps the logical extreme in this idea. Sure, you could use tubs of ice and just open up the cellar doors,but that limits the size of your coolth storage, and takes up some cellar space. The SHCS earth tubes let you use the earth as your tub of ice...
Another thing occurs to me. Salt water could carry more coolth. It would also kill most soil organisms, but not perhaps mold and mildew. But one might use a saltwater tank to cultivate lactobacillus ,and then send those guys into the earth along with the saltwater to compete with any possible mold.
Ice cold dirt pickles for sale!

SHCS style earth tubes without a fan, might prove even harder to pull off for a heating retaining structure, as you would be fighting the natural inclinations of hot air. But one commen solar food dryer design use a solar chimney to create a down draft, so it seems possible.
Two solar chimneys, one on either end of the SHCS tubes,designed so one has more draft than the other , could work.
The far end could have a place to put a candled or build a small fire , thus starting a draft, but that would be less than passive , even if it would still qualify as "natural".

Thank you William.

I am aware of your suggestions, i didn't mention them since it would have complicated the thread from the beginning.

My idea was to treat the issues of how to get the earth mass warm/cold separate from how to keep it that way.
So the starting of this thread was how to keep what was gained.

The umbrella idea is a nice one since it is a passive system.
It works by enlarging the area/volume of mass that is closer in temperature to what we have in the center.
That leads to less conductive losses thru the surrounding surfaces.
The important thing is to use enough mass to make the heat transfer take 6 months.
With that we gain 6 months of warming and 6 months of cooling, therefore an almost net zero annual.

So as long as there is perpetual 6 month cycle, our central mass will stay at the same temperature.

As said above, it's important to have enough mass for this to work.
But the ground beneath our feet has enough.
We still need to think 3d.
We saw that 2m (6ft) depth is enough.
But to make a volume we still need an area.
What i have found thus far is that heat travels roughly 6m (18ft) horizontally in 6 months.
So that means our desired volume must have at least that distance all around it's horizontal area.

That is the first area needed to protect from heat transfer and water.
Protecting the ground from heat transfer is easier than protecting it from water above (rain).
Just as you, i did like the idea of using 2 separate systems for the 2 issues.

I did not do the math of performance vs. cost of using dry sand vs thin blocks of aerated concrete (pretty cheap around here) but i will do it next.
Aerated concrete seems to be a good candidate since it can work in ground contact, is a more natural material and has better insulative properties.
Important thing here is that we don't need a lot of insulation.

Hardest part seems to be the water protection.

For the cellar, a large barn/warehouse would work better than a pavilion since it conditions somewhat the inside space.
It's purpose is to shed rain away from the ground beneath and as a bonus offers storage space or whatever one fancies.
A small volume beneath this structure's insulated floor will be the actual cellar.
So we have multiple functions of this construction.
The umbrella is made of the roof + floor insulation.

For the house, it seems simple (not really).
Just do extra wide overhangs and insulate the ground beneath them using dry sand / aerated concrete or whatever available and stone pavement or whatever available above.
My issue is, how would a structure look with 6m (18ft) roof overhang ?
Or perhaps i make a large pavilion high above and a small "house" in the middle, without roof ?
Or, to improve on function, do a 2 level structure with large overhangs, the lower level is the actual "house", the upper is another barn/warehouse.
Must do a 3d sketch to see how that looks.

But for a greenhouse, permanent, temporary (attached to the house or not) ?

If living on a hillside, issues are simpler, just partially or totally bury the structures in the hill.
This will improve a lot on the "umbrella's" effectiveness.

These are some of my thoughts.
I will make another post to treat the the issues of how to get the earth mass warm/cold plus the unresolved greenhouse situation.

So, first, how do we get the mass warm/cold.

Warm is easier, just expose that part to the sun and that's it.

Cold is harder.
It is simple if using an active system but that has more issues than it's worth it.
If a passive system is desired (of course), then it gets interesting.
If this system also wants to be simple, even without moving parts, then it gets even more interesting.
The simplest system is to just use air.
Determining how to get the air moving thru or around our mass can be difficult.
Remember it's winter time we capture and store cold so no sun to make a draft.
We must rely on "wind", natural or induced.
A network of ducts around our mass, with one end lower and one much higher in the air might work but i don't know how effective it will be.

If some manual labor is accepted, opening some doors during cold periods might fit.
This cold can be stored in frozen water volumes (bathtubs or otherwise) when we need to store a lot quickly.

To recap, i made a table on the difficulties of capturing/storing from a structure/umbrella natural building pov.

	Warmth	Cold
Capture	very easy	a little hard
Retaining	hard	pretty easy

The extreme in this table is heat retaining, more so if the structure is a greenhouse.
I will try to make some drawings on possible solutions for different types of structures.

It seems to me that using a greenhouse on the south side of a house, permanent or temporary, has more advantages than disadvantages.
And the southernmost space (warehouse) can be used to store the water from all that roof+glazing area.

This is easy to do on the S-N axis.
However, at the moment, i don't know how to achieve the umbrella effect, especially the rain protection on the E-W axis for the greenhouse part.
I can't use the roofing method unless that is also transparent.
Come to think of it, it kinda makes sense.
And that could also double as a temporary space.

Any more ideas especially for using natural materials / methods / techniques will be very welcomed.

I've been looking at this a lot and I think a man-made, but non-synthetic material is great for insulation - rock wool. It's high-embodied energy, but an in-ground insulative product needs several critical criteria - water resistance (it sheds), mold-proof (won't mold), flexible (they have such products), and tough (it doesn't tear easily). Of course, it needs to be insulative.
Rock wool is about R24 - which is great. I think you could use it under a large deck. One of the problems I see with the whole process is you either need a rigid insulation - which is prone to breaking or, in the case of expanded rock allows particles in/tears the umbrella, etc./ or has a pretty low R-value. Rock wool will compress, but it has some structural integrity - much more than Pink. It can be ordered in bulk rolls like a carpet.
Meantime, it's awful hard to source in Canada - looking at $500 shipping from China for $500 worth of material.

Anyway, for a serious project, I would say rock wool is a best-practices solution.

Kelly,

Actually, it's the "waterproofing" part that's the most challenging.
For insulation there are alternatives, as you already observed.

The waterproofing is challenging because it has to be very good and easy to maintain in time.
Remember that nothing lasts forever.
So a serviceable component, even if more expensive and difficult to install in the begining, would pay for itself multiple times in it's lifetime.

Ionel, trying to make sense of complex ground physics and mechanics without the proper data to design to is very difficult and can yield an incorrect design approach. I would suggest for starters a full geo-tech report of the site by a Professional. If that is too expensive I would suggest taking soil samples at various depths and locations to a lab to obtain the design properties needed to design to. If you want to post that site specific info we can look at how to resist the geo-environmental loads. If trying to understand and design to seasonal loads that will require more testing, the single lab test data will provide some limited seasonal data that needs to be interpolated annually and over the years or expected building life cycle. Temp, pressure, flow, gradients based on plastic, shrinkage, moisture indexs would be some minimum data needed. I take this data into dynamic software to see the fluxs in action. I use solidworks or flowmaster but I think WUFI does it much cheaper but not as good. A preliminary detail foundation design and material properties as well. There is no general design guide when it comes to these physics and mechanical properties critical to foundations especially.

I have such a design now waiting for test results before I can finalize the design and start breaking ground on it. I'd never build any structure anywhere without it since there are to many unknowns and variables that can cause alot of downstream damage, especially an inaccurate design that makes matters worse like cupping/dishing. Here in America our building codes for structure and energy require the test or we can not get a permit in most jurisdictions, and our Environmental Protection Agency is a part of those codes that are getting striker and more regulatory, due to water, crop contamination, foundation failures, etc....They do not allow theory or guessing for safety reasons. I have seen building's completely collapse into the ground with people in it, search u-tube.

Interesting read tho, nice job!

First...very interesting thinking (perhaps a bit of over thinking?? ) but I like, very much the conceptualization.

I also must concur with Terry completly his assessment. Unless following a "traditional vernacular modalities" (and one that is completely understood in both design and facilitation for a given biome type) it is very advisable to go with the guidelines as Terry has outlined them...in my view. I too have seen some horrific events with "foundation fails caused by "experiments" and "I think" concepts being done in "real life" applications without proper vetting and testing by DIYers and related inexperienced builders...

I think that clay is a good natural alternative as a water barrier, however, you need to do it right and it needs to be maintained. Clay has been used to seal flat roofs for centuries, if not millennia.

Another natural option would be mimicking the algal crust of desert soils, but that would definitely be experimental.

Buried plastic is pretty close to permanent as long as it does not tear or puncture from settling, rocks, roots or critters.

Expanded clay and shale, vermiculite, perlite and foamed glass may require thicker layers than EPS and other foam alternatives, but they are relatively inexpensive, especially when purchased by the truckload. It is all going to be buried, so what does it matter how thick the insulation layer is?

If one lets go of the earth covered/green roof, the level of complexity and cost is reduced significantly -- but it is not, perhaps, as aesthetically or idealistically satisfying.

A traditional bordei with an insulated apron surrounding it might be an interesting project.

Terry,

Thanks for the input.
Our codes also require samplimg the soil up to 3m depth (10ft) at least.
I have not done such a test since my land is large and i have not decided where a potential structure will lie.
Even so, i know this hill is a result of an ancient waterflow which does not exist anymore.
Soil is luvic/clayei.

I am not looking right now at foundation details or any structural element in particular.
When i want that i will cal my archtect/PE and they will tell me if i'm sane or not or how can i make it work with or without modifications.
They also know what to do to comply with the arcane and too conventional codes.
Also, my drawings were just for trying to visualize how i can protect a small piece of ground from the elements.
My largest enemy is not heat/cold but rain.

So take all of this as concept and not actual structural.
I just want to know if there is a "natural" way to realize what i'm thinking of or not.
I might just be bordering insanity in my thinking and i need others to tell me if so.

Jay,
Due to circumstances i am forced to think more than i act (actually acting is close to nil) so bear with me if i jump the horse sometimes ... occupational hazard ...

My line of thinking is to use whatever vernacular exists and adapt or extend if possible/feasible to what i'm pondering.
Like putting a (too) large roof overhang over a building.
Besides the structural snow/wind loads which will be taken into consideration and also an "unusual" appearance, what would be the issue actually ?
Having a larger pece of earth stay dry around the construction ?

So this is my line of thinking.
What and how to do, if at all, to reach a dry, little insulated area of earth around a building (the possible types i have enumerated).

Andrew,

Clay is excellent for sealing and waterproofing with only one caveat : it must always stay wet/moist, otherwise it will crack.
My situation has bone dry months and very wet ones.
Clay won't help unless it's very, very deep.
I already have deep clay but putting insulation down there ...

Regarding plastic foil underground, punctures in it are guaranteed.
And i don't know of the longevity, maybe 50 years for the heavy duty style like Firestone EPDM or dimpled foundation membrane.

So please, if you can think of anything that does insulate and/or protects from the rain a small piece of land, besides what i have sketched before, please share.
Of course, all natural or similar materials.

I do not want to distract from the topic of heat storage but please keep in mind that radon, a naturally radioactive soil gas, may be present in earth sheltered buildings or basements depending on your geography. Radon also enters houses in the water from drilled wells. Your radiation exposure depends on the concentration of the radon and length of time you spend in the space. Deep breathing such as from working increases your intake also. Radon mitigation systems are based on a plastic film and vent pipe typically with an electric fan pulling the gas up the pipe but lower concentrations could be managed with natural ventilation.

Just a thought;
Jim

Jim,

Thank you for your concerns.
The people in this part of the world have built structures from off ground to almost completely underground for milenia.
I'm sure if Radon was an issue, they would have noticed.

I first heard about Radon while reading US based writings.
It's clear that over there it is an issue.
For other parts of the worls ... i don't know.

...I'm sure if Radon was an issue, they would have noticed...For other parts of the world ... i don't know.

Hi Ionel

To Jim's point (and he is correct) Any builder should know this information. There are many areas in Europe (especially with granites and granite based soils) that do have it and unwisely ignore or do not test for it. This is (and can be very chronic) health concern and does affect rural populations without them being aware. This is one more area of "understanding" that to many novice DIYers overlook. Please ascertain if it is an issue in your area, as even low level exposures over time are a health concern of some note.

Regards,

j

The closest thing to a soil umbrella in the conventional literature is a landfill cap or cover.

Take a look at this document. It may give you some ideas for arid climates:

http://www.sandia.gov/caps/ALCD.htm

They recommend dry side (more dry than wet) compaction of the clay layer, if used, to minimize cracking.

I am not sure if the Anisotropic Barrier, and Evapotranspiration (ET) Cover they mention would be effective in more humid environments.

Also, I was wondering if desiccation was an issue, could you use some type of water retaining soil amendment to the layer above the clay, like expanded clay or shale, to keep the clay layer moist?

If you have to deal with wet years or heavy snow, you may not be able to avoid using a geomembrane. That geotextile-bentonite mat looks like a good solution, but I don't know the price.

Jay,

Thanks for the concerns.
I have many friends and relatives that built homes around the area.
I also have talked to architects and builders/PE.
I've also looked at what local permits look like.
Also, at what, how and why was built historical.

None of these sources had any concerns about Radon nor any means for mediating it.
I also have some geologic maps and one of my friends is a geology graduate.
From what i could gather from these sources, we have no granite around.
I know there is some basalt to the south and some diorite to the north.

Andrew,

I also suggested that similar methods like cob or rammed earth may be employed.
But my climate alternates the dry and wet violently.
Primarily, summer is dryer and the rest is wetter.
But summers we have high heat resulting in crust and deep crack formation.
At the same time we may have high rain making soil wet.
So the alternance between wet an bone dry can come in a week's period and not only seasonally.

Personally, i don't know what natural material could work in this situation.
Not even a man made material that will last long enough (think EPDM rubber).
If this water protection layer would be placed on top of the ground, a shingle system like in the ceramic roofing tiles but made of stone slate can be employed.
It has to be on a slope so that water can just flow down without having the time to infiltrate between the tiles.
Also not steep enough since the slates will just go downhill.
Advantage is it can be walked upon.
Disadvantage is you need a lot of slates large enough which might prove expensive and labor intensive.

One solution that i thought of was to use whatever roof system available (metal sheet, classic tile, etc) a little off the ground, enough to make it serviceable and not encourage nasty local fauna to settle underneath.
This would not be considered walkable area but might be made useful by doubling as solar hot water panel installation area or for any other solar capturing thingie (solar dehidrator anyone ?)
The uses of this "roof" are limited by the imagination only.

Ionel,

The umbrella or apron only needs to go 6 to 8 meters beyond the exterior wall. Perhaps a combination of large overhangs and paved patios/terraces would suffice? It would suppress the number of mosquitoes near the house as well. A container garden and some ramadas(pergolas) would help to beautify the paved space.

Cob may be a viable option. For longevity, you may want to replace straw fibers with fiberglass or basalt fibers used to reinforce concrete. You can do some experiments if the material is readily available.

The Sandia article mentions that when installing the clay layer for their Subtitle C solution, it developed deep cracks within 15 minutes. A good cob mix shouldn't crack. The big question is whether added sand and fibers will facilitate water passing through the clay layer.

Thanks Andrew.

I think a combined system might prove best. Price will be decisive tho ...

Regarding the waterproofing, this layer can be in 2 positions.
Right on top of the soil or somewhere at a depth beneath the surface.
If on top, conditions are harder for a clayey material.
If beneath, then it would be moist-er than on the surface.
However, whatever insulative material would be used must work in these damp conditions without it's characteristics compromised.

Cob is naturally dry. When water comes in contact, the little clay in the composition (1:3 clay:sand) will absorb that water and swell a little.
This will happen until saturation. Any water after this point will just wash away, possibly taking the clay/sand with it.
When dry weather comes back, the cob will dry out, hopefully to it's original state.

I f put on the surface, it will be subject to erosion.
If underground, it will work better.
The only thing is that whatever insulation beneath this layer, it must work in damp condition.
Most natural materials i know of don't do that.

Perlite (particularly silicone coated), foamed glass and mineral wool will not lose their insulation value if they get soaked and can dry out again. Resin foams, even closed cell foams will degrade if continuously soaked in water.

Under the umbrella, ideally, any insulation will be dry. If it is wet under the umbrella, insulation will be the least of your concerns. The benefit of these mineral-based materials is that you can repair the umbrella without having to rip out and replace the insulation layer.

I read that the Timisoara region used to be marshland and that, though now drained, there is a very high water table. Is that what you will be dealing with, or are you looking at building sites on higher ground? There has been some discussion about wofati or PAHS being built in high water table areas.

In researching cob as a sealant, I notice that there was a discussion earlier this year about using cob to seal the wofati structure (not the umbrella) instead of plastic.

Thanks Andrew for the time taken to post this info.

Of the materials listed i can only access the rock wool (we call it basalt wool).
And even this one is the most expensive among all, easily available, insulating materials.

If the umbrella is of a "roof" style, we are in business.
Whatever insulation used will be dry.
The only protection measures that must be taken is that no wild animals make home in it and that no wind can blow snow between the "roof" and insulation during winter.
This is quite nice since this kind of approach is suitable for many types of structures.

However, it might not be suitable for all cases.
For these corner cases (mentioned before) i am trying to find possible solutions.

Regarding my region, the marshes were drained some hundreds of years before.
Still, there are areas with high water table but mostly on the flatter plain areas.
My site is on a hill.
Difference in altitude from lowest to highest is 40m (120ft).
It is sloped both on the south and east.
You can take a virtual tour here.
My land is up the hill, to the left of that dirt road.
I haven't done any drilling to reach the water table but my expectation is that it's a lot deeper than 2m (7ft).

I have read the discussion about the wofati.
I still don't know how i can do a non "roof" style waterproofing on the surface, even less so if buried.
A buried system might be nice since i could grow something on top but the roots will harm the system.
Therefore, a surface system i think is the best of all worlds.
It might look something like the drawing attached.
Again, it is to be used only in those spots where the "roof" type can not be used.

Of course, cost will be higher but if there is no choice ...

Hello, me again.

I just got an idea.
What if the insulation was Straw Bales ?
I mean, they have a roof above them and they can be protected by a thin gravel layer beneath from the soil humidity until the soil gets dry.

Advantages:
- huge amount of insulation
- can be replaced if damaged, virtually forever
- doesn't cost too much (at least around here)

Disadvantages ?
- Can be prone to fire but if using a small clay coating we're covered
- critters hiding inside, might be mitigated by the clay "plaster"

Other options for insulation might me thatch as used on roofs or whatever is available locally.

What do you think ?
When the time comes, i might just try this.

PS
At least around here, the cost of bales/sqm is equal to the price of rock wool in 5cm thickness.
But the bales are 40cm thick.
Interesting choice to be made.

PS 2
Any such contraption is economically feasible only for large spaces, otherwise the area under the umbrella will be larger than the actual useful area.
That or reduce the size of the umbrella with the accompanied reduced performance.

PS 3
Some graphs listing useful/umbrella area ratios for an umbrella width of 6m and 3m.
It can be clearly seen that only at about 1200 sqm the umbrella area = useful area in the 6m case.
For 100 sqm, the umbrella is 4 times as large as the useful area.
If the umbrella is to be used for something else (like solar panels) then it's ok.
Otherwise it's a lot of wasted space.
For the 3m width, we have ratio 1 at about 300 sqm, much better.

Hi Ionel,

I wish I had time for more lengthy discussion on your thoughts, but alas it is the busy season for building and work...

In short:

SB does not respond well to being "sealed in." It needs a very permeable finish on both sides. In any roof application I have seen, it has either failed, and/or is waiting to fail.

SB has a tendency (a strong tendency!) to decay from deep inside out. This can take years to decades to reveal itself. Unless actively monitored and check...such as in "test walls/roofs."

If you did not mind designing a supper structure of timber framing and a "attic crawl space" or "service chase" between the SB and the outer umbrella of the roof that also facilitated ventilation such as found in "cold roof" systems...then this concept is not only viable, it is probably superior to a "mineral wool" thermal envelope. The roof thickness would be greater than 1.5 meter I am afraid to be not only "service accessible" but also "repairable should there be a leak and some SB replace. I personally don't see an issue with this thickness (or greater) for most designs of "earth bermed" or "WOFATI" style fossorial architecture....

Regards,

j

I agree with Jay bales need some strong knowledge of vapor of water management not only high perm but very high hygroscopic (sorption and capillary rates) membrane surrounds. Roxul makes a "comfortboard IS, or "Drainboard" for contact with earth. I talked with them today they are experimenting using it under slabs but the compression, creep, and deflection can be an issue. Best design practice is to take the loads away from the insulation by another means (IE: Suspended slabs, roofs, etc). It can take around 731 PSF @ 25% deflection compared to foams most use at around 5-10 PSF @ 10 % deflection(max before it cracks in tension on the under side common to earth from bending/bowing ). Go figure?

Experimental slab home: http://passivetopositive.com/projects/passivebirdhouse/ .....Engineers struggle with "compression" but there is more creep is a bigger concern to me there is no data to design to, same with bales.

The very first thing that HAS to be understood are loads before developing ideas, but we already mentioned that above. Most roofs have anywhere from a 20-50 PSF environmental depending on ground snow loads, seismic and wind zones to get wall/soil shear values. On top of that the dead weight of materials and live loads are added. Nice to come up with concepts but if they can not take the loads they go out the door fast! .

I think I read Paul Wheaton talking in a wofati thread and saying that the use of plastic for barriers was because plastic was easily available and that people had been focussed on other aspects of design and build i.e. there was no need presently to develop a non-plastic barrier. But there is no reason why it couldn't be done. Something like that.

So I start thinking about the plastic barrier and what is its natural analogue? Canvas treated with pine tar? With design allowing for monitoring/maintenance or test models? Not sure if I have followed all the technicalities in this thread so sorry if that's not relevant.

Bill Bradbury and I developed designs on the breathable wall thread. The design has different surface properties than the core that need no poly as fungi food and vapor barrier to stop drying. The surface he burnishes lime to a pore size to not allow liquid water (large water molecules, small is acceptable, I forgot the size) in but is vapor permeable (30-40 perm) to allow access to management systems such as certain clays with a large surface areas or holding capacity pore structure that has high absorption/desorption/capillary (drying), that in combination with passing heat or cold air in cooling environments through the material (~ .2-.3 air changes per hour) to allow drying every 48 hours and phase change. Easier to do with walls and roof than under slabs. There are many ways to design materials that manage ground pressures, vapor/'relative humidity, temp gradients; depending on where the high and lows are, many materials that have the sorption rates, compression strengths, deflection, creep, rock materials primarily. Limecretes, rockcretes, concretes, composite designs of the right geometry and composites that also thermally break, based on test that are site specific.

Roxul or thermafiber will still want a vapor retarder (Class 2-3) to attempt to get that robust surface design or pore structure size they do not spec out, it's hit or miss, hence the testing.

Canvas treated with pine tar? With design allowing for monitoring/maintenance or test models?

Correct with emphasis on preliminary test data no guessing ...and a qualified person to analyze the test data, use it to make design decisions, write and publish design guides, code, etc.....

Hello everyone,

Thanks for answering, working season et all.

Jay has good intuition.
I imagined the whole system as something like a skirt kind of porch.
That means light timber frame (only for snow and wind load), high up the ground (1 - 1.5m) for servicing access.
On the ground a layer of gravel for drainage and somewhat moisture break.
On top of that bales lightly plastered with some clay recipe, mostly for fireproofing but maybe for some animal proofing.

Advantage if your bales are own production.
As i said, even if they rot, you have them in great supply.

I have to do the math on costs tho.
That might prove very interesting and turn everything upside down (look at the area ratio charts).

Jay has good intuition.

Yes he does a very educated man I respect, one of the only reasons I post on this site, not that we always agree but for the most part we do in our own way in the big picture. We permies have the same goal to change the building community and I believe we have a bright future. I'm after the sub-division and International code, the big picture.

I'll probably be next to experiment with mineral wool underground on my spec/production designs to break ground this year if I can get the financing and around code. I'm planning on buying test meters and developing underground test with it to start, but with different skins. We really do need to get away from poly. I been a test Engineer in many muti-million dollar labs (I have my resume to offer, check out my Linkedin profile and design-build experience in the USA, Japan, China, Europe.. I may be heading to Japan soon for design work) and I just cannot afford the equipment if anyone has funding for natural building's PM me. As a Project Engineer/Lead/Engineering facilitator, I also have other world class professionals I network with to bring in as required and get Ionel and Rose, other permies, the answers they seek. I think I can offer an investor a decent ROI and business plan. Getting in ground leads to thermocouples and psychrometers, pressure diaphragms, etc, strain gauges, under there is going to be a challenge and cost. Then the next challenge is getting the data to International Code an to you all accurately. Challenges what I live for!

Thanks Paul and Ionel for the thread and for the ability to communicate. I appreciate it!