Sharing information and promoting earthbag building
Questions answered by Kelly Hart
Q: How much insulation value do you get from earthbags filled with soil?
A: Soil is generally a very good thermal mass material and very poor at insulating, except that, because earthbag walls are usually quite thick they do provide some insulation from the outside temperature. The problem is that once the bagged material gets warm or cold it likes to stay that way for a long time, which can mean uncomfortable temperatures inside. In climates with extremes of temperature (either hot or cold) it is best to fill the bags with an insulating material.
Q: In designing a hybrid passive solar home for myself, your idea of using scoria in earthbags fits my particular needs* perfectly in ONE of the exterior walls (*a material unaffected by moisture yet insulating, thick for aesthetics, inexpensive, natural & easy). My concern though is its R-value. From what I have been able to find, it is only .6 to .8 per inch....which, is less than half of what I'm looking for. However, you have mentioned an efficiency in your earthbag/papercrete home which would indicate something very different. Do you think this may be due more to the continuous layers of papercrete than the crushed volcanic rock itself? If that is the case, I will have to rethink my use of scoria in earthbags as I am wanting to use earthen plaster inside and out (for various reasons) yet still have a highly insulative material within that is unaffected by moisture.
A: This is an interesting question, and one that I cannot give you definitive answer for. I don't know of any tests that have been done on the R-value of earthbags filled with scoria, although it sounds like you found some data somewhere about scoria.
Our earthbag/papercrete home in the high mountains of Colorado did perform extremely well in terms of insulating value, there is no doubt. After a sunny day, the house would stay comfortably warm inside even without extra heat, even if the outside temperature plummeted into the teens. I, and others, have compared this performance to that expected with strawbales, which are rated at around R-40.
Papercrete is said to have an R-value of about 2 per inch, and my walls had an average of maybe 5 inches of papercrete, which would account for about R-10. The other say 15" of bagged scoria would then account for the rest, which works out to R-2 again.
So my empirical guess is that this is a better value to work with than the lower figure...but then I have no proof. Certainly the fact that the bags were well-sealed with the plaster is very important. Also, the size and cleanliness of the aggregate might be a factor. I used about 3/4" aggregate, with very little fines, so there is a LOT of trapped air in there, which is very good insulation.
C: R-values for lightweight aggregate are readily available (for example, cinders = .59/inch, pumice = .86/inch). I have not seen any test criteria though. However, if one was to round cinders up to an R-1/inch (a pretty big margin of 40% more), a 15" bag would only give an R-15 rating. With your 5" of papercrete, you'd then have a total of R-25 or thereabouts. While much lower than "R-40", an R-25 still coincides with your comparison with strawbale.......IF you adhere to the findings of Oak Ridge National Laboratory which found two-string bales laid flat equaled R-26.
Also, there is quite a bit of variation in the quality and density of strawbales, so the R-26 value for that may be undervalued in general. The only way to know for sure would be to run a scientific test with the earthbags, and even then, the results might vary depending on many variables, such as type and thickness of plaster, etc.
C: (Owen Geiger): I've been quoting R-30 for bales. The old books (and tests) claimed R-40, but most people are in agreement now with R-30.
A: I built my house in the mountains of Colorado, which can expect freezing weather 9 months out the year (It is not unusual for Alamosa to be the coldest place in the US...often comparable to North Dakota!), with earthbags filled with scoria, a type volcanic stone. I used a crushed gravel of about 3/4" minus, and tried to eliminate as much of the fines as I could. This was put in standard 50# rice bags, which create a wall about 15" thick when plastered. This house was a passive solar design, and performed remarkably well, often needing no additional heating at night if the day had been sunny, even in weather in the teens F. Obviously, the quality of pumice or scoria would vary from one location to another. My comparison of the insulation value of this house as compared to strawbale was empirical only. You can see pictures and description of this house at here. There is a LEED analysis about this house described at here. Other natural fill materials that are insulating include rice hulls, perlite, and vermiculite.
Using the conductivity values I've found elsewhere, we can expect a nominal wall R-value (in US units) of 20 to 32 [U-value in international units of 0.18 to 0.28] - somewhat less good than the figure which you yourself cite, so I'm wondering what the basis for your estimate is. Of course, the thermal mass inherent in the system is also important (though not an alternative to good insulation levels)
As I mentioned, my assessment of the R-value of the earthbag walls of my home is not scientific. I might add that this wall system includes a fairly thick (average perhaps 1 1/2") layer of papercrete plaster on both sides, which in itself adds roughly R-6 to the wall...
I haven't found on your website the sort of technical detail that I'm looking for - especially (i) actual numbers for properties of materials, (ii) cross-sections of design details (your construction photos show a lot of gaps where bags meet, and I'm wondering how you dealt with this and so avoided the inevitable cold bridging problems;
As I mention above, the walls are thoroughly plastered (in my case with papercrete) and this really does seal most of the cavities. Where the cavities remain, there will trapped air, which does not offer cold-bridging opportunities.
I'm also wondering how you handled windows, doors and wall-floor junctions?
Most windows were sealed into place with the papercrete plaster. The doors were framed with dimensional lumber, which itself was sealed either with papercrete or caulk.
Any actual numbers for energy consumption for your house (or anyone else's, of the same construction type - together with location and an indication of occupant thermal expectations)?
This was a passive solar home. The primary back-up heat for the first few years was a wood stove, and we consumed no more than about 2 cords of wood each season. Then we converted to a direct-vented propane gas heater, which averaged about $60/month/year...at about $1.20/gal. at that time. These figures are dredged out of my memory... About half of our electricity was PV, and the rest from the grid...but none of this went into heat.
Q: Our soil at the house site (in Grenada)
is primarily red clay. We have done some soil tests and it seems to be just about right and will create a strong structure when complete. But we are concerned about the interior temperature and humidity levels. Volcanic gravel is widely available and can be delivered to our site, though this involves added expenses and the extra labour to bring the gravel uphill from the driveway. But what is the best choice clay soil - or - scoria...?
A: I see from a quick Google search that Grenada is definitely tropical, with an average temperature of 82 degrees F. and rain much of the year. While scoria provides excellent insulation, this advantage will eventually be overcome by ambient temperatures in the tropics I think. Even with lots of thermal mass on the inside of the house being insulated from the outside heat, what will keep it cooler over time, especially if the nights don't cool down all that much? I presume you want to keep away from running air conditioners, so the insulation might not do you all that much good.
Q: Have you ever heard of anyone mixing perlite or vermiculite with the scoria in the earthbag or, mixing perlite or vermiculite into plasters?Knowing I won't have the extra insulative benefits you had with papercrete, I'm trying to think of ways that might boost the thermal efficiency of scoria filled earthbags even more in my project, if for no other reason than peace of mind. Or, perhaps I could do as you did and use papercrete over the bags then come back and apply a finish coat of earth plaster over that.
Q: I couldn't find the picture and details of how you used scoria behind your dome. What were the dimensions? I'm thinking of using scoria for my zero energy house, both in the bags and between the walls and earth berm. This seems like the most effective design: passive solar, scoria filled earthbags, earth berming, super insulation in the roof. The current design is semi-circular or a curve close to semi-circular, with a glass wall and planter in the front. My goal is to achieve zero net energy usage and extremely low embodied energy.
A: Basically, I filled many of the lower bags with sand in that north wall for more thermal mass. I allowed about a foot and a half gap between this wall and the natural earth bank, which I then filled with scoria after having lined it with the 6-mil plastic. (I can't remember now whether I used one of two layers of plastic; I know I used two over the pantry dome.) The bags above the natural ground level were filled with scoria, so I then lifted the plastic apron up to the height of just above where the eventual berm would be and embedded it in the next course of bags. Eventually that whole back wall was substantially bermed. I have long been convinced that really the only chance for a "zero-energy" house would be either substantially bermed or underground. Paul Shippee came pretty close to it back in the 70's with his SunEarth house ( http://dreamgreenhomes.com/plans/sunearth.htm ), and this was earth-sheltered. You could not call this house low-embodied energy however, since it is mostly concrete.
Q: What is the R-value of perlite or vermiculite?
A: I think that an average of 2.8/inch for perlite and 2.3/inch for vermiculite would be appropriate, given some on-line research that I have done.
Q: I am interested in using rice hulls in bags as an alternative to fiberglass in the earthship type home that I am building. I need some direction on how to proceed. See my house at www.flickr.com/photos/whatisupwiththestanleys
A: I've never tried using rice hulls in bags myself, but I understand that they make excellent insulation. First you need to find a source for the rice hulls, which should be quite inexpensive if you can find them locally enough. I've heard that there are rice processing plants in Texas and Florida, and perhaps some other southern states. I would not recommend using bags filled with rice hulls in bermed situations, where the bags can't breathe well...
C: I live in Arkansas which happens to be the largest producer of rice in the United States. I can get a truck load brought to my land for $1200 which is about a 2 - 3K savings over fiberglass or cellulose. My second choice was the recycled blue jean batts which are 2X the price of fiberglass. So, rice hulls it is. I spoke to the lady who built the rice hull house. She was not in favor of putting the hulls in bags. She liked the idea of sealing off the ceiling and then blowing them in like cellulose. So, for now that is our plan.
Q: I was thinking of using paper as insulation placed in bags. Would this work?
A: Dry shredded paper makes great insulation, and is sold commercially (usually with borax added to keep pests away) as "cellulose insulation". This could be put in bags and stacked for building, but it would compress a great deal, so the only realistic way to build with it would be as in-fill in a post and beam structure, or some similar arrangement where the bags don't bear any weight.
C: It seems like with papercrete you did not have to worry about humidity in Colorado. Instead you had to tackle another beast in cold weather, that we don't have to worry about in Hawaii. Looks like papercrete provides a cozy feeling with good insulation in the winter.
A: Yes, papercrete provides very good insulation, but it may not be the best material to use in Hawaii because of the humidity, which can promote mold forming on it. Actually, even in Colorado, I am not sure that I would use papercrete again, because it does not hold up to the weather as well as cement stucco would, especially on the outside of a dome.
Q: We recently bought 5 acres of land in East Texas, which we plan to build our Earthbag home on. We were wondering if it would be possible to build the home with soil from on-site in the bags and then somehow attach the fiberglass type insulation to the outside. We live in a very hot and humid area, so we are very worried about the insulation and about the potential for mold. Another idea we had was the bags of cellulose they sell at Home Depot. It would be a more green alternative and doesn't seem to be too expensive, but we're not sure how much we would need for a 1,000 sf home? Would it be mixed in the bags with soil or would the entire bag need to be filled with cellulose?
I have seen where you mentioned rice hulls on the FAQ section but have been unable to find anyone who sells this in our area. Any ideas you have would be greatly appreciated! We really feel like the
A: Conventional fiberglass batt insulation requires a framed void to attach it to, which is what a typically wood-framed structure provides. It would be hard to make it work with an earthbag wall without adding some sort of framework to attach it to. Cellulose insulation is a somewhat greener alternative, but it also requires some sort of framed space to support it. I am afraid that bags of cellulose would probably compress over time and lose much of their insulation value. Mixing this with soil would not likely add significantly to the insulation factor. Another possible fill material is perlite or vermiculite, but this is likely to be more expensive.
Or, you could make the home with earthbags filled with soil, and then use a layer of rigid insulation on the outside of the wall before plastering...or plaster the whole thing with a thick layer of lightweight concrete...There are many possibilities.
As for mold and humidity, the best thing is to keep the walls breathable, and have a good roof with eaves (if this is the style of building you are doing). If it's a dome, then it may be necessary to have a moisture barrier on the outside, and provide lots of good ventilation within.
Q: My colleagues and I are evaluating earthbags as a way to insulate existing potato storage warehouses. A typical building would be framed by reinforced concrete columns, in-filled either with reinforced concrete panels or blocks of cut natural stone. My idea is to build a vertical earthbag wall outside the existing wall. The existing roof would be extended outward to protect the new wall. I plan to fill the rice-bags with scoria which is readily available. In general, I will build the wall according to Dr. Geiger's article, "Step by Step Earthbag Construction". Should the earthbag wall be butted against the existing wall, or should I leave an air space?
A: The potato storage buildings that I am familiar with from Idaho are generally substantially underground, with earth-covered roofs over pit storage areas. It sounds like these are not even bermed with earth. No air space is necessary; it will be easier and more secure to butt the bags against the existing wall.
If butted against the existing wall, should I attach the earthbags to it? If so, how?
A few ties to anchor the bag wall, especially near the top, would assure that it will stay in place over time. This could be done with loops of wire running through the masonry wall and around the bags, perhaps at 5 foot intervals.
How tall can I make a vertical earthbag wall?
There is really no limit, especially if anchored to the wall as described above.
Q: I am building it right next to the ocean in Nova Scotia and plan to fill the bags with cob.
A: Filling the bags with cob in Nova Scotia may not give you enough insulation for the structure to be very thermally efficient. You might consider adding some sort of external insulation, or filling the bags with a more insulating material...which can also affect how high the walls go.
For some reason, I thought that cob was very insulating if it was thick enough. Do you recommend a material that we should add or use instead?
While it is true that thick walls of thermal mass material will provide some degree of insulation, this is really only advisable in a fairly moderate climate. You might read what Michael G. Smith writes about this aspect of cob. I filled the earthbags for my house high in the mountains of Colorado with a crushed volcanic rock that has a lot of trapped air, and this worked out quite well. Other possibilities include, rice hulls, perlite, and vemiculite...or you could fill the bags with soil and then insulate the outside with a layer of foam insulation.
Q: I was wondering if spraying foam insulation on the outside of the earthbags would work well? I'm guessing the main reason not to do is environmental (using polystyrene)? How about soy-based spray foam? It could then be topped with a more weather proof coating like stucco, etc.. Wouldn't this solve the insulation issue?
A: I don't see why this wouldn't work. The Monolithic concrete domes are insulated this way.
Q: I was thinking about stuccoing my house with concrete stucco because it is more waterproof than earth plaster. Dunedin rains a lot. If I did would I need extra insulation between the stucco and the earthbags?
A: This depends on your climate, the design of the house, and what the bags are filled with. In anything other than a very moderate climate, it is usually better to provide some form of insulation in the walls. This means either filling the bags with an insulating material (such as crushed volcanic rock) or adding a layer of insulation to the outside, as you propose.
Q: How can pumice or mixed pumice and earth be stabilized without large cement coverings or lots of wood?
A: This is where the earthbags come in very handy, because they can hold the loose pumice in place, and then a thin earthen plaster can be used to protect the bag material. It is possible to make pumicecrete that will support itself, but this does use cement.
Q: Earthbags, like other masonry, fits into the dry tropical areas as an excellent climate responsive material to create indoor comfort without artificial temperature controls. The humid tropics have other constraints. I am a volunteer designer working on training centers for national literacy workers and translators with Wycliffe Associates. Many of our projects are in the humid tropics. Termites often find ways through floors to devour wood structures in walls. Walls need to hold little heat to prevent condensation between night and day temperatures in the very high humidity. Insulation to keep out high daytime temperatures is a plus.
A: Very thick earthen or masonry walls will work in some hot, humid climates (if they aren't too hot), as they tend to create a very stable temperature over time. Condensation is usually only a problem when warm, humid air makes contact with a much cooler surface, and such walls are not likely to be that cool. But I agree that a fully insulated wall is really the best, and this can be achieved with earthbags filled with pumice. Termites are not interested in any of this.
Q: Is there a proportion of earth to pumice that allows earthbag construction without additional wood, steel, or bamboo reinforcement? What specific heat and thermal conductivity would this mix have?
A: You can certainly mix pumice with earth, and the folks who wrote "Building with Earthbags" advocate this, but I don't really see any advantage to doing so. This severely limits the insulating qualities of the pumice. Either of these techniques, however, require very little wood, steel or bamboo reinforcement. Usually just some barbed wire placed between the courses of earthbags is all that is needed to make very durable walls.
I do not have technical number for heat and thermal conductivity for these systems. My empirical evaluation of pure pumice is about R-2/inch for the insulative value, and the more earth that is added, the less this number would be.
Q: What do you think of using styrofoam (currently not recyclable in Seattle) as fill or partial fill in earth bags? I would think the insulation factor would be better and the material could be used for something other than land fill. I don't know what the structural effect would be of using such a light weight material.
A: Using styrofoam in earthbags would certainly provide good insulation, but it would not provide a load-bearing wall. If you used something like a post-and-beam construction for the framework of a house, this could be in-filled with bags of styrofoam.
Q: I've recently acquired some land in southwestern Alaska and have been thinking about various options I have for building a small dwelling there. I'd like to do something simpler than the usual log cabin, and I was looking at your earthbag structures and wanted to ask if you thought a small earthbag dome would be good for such a place--the average January temperatures are in the teens and 20s, though it can get well into the negatives during a cold snap. And there is usually about 25 inches of rain per year and 65 inches of snow. If an earthbag dwelling seems feasible, would you recommend increasing the width of the walls? I think the shape would be fantastic for shedding rain and snow. Also, do you think the walls would be strong enough to be partially submerged (i.e. berming up to several feet around most of the structure)? Also, would you recommend using something other than papercrete for the exterior? I really do like the earthbag idea a whole lot, and I'll want to use as much local material as possible.
A: I see no reason why an earthbag dome wouldn't work for you in Alaska, but with the cold weather you would be better off if it is well insulated. Just filling the bags with soil won't provide much insulation. Berming the dome, as you suggest, (or recessing it into the ground) would help with this, but still would not be enough. The best thing to do is actually fill the bags with an insulating material. Is there light-weight volcanic rock in your area? I used this (scoria) in a crushed form to build my house in the mountains of Colorado, and it worked very well. Other possible fill material is perlite or rice hulls (but these may have to be imported.)
The other approach to insulating the dome is from the outside once it is made. I did use a papercrete plaster on my dome, and this is also good insulation, but only if it is kept dry...and that is hard to do since it absorbs water like a sponge. Spray foams are another option, but most of these are not so natural. Lightweight concrete stucco might work, but again you need a source of lightweight aggregate. So you have some choices and possible trade-offs to consider here.
Q: If we put 4'' of styrofoam on the outside of the wall, would we need to bother plastering the bags directly, or would we just tack the foam against the bags, cover everything in chicken wire and and plaster over the foam?
A: It is common practice to lay cement-based stucco over insulation panels that have a stucco mesh attached to help with adherence. This should also work with stabilized earthen plasters. You would want to make sure that the panels are well attached to the bags, with wire or twine, or possibly large staples if they hold well enough.
Q: Here in Panama we have the advantage that we don't need to worry about cold weather, so I am not sure if the bags you propose to be filled with earth (for thermal mass) on the Baggins Burrow design serves such purpose (insulation against cold?).
A: You may not have much cold weather in Panama, but you certainly have a fair amount of heat, and this is where all of that thermal mass will serve you well, in helping to stabilize the interior temperatures and not get too hot inside. It works both ways.
Q: Would it be okay to add rice hulls to the earthbag to add insulation value to the mix or would it cause trouble?
A: Rice hulls do indeed provide a great deal of insulation when used in bags, but I'm not sure about mixing them with other materials, such as soil...this would likely diminish their insulative value considerably.
Q: Building in Africa would you advise to built into the ground a bit deeper so that the building is more cool?
A: Yes, I believe that in hot climates it is especially beneficial to dig into the ground to take advantage of the relatively cooler temperatures there. You can probably use the earth that you excavate to fill the bags.
Q: My husband and I are buying land in Northern Arkansas. They have hot summers that are super humid, and cool winters with barley any snow, but it does get chilly. We are going to be living a travel trailer untill we can get the land ready for homesteading. But we need buildings for animals...nothing huge, just for goats. It must have an angled shed or flat roof. I have looked at several pictures of homes that look like there are beams and then another layer of earth bags put on them and plastered or stuccoed. Is that correct?
A: It is possible to design an insulated shed roof by providing rafters for support, covering this with a heavy wire mesh, and then adding very light-weight bags filled with rice hulls or such for insulation. To then shed the water this would then need to be covered by plastic sheeting that would be protected with plaster (probably with more wire mesh in it). This is all pretty elaborate. For an animal shed I would suggest just using inexpensive corrugated metal for the roof, and then suspending insulating bags beneath it if you want the insulation. See http://earthbagbuilding.com/articles/ceilings.htm
Also for insulation is it possible to cement or stucco the wall, then use cotton blue jean insulation with a layer of chicken wire over it, then stucco that too? That way it's a little warmer?
It might be possible to do this, but I would be concerned that the cotton material would get damp in the process and then remain so, eventually rotting and providing poor insulation. A better solution to make an insulated earthbag wall is to fill the bags with insulating material in the first place. You can use rice hulls, crushed volcanic stone, perlite, vermiculite...
Comment: We're looking at building a tipi with these bags full of rice hulls at Pine Ridge. Here's a picture. This is what the Riceland 50 lb bags are like. They are very much like straw bales, except that the sandbag wrapper makes them even stronger. The size is approx 11 x 20 x 30.
Response: This should certainly simplify the building process since you won't even need to fill the bags! How much do they charge for those bags of rice hulls? Are the bags polypropylene?
C: The bags are a very strong polypropylene, and very well packed, like a straw bale. They are somewhat slick, so a netting would be required for the stucco and plaster. The bags are $6 each, fob Jonesboro Arkansas. They come 16 to a pallet, 48 pallets, 768 blocks to a truckload.
Q: I am planning to build eco domes in the Caribbean. I read that using a lot of dirt gives it more thermal mass and less insulation. It is hot and humid here so what do you suggest?
A: You're right that dirt provides more thermal mass and less insulation. The best situation in most climates is to have both thermal mass (on the inside) and insulation (on the outside), but this is not so easily done with earthbags. Since they are so thick, you end up with a lot of thermal mass material if you use dirt, which tends to even out the temperatures inside over time, and make the home more comfortable. Thinner brick or concrete walls will radiate the heat much more. The best situation is to recess the home into the ground some, or berm soil up around it to help keep it even cooler. The other way to go is to fill the bags with an insulating material, such as rice hulls or crushed lightweight volcanic stone. This will insulate the enclosed space better from the outdoor heat, and then if you also include thermal mass materials (heavy stone or tile) inside, then the house will be especially comfortable. Adequate ventilation is important in any case.
Q: Regarding rice hull homes, does it matter if the hulls are whole or ground? Why? Some processing plants only have ground hulls available.
A: I would think that the hulls would provide better insulation if they are left intact rather than ground, because then they will create more effective air pockets. Also, ground or powdered hulls might tend to hold more moisture, which could lead to rotting and less effective insulation.
Q: I haven't decided whether to sink my first dome into the ground a few feet like the Honey House or just build it on grade. In your opinion, are the benefits of the sunken dome worth the effort (or cost) of excavation? I've heard it could make the dome cooler, but I'm also thinking of possible handicapped access at some point (I ain't getting any younger, after all)
Q: I've been searching for some natural alternatives to ceiling insulation. I came across your article about
A: You are probably right that the spaces between bags will allow more heat loss that other areas, but I think that this can be minimized by pushing the bags tightly together. Think of a bunch of pillows being pushed together to form a solid thick blanket; earthbags also have this degree of flexibility, so you can really smoosh them together to form a uniform insulation barrier.
Both rice hulls and vermiculite have been used effectively for many years as loose insulating material in residential situations. Any tendency to absorb moisture will eventually be offset by their ability to release that moisture, as long as the wall or ceiling has some degree of breathability.
Most rice processing in the US is in the southern states, but I know that rice is also grown in California, so that might be your closest source. Some of the processing plants are now marketing bagged rice hulls for mulch and other purposes, so it may be more widely available as time goes on.
Q: Could one mix a 70/30 sand clay mix with rice hulls to provide insulation and not degrade the structural integrity of a building?
A: Rice hulls are supposed to be very good at insulating, but this is primarily because of the all of the trapped air that occurs when they are confined to a bag and plastered over. I'm afraid that if they are mixed with soil, the primary benefit would be diminished considerably because the soil would fill the voids around the hulls, and provide a solid with more the characteristics of thermal mass. It is like the straw in cob or adobe doesn't really provide much worthwhile insulation.
You would be better off using the hulls themselves and then plastering both sides with a stiff plaster with mesh imbedded to create a kind of "structural insulated panel". Other natural insulating materials of mineral origin are crushed volcanic rock and perlite, if either of these are available in your locality.
Q: I am going to build an addition to my main home. I am using earthbags to build the walls. I am going to build a rubble trench. The walls will be load bearing. The addition will be round with a masonry stove in the center that will be load bearing as well with timbers running off masonry stove to the earthbag wall. I live in N/W Indiana. I also want to double stack the wall. Kind of like when staking hay bales in your barn. The first row will have two rows of bags placed end to end in a full circle. The row after that will be bags placed side by side. What do think about my plans?
A: I think that your idea to make a double wall makes a lot of sense, especially if you were to fill the outer bags with an insulating material, such as crushed volcanic stone, perlite, vermiculite, or rice hulls. The inner wall then would become the load bearing one, and the outer wall would provide the needed insulation to make you home truly energy efficient. As an alternative to this, you might leave a gap between the rows of bags, so the the inner space could be filled an insulating material.
Q: We are building our earthbag home in Patagonia. We have the perfect soil mix on lour land, so will get a backhoe to level it and dig it up, and then we will use it for our bags. I have decided that I want a light framed wood /tin roof (wood and corrugated tin being the most common building materials produced here in Chile). So, I am wondering if the wood (plywood) and tin of the roof, and paper vapour barrier combined with the the air space between the bags and the roof - a six meter dome with a two tiered roof that falls down to three meters - extends out to at least a meter at bottom - will provide enough insulation for the walls which will be thick not to cool us down in the height of winter? I understand about thermal mass and we're building it into the plans, but what about when there is not enough sun? We cannot get straw here for insulation, pumice is large and we're trying to think of other alternatives. Any ideas?
A: The metal/wood/air space roof over your earthbag dome will provide a little bit of insulation, but not very much. I know that it can get fairly cold in Patagonia, so I would try to get more insulation between your roof and the bags. Is is possible to have the pumice crushed? This can be bagged, like I did with my house, and you could actually build the upper part of your dome this way. Other natural insulation materials that might be available are rice hulls, perlite, vermiculite, wool, cotton, or even papercrete.
Q: I'm considering using slipstraw to insulate the outside of my planned first 8.7' dome here in the UK. Apparently it has been tested to achieve an R value of 1.58 per inch. The benefit of slipstraw to cover a dome as I see it is the fact that you can simply slap it on, not having to worry about trying to strap straw bales to the dome surface. Do you think there would be much cold bridging due to the clay in the mix ? What would happen if it got wet ? Would you advise covering it with a waterproof membrane in our wet climate ? I guess I'd have to wait until it completely dried out before I added a waterproof membrane ? Do you think diluted PVA glue mixed with straw may be a better option?
A: Slipstraw does provide good insulation because it is mostly loose straw with just enough clay added to bind it together. I have never heard of it being used to insulate a dome, and probably for good reason. As you suggest, it would need to be protected from moisture, and this is very difficult with an exposed dome. A moisture barrier that would protect it would also hold in that moisture if it ever did leak, leading to rot and failure. Light straw-clay walls need to be breathable and under roof eaves to work well as exterior walls. The use of PVA would not likely improve the situation.
Q: I am wanting to have as much mass as well as insulation in my house. Would it work to fill the bags halfway with earth and then finish off with the pumice. Then lay them with the pumice on the outside? I was thinking about doing 2 separate rows, but my helper suggested that I find out if this idea would work.
A: The problem with filling and laying the bags the way you propose is that they will not form a very solidly interlocked wall with a running bond (like bricks). There is another approach that resembles what you describe shown at earthbagbuilding.wordpress.com, but this idea has not been tested to my knowledge. Two separate rows will also work.
Q: I have checked around and found volcanic stone and perlite, both of the landscape variety, easily accessible. Is this the correct material or is there a special something I should look for?
Is your house one bag deep of volcanic rock only? Is lime plaster inside and outside one bag deep volcanic bag wall sufficient for exterior walls? I can not figure out from everything I have read if I need 2 rows of bags; one for maybe lime dust type fill and one of volcanic rock?
I am also stuck on the floor... would a layer of volcanic rock under a slab = insulated slab? Or would you mix volcanic rock into the rubble? Where does the moisture barrier go in the rubble foundation? What is your experience in hind-sight with your foundation and floor?A: Yes, either the volcanic stone or the perlite should work for filling the bags, although you might check the price, since this material for landscaping might be quite expensive. You want a light-weight material that has a lot of trapped air in it.
Yes, the earthbag house I built in Colorado was one bag thick, with volcanic stone as the filler for most of it. I used a papercrete plaster on most of my house, with a lime finish coat on the inside, and this worked in that climate. In Maine, you might be better off using conventional earthen or lime plasters on the inside and cement-stabilized earthen plaster or lime plaster on the outside.
I did use crushed volcanic rock (about 6-8" deep) as an insulation material under my floor; it was not mixed with rubble. I put the moisture barrier on top of this, partly because I then poured an adobe floor over this and I didn't want the wet adobe sinking down into it, and the natural soil was almost pure sand that drains very well. In a situation where the soil might tend to wick moisture upward, it might be better to start with the moisture barrier and lay the volcanic stone over this.
My house performed very well thermally, and there is little I would change about the way it was built. From what I can tell from your house concept, it all looks fairly reasonable, but of course there are many details left unexplained. The plan obviously has many green and energy efficient features.
C: I wish I could figure out how to use rice hulls so they're stable. What's needed is a natural 'glue' or binder that doesn't attract insects or mold. Something cheap and natural with good compressive strength. The final bag fill would look like rice crispy bars. That would revolutionize earthbag building!
R: Here is some information about rice hulls: ASTM testing has conclusively demonstrated that , without additional chemicals, rice hulls will...
Q: Can you give me a brief description on how one would put insulation on the OUTSIDE of the building? Are we talking styrofoam sheets that are then plastered over? Just curious to know the effective types of insulation for the outside. And is this done before the plastering or can it be done later (an additional layer) if the non insulated building isn't warm enough?
A: It is common practice with rammed earth and adobe buildings in cold climates to insulate them from the outside. I have seen this done with 1 1/2" rigid insulation panels before being plastered. Obviously they need to be attached with long spikes driven at different angles, or in some other way. And then the plaster needs a mesh to help support it.
Q: I am looking into building an earthbag house. I also bought a book called Earthbag Building. They suggest using 50:50 ratio of the clay to sand ratio to the volcanic rock, specifically pumice. Because you have already built and lived in a an earthbag in this climate I would greatly appreciate your advice. I was wondering if you filled your bags entirely with scoria? No ration of clay and sand? When you tamped how did that work? I have tamped some earthbags that had a clay and soil ratio and am having a hard time picturing tamping a bag of scoria and it having stability. When tamping should I still be listening for the special thwak sound?
A: I completely disagree with Kaki and Doni about adding clay or sand to the scoria or pumice, as that will greatly diminish its insulative properties. I used straight crushed scoria in my bags and this worked out just fine. The house is standing proud as ever a decade later. I did tamp the bags and the scoria packed into a fairly solid mass because of all the irregular, sharp edges. It doesn't form the same sort of solid block as adobe soil would, but that doesn't matter once the walls are plastered. The tamped bags of scoria do not ring like adobe soil, but feel plenty solid. Do some experimenting.
Q: I have a question about earthbag homes. For your scoria-filled Riceland earthbag dome, I'm curious to hear what you did for thermal mass given that the bags were filled with insulative material. Are scoria-filled bags enough, or do you find that more thermal mass is needed? I ask because I'm planning an earthbag house in the mountains of New Mexico where the temperature varies quite a bit from season to season, so I'm wondering if scoria would be enough or if I should plan for two layers, one filled with earth and the other filled with scoria. Would single bags sewn off for 4 or 5 inches worth being scoria work better? Essentially, what is the right balance of insulation vs thermal mass? And how can one go about figuring this out for one's climate?
A: Actually, since that dome was not intended as living space, we weren't too concerned about the balance of mass/insulation. However for the house, which was also primarily built with scoria filled bags, we made sure there was plenty of thermal mass in various places throughout the structure, including the flagstone/adobe floor, earthbag stairs and landing, and interior columns.
You could build with two layers of bags as you suggest, but that much mass is usually not needed. In your climate, the insulation of the scoria is more important, and you would want the full thickness of the bags for this. For a more technical discussion of the proper balance of mass and insulation, I recommend Ed Mazria's book: The Passive Solar Energy Book: A Complete Guide to Passive Solar Home, Greenhouse and Building Design by Edward Mazria, 1979. Even though this book would seem to be dated by its publication date, I still consider it to be one of the best all-round guides to passive solar design, whether for home or greenhouse or both. I often refer to my tattered copy of this book when I want to know what the experts think. Ed is an architect working in New Mexico.
Q: My idea is to fully berm three sides and insulate the Southern side and the ceiling which would both be stick framed.
A: The thing about an uninsulated berm like you propose is that it will continually try to bring the temperature inside the house down to its level (around 50 degrees F. perhaps) so you will need to supply heat much of the time to compensate. The Earthships use large berms like that, as do PAHS (passive annual heat storage) designs, but they still insulated the berm itself at some distance around the shell of the house. You could also do this, using easily transported sheets of rigid insulation if you want. It can take a year or so before that bermed soil becomes sufficiently charged with heat to be noticed much, however.
Q: I should have no problem getting volcanic stone here in Ottawa. Should all the bags of the building be filled with the volcanic stone ? I was curious if it would be any advantage to build the exterior walls double thick with the outside bags having say soil in them and the inside layer having the volcanic stone ? Or perhaps with a layer of foam in between the double thick wall?
A: That is convenient that you are able to source the volcanic stone. In the house that I built, I used bags of scoria in all locations that made direct contact with the atmosphere; there were other places, such as interior buttress columns, stairs and landings where the bags were filled with soil.
Q: My husband and I would like to build a partly earthsheltered farmhouse--sort of like a hobbit house or old Icelandic house, but not sunk into the ground, and more open on three sides). Originally we looked at strawbale, but it isn't suitable for underground, and is actually quite expensive. We don't want to use cement etc etc. The property we're hoping to buy is near a wetland, but on a hill that seems to be high and dry. We want to build into a hill, and are trying to find out more about drainage, waterproofing and so forth. We want to build using materials as free from offgassing as we can. We will be on an extremely limited budget, and going for practical rather than fancy. If we use crushed stone for a foundation, what floor insulation is best? My husband wants to use Roxul for the walls, since it's clean and locally produced. (It gets very cold up where we'll be building.)
A: I think that earthbag construction would likely be ideal for what you have in mind. There generally is no problem with berming or placing earthbags below ground, as long as the fill material can withstand such conditions.
Q: My wife and I live in Arkansas. The climate is mild but has a hot, humid summer. We want to build an earthbag house with at least two sides, the Northern and Western, bermed. We also want an earth-sheltered roof. We are concerned about moisture issues given the climate, and about the structural integrity of the living roof designs we have seen, if we try to construct any of them on earthbag walls. Most of the earth-sheltered roof designs we have seen are concrete poured. We will be building a house for a family of seven, and would like to make the most economical choice as well. We are open to building above ground, as well, if that is more economical and or less complicated with comparable comfort from the summer heat. How does perlite work out with a living roof/berming? We also have a large amount of pure silica sand--would this be a good bag filler? What suggestions do you have concerning these issues?
A: Living roofs are nice but they do require a much heavier duty support structure, which can be more expensive. The soil on these roofs provides only a modicum of insulation, so even with earth-sheltering there is a need for additional insulation. So a very well insulated, light weight roof can be both cheaper to build and very comfortable in your climate. All of the benefits of berming the sides of the homes can still be employed.
Q: I keep thinking about insulation. Why not use recycled packing peanuts? Mine don't seem to absorb water. Why don't we use them for backfill to insulate bermed buildings? Use 12" or more around the building. 2' below soil surface narrow down to none with vertical styrofoam insulation around the bag walls. Or would it stay put during construction mixed in peanut clay? Would earth plaster make it flameproof enough for interior that way? Include some plastic garbage scrap pieces to add stiffness against compression on exposed walls?
A: I do think that recycling EPS foam products has great potential for insulating structures. We're planning to use it for ceiling insulation on the Mexican project. Actually, the idea is to use a common leaf shredder to run bulk trash styrofoam through and collect in bags. Does it work below grade? Well it appears that it depends on what type is used. I found the following information at www.polyfoaminc.com:
Recent Independent testing of below grade insulation has determined the water absorption of Foam-Control EPS and an extruded polystyrene (XPS) product. Samples of EPS and XPS were excavated from the exterior foundation of a building in St. Paul, MN. The insulation was placed into service in 1993 and had 15 years of use as vertical wall insulation separating the heated building foundation from soil.
Q: Do you think that in the tropics where temperatures vary little and earth temperatures are close to air temperatures, that thermal mass in walls is a bad thing for humid areas because moist air will continually condense on slightly cooler wall and floor surfaces?
I doubt that the earth underground will feel cooler than the outside air during the coolest part of the night also.
Yes, but it is generally during the day that people are active, so that is when it is more important to have cooler temps.
I think that buildings below grade should not recommended for hot humid areas unless they are made of gravel bags or sand.
I think that all earthbag walls, regardless of what the fill material is, should be protected with a moisture barrier on the outside before they are bermed. Therefore, I see no problem with using adobe fill in the bags that are bermed. I'm pretty sure this is what Owen did with his totally bermed multi-purpose mini-building in tropical Thailand, and I have heard no reports of problems with condensation inside.
Owen: No humidity/condensation problems or leaks in the dome any time of year. And there's poor ventilation to boot! And it's totally earth sheltered. During the dry season I water just enough to keep the grass healthy. But it rains like crazy in the rainy season. The ground can get covered with flowing water even though we're on top of a hill! So yes, the dome gets totally soaked for months.
Q: We live in BC, Canada where winters can drop to -30C. These temperatures don't last long, but it can be cold. We're planning a small cabin (non-dome), 12 by 22. I see that some folks are insulating their bags with pumice. Have the (insulating) results of such projects been promising? Is it necessary to entirely fill the bags with the insulating material, or could I cut it, say 50/50, with the dirt I would otherwise be using? This would be a much more economical option for us. I realize that it wouldn't be as insulating, but would it help?
We built an earthbag root cellar last year using straight dirt, but the thing was built into a bank. I'm wondering if I bank up dirt on 3 of the four walls of the cabin, just under the windows, is the insulating material even necessary for a cabin this small. The floor and ceiling will both be well insulated, and the space will be heated by a wood stove.
A: The earthbag house that I built in the mountains of Colorado, where it gets even colder than that sometimes, was quite comfy, mostly heated with passive solar. I filled the bags entirely with crushed scoria, a lightweight volcanic stone, and then plastered it with papercrete, so it was quite well insulated (about equivalent to strawbales I estimate). In your climate I would advise filling the entire bag with insulating material.
Q: I was somewhat discouraged to learn that earthbag type construction is not as effective in colder climates such as we get out here on the northeast prairies of Colorado. I have read about the dividing a bag down the center to use insulation in one half and earth or volcanic rock in the other. This technique does not lend itself to filling bags with a Bobcat style bag filler as shown on one of your fine links. As I looked at the options I thought that we might make the earthbags work along the lines of "double panel precast concrete". The way I see it we could place a 2 foot wide (or what ever width would match the bags stacked to close to 2 ') 8 foot long sheet of rigid foam board laying on its side and bag equally down the length and up the side. Once the top of the board was reached, place a U shaped rebar staple straddling the insulation long enough to reach the center of the earthbags and spike in place. I would guess that one of these saddle type staples every 2-4 feet would be enough to hold the inner and outer wall sections to each other. I know that this effectively doubles the number of bags needed, but perhaps it would be worth it. The one thing that I can see right off as a down side is that this would probably force us to use only straight wall floor plans. I do not think the rigid insulation bends well enough to allow for use of the beautiful curved wall designs. Does this seem to be a reasonable idea?
A: Earthbag building can be very effective in cold climates, as evidenced by the earthbag house that I built in the mountains of Colorado (over 8,000 ft.), not far from you. I filled the bags with locally available scoria, a lightweight volcanic stone. Other possible insulating fill material is perlite and rice hulls.
Q: I am considering to use earthbag as an insulation for a Timber Frame (Post and Beam) structure and I believe that this is possible and would like your advice on this. I will be submitting my 40' X 24' Timber Frame blueprint to NC Structural Engineer very soon and he will assist me in designing a crawlspace foundation. I was wondering if it is possible to use earthbag starting at the ground and up against the crawlspace foundation and the structure??
Yes, I think that it is best to start the bag insulation wall from the ground up, so that it is not relying on the wooden floor for support, and also so that your timber frame will be visible from the inside.
How much does a bag weight per SQ. FT.? Would a smaller bag with less weight still work well?
The weight really depends on what the bag is filled with. Most truly insulating materials are quite light, for instance the scoria that I used only weighs about 35 lbs/bag. Other light-weight insulating materials, like perlite, rice hulls, and vermiculite, are perhaps even lighter than this. Soil is obviously much heavier and the bags can weight up to 100 lbs., but this is not considered very good for insulation. Smaller bags do weigh less.
Q: My permanent residence in the Pacific Northwest is too cold in the winter and too warm in the summer. After reading Dr. Owen Geiger's post about using earthbags for yurt and tent insulation, now I can't stop thinking about using earthbags to better insulate the house. In your opinion, is it feasible to replace our existing insulation with earthbags?
A: Earthbags can certainly be used to insulate structures. Whether this is appropriate in your situation depends on various matters of practicality. As Owen mentions in his blog post, earthbags do take up quite a bit of space, so if they are put inside a structure, this can be a problem. If they are placed outside, then they need to be protected by a roof and have some form of foundation. You ask about replacing existing insulation, which is usually in a wall cavity. If this is the case, then it may be pointless to use earthbags, since the wall cavity itself can contain whatever insulating material is used.
Q: My friends keep telling me that I won't be able to live in an earthbag house during our summers as it is not only hot but very humid as well (sometimes 100% humidity) and unlike other deserts, the nights very seldom cool down as well. I told them that I will add wind towers but was told that it won't help unless we have a breeze. I don't think we will have much of a breeze during those 5 very hot months (sometimes up to 50°C - 122°F) can you please give me some advise? I really would like to build with earthbags as I am always sick whenever I am in a concrete building.
A: In a climate like the UAE, heat and humidity is obviously the main thing to deal with. I looked on a chart of underground temperatures around the world, and it appears that in that region you can expect underground temperatures to be around 27°C (81°F). all year round. Now that sounds pretty warm, but not unbearable to me...certainly better than anything approaching 50°C.
Q: I am curious about Oat Hulls. I live nowhere near any rice farming, but there's lots of oats grown in Manitoba and the hulls are burned as garbage. Would Oat Hulls be a similar enough product to Rice Hulls to build an earth bag house with?
A: That's an interesting idea that I hadn't encountered before. The bit of internet searching I did suggests that oat hulls have been used in a variety of ways, including as fuel for burning in furnaces and the manufacture of panels for building. Whether they would work as well as rice hulls as insulation is not clear, but they might. If you have the time, you might experiment a bit with some bags of oat hulls in a simulated wall and see how it behaves over time. Let us know how it turns out if you do this.
Q: When using rice halls to they have to be fresh or dried or ground or unground when building the earth home?
A: You would want completely dry, whole hulls.
Q: I was wondering if I build my earthbag home just using rice halls will it still be fireproof, mold proof, bullet proof, move with an earthquake, tornado strong and be bomb resistant?
A: Rice hulls are said to resist burning and rotting, but that doesn't mean that they are fireproof or mold proof; under certain circumstances they probably would burn or mold. They would almost certainly not be bulletproof. Earthquake tornado and bomb resistance depends on many factors, especially design, but with rice hulls this is rather unknown.
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