Well, hopefully Sherri and I will love our underground house. “We don’t like our underground house” was the title of a blog by MizBejabbers who wrote about the pitfalls of her underground house.
MizBejabbers’ earth shelter in Arkansas. Check out her site for more pics, but this was the best one ;^(
Miz tells about how they moved into an earth sheltered home 18 years ago (built by TerraDome for a previous owner, who may have covered up the problems to sell it) and how it has not lived up to the earth sheltered promise. She writes about how it had all the fears (leaks, mold, etc.), but without the benefits of energy efficiency. She also talks about increased construction cost, severe depreciation, pests (bugs, rats and nosy people), etc. She does have a section on “happy things” such as feeling safe during storms, enjoying the peaceful quiet, etc. but concludes that these were not worth the pain.
She even blogs about mini tremors, which she thinks are earthquakes cracking the house, but I suspect it is the house cracking and settling as the soil underneath is slowly eroded. No earthquakes required.
For someone like me who is considering a similar investment, this could be a blog from my future, so I read it very carefully…
My conclusion was that this house was just designed and built really badly and in the wrong time and place. By time, I mean that it was built in the early 1980’s when few people had worked out how to do these properly. Lets go thru the issues, as far as I can tell from the blog.
The site: This house is set below the road on the side of a large hill overlooking the Arkansas river. The U-shaped design that Miz mentions sounds perfectly designed to catch all the surface runoff from the hill above and funnel it toward the front door. What is probably happening under the ground is even more threatening… Hills do interesting things to water tables and an earth sheltered home may be sitting in an underground aquifer, like a wet pebble in a stream. Try a quick Google image search for “artesian well diagram” if you are not familiar with the concept. Miz acknowledges that the french drains are not sufficient in capacity or well placed to drain water away before it enters the house.
Our site doesn’t have such a majestic view, but it is on the top of a hill, and our hill is very permeable sandy loam that will dry out nicely. Before I bought my land, I walked around during a thunderstorm and made sure the water didn’t collect or run. After buying the land, and looked “deeper” and buried moisture sensors more than 10ft down for my Soil Temperature Experiment.
The construction:In the comments after the article, she mentions that the house was built on fill (to make a terrace on the side of the hill). If there was water flowing down, around and under her home, fill soil would wash away more easily and would lead to further settling and cracking and leaking. My home will be built on undisturbed soil with a high compression rating and no erosion threat.
She also blames a “bad batch of concrete” for the living room roof crumbling. I am not sure if that was really the problem (or if the bad conditions just wore down otherwise adequate concrete), but The TerraDome homes are monolithic structures which are poured into proprietary modular forms. If the concrete is not carefully mixed and poured, there is no good way to fix it later.
My home will use shotcrete, which (when done right) is considerably stronger than any poured concrete because of its lower water content and the way it is compressed as it is shot onto the wall.
Miz mentions metal ducts rusting and falling apart, I will be using only HDPE ducts that will never rot or leak. We also plan to heat our home with radiant floor heating, a method better suited to the heavy concrete construction. We will still have ducts, but only for ventilation and de-humidification.
She mentions drywall rotting and molding, internal wooden walls being eaten by termites, etc. we won’t have any of that in our all concrete house with a specfinish gunnite surfaces.
The waterproofing: TerraDome, like other earth sheltered builders (including Formworks) with “proprietary systems” does not use a waterproofing umbrella. Instead they insist on more traditional methods used for waterproofing regular basements, glued or sprayed directly to the walls. These include bentonite clay or a “tar modified polyurethane elastomer applied as a liquid”. These directly applied methods are pretty useless if the concrete cracks more than 1/16th of an inch. Even applying something like a pond liner right over the concrete before backfill is not as good as an umbrella (away from the concrete) because it can be torn by the movement of the concrete and does not help with thermal mass.
Applying the waterproofing and insulation directly to the structure also excludes the surrounding thermal mass and allows water percolating thru the ground to strip it of its heat, both of which reduce thermal performance when compared with an insulating umbrella.
It also sounds like the soil around this home was not properly drained. The French drains mentioned are not well placed or of sufficient capacity to handle the location on the side of the hill. This moisture increases the weight and lateral (hydro-static) force on the walls. Cycling moisture levels are even more damaging.
An interesting side effect of applying the waterproofing directly to the structure, and then draining around it, is that you need to make a choice about the moisture level of the soil above the water proofing… Do you want it to be dry for the structure beneath or do you want to keep plants living on the surface? It is difficult to have both. Miz ended up shutting down her sprinkler and letting her plants die. Eventually, they had to remove the covering soil completely. The umbrella solves the problem by requiring that you drain only the soil under the umbrella and allowing you to maintain the moisture in the soil above.
My home will use an umbrella with three layers and I plan to go overboard on the french drains under the umbrella. It also helps that my soil is very permeable.
Conclusion: I think I can avoid the problems shown in this blog, but I need to keep my eyes open and be as careful as I can. I am sure the builder of this home didn’t expect these problems… And neither did poor MizBejabbers when she and her husband bought it.
Caveat Emptor! Buyer beware! When buying an earth sheltered home, you must be doubly careful to check it out before buying.
What is the latin phrase for “this may be harder to sell?” There is always some mistrust between the seller and the buyer, but this gets worse when the item, your earth sheltered home, is difficult to inspect, because it is buried, or difficult to compare, because it is unique or custom built. Economic Game Theory would suggest that because the seller knows much more about the house than the buyer (informational asymetry), he would only be willing to sell the home at a deflated price if the actually thought it was worse than the buyer thought. Sellers who’s homes have no issues would be less likely to sell for less than they thought the home was worth. This would reduce the percentage of good earth sheltered homes on the market even further. Buyers could deduce this and realize that a large portion of earth sheltered homes on the 2nd hand market are likely being dumped by their owners. Therefore, sellers would be willing to offer even less. This is why earth sheltered homes tend to suffer heavier depreciation than other homes even thought they should last longer. Blog articles and anecdotes and even random experiences with cold damp basements only make it worse.
If you want to prevent or at least reduce the depreciation of your earth sheltered home, just in case you ever need to sell, you can do things to reduce the buyer’s doubt. I will start by taking detailed photos of the construction. I also plan to bury sensors (temperature and moisture) and keep good long term records. Other maintenance and utility records also help to establish the efficiency of the home. Not painting, or other wise covering, the inner surface of the home will also help to preserve trust during the sale process. The effect of these efforts would be similar to the effect of selling a used car and including a full set of records; including gas mileage for every fill-up, maintenance records, a car-fax report, etc. Increased buyer cconfidence will translate into higher offers. Of course, it only works if you actually build a good earth sheltered home ;^)
The blog mentions their attempts to enforce a warranty or get money from TerraDome or the builder, or the previous owner, but all failed. I don’t expect to get a warranty and I will have no one to sue but myself, so I will need to select the builders carefully and make as sure as I can that the concrete mix is a strong one.
Earth Tube Basics
Earth Tubes are basically tubes or ducts buried in the earth for the purpose of exchanging heat between the air in the tubes and the earth. They are often referred to as “Earth Air Heat Exchangers” (EAHX) or “Air-Ground Heat Exchangers” (AGHX) or a variety of other names. In hot climates (such as Australia) they are often called “cool tubes”, but they work just as well for warming cold air. They are generally used to moderate the temperature of fresh air entering well sealed homes and are a particularly natural fit for Earth Sheltered homes.
Most home owners who install them realize that, while they are dealing with very ancient and intuitive technology, Earth Tubes are still poorly understood and somewhat “experimental”. There is much doubt about the performance or cost effectiveness of earth tubes, but I suspect that the poor results are often the result of poor design. While I am unlikely to put all my “eggs” in the Earth Tube basket, I believe they can be an important component of any good passive solar design.
Trying to heat and could our homes is like bailing out a leaky boat… You can keep bailing or try to plug the holes.
In winter, the fresh air outside is cold. Our homes are full of small cracks (intentional or unintentional) and that cold air finds its way in. Of course, we use a variety of mechanical systems to heat that air up to a comfortable temperature. However, that warmed air escapes again pretty quickly and is replaced by new cold air, which is heated up again. In summer the process is reversed, with expensive machines extracting the heat from our homes while hot air is pouring back in again thru every crack. It is like trying to bail out a boat that is full of holes, if we didn’t have machines to take care of the work for us, we would never put up with it. Infiltration is said to be the single greatest waste of energy in the average home. (The leakage in the average home is equivalent to leaving a 3’x3′ window open all year, it gets even worse when the wind blows. According to the U.S. Department of Energy, Americans spend 30% of the nations energy adjusting the temperature of the air in their homes. )
Many PassivHaus builders spend a fortune trying to keep this outside air out, while the earth covered portions of earth shelters are naturally airtight. Either way, homes need fresh air to be healthy. If you bring that air directly in from the outdoors, you will need to heat it up to room temperature. The goal is fresh air exchange without giving up the weather tight advantage completely (and just drilling a big open hole in the wall). One possible solution is an Air to Air Heat Exchanger (or Heat Recovery Ventilation (HRV)) that attempts to retain heat by transferring it from the outgoing air to the incoming air. These units can also filter air and usually include a blower and other active components. They easily cost several thousand dollars.
Heat recovery ventilation, often with an earth-to-air heat exchanger, is essential to achieve German Passivhaus standards.
The earth tubes are just a lower tech, passive way to do something very similar. They tap into the heat storage capacity of the earth to moderate incoming air all year long. They can be used with above ground homes, but are a particularly natural fit for an earth sheltered home.
In many cases, both air to air and air to ground (earth tube) heat exchangers can be used. It is relatively common to install air to air heat exchangers within the home (such as in the basement) fed tempered air by earth tubes.
Basically, in an earth sheltered home with an intake earth tube, the cold winter air is drawn into the tube by convection or fans and absorbs heat from the earth on its way. By the time it enters the home, its temperature is significantly moderated by the earths temperature, but it usually still needs some additional heat. This additional energy could come from fossil fuels, a wood stove or passive solar. Of course, less additional energy would be required than if the air were drawn in directly from the outside. After being used in the home, the air is eventually expelled (again either due to convection or assisted with fans) thru an exit earth tube where its energy is absorbed back into the earth…
If the exit pipe runs near the entrance pipe (as shown in the above image), exit heat can actually be transferred to the incoming air (similar concept to an HRV). This is known as a “Camels Nose” heat exchanger. Other layouts include the use of Bernoulli’s principle and/or a solar chimney to draw the air thru the tubes and home and out the roof.
Earth Tube Concerns
A variety of concerns are often stated as reasons not to use Earth tubes. These range from discussions about cost/benefit analysis to serious health concerns related to mold or radon. In general, these are due to experiences with improperly installed earth tubes. This section of this page grew too large and was broken out to a separate page on Earth Tube Concerns.
Types of Earth Tubes
While the majority of users only use earth tubes for moderating fresh air, these simple “air to ground heat exchangers” can be used in other ways. I would like to use Earth Tubes for 3 main purposes.
1) Fresh air moderation; these basic earth tubes bring fresh air into the home (ventilation) and allow stale air to leave. Passing thru the earth moderates the temperature of the air and reduces the load on the heating or cooling systems. I created a separate page to discuss ventilation requirements here.
2) By-passive Solar; these earth tubes never enter the home. Instead they form a loop between the solar hot air collector and the soil under the home. Solar energy heats the air in the collector, it travels under the home where the energy is absorbed into the soil and then the air returns to the collector to be recharged. Since it doesn’t matter how stale the air is, a closed loop design where the solar heater reheats the air that just passed thru the loop is the most efficient.
I have an “interesting” idea that I think I can incorporate for minimal incremental cost… I plan to configure my french drain system to use loops with an inlet and outlet rather than the traditional branched configuration. This will allow me to push solar heated air thru the tubes to warm up my foundations. I could use the standard 4 inch HDPE drain pipe, or I could improve the performance with the 50% more expensive 6 inch pipe. If I try it, I’ll let you know how it performs.
3) Heat Exchange loops within the home; these tubes are relativity short and simply provide additional heat exchange between the air in a room and the surrounding soil. The loop would connect the a vent near the floor with a vent near the ceiling. The room air is allowed to pass thru the duct circuit to be moderated by the earth. For instance, in a warm room, the air near the ceiling may pass into the duct where it would be cooled (and dehumidified) by the cooler earth. This would reduce the buoyancy of the air, causing it to sink and draw in more warm air. The cooler air would fall out the bottom vent and help cool the room. If the room is cooler than the earth, the system would reverse and warm the air. If the room is better off without the heat exchange, you could just close the vents.
I imagine that it will be important to deal with the condensation that may form or drain out of the tubes. A tiny weep hole to the earth may be sufficient.
I plan to try at least one of these on my future office.
Earth Tube Design
Earth tubes can be designed many ways. I broke this section on Earth Tube Design out into a separate page.
Earth Sheltered Ventilation
Earth Tubes can be used to provide ventilation, but it is important make sure they are sized adequately… I broke this section on ventilation out into a separate page.
I can share some good Earth Tube related links I found here on a separate page.
Buying the right plot of land is an important part of the overall process of building an earth shelter. The story of my land buying saga can be found in this blog post, here on this page I am more focused on the tools and process of finding the best piece of land.
Real Estate AgentI am starting with finding a real-estate agent because you really need to. As much as I dislike the system, there is no getting around it. As they say in Detroit, “Hate the game, not the playas”.
Personally, I could not find a real estate agent who specialized in empty lots, probably not enough money in it. I ended up going with someone who was at least living and working in the area where I wanted to buy. I thought that the agent was driving around all day and might have some inside track on where the good land was, but nope. I got no good leads from my agent. She didn’t seem to have a good understanding of what I was looking for and only suggested a few small flat lots in neighborhoods of colonials. I don’t recall our agent visiting any of the properties with us (except the last one after we made an offer), and probably couldn’t have helped if she had. My agent was always apologizing for not being very helpful often volunteering to help with things like checking if a property had been perked or had liens against it, but (once I found out how) it was faster and easier to do that myself. My suggestion is to ask your real-estate agent where to find all the tools you need from the list below… (they probably won’t volunteer the information, but they might tell you if you ask).
Generally speaking, Real-estate agents use the MLS (Multiple Listing Service) and key in some search terms like size of the lot and price range you are considering… You can do this on the internet for yourself. I found that the agent always wanted to give me a longer list (as if that were some how better). When I did my own search, I spent a few extra minutes up front to enter search terms that excluded areas and lot sizes I wasn’t interested in reviewing, and that saved a lot of time over using her lists. Most MLS searches also let you setup a recurring search so that a new list is generated each week (based on your criteria) and sent to your email. You can read more about MLS in the next section. However, it is important to note that, often, the MLS listings don’t actually tell you exactly where the lot is and you will need to contact your agent to get the specifics (this is just part of the information asymmetry designed into the real-estate process). So, use them when needed, but don’t rely on them to help you find a nice piece of property.
Real-estate agents work out separate contracts with each client. They typically say that 6 percent of the sale price goes to the agents (split 3% and 3% between the agencies, and then split again so your agent actually only gets 1.5% and his/her agency gets the other 1.5%), but there is no rule about this. Your agent may want to charge 7%, 4% for him and 3% for the other agency. This 1% increase almost doubles his interest in you (from 1.5% up to 2.5%). Others may work out lower prices, like 5.5% just to stand out. The seller can negotiate and see where they end up, but buyers don’t usually get much choice here. However, your agent will want you to sign a contract with them so you can’t “see other agents” at the same time. You can alter this contract. For instance, you can set a time limit shorter than their 6 month default, “Find me something in 2 months or I get another agent”. The main thing we changed was to add a provision that if we found a FSBO (for sale by owner) property on our own, we didn’t owe her anything. She didn’t like that much, but I refused to pay her for property that was never in the system. The compromise was that if she told us about the property before we found it ourselves, we would still pay her 1.5%. As it was, she never gave us any FSBO leads and we ended up buying thru the regular MLS system, but I was glad to have that option in place anyway.
Keep your expectations low and maybe you will get lucky.
MLS The MLS (multiple listing service) is an internet database that real estate agents can use to exchange info about what properties are available on the market (it also lets them organize contractual unilateral compensation deals, etc.). This is their main tool! In the 1880’s, the MLS was on paper. Agents would meet once a week to exchange info and contract offers, “help me sell my inventory and I will sell yours, we can split the commission”. In the digital age, there is a data standard so all the agencies can work together with reciprocal access agreements in place. There is a governing body that makes sure that real-estate agents with access are working in a way that benefits the community, for instance, low cost agents are usually shut out for undercutting the market. There are also some restrictions on how much info your agent is allowed to share with you. FSBO (for sale by owner) brokers can add listings if they charge a sufficient amount to discourage the idea, but other agents may choose to filter those out and never show them to potential buyers. The full listings can hold hundreds of data fields, but agents are not required to fill them in completely and often strategically hold back key information.
Many of the data fields relevant to the real-estate search are also available to anyone with an internet connection. The MLS.com website is the official window on the MLS database. Some Real-estate agencies have their own websites that act as a window to the MLS, for instance, here is the Coldwell Banker site, and here is the Century21 site. They are not allowed to use MLS in their URL or as a search term. However, they can setup their windows to show only certain data fields or ranges and can lay out the data to make the search tool easier to use. Some companies end up making it difficult to do a land search, in which case, you could just try a different site. Some sites filter out listings they don’t like, such as “For Sale by Owner” listings or listings in areas they can not sell.
Some listing agents don’t like to provide enough information for you to find the lot yourself. They may just give the town or the nearest major cross roads. But you might get other information, such as a GIS screen shot or a PID number that you can use to figure it out. If you can’t, you will need to contact your agent who will contact the listing agent to get the info. Of course this adds an annoying string of phone calls and possibly several days of waiting… But it is all part of the real estate “information asymmetry” designed into the system.
Google Maps It is hard to believe that we got along before Google. Google maps are very helpful in exploring properties for sale. Instead of driving all over the place, I always explored with Google maps before getting in the car. From the satellite perspective, you can see water features, forest features, figure out sight lines to nearby homes, look for nearby train tracks or garbage dumps or prisons, etc. You can quickly key in directions to your work or church to see if the location is too remote. When it comes to planning your physical trip, you can enter all your addresses into Google and shuffle them to find the shortest route.
I always took some printed pages with me because looking at them while standing on the land is a powerful combination. Make sure you understand which way is north imagine how the sun will travel across the property.
Google Maps does provide some “GIS” like tools, such as their terrain map option.
GIS Maps
GIS Maps have many very useful layers, particularly the ones for soil type and lot boundaries
These GIS (Graphical information System) maps can provide layers of information, such as soil type or lot boundaries, that are very helpful. I found some on my county’s website. Do a search for GIS and your county name to find your own. You should always explore the rich information before considering buying any lot. I would usually look before bothering to drive out to a lot.
GIS Maps are very useful when searching for land. Click for the full screen shot.
Always look at “natural” layers like “soil type” or “watershed”. I actually found the watershed layer to be a good pair with the topology layer because the rivers always run down hill. The Soil maps go well with the additional info you can find in NRCS (USDA) soil maps. The land use layer was also helpful. You will also want to find areas that have been declared flood zones or wetlands or “Well Prohibition” zones. GIS may also list public services, etc. You could also display “parcel” annotation and features, which provides the lot boundaries, acreage, right of way, easements, etc. The PID numbers can be used to find out who owns the plots, what they paid for it, what taxes they pay, any leans against the lot, etc.
Another cool feature of GIS is the historical aerial photos. As you hopefully realize, google maps is not a live image. Google maps just uses the latest satellite photos and updates them from time to time. With a GIS system, you can look at older photos to perhaps see a different season or earlier time. I was able to see aerial photos from back to 1940. I could see what my property looked like when it was a corn farm long before it was subdivided.
NRCS (USDA) site
I generated a custom report for any property that I was seriously considering
The NRCS (Natural Resources Conservation Service) of the USDA (United States Department of Agriculture) has a wealth of information on their website. Follow the links to get to their “web soil survey” and this mapping application. Go into the mapping application, find the lot your are interested in and use the tools to draw your AOI (Area of interest) on the screen… Then you can generate all sorts of advanced reports on the soil type, usage, etc. The maps are similar to what you find under GIS, except with much more detail. The reports take that soil information to another level.
Property/Parcel lookup Most counties maintain a website where you can look up any piece of property by the PID number (which you can find on the GIS maps). This is the website for my county. You can enter a PID number and find out a lot of info about the site. You can discover who owns it (along with their address and phone number), what they paid for it (and the history going back), the tax information, school district, etc. A near by link will lead you to well and septic information also. You may want to look up the neighboring properties to see how deep their wells were or how much they paid and when…
Cellphone / Smartphone These little gadgets are indispensable. I used the mapping functions on my smart phone, I used them to find the directions/distance to the nearest 7/11 or Target store, etc. Partially, this check was to understand the area, but I also made sure to test from the site (data and voice) to make sure that the reception was good. You may want to make sure that you can’t get a cell phone signal, to each his own ;^)
100 ft measuring tape
Make sure your home will fit on the lot. Allow for what ever setbacks apply.
I usually took a measuring tape or at least a 100ft long piece of rope with me to each site. I had a basic idea of how wide and deep my home would be and I would always make sure it would fit. Don’t forget about “setbacks” that limit how close you can be to the neighbors.
Compass For a passive solar home, the orientation of the lot is very important. You will want to check for “solar access”; that is check to make sure that the path of the sun is largely unobstructed, particularly the winter path. Hopefully you have an idea of its winter path in your area, if not, you should look that up before you head out to investigate the land. You will want to check the southern sky for buildings, trees, mountains or other obstacles. If you lot is on a hill, you will want to make sure you are on the southern side of the hill (lots on northern slopes tend to be cheaper, at least in colder areas). But you can’t really do any of that if you don’t know which way is north or south.
The Google and GIS maps should help, but it might still be handy to have a compass as a double check. Never just believe your real-estate agent ;).
One final note on using a compass is to check for solar orientation… Be sure to check your magnetic declination (<== the Wikipedia entry is pretty good). The solar orientation is based on “True North”, the poles based on rotation of the earth as it orbits the sun… Not the “Magnetic North” that your compass will point to. The difference between these is the magnetic declination. In Michigan, it is not a huge problem, but you should check the declination in your area… This website, http://magnetic-declination.com/ should help. In Minneapolis, Magnetic and True North are nearly aligned, so magnetic declination is less than half a degree off. But if you live in Maine, it could be off by more than 17°W. Over in Seattle, it is almost 17°E. It gets really crazy in Alaska or areas of Northern Canada. Orienting your home by a compass would be a big mistake if your compass was off by more than 15°.
Magnetic declination changes as the magnetic pole moves around. Make sure your map/info is current.
Also note that magnetic declination changes a little each year as the north magnetic pole tends to drift around. When I bought my lot in 2009, the magnetic declination was 6°W of “True North”. Today I checked and it is 7.3°W.
If you got the magnetic declination off a printed map (it is usually printed somewhere on any decent hiking map), also check the date. If it is more than 2 years old, you might want to check with a newer source to make sure it is still “close enough”.
