Passive Cooling

Sorry for the lack of posts. I’ve been busy doing summer things, seeing as it’s summer and all.

Last time we were talking about how to keep your house warm using only the sun. That’s called passive solar heating. Today, we’re going to talk about how we stay cool during the summer.

When we talked about keeping things warm, having good solar gain through south facing glass was a key part to that. However you might wonder that having all that sun exposure would make things really warm during the summer. The first thing we do to help with this is angle the glass that is facing the sun so it is perpendicular to it during the winter. This will give us the best solar gain when it is cold, but it will also reflect much more of the light away during the summer. The angle of the sun during the summer is much higher, so it will hit the glass at a much steeper angle, causing more light to be reflected away. Here are some simple diagrams.



So just by the fact that the sun is higher in the summer, means we have less solar gain. However, the sun is also stronger during the summer, so the angled glass alone will not suffice. To further help with this, modern Earthships make use of something referred to as a double greenhouse. That’s a bit of a misnomer, but I’ll explain as we go along.

If you’ve been following along and looked at the tour posts, you’ve seen that on all of the global model Earthships there is a long hallway that you come into first when entering the house. This hallway always has copious amounts of plants in it up against the glass. Examples of this can be found on the Global2 tour


… and the Suttan tour.


On the right side of the pictures you can see the angled glass that faces the sun. On the left side you can see another wall of glass. This creates a buffer zone in the main greenhouse. The temperature can fluctuate within the main greenhouse, but in the living areas, the temperature remains constantly comfortable. To give you some idea of where the sun is in relation to the green house, I have some pictures.

Here is a section drawing of where the sun falls during the summer.


As you can see, the sun will only fall within the buffer zone created by the two glass walls. We can also further help reduce the solar gain buy using window shades or blinds. You can see those in picture of the Suttan house above.

Now in winter, it looks like this:


Now the sun light goes all the way to the back of the room, covering a lot more area that will absorb the heat. Make sure your floors are made of something with a lot of thermal mass: brick, flag stone, tile, concrete or adobe are some options. You don’t want to use things like wood, carpet or vinyl as those will act as insulators and you will lose all of that heat coming into your house.

Back to cooling. With the sun beaming down in the front during the summer, it will make that greenhouse fairly warm. Unfortunately, I don’t have any pictures of this, but up in the ceiling of the greenhouse are openable skylights. This will naturally vent the hot air from the greenhouse out the roof, as we all know, heat rises. However, this isn’t all. There is one more feature used to help with overheating during the summer: cooling tubes.

Cooling tubes are 10″ diameter (25.4cm) steel culvert pipes that run into the back of the house from the north side. The north side of the house is all bermed up with earth right up to the roof, so the cooling tubes are buried deep in the ground. You can see the cross section of a cooling tube in the pictures of the sun angle during summer and winter above on the bottom left side.

Because the cooling tubes are buried in the ground, they tap directly into that constant 15 degrees C that the earth maintains. Any air moving through the tubes will be cooled to that temperature, so all we need to do is get it into the house for further ventilation. We don’t use any fans or other mechanical devices, we use pure convection. Take a look at this picture:


Above the door in each room, an openable window is placed. By opening it, we tap into that natural draft happening in the greenhouse. Remember, it’s pretty warm in there with the sun shining down on it. We have those skylights open up top, letting out the hot air. With the venting windows open above the doors, this will naturally pull cool air from the tubes into the room. Warmer air will be pushed out the vent, into the greenhouse and up and out the skylight.

This maintains a constant cooling airflow through the rooms where the people are and it uses no mechanical or other powered systems to do it, just naturally occurring phenomenon. Pretty elegant when you think about it.

Now I’ve skipped over some details to try to keep from overwhelming you all at once. For instance, how do you choose what angle to put your front face glass at for optimal sun gain? Well, it depends on where you are in the world and a few other factors, but I’ll save that discussion for next time.


Passive Solar Heating

Today we’re going to talk about thermal mass, insulation and all sorts of other fun things, boys and girls. But before we begin, let’s set the stage.

What would you say if I told you there was a way to build a home in which you would never need to pay for heating and cooling ever again? No, I’m not talking about finding your own personal oil well, or natural gas deposit. This home would maintain a comfortable temperature year round, regardless of climate and it would not burn any type of fuel or electricity.

Sounds too good to be true? Stay tuned and I’ll show you how.

First, let’s talk about mass. Mass is a term we use to describe the quantity of matter contained within a volume of space. If I have a liter of marshmallow and a liter of concrete, the concrete has more mass as the molecules that make up its structure are packed much more tightly. The more molecules you can pack into a volume, the more dense it will be and the more mass it will have.

Now, heat and mass get along very well. The more dense mass you have, the more heat it can store. You might imagine putting an aluminum pie plate in the oven along with a cast iron frying pan. Turn the oven on and heat them both up. Then take them out of the oven. The aluminum pie plate will cool down pretty quickly, but the cast iron pan will stay warm for quite a bit longer. This is because the cast iron pan has much more mass than the aluminum pie plate.

Okay so far? What about insulation? We talk about insulation a lot these days, but what is it really? It’s a material that can be used to block the transference of temperature. So, you want to insulate your house to keep the heat in and the cold out during the winter. Let’s discuss how this is done in a conventional house.

Conventional housing, generally, uses a wood frame structure which is then insulated around on the outside and covered with a wrapper, something like siding or brick perhaps. We put a peaked roof on it, insulate the attic, and slap some shingles or other roofing material to keep the rain and snow from falling into the house. In general, conventional housing is designed to keep the outside elements outside as much as possible.

There is an issue with this though. If it is really hot outside, we have to add artificial cooling to the building to make it livable. Similarly, if it is cold outside, we need to add heat to the building otherwise everything would freeze, no matter how much insulation you have, unless you live in an airtight bubble and never go outside. I don’t think you’d last too long in that situation.

Hmmm, time to do some more experiments. Lets look at this one:


You could think of the first case, with the glass jar full of air, as a representation of a conventional home. What we do is heat and cool the air, but as you can see, air doesn’t hold temperature very well. It will equalize to whatever the ambient temperature is pretty quickly. We could add insulation to the jar of air, but it still won’t hold its temperature nearly as long as the insulated jar with water in it.

So, lets use our imaginations and consider what it would be like if we were to live in jars like these:


Am I suggesting that we all should be living in jars full of water? Not really. But the concept is valid. With these ideas about mass and temperature, the ideal outer wall in a house would look like this:


Using a dense mass to hold temperature, we insulate it against the outside and then the mass will stabilize the interior temperature of the house. When there is a temperature difference between the air inside the house and the mass of the walls, the heat always travels from hot to cold. So if the walls are warmer than the air, the heat comes out of the walls to heat the room. If the walls are cooler, they will pull heat out of the room.

Now if you’ve ever heard anything about geothermal heating and cooling, you would know that once you go down past the frost line, the temperature of the earth is stable around 15 degrees C (around 60F). You can experience this simply by standing barefoot on a concrete floor in a basement. It feels great in the summer when it’s really hot outside, but it feels quite frosty in the winter when you’re trying to stay warm. In actuality the temperature of that floor doesn’t change much (without working at it, anyway); it’s stable throughout the year around 15C. Geothermal heating taps into this and we’re going to do the same thing, but without digging big holes and running pipes that pump water around all of the time.

Remembering that we want to have some dense mass walls, we’re going to put them in direct contact with the earth. Oh, we’ll probably put down a moisture barrier first, but the mass walls need to be in contact with the earth to get access to that stable 15C temperature. Forgetting everything else, if you were to just do this, insulate the walls and close in the house, your house would maintain that temperature of 15C. (There are a few details I left out, but this is getting long :P) That’s not super warm, but your toilet and other plumbing will never freeze, for one thing.

So, we have our massive walls attached to the ground and then we make sure to insulate them so they can keep their temperature. But how do we get things warmer when we need it? We use a simple thing called the sun. If we look at the regular approach to sun gain in a conventional house, it looks something like this:


What we need to do, is reconfigure the house so it faces the sun as much as possible. This would be south in the northern hemisphere and north in the southern hemisphere.


Does this really work? Can you heat your house in winter just with sunshine? The answer is a resounding “YES”. There is a good chance you have encountered this phenomenon yourself. Ever have one of those really cold, yet sunny winter days? Have you ever been driving into the sun on a day like that and find yourself turning the heater down or even off? Heck, you don’t even need to be driving. Just park your car with its windshield facing the sun for a while and then get in it. It may not be super toasty warm, but it will certainly be much warmer than the outside temperature is. This works the same way during the summer, when you come back to your car that is parked in the sun and find the interior is like a blast furnace; i.e. much warmer than the outside.

There is a tremendous amount of solar energy falling on every square meter of land and for the most part, we completely ignore it. What a waste.

So, we have our mass walls, they are insulated. We’ve aimed the house to the sun, with lots of glass there to let it all in. We’re also going to berm up the house on the east, west and north sides, which will further work to keep that stable temperature inside. It does this by raising the frost line up closer to the roof, thus ensuring that your structure won’t be heaving from the frost in spring/autumn.

The sun comes up in the morning, shines in our windows and heats up those mass walls we have. At night, when the sun goes down, the air in the house starts to cool and the temperature we stored in the walls comes out, keeping the house at a stable temperature.

Now you know why Earthships are built using tires packed with dirt. This provides the mass that temperature can be stored in. This is really just a simple man’s version of pure rammed earth building techniques. It has the advantage of using up a huge waste resource we have, as well as breaking it down into sizable brick-like chunks, which you wouldn’t be able to do with traditional rammed-earth as you’d need to tamp the whole wall at once to avoid cold joints.

Anyway, that’s the basics behind how to heat your home without burning fuel or using electricity. It’s completely passive. I have left out some details to keep it simple and I haven’t talked about cooling yet either. I’ll save that for another post πŸ™‚

Where do we go from here

After all of my adventures down in New Mexico, I bet you’re wondering what’s gonna happen next. I didn’t go down there just for the scenery and to get into shape pounding tires πŸ˜›

There are always multiple steps in any plan, so let’s go over what we have:

  1. Fix up old house in preparation for selling.
  2. Sell old house.
  3. Rent a cheap place out in the country while looking for a piece of land to buy.
  4. Get some hands on Earthship experience.
  5. Buy a piece of land where we are going to build.
  6. Get final design and architectural drawings for the Earthship.
  7. Prep the land for building (build a driveway, clearing trees, etc)
  8. Apply for the building permit.
  9. Start building.

With steps 1 through 4 already completed, we’re onto step 5.

Buying land, as I have discovered is an interesting affair. First of all, you have to find something you like. This can be quite tricky. Some people have difficulty walking into a house that is for sale and imagining their own stuff in it. Now try to imagine you don’t even have a house, you just have a chunk of land and you need to imagine changing the landscape to include your home. It’s even more challenging if the land you are looking at is full of trees where you want to build. It makes it difficult to picture.

Anyway, I will soon have more news and info about buying land, so stay tuned for that.

After buying land, you need house plans from an architect. For conventional housing, this is usually pretty easy. Most commonly, you pick an existing design and maybe have a few tweaks made to it by a licensed architect. Most people don’t start from scratch.

In the case of Earthships, there are generic plans that you can buy from Earthship Biotecture for one, two, three and four bedroom global models and a few other designs. We’ve decided to go a somewhat hybrid approach.

I am currently designing my own Earthship based upon the global model and other Earthships that I have encountered. So, much of what we want in our own Earthship will be very much like the global models you have seen pictured in the tours, but, I am also incorporating some ideas that were used on an Earthship that was built in Vermont.

In the end, though, I’m not an architect, so I will need to hand off whatever I have come up with to an architect to create final drawings. I’m well aware there will most likely be changes, but it’s a fun, if not time consuming, experience to go through the process of designing your own home. You learn a lot just building it virtually, and the only thing it costs you is time. Can’t waste materials that way πŸ˜‰

I’m using a program called Sketchup to design my Earthship. I’ve previously started two other designs, which I abandoned for various reasons. I started this new one after finishing my academy session down in New Mexico. It gave me some new ideas πŸ™‚

So, that’s where we’re at right now. I’ll keep everyone posted as to what is going on, and I do promise I will get around to doing more technical articles soon.


If you have been following along, you may recall I mentioned doing a tour up in the mountains at an Earthship community called REACH. Well, I’ve saved that tour for the last one. REACH stands for Rural Earthship Alternative Community Habitat and I saved it for the last tour, as it was one of my favourites. Mostly because of the location: up in the mountains with lots of trees. All of the other Earthships we toured were out in the desert. This was a nice change.

Let’s start with some outside pictures. This is what the area around the Earthships looks like: steep hillside with lots of pine trees.


Turning around and looking at the valley, this is what you’ll see.


Here is another one, way up on a cliff.


We toured two Earthships up a REACH, so I have lots of pictures for you. Things will jump around a lot, but I will do my best to fill in with explanations.

The first one we toured was a nightly rental, and also for sale. First thing we see in any Earthship: plants. Including a cactus.


And another look at the cactus, with the mountains in the background.


Opposite the plants was this small seating area. Just enough room for a comfy chair, in front of more plants that looks out at the view.


The other thing you’ll notice is stairs: there are a lot of them. You’ll think you’ve seen most of the house and then you’ll discover yet another set of stairs leading to yet another room. All of the Earthships up at REACH are built as a series of tiers, so you can imagine there are a lot of stairs everywhere.


Going up those stairs leads to another seating area / living room where you can once again enjoy the fantastic view. Here is a shot of one of my fellow academy students doing just that.


Here is what that view looked like.


Next we have a bedroom, similar in style to the ones over at Phil’s place. There is the loft above with the bed and a seating area underneath it. I’m not entirely sure, but it looks from the picture that the area underneath has another platform that would take a mattress for another bed. Right beside the fire place too.


Up top we can see the bed.


Coming back down a different set of stairs, we’re now into a bathroom area.


Here is a better view, looking out the windows in the bathroom.


This one just had a regular bathtub, but it was right up against the glass. That’s one heck of a view when you take a shower πŸ˜›


Moving further east, there was a doorway to outside from the center of the house. This is what it looks like standing in the doorway looking out/south.


If you walk out the door and look to the east, you’ll see this.


If you look down the hillside, you’ll see the top of the next house below. We’ll be visiting the interior of that one too, later on this tour.


Looking back towards the west, you’ll see the door we came out of on the right side of this next picture, as well as the rest of the front of the house.


Now we’re back inside at the kitchen. The refrigerator in this house merits special attention as it is completely passive. It doesn’t use electricity or funky gasses.


It’s a thermal mass fridge. It has an air vent that you would open at night to let in the cold mountain air which then cools the thermal mass built into the fridge. You close the vent in the morning and the fridge stays cool during the day. At least that is the theory.

The problem with this one is they used beer in cans as the thermal mass, but visitors keep drinking them πŸ˜› It’s also a manual process, so if you forget to open or close the vent, you may or may not have the cold stored in the thermal mass. This fridge is also twenty plus years old.

There wasn’t anyone staying there at the time, so there wasn’t much in the fridge, but you can see the beer can thermal mass in the walls.


Next we have the kitchen sinks, right up against the glass like in some of the older Earthships. Great way to use sunlight to dry your dishes.


Beyond the kitchen, we come to an indoor cistern. It’s neat to have, but it also acts as a big heat sink, so they don’t recommend them for colder climates.


Most of the beds in these Earthships are up on platforms. Here I am standing on a stairway, taking a picture of the opposite stairway that leads up to a bed. Under the bed is closet storage.


Here is a shot of the bedframe, though it didn’t have a mattress on it at the time.


Walking around to the other side of the platform and looking back, you can see the fireplace built in to the sleeping area.


This was in another section, but here we have another small sleeping platform built into the back of the house. Quite the precarious perch and not for those who are prone to falling out of bed at night. Definitely not to code either πŸ˜‰


Back outside, we’re at the far end of the house now, looking back along the front.


As I was wandering back through the house, I discovered another set of stairs I had missed. Low and behold, there was another bedroom up there.


All of the walls were a funky blue colour and this bedroom had its own en-suite bathroom too.


This is looking into the shower stall. Nice decorative edging there using the polished rocks.


Here is a better shot of the bed.


And the other side of the room, with the fireplace.


Time to leave that one and journey over to the second Earthship on this tour. No, this is not a picture of it from a distance, it’s just another mountain-side shot.


This is a shot of the exterior of the next Earthship on this tour. This one is owned by Kirsten and Ron. Kirsten was the woman who did all of the admin for the academy and Ron is a crew member as well as he taught some of our classes.


Yay, more plants… and more mountains.


This was the first bedroom we came too. Again, it’s up on a platform with storage underneath.


This is a picture of the custom tub in the bathroom. Unfortunately, you can’t see the set of stone steps up the left side of the tub.


Fortunately for you, I have another picture of it from an Earthship book I have.


Next we have a living room area, with some built-in seating and shelving areas.


Here it is again, so you can see it from the other direction.


If you turn around and look out the window from there, this is what you see: more plants and a great view.


It’s kitchen time, with Phillipa and Denina. Okay, maybe not. This kitchen looks very similar to the last one, in terms of layout, but it has the standard Sunfrost fridge and a fancy/schmancy gas stove.


No picture of the sink this time, but you can see the planters they have in the kitchen as well as the blinds on the windows. They also have that huge aloe plant in there.


Hmmm, more stairs. I wonder where these go?


Ah ha! Another bathroom. This one didn’t even have a separate area for the shower, it was just part of the room. No shower curtain or anything.


Two more bedrooms were up here as well. This is the first one.


It had some funky built-in shelves with drawers.


Bedroom number two.



At the far end of the house I came across this. It looks more like a nightmare than a WOM to me.


At the far east side of the house, there was a pleasant little patio with chairs and a barbeque.


Looking down from the edge of the patio, you can see that we are standing on yet another room.


I shot this panoramic of the valley standing on that patio.


This is the stairway that leads down from the patio to that room that is under it.


Nice fancy stained glass door.


The room under the patio wasn’t very exciting. It was mainly a junk room with odds and ends. It was like a sauna in there though, and that was just from the sun shining in the window. I did take this picture, however, of the back of the room.


That, my friends, is the mountain rock that all of these homes were carved out of… by hand. There weren’t any roads up there at the time, so they had to build one and it is dang steep.

They couldn’t get any big equipment up there either, so most of everything that was needed to build all of those Earthships was carried up by hand. A lot of labour went into building these places.

Originally when they wanted to build up there, the county said they were nuts as there wasn’t any water or power or anything. So they let them go ahead, thinking they would have to give up. Well, they were quite successful. There are about 30 Earthships up there.

Unfortunately, the county put a stop to building up at REACH. One of their main arguments was that no emergency vehicle could ever make it up there if anyone needed to call 911.

It snows up there a lot too. It is the mountains, of course, and Taos is known for its skiing. It is awesomely scenic though and a great spot to spend even just an afternoon.

That’s all of the pictures and that is the end of the Earthship tours I took while down in New Mexico. I’ve been home for over two months now but Earthships are still very strong with me. We’re working towards building our own so there will be more posts about that. I’ll also be putting up some technical articles, explaining certain areas. These would be good ones to ask any questions you may have about the whole process.

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