advice request: building an earthship-inspired wooden house

Hi folks!

I've been planning a small wooden house to build in a small property I'm developing. I chose wood considering cost (I get a local carpenter to build it) and also because it feels more "natural".

Recently I began doing more research on earthships and passive houses, and would love to get something like that. Unfortunately, the costs and resources are out of my reach.

So, I've been redesigning the wood house to integrate more principles from earthships and passive house design. I would like to discuss it with someone who has a bit more experience, just to check if I'm not making some major mistakes. I don't expect the wood house to perform as good, but as long as its better than standard wooden houses, its already a win! I just don't want to make things that won't work because I didn't do X, Y or Z as well!

Here's a photo of my current house plan: https://i.imgur.com/sl6XGJw.png

So these are basically my questions:

1 - the south(sun)-facing wall will just be vertical, and not tilted like in an earthship. Would that be a problem?

2 - do I need to integrate some sort of window on the roof to allow hot air to escape, or opening the wall windows will be enough?

3 - I wont have enough room to place a rocket mass heater(which would be amazing!), so probably a standard wood-stove will have to do it. I can try to put some more mass around it, to hold heat. But will it be enough to get hot air to the rooms?

4 - Not having windows anywhere except south makes sense, but in this case, will it be worst since I wont have enough air movement to take hot air out?

5 - (related with previous) will I be able to implement a cooling vent (underground) like earthships do, in this kind of design? will it work at all or do I need some more elements to get the convection thing working?

sidenotes:

* I plan to have plants to provide shade both on the south and west side
* the roof overhang will be enough to cut most of the summer sun from the windows
* the bathroom location is on the west to act as an extra barrier between the sun and the bedroom... but I know it should be near to the kitchen for more efficient plumbing, hot water, etc.

Any other tips or advice?

thanks in advance!!

Hello Nuno,

Not an expert here but a few things I can tell you:

--the angle of the south-facing window isn't such a big deal, it's already a big step forward that you're orienting your house to the south instead of ignoring this entirely
--if you haven't looked into the wofati design, it's worth considering.  My understanding is that it hasn't been optimized yet, but the basic idea has been time-tested and is quite aesthetic.  Even if it isn't optimized, it would still greatly moderate your temperatures around the year (the ati part of wofati is "annualized thermal inertia").  It may be too late with where you are in your process, but maybe some aspects could be worth considering?
--putting mass around your wood stove is a good idea--and you actually don't need to heat the air as much as you need to heat _you_--someone on here posted they lived in a really leaky cabin, but added mass around their stove and could be comfortable and warm.  This worked better for him than if he'd tried to insulate.

Keep us posted on your process!

Joshua

As for the hot air escaping--from what I've learned, hot air rises, so as long as the exit point is higher than your head, you'll be comfortable...and the air overhead may be a bit hotter and radiate downward a little but it'll draw out.  

Hi, What is your climate like? How many months do you have to heat your house in winter, and how many months do you have uncomfortable heat in summer? These are the first things to clarify before you make your design.

I have many years experience in living in houses that are passively heated and cooled, with some similarities to earthships but several differences.

Yes, vertical south-facing windows are much better than sloping glass, in my experience. Sloped glass overheats horribly in summer, but vertical glass gets much less sun in summer because the sun moves high overhead in summer.

An overhang over the south windows or wall reduces summer overheating. Depending on your latitude (how far north you are) and how much overheating you might suffer from, you design your overhang. I suspect that in Portugal the sun is not as high as in the tropics, and you may have very hot summers, so you might want a very large overhang to reduce overheating. I think you can probably find a solar design website that lets you calculate how wide an overhang is needed to shade a window of X height at X latitude. The lovely thing about passive solar heating is that the sun moves lower in the southern sky in the winter, so in winter the sun shines under the overhang and into your house.

East, west and north facing windows get sun during summer mornings and afternoons, so minimising windows on those 3 sides reduces overheating. West-facing windows are the worst for overheating, because they add direct solar gain during long summer afternoons when your house is already warm from the hot air of the day. Exact south-facing windows with a good overhang get no direct sun at all in summer. It's nice to have some windows on all sides, for nice cross-ventilation when you open the windows, and for the aesthetics of the rooms, but make them small, and try to shade the 3 sides with plants or trees.

An aspect of earthships that I like is thick earthen walls for thermal mass. Our buildings use rammed earth (not filled tires) and this thermal mass stabilises the temperature summer and winter. Other materials than earth are possible, but thermal mass is essential for a passively heated and cooled building. Today on 11th June our buildings are nice and cool inside even when it gets up to 28C outdoors at this time of year. By late summer, August, the thermal mass is no longer so effective, as it will have heated up by then. Similarly, for the first half of winter, our buildings stay warm because they still hold the heat of summer.

A solar-heated wood-framed building without major thermal mass suffers from cooling too quickly and heating too quickly. Insulation does not help this problem at all. Thermal mass walls can be stone or concrete, but earthen walls have nicer qualities in my experience, though there are places and reasons that make stone or concrete necessary. Water is also a very effective thermal mass material, and so tanks of water (possibly including plants and fish) can be used. I've seen three successful houses using water tanks for thermal mass in passively solar heated houses in Cape Cod, US, where the houses were wood framed with insulation.

If your heating needs in winter are not very heavy, with south facing vertical windows and good thermal mass, you may need very little or no backup heating, so a small wood stove might serve your needs better than a rocket mass heater. A small stove can heat up a room up quickly on those few nights or mornings when you need additional heat, and some of its heat will be stored in the thermal mass walls, if you have those. Rocket mass heaters sound great for cold northern climates with long winters, many months of needing to heat houses, and cloudy winters with low sun angle making solar heating less effective. I don't know a lot about Portugal but I think maybe you don't have those conditions.

Hi all! thank you for your comments and suggestions!

@Joshua, hum, that's a bit confusing to me. In other discussions on passive houses the idea seems to be that closing all the leaks is one of the most important things. but for me it also makes sense to give priority to other things. I think radiant heat (from a wood stove) doesn't escape that fast due to air leaks (like hot air from a pellet stove). Will look at the wofati, thanks! although the idea I have about it is that - much like earthships - it requires quite a bit of manpower to move a lot of earth. Other problem is being allowed(legally) to build such a thing!

@Rebecca, I'm about 38º North. Summer months are usually very hot and it usually lasts for about 4 months. Winter is cold (0ºC) and also lasts 3-4months. Usually, no snow.
So perhaps some small north-facing windows (well insulated) might help with the cross ventilation.
With a wooden house I think having a lot of thermal mass might be a challenge, but thats why I thought of adding a rocket mass heater.. if it wasn't for all the room it takes :/

this house is 60m², so its quite a challenge to fit all "ideal" things But like I said, I'm not trying to achieve 100% efficiency, rather just to improve on a standard wood house design

Hi Nuno,
I think what you are describing could be covered with Mike Oehler's house designs, there are several youtube videos of his $50 and up house. Instead of using a normal woodstove, install a rocket mass heater for more efficient heating. Oehler has some design principles for good lighting and preventing leaks, I highly recommend you read his book and if you can buy the package deal from this site which includes the 3 video set for his design course, which has some really good info as well. I got the digital streaming option here and it works very well.

I'm actually planning to do just this on my flat property, going down about 4 feet to get the soil that will cover the roof and berm up the sides, and use the PAHS "umbrella" over it to shed water away from the structure to improve the thermal flywheel for passive heating/cooling (like the wofati also employs) as dry soil works better than wet soil for insulation and heat storage. PAHS also uses air tubes that run under the umbrella to transfer heat to and from the earth, warming the air in the winter as it comes in, and cooling it during the summer. Flat windows are fine, again check out Mike Oehler's design.

One suggestion I would make is to flip your living room/kitchen, and also swap your bathroom and bedroom so that the bath and kitchen are next to each other, to share a single wall for plumbing. If you plan to use the metal roof for rain collection and a cistern, it can be placed near this shared wall as well.

Hi @Mark,

thanks for the suggestion, will check it out! Much like the wofati, I'm afraid that "underground" stuff wont be legal to build... but will need to check it out!

Regarding the bathroom, I put it there to create an extra buffer between the western wall(sun!) and the bedroom, but I understand your point. Maybe I can place bathroom and kitchen on the west side and the bedrooms in the east. (will also be better to not enter the house directly into the bedrooms, I guess)

I would suggest a door at each end, and if you have a transom window above each which can be opened, you can create a cross ventilation feature or at least have a high point for hot air to get out, and a lower window or air tube to bring fresh air in.

I would suggest earth berming on the east and west sides as well, which can still have windows too. Several feet of earth will help cool the room a good deal. I don't think you'd have any issues with an earth-bermed room, just call it a walk-out basement which are pretty common.