Basement Home

[jhambley]

I have both the luxury and the curse of designing a new home from the ground up. We own 80 rural acres in Kansas with a south facing exposure. I'm not very optimistic about the state of the economy or our infrastructure. With that in mind, I'm beginning a mind exercise to develop a sustainable/off grid homestead. So many "green" home designs either involve extremely expensive active systems and I'm neither rich nor interested in super hi-tech solutions.

With home heating and cooling being the largest percentage of a home's energy requirement, I'm thinking of building a basement home. I'm basically talking about a earth bermed walkout basement with a roof on top. I'd pour a basement (with side walls) leaving the front open to frame with traditional materials and facing the southern exposure.

My gut feeling is I should insulate the ^%%$# out of the shell and use the relatively narrow temperature differential of a comfortable inside temperature (say 70 degrees) to the ground's year round temperature (say 55 degrees). Not being able to run an air conditioner from a renewable source (solar or wind), I'm trying to minimize the cooling load. Cooling seems to be the bigger challenge than winter time space heating with a wood stove. I'm thinking I could power an energy efficient air-air exchanger to keep the air fresh.

A few questions:

1. Does this insulated shell approach make the best use of the ground temperatures for summer time cooling? Or should I be trying to take advantage of the earth contact as a cooling source?
2. How much heat gain will I have through a super insulated metal roof and south facing wall that aren't earth covered?
3. Any concerns about living without air conditioning or a dehumidifier in such a design?
4. Are there any other low-tech ideas for building a home that wouldn't be miserable to live in during a hot midwest summer?

That's for helping me "what if" my way to a solution!

JH

[jbos333]

Check this out for some ideas: http://www.city-data.com/forum/tennessee/359683-going-off-grid-east-tennessee.html

[tommytebco]

there are three projects in process that are similar to your intent. search for Eaglesj, speedfunk and one other I can't remember
A little help???

[jhambley]

Here is another earth sheltered home blog.

http://www.ourcoolhouse.com/

Interesting that they took a completely opposite approach and isolated the building from the earth with insulation while the other link you posted used no insulation between the earth and the interior of the home.

I'd love to hear other's comments regarding these two opposing views.

[Squirl]

1. My vote is for insulated shell.  I read a book on underground houses once.  Moisture is an issue they deal with. Cold concrete + hot moist air = condensation.
2. Almost no heat gain from the roof.  Heat rises, and a ventilated roof with insulation in between should give little heat gain. 
You can get large amounts of heat on sunny days on the south wall.  I would love to see which is more efficient between passive solar windows or a passive solar air heater.  Proper overhangs and shading in the summer will be important.
3. Yes.  I would try and design it for good ventilation.
4. Do you mean low tech, or low cost?  Extra insulation isn't high tech, just expensive.


You can sometimes run AC off grid.  Mini splits can be more efficient than a window unit.  In the summer, when it is sunny is when you will have the most solar power.  Another strategy people use is not to cool their whole house.  They have the A/C in a reasonable sized room or enclosed area.  I have even seen an enclosed bed that had the AC just for it.

[jhambley]

Thanks for your reply Squirl.

4. Do you mean low tech, or low cost?  Extra insulation isn't high tech, just expensive.

I mean using a more "passive" than active systems approach. I used damp sprayed blown cellulose insulation in my current home.  Loose blown cellulose insulation can be inexpensive. I'd load the south facing wall (maybe 12" thick) and attic with tons of insulation and ventilate the attic space above the insulation.

[John Raabe]

I don't think you would be happy with an uninsulated concrete shell in contact with the cold wet soil. I would insulate the concrete walls and slab with a couple of inches of exterior blueboard insulation and then have a drainage plane (gravel footing trench and backfill) on the other three sides that drains to daylight any water from the soil. This will keep the walls dry and lets the mass serve as an internal thermal flywheel. You can design your south wall glazing to get passive solar inputs during the heating season and then adjust the roof overhang or movable shades to restrict heat gain during the higher sun cooling season. You will want some venting windows on the other three sides to take advantage of cross ventilation. This will go a long way in reducing both the summer (cooling) and winter (heating) loads.

See my Sunkit for help with site evaluation and preliminary sizing.

PS: As Squirl mentions a well insulated (your cellulose will work well here) and vented roof will add little to the heat load.

[jhambley]

Thanks for joining the conversation John. I'll check out your Sunkit.

If I could pick your brain for a second more, I have a question on cross ventilation. I've built a small cottage that is only 16' wide. The prevailing winds are from the south and I placed windows across from one another on the south and north walls of the building. I get great cross ventilation. My question is, how much wider than 16' can I build and still expect a great deal of natural cross ventilation. For example, if I were to build a 32' wide home and configure the windows in the same manner (assuming no interior partitions) , could I still expect good cross ventilation?

Thanks again for your time and helping all us "would be" builders with such a great site!!!

JH

[John Raabe]

Yes the airflow through the window areas should be about the same as it would be in the smaller house. This would be a smaller percentage of the total volume of house air however so you would probably want more opening window area in the larger house.

[jhambley]

Great, thanks!

[jhambley]

I'm toying with an earth berm barn look. This is the best I could do using a Word processor as a CAD program

[John Raabe]

Does the job...   


Looks to be worth exploring.

[PorkChopsMmm]

You want to look at this guys build. He built a near identical house to the one you are describing in Maine. He goes through the entire build... insulating the foundation, building the walls, berming, finishing the structure, etc. Lots of good info.

http://thehomesteadingboards.com/

[jhambley]

Here's another thread that the owner sent to me along with their comments about what they would do differently.

They wrote:

I've been living in mine for about 3-4 years now. I would only change a few small things:

1) Whole house dehumidifier (I currently run one on each end of the house and am planning on switching it to the entire house version)

2) Switch a few things around in the utility room but overall it's not to bad of a setup.

Here is the links to my build threads:

http://tinyurl.com/9z7ppd8

http://tinyurl.com/cjjrzdt

[jhambley]

It appears a major challenge is keeping these homes from getting damp. In an off grid situation, an air conditioner or dehumidifier are not very practical unless you want to run a generator all the time. Any suggestions?

[John Raabe]

Insulation and a well drained footing and backfill are needed to insure that you keep the concrete from transferring soil moisture to the interior. See my reply #6 above.


This diagram might help.

[jhambley]

John,

I appears some of this moisture is "owner" generated from propane appliances (off the grid favorites like, stove, refrigerator,etc) , and showers.

[John Raabe]

Yes, that is true. But there can be the same problem in frame houses. In fact, the problem will show up earlier in a frame house since you have a huge thermal and moisture sink in the masonry. Ventilation is the answer to interior generated moisture. When you go all German Passive House and seal everything up, then you need HRVs and air to air exchangers. But that is another power draw not needed when you can just crack a window.

[jhambley]

So in an off-grid situation, would you simply crack windows in the Spring or do you need more active ventilation like whole house, bathroom fans etc?

If you plan on using the masonry as a moisture sink, does that assume you place all your insulation/vapor barriers on the outside of the building?

Would keeping the concrete exposed on the interior prevent potential moisture issues behind furred out walls covered with sheet rock?

[John Raabe]

So in an off-grid situation, would you simply crack windows in the Spring or do you need more active ventilation like whole house, bathroom fans etc?

If you plan on using the masonry as a moisture sink, does that assume you place all your insulation/vapor barriers on the outside of the building?

Would keeping the concrete exposed on the interior prevent potential moisture issues behind furred out walls covered with sheet rock?

Yes, use windows and cross ventilation for moisture control. As you get better electrical capacity you may want a cooking and bathroom fan so you might nstall them initially to save tear up later.

You want your insulation and moisture barrier on the outside of the concrete. Your masonry will automatically be a thermal and interior moisture sink - you want to keep out external moisture - the interior will take care of itself and will equalize throughout the house. If you have done this right you will not have moisture issues behind furred walls. I would not put another vapor barrier in these interior walls.

[jhambley]

Great...thanks for all your advice!