passive solar earth berm house. New build coming too soon

We, my wife and I are set to close on selling our current house just at the end of August. We will be living temp in a friends almost finished mothers suit in his basement. Next up, we are buying land and attempting to juggle the many pieces of going against the grain of the system. I say that as we are using a local bank to fund most of our venture, it would be oh so much easier if we had all cash.. Only battle then would be the county inspector. We do have a small bit of cash, hopefully it will be just enough to cover the gaps. I am writing to see if any one can offer advice, comments and food for thought. I have been reading about this type of build as much as possible. And now for the highlights...

We are using a local builder who has built passive solar homes but this will be his first earth berm
I have a family unit that does wonderful custom home builds and is into technology such as SIPs, etc. He is and has been a great sounding board.
We are have a top limit to spend and with this limit we hope to be mortgage free in 10 to 15 years. Oh freedom never sounded so good...
3 bedrooms, a small office, 1 bathroom, nice kitchen, mud room, and earth berm green house
approx 1000 to 12000 sqft not counting the green house.
Will have shed style roof with EDPM rubber roofing which a family member can install.
Bathroom will eventually have custom tub/shower to allow relaxing and multiple shower heads
Hope to finish the house just enough for the county to give us the certificate of occupancy
3 sided concrete with SIPs front and roof.
Thinking greenhouse will utilize double sheet plastic air separated with back half of roof finished with edpm. Original thought is green house will be 20 x 20. May need to reduce size. want to grow a lot of food. also thinking dirt floor with woven poly floor designed for green houses (other than the main growing area)
Wood stove heat with high efficiency Wood stove
We have a general contractor friend that does insurance repairs for distaters. We are hoping to get all sinks, cabinets and first shower from him. To use only for county inspection or until we find that something amazing.
rough size 20 x 60


Not sure about mechanical
Want to utilize grey water though our county doesn't approve (after mod)


Currently have 11 hens, looking to increase to a self sustaining flock and using 6 to 12 for meat annually.
Thinking of keeping two summer pigs
Will do all completely free range or paddock type.



I have some rough drawings that I will try and clean up and post on here. Thanks for reading and I am hoping to share and receive advise from those who know or have great insight!

Sounds like a fun project! It also sounds like you are considering an attached greenhouse?

since you are planning on an edpm roof, you might want to think about making it a living roof. If you did, you could grow food on the roof as well as reduce the heat intake in summer, keep the heat inside easier in the winter. for the green house, if it is going to be connected, see if you can get windows from a ReStore these are pretty easy to modify to double pane for houses and they also work well for glass greenhouses. We found lots of tempered glass sliding doors at our ReStore which will become the walls and roof panels of our greenhouse. I've had plastic covered green houses and they work well but degrade quickly, this means every year or two you replace all the plastic. Gray water can always be used for gardens and if you install an inline sand filter it may be good with your county. Would love to see your drawings.

People should be aware that used windows might have low SHGC values due to the type of Low-E coatings typically used. This could make it less efficient than having no windows at all, even on the south.

Been a little busy moving.. Havent really had to much time to focus on the fun part. I'm glad to see replies.

The home plan has shifted a bit. It has been pointed out to me that a square house is cheaper to build and on paper it actually works out to have more room. So I think we will line the 3 bedrooms up on the east side, keeping the north fully earth bermed and all other plans the same.

Yes i do hope to have a green house attached off the mud room on the west side, earth bermed north side. I have been looking at GAHT systems and it seems very DIY and doable. I was thinking of using the plastic to get things going and upgrading later. Have a few questions there still.. I have a plan to figure out more about the hybrid water heaters and if they would work in the green house. I understand they are more efficient in the higher heat areas, can cool areas and cause a swirling of air. All good things for a green house. In theory sounds like a match.

It seems I have found place for a cellar in the floor plan, that is exciting. I need more information on conditioning of the air in the space.

One of the main goals for this home build is to keep maintenance as low as possible. I could be incorrect, with a living roof i would suspect there would be more maintenance and possible work down the road. not to mention, its not a common practice hear and I can only imagine calling for help after the talks i have had with many local builders just talking about earth berming. I have dreamed though about a living roof though.

Looking at whole house air circulation units.

Trying to figure out if I can squeeze storage space in front of the house like a loft utilizing the highest part of the shed roof.

Still have little more than a napkin sketch. Will get this in better shape after the storm of moving blows over.

Considering using spray foam for roof and east and south wall instead of SIPs. Cost is less and it is easier to work with upfront. The thermal bridging in the roof would be minimum with the use of TGIs. As for the walls. Initially I was thinking 2x6s on 24" center but now I am wondering about a double set of 2x4s with an offset to avoid thermal bridging and still using spray foam.... Any thoughts on the trade off?

As for the grey water, last time I read through my county requirements I remember reading the grey water must be died and ran through some type of treatment and could not be daylighted. I am looking at ways of incorporating grey water piping under the slab and not raising questions.

What are our low cost house covering options?


The search for land will be starting in a week or two.

Willy, you probably shouldnt get too far into design, napkin stage or not, without having the building site in hand. I suggest finding a spot that you could have enough room to separate the greenhouse from the humanhouse.

Brian that sounds about right. A few good things about napkin sketches. Firstly, I have neve done this so a few revisions would be a positive for me. Secondly, I am Hoping this is a basic enough floor plan that will allow for slight adjustments to most any property. Thirdly I need a budget. So if any of the above reasons aren't good enough the budget is. We are sticking to a tight budget to allow for early payoff. With of course maximizing land.

Please do tell me, why not connect the greenhouse? It will be seperate from the house by the mudroom. Also it will share the same earthbermed north side wall.

The more simple the plan, the more it can make sense to pre-plan so its certainly not a waste of time especially with generalized bubble ideas. For rough budgets, knowing a square footage and rough price per sqft is useful at this point too. Usually site work is one of the biggest unknowns and reason for variance.

I think connected greenhouses are usually a bad idea because they have more temperature extremes and humidity than what we want for our homes. My question would be why attach? Iam guessing the reason is to save on excavation and infrastructure costs in relation to your earth bermed north wall.

Good passive solar designs will perform best with the right balance of air-sealing, insulation and fenestration. Greenhouses usually complicate things and hurt performance overall when sharing a wall with the house.

My idea of the best annualized western elevation, in our mixed-humid climate, would be NO windows with an airtight and highly insulated wall with wide roof overhangs and preferably big deciduous shade trees blocking the setting summer sun. The more the wall, or western elevation deviates from that description, the more it will negatively influence the home's performance on a net annualized basis and the wall (and house) will be subjected to higher humidity from the greenhouse.

There are pros and cons to everything in building design, we just have to weigh them for our individual situations. Here's an older article on the passive solar earth sheltered home my wife and I designed and built 30 years ago. http://www.builditsolar.com/Projects/SolarHomes/Doug/DougsSolarHome.htm
We still are living comfortably in it. There are things I would do differently, like more insulation and lees mass in exterior walls. And here's some tours-







Any questions, just ask.

Brian Knight wrote:The more simple the plan, the more it can make sense to pre-plan so its certainly not a waste of time especially with generalized bubble ideas. For rough budgets, knowing a square footage and rough price per sqft is useful at this point too. Usually site work is one of the biggest unknowns and reason for variance.

I think connected greenhouses are usually a bad idea because they have more temperature extremes and humidity than what we want for our homes. My question would be why attach? Iam guessing the reason is to save on excavation and infrastructure costs in relation to your earth bermed north wall.

Good passive solar designs will perform best with the right balance of air-sealing, insulation and fenestration. Greenhouses usually complicate things and hurt performance overall when sharing a wall with the house.

My idea of the best annualized western elevation, in our mixed-humid climate, would be NO windows with an airtight and highly insulated wall with wide roof overhangs and preferably big deciduous shade trees blocking the setting summer sun. The more the wall, or western elevation deviates from that description, the more it will negatively influence the home's performance on a net annualized basis and the wall (and house) will be subjected to higher humidity from the greenhouse.

An attached greenhouse can add solar heating capacity, it depends on design temps, thermal mass, glazing, insulation, climate, etc. A low mass attached sunspace will definitely help with winter heating, as it can go cold at night. Both need to be able to be closed off from the main living space when desired. Check out this article-
http://www.builditsolar.com/Projects/Sunspace/LowMassSunspace/TestsLowMassSunspace.htm
and my attached solar greenhouse-
http://www.builditsolar.com/Projects/Sunspace/DougSolarGreenhouse.htm

Doug thanks for the input. I will be glad to watch the videos and read the info at builditsolar. Its actually good timing as we just secured property and have started the process. There have been a few changes in the design idea. At this point we are still working off napkin sketches but.. I had a chance to visit a few homes and more time to think, think, rethink and think some more. I am very interested in a conditioned crawl space vs a concrete floor.

Pros of Conditioned crawl space vs concrete slab for my lifestyle:

Ability to add and remove plumbing, electrical after initial build/installation, radiant heat (think greywater, additions that wont make the first build and in general any changes that come about later)
placement of HVAC/mechanical equipment thus keeping footprint of finished space small
Use of air bank in crawlspace (this is major for me)
Air bank in crawlspace is like basement/earth berm temps
possible dedication of an semi small finished area for storage only
I dislike concrete slab as main floor from a comfort level. (learned this as we now live in a basement)
Concrete slab is not forgiving for children falls and or falls in general

Cons of switching to conditioned crawl
Will loose thermal mass
increase in cost
Loss of direct earthberm to living space contact (though same potential of earthberm due to circulation of crawlspace air)


It also looks like our initial footprint has dropped back to 24 x 36 with a second level and a semi loft feature. Leaving in tact 75% of the second level as livable area. It is still planned to keep the bottom level, north wall and earthberm wall though it will start atop the footer now and will not make all the way to second floor, depending how deep crawlspace is on north side. A typical truss roof maybe used to keep a "normal" build and profile. Though it will be conditioned and used for storage. The second level will be used for bedrooms and bathroom. THe first for larger bedroom and main bathroom, kitchen, laundry, living area.

A few other highlights..

Considering utilizing solar radiant heating. Maybe an after build installation to reduce initial costs.
Layout and lot is not leaving an easy method of addition of Greenhouse
Cellar and mudroom still planned
Placement of house and garden will force focus on an amazing overlook of all things growing.
Confident that the conditioned crawlspace and proper air movement/control will help tremendously heat and cool the living spaces for little cost of moving air.



questions for thought and input.

Considering using the heat pump style water heaters that pull heat out of the air. These have a backup heat element and are highly efficient. I think there would be great benifit to placing this in the conditioned attic.

If just about all windows are facing south, and there is little thermal in the floor, will there be a passive solar aspect to this build? There will be a rear concrete wall but I doubt much if any direct sun will get to it. Will the radiant tubing count as thermal mass?

If you are going to go with the conditioned crawlspace, I suggest exterior insulation for the foundation, right down to include the footers. This will incorporate more thermal mass into the conditioned space. Be sure to provide either a physical or chemical barrier to prevent termite damage to foamboard exposed to soil.
I think the effect of a berm which is insulated off from the living space is minimal. If thermally connected to the living space as well as ground, it has the ability to absorb infinite amounts of heat, not good in winter.
Heat Pump Water heaters (HPWH) take heat and humidity from interior air year round. You decide if this is a good thing in your climate. They are expensive, and do require maintenance. I prefer a solar water heater, which I have backed up by a wood fired coil and a heat pump beer chiller, as well as resistance heat. Will your conditioned attic exchange air with the living space? If so, the HPWH will chill the attic air, falling into your living space. If not, it may chill the attic air in winter to a point where it is inefficient to run. I know this is where the backup comes in, but this will be sooner than if it is in outside air.
Willy wrote-"If just about all windows are facing south, and there is little thermal in the floor, will there be a passive solar aspect to this build? There will be a rear concrete wall but I doubt much if any direct sun will get to it. Will the radiant tubing count as thermal mass?"
Sure, passive solar will heat a home without much thermal mass, but there will be greater temperature swings. Thermal mass stabilizes temp changes. Direct sun striking dark mass is more efficient than mass out of direct sunlight. The water in the radiant tubing has some thermal mass, but not much. Thermal mass works best when it is exposed to direct sun, and has lots of surface area exposed to the living area, and is well insulated from outside temps. Doug

"If you are going to go with the conditioned crawlspace, I suggest exterior insulation for the foundation, right down to include the footers." - I like this statement. I had not thought about this. My initial thoughts are to use a spray foam inside the crawlspace, I'm not sure if the spray foam can be in contact with the soil. I have this on my questions list for the spray foam installation company. Is your point to insulate on the exterior so that the crawlspace and footers are a thermal mass? In my thought process of interior insulation, this would not be the case.

I like the idea of the amount of power the HPWH uses. I also like the idea of letting a device perform double duty. Thus why I was thinking of putting this in my attic. I haven't figured out if there would be sufficient heat to warm the attic in the winter.. I am hoping to avoid adding much heat in general so I need to be careful here. It is possible that in lieu of the HPWH i could install a standard water heater and add a solar WH in time, something I want to do any how. I need to get in touch with a radiant heat supplier so that I can figure out cost and better understand the details. I really like the idea of a drain back system, draining back into the crawlspace to serve as as a pre warmed thermal mass for which the house air is circulated around. I see I have a few questions in general still about heating my home. Of course i know all to well about the wood stove. It is my hopes that this becomes a sunday enjoyment and not a constant..

I secretly understood but just didn't want to admit it that by switching from a slab to a conditioned crawl, I'm loosing the title "Passive Solar". Or at best, its not a selling point anymore. I just don't think I can do with the slab though.. So sad. At least though, I wont have to turn on many lights during the day!!

Doug - Can you clarify this statement? "I think the effect of a berm which is insulated off from the living space is minimal. If thermally connected to the living space as well as ground, it has the ability to absorb infinite amounts of heat, not good in winter. " What kind of advantages can I expect from my first floor, north wall being earth bermed? The lot lends its self to an earth berm or not as the grade could be taken either way. One thing I do like about the earth berm from a cosmetics approach is that I don't want any (maybe one in a bathroom) north side windows. However this is the side every one will see, so burying half the wall will make my house almost look normal as the wall will be pretty blank. My thought on function is that the earth will provide a constant temp, out performing even the best insulation techniques. My thought is to insulate the outside of the wall (to the footer is a great idea) and I'm not sure on the inside. A concrete wall is not as functional as a stud wall for living so... Still on the fence. My other alternative would be to not earthberm (totally changing my theme) and utilize a SIP wall with no windows..



I know sharing this idea via a web forum in text only and it is crude at best. But I really am just putting this all together. Any help, ideas, ect, even if I didn't ask for it or it doesn't sound like its in my plans are excepted. Very soon our plans will posted to this forum. They are becoming more and more concrete and I am starting to feel very good about them.

Willy Walker wrote:"If you are going to go with the conditioned crawlspace, I suggest exterior insulation for the foundation, right down to include the footers." - I like this statement. I had not thought about this. My initial thoughts are to use a spray foam inside the crawlspace, I'm not sure if the spray foam can be in contact with the soil. I have this on my questions list for the spray foam installation company. Is your point to insulate on the exterior so that the crawlspace and footers are a thermal mass? In my thought process of interior insulation, this would not be the case.

I like the idea of the amount of power the HPWH uses. I also like the idea of letting a device perform double duty. Thus why I was thinking of putting this in my attic. I haven't figured out if there would be sufficient heat to warm the attic in the winter.. I am hoping to avoid adding much heat in general so I need to be careful here. It is possible that in lieu of the HPWH i could install a standard water heater and add a solar WH in time, something I want to do any how. I need to get in touch with a radiant heat supplier so that I can figure out cost and better understand the details. I really like the idea of a drain back system, draining back into the crawlspace to serve as as a pre warmed thermal mass for which the house air is circulated around. I see I have a few questions in general still about heating my home. Of course i know all to well about the wood stove. It is my hopes that this becomes a sunday enjoyment and not a constant..

I secretly understood but just didn't want to admit it that by switching from a slab to a conditioned crawl, I'm loosing the title "Passive Solar". Or at best, its not a selling point anymore. I just don't think I can do with the slab though.. So sad. At least though, I wont have to turn on many lights during the day!!

Doug - Can you clarify this statement? "I think the effect of a berm which is insulated off from the living space is minimal. If thermally connected to the living space as well as ground, it has the ability to absorb infinite amounts of heat, not good in winter. " What kind of advantages can I expect from my first floor, north wall being earth bermed? The lot lends its self to an earth berm or not as the grade could be taken either way. One thing I do like about the earth berm from a cosmetics approach is that I don't want any (maybe one in a bathroom) north side windows. However this is the side every one will see, so burying half the wall will make my house almost look normal as the wall will be pretty blank. My thought on function is that the earth will provide a constant temp, out performing even the best insulation techniques. My thought is to insulate the outside of the wall (to the footer is a great idea) and I'm not sure on the inside. A concrete wall is not as functional as a stud wall for living so... Still on the fence. My other alternative would be to not earthberm (totally changing my theme) and utilize a SIP wall with no windows..



I know sharing this idea via a web forum in text only and it is crude at best. But I really am just putting this all together. Any help, ideas, ect, even if I didn't ask for it or it doesn't sound like its in my plans are excepted. Very soon our plans will posted to this forum. They are becoming more and more concrete and I am starting to feel very good about them.

Yes, exterior insulation will add the mass of the foundation to the homes mass. Spray insulation is expensive and most is petro based-soy foam is even more expensive. Use 4x8' sheet Extruded polystyrene (XPS) for the exterior insulation. I recommend dense packed cellulose for the walls and roof insulation. Berming outside a well insulated wall does little, Look at PAHS Passive Annual Heat Storage http://www.norishouse.com/PAHS/UmbrellaHouse.html Either include the berm in the insulation envelope, or insulate it off from the home.
Opening a shade to let the suns heat in is passive heating. Your lack of mass in direct sun will make for greater temp swings, but it's still passive solar heating. Mass is not insulation! Many people make this mistake-earth temps are relatively constant year round at a depth of 6-8', so a berm will not do much as insulation. Insulation is more important than mass. Use advanced framing techniques to minimize thermal bridging, and blow cellulose into them. http://www.toolbase.org/PATH-OVE
http://www.birdinsulation.com/helpful-info/cellulose-myths-dissolved

http://www.greenbuildingtalk.com/Forums/tabid/53/afv/topic/aff/14/aft/79917/afpg/3/Default.aspx

http://www.ehow.com/info_7842200_fiberglass-deterrent-mice.html

http://isofloc.com/index.php?questions-answers

http://www.edcmag.com/articles/web-exclusive-cellulose-insulation-superior-to-fiberglass-and-kinder-to-the-environment

Great advice and links from Doug. Always nice to hear from those living in similar planned structures. With all this focus on energy performance, insulation and thermal mass details I think there needs to be more attention payed to air-sealing. Its not uncommon for these types of projects to miss out on this performance factor which is probably more important and affordable than insulation.

Agree that thermal mass TM is a minor detail when evaluating passive solar performance. Its more about how an airtight and insulated envelope uses its windows and overhangs. However, TM does help compensate for too much glass so you should scale back your sun-facing glass without mass on the floor.

Its kind of a shame to see you dismiss the slab. Iam not sure which is the bigger deal breaker, future renovation or safety concerns. For renovation, I dont think its a big deal. The only electrical in a slab would be for a floor outlet or kitchen island. The only plumbing other than the main supply would be drain lines. This stuff can be changed in the future but if you do a good job on the floorplan, it will be unlikely that it ever needs to be changed. As for safety, you could always cover the main traffic areas and leave the sunlit areas un-covered. Is a concrete surface that much different than tile? I feel its not.

There are more problems with crawls. As you mentioned, if you dont want a cave under your home (vented crawl) you need to seal and insulate down there and possibly add space conditioning. This is difficult and expensive. Because of the low headroom, substandard trade work is typical. The space usually needs a low point to drain to daylight which complicates air-sealing.

Anytime Iam faced with a crawlspace lot, I much prefer to fill it up with gravel and pour a slab. This alleviates ground water and moisture concerns while giving an excellent opportunity to run a passive sub-slab drainage and radon vent.

I agree that better performance will be gained by insulating the exterior of crawlspace or basement walls. However, the performance advantages may not be recouped by the extra costs and PIA of insulating the exterior. I agree that XPS foam is a good choice but I think closed cell spray foam can be better if you can get it by code enforcement and get a good price. Both foams can be in contact with dirt but I like to protect it with dimple mat drain board that drains to exterior footing drains. Termites are a huge concern with exterior foam underground. It needs an inspection strip break between wood and chemical termite treatment around the foundation. They do make some XPS with protection built in.





On this project we spray foamed the bermed wall the same time as under the slab then used XPS covered with stucco for the above grade finish. I cant tell in this shot but the contractor installed the dimple mat backwards when I wasnt there. I made him dig it out and re-install it with the fabric facing the dirt, like its suppose to be. Second shot goes in the home manual showing locations of underground utilities which is the exterior foundation drain in this case. We stacked boulders for retainage against the stair step thingy.

Love your idea of HPWH. Not too sure about the attic though. The best places for them in the north are basements but considering you may be overheating with all those windows and not much mass, an upper floor room or loft could be fine. Love solar too but unless you enjoy working with these systems, be prepared for trouble and maintenance. Even if you go solar, do a HPWH as the backup if possible. Most models are cost-competitive with well made gas water heaters and I think the GE model is lower in up-front costs already. When you include the energy costs they are almost always a better value than conventional water heaters including solar with high maintenance needs. Dont ignore the summertime cooling with dehumidification benefits of HPWH.

Agree that you will not see much performance benefits from berming. PAHS is largely un-proven. Insulation should be placed against the wall. The main performance advantage is lower Delta-T compared to the outdoor air temps and eliminating unwanted solar gain through windows and wall surfaces. This helps of course and makes sense when matched with the right site. Going out of your way with earth moving equipment, waterproofing and underground insulation is un-likely to pay off compared to a 2012 IECC code minimum wall with good air sealing.

Brian wrote-"PAHS is largely un-proven."
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There are several folks in the underground house Yahoo group I'm in that have been living in PAHS homes for years. There are several around the US. They are proven. Doug

https://groups.yahoo.com/neo/groups/UndergroundHouse/info

http://terrafirmo.wordpress.com/

Here's some links to check out-

https://www.thenaturalhome.com/passivesolar.html

http://fugadeideas.org/paccs/forum/viewforum.php?f=3&sid=ed2fd1ea976478ea11fed30c01d089de

http://www.subsurfacebuildings.com/UnderGroundbutNotUnderground.html

www.subsurfacebuildings.com/DiggingfortheGreen.html

http://www.buildinggreen.com/auth/article.cfm/1998/4/1/Thermal-Mass-and-R-value-Making-Sense-of-a-Confusing-Issue/

http://www.subsurfacebuildings.com/Twenty-FiveYearsUnderOhio.html

http://www.homeenergy.org/show/article/year/1999/id/1515

http://www.toolbase.org/PATH-OVE

Well Doug, at least you didnt go so far as to say PAHS is largely proven. I standby my statement as largely un-proven. Perhaps the truth is somewhere in between but the lack of "proof" is discouraging to say the least.

Iam not asking for proof as I think that would be in the eye of the beholder. Still disappointed with the links and available info on PAHS projects. Ive tried several times but cannot access the yahoo groups posts. I would hope that there would be more data or information than a yahoo group discussion anyhow. Looking at the PACCS (PAHS?) link, the last post was almost 2 years ago and there is a serious lack of discussion and information for a building strategy that makes such bold claims or has so much potential.

I loved the terrafirmo link. This is similar to an underground home that I have brewing in my mind. Easily engineered and low labor costs. I would love to see more information on energy costs or temperature monitoring and can almost guaranty that the home would be performing better with insulation at the wall.

I want to make sure folks understand the difference between "underground building" and PAHS and the problems I have with the latter. Underground building does not equate to PAHS. To me the main difference is that PAHS does not insulate the below grade walls. This creates a heat sink and makes it more difficult to control the indoor air temperature. All the talk of temperatures evening out through the seasons is more hypothesis than theory. I go so far as to say it does not work. Insulation does work. Why go through so much expense and risk to try to prove otherwise with the results that are out there for review?

Brian Knight wrote:Well Doug, at least you didnt go so far as to say PAHS is largely proven. I standby my statement as largely un-proven. Perhaps the truth is somewhere in between but the lack of "proof" is discouraging to say the least.

Iam not asking for proof as I think that would be in the eye of the beholder. Still disappointed with the links and available info on PAHS projects. Ive tried several times but cannot access the yahoo groups posts. I would hope that there would be more data or information than a yahoo group discussion anyhow. Looking at the PACCS (PAHS?) link, the last post was almost 2 years ago and there is a serious lack of discussion and information for a building strategy that makes such bold claims or has so much potential.

I loved the terrafirmo link. This is similar to an underground home that I have brewing in my mind. Easily engineered and low labor costs. I would love to see more information on energy costs or temperature monitoring and can almost guaranty that the home would be performing better with insulation at the wall.

I want to make sure folks understand the difference between "underground building" and PAHS and the problems I have with the latter. Underground building does not equate to PAHS. To me the main difference is that PAHS does not insulate the below grade walls. This creates a heat sink and makes it more difficult to control the indoor air temperature. All the talk of temperatures evening out through the seasons is more hypothesis than theory. I go so far as to say it does not work. Insulation does work. Why go through so much expense and risk to try to prove otherwise with the results that are out there for review?

You have to join the Yahoo group to see the past messages. I won't argue with you, join the group, search "mtncats" and "john hait", as they have designed, built and lived in successful PAHS homes for years. There are others also. They external walls are insulated in PAHS, contrary to your claim, the insulation just includes some dry soil around the exterior walls, to add to thermal mass, which gives it the ability to store summer heat for winter. Doug

I did try joining and I can see myself signed in with my yahoo email but its not letting me look at the posts for some reason. Please dont see this as just an argument but even more important dont stop posting with your veiwpoints. I think everyone benefits from these discussions including myself as I wrestle with the concepts.

I understand that there may be successful projects out there but they are sure are hard to find. There seems to be a bit of "earthship secrecy" as to how these projects are performing and an obvious lack of pictures and construction details.

Ive talked often in other threads on my skepticism of achieving dry dirt in most climates but lets ignore that for the supposed thermal benefits. Most dry dirt is more thermal mass than insulation. I understand that the PAHS includes a layer of insulation, but its so far away from the exterior walls, it may as well not be there at all. I think the "dry dirt" layer is going to track much closer to typical underground soil temperatures. This can be beneficial during the cooling season but harmful during the heating season.

The real danger is that the wall is going to be closer to the dew point. Most current sub-slab and basement wall insulation recommendations are for stopping condensation. By keeping the insulation against the wall, this risk can be practically eliminated with recommended interior relative humidity.

I think the insulation in PAHS is a waste. Its too far away to do any good. All that extra thermal mass impacts the home performance for the worse, not the better. Extra thermal mass is easily overshadowed by ACH50, exposed/above grade wall insulation and window performance values. By placing thermal mass in between the underground wall and insulation, you lose the ability to easily control indoor air temperature.

Here's an article for Willy on building efficient exterior walls. Doug

Thermal bridges might seem small, but they can be a source of significant energy loss. A superinsulated home is only as good as its resistance to heat flow, and that means addressing thermal bridging during the home’s design and construction.
http://www.homepower.com/articles/home-efficiency/design-construction/back-page-basics-thermal-bridging

Brian Knight wrote:People should be aware that used windows might have low SHGC values due to the type of Low-E coatings typically used. This could make it less efficient than having no windows at all, even on the south.

By no windows at all, do you mean an unbroken wall, or holes in the wall with no glass in the holes?

Yeah Peter, that's a poorly worded statement. I certainly didn't mean "holes in the wall" as that violates what I see as the most important performance factor of a passive solar home: air-tight as proven by a blower door test. When people ignore the importance of airsealing their envelopes, they end up with cracks and holes that when combined, account for areas as large as window openings. I think most people understand the need to close windows and doors when heating a structure and we should view airsealing in the same light.

R-value and thermal mass considerations are typically less important than closing windows and sealing up all the cracks and holes that act like open windows.

What I meant is that you may be better off with solid wall area (insulation) than low SHGC glass, even on the sun-facing sides. A used window with a low E coating may have a SHGC glass value of .28. Compare that to a low-e window designed for admitting solar gain (high SHGC glass), which may have an SHGC of .6. The windows would have the same U-factor but the high SHGC passive solar glass would admit around 60% more heat!

As we build tighter and more insulated structures, the importance of sun-facing window area drops. Homes that are not passive solar or have any extra thermal mass can perform better than this thread's title by paying strict attention to airtightness and insulation. This is good as air-sealing and insulation are more affordable than windows.

People trying to fit used windows to a new build face an uphill battle when it comes to energy performance and will probably benefit from very conservative glass to floor ratios. Not only will used windows have questionable SHGC values, perhaps more importantly, the relative crummy U-factors can be a major drag on performance.

Used windows that open (operable) will probably leak a lot more air than a new window which could be the biggest performance killer of all. Double hungs should be strongly avoided. A well sealed non-operable (fixed) window is safer but its a challenge to find them with high SHGC and low U-factors.

Thanks for all the input. There is so much information here for me. I think this has changed my course a little. Maybe even time to change the title of the thread..

I agree with all input regarding building tight. Also agreed with minimizing thermal bridging.

What I had not considered and is still a bit of a mystery, though I think I'm getting it.. Is how an underground wall can be out performed by high standards, tight, stick built wall. The biggest reason I was going from here was the fact that my last, "newer", poorly built home had a basement and it always produced mild temperatures. my house was so poorly insulated. i concluded that on the hottest of days, if I left a window open on the north side of the basement, It was better cooled than my upstairs with fancy AC running, a lot. So this gave me the need for an earth berm... Now it seems that it was poor demonstration as I'm comparing apples to oranges?? And I would be better off building my wall than pouring and earth berming my wall. Did I get this right?

My thought on the exterior walls; 2 options, contractor comfort and cost depending - SIPS or 2x6 stud with exterior rigid foam and dense packed cellulose. (Amount of exterior is unknown at this time). The DOE has a great info graphic (that I can't find at the moment) that shows this but instead of OSB, it shows rigid foam. It also shows two layers with opposite seams. This all makes since to me. The potential issue I see is contractor comfort with multiple layers of foam and potential long screws for siding (siding material still undecided). SIPS, in my research seem to speak for themselves. Any input?

Attic - Was really hoping for a conditioned attic however the following cons.. Higher cost for trusts, harder maintenance to determine roof leaks, higher cost to obtain high R value. With a non conditioned attic, I can for the a lower cost utilize blown cellulose to an absurd R value. Like 36 inches +. I can even come back and add to this myself if need/want be. This will stop thermal bridging and keep standard low cost trusts in use with standard roofing, etc. From what I understand cellulose is the best environment choice.

The floor/foundation system is the only one that is still a question.. My thought is to keep the crawl space, insulate from the inside with closed cell spray foam. Add a nice rock floor over the main area that receives the most sunshine for potential heat retention. I am still considering the radiant floor heating though that would be an after the build install. My concerns are that I will have a funny looking north wall. Will include one window on each level. Over the stove (with a pie rack ) and in a bathroom.



As I mentioned a few times, Cost, low maintenance and efficiency is really driving this home. As with others, I want best bang for my buck. Though, I actually think its possible. I think I need to get some of these sketches up and start talking pictures and details. A big concern is who is going to build it and how well they can minimize air leakage. So I want to make the best of detail drawings to include in my package.


What a change from my original point though I feel its an informed change..


I have not found a large market of air recovery units? What are some suggestions?

Great Willy, when can we start charging Its a great question as to how an above grade wall can outperform a below grade wall. I think all things being equal (ACH50, Rvalue, no fenestration, protected from H2O) an underground wall WILL outperform an above grade wall. Its exposed to a much lower delta T than the above grade wall and not subjected to direct solar gain.

Year round performance is what to keep in mind. Most of us have experienced the comfort of a below grade space on a hot summer day. Such spaces tend to hurt performance in the winter but the bigger problem is the condensation risks. When you vent through these spaces during hot humid weather you are increasing the concerns. Underground walls should have enough insulation to keep the interior surfaces above the dew point. Keeping interior humidity low is the other contributing factor.

When comparing the performance attributes of resistance to water (bulk and vapor), above grade walls have the advantages of better gravity, drainage and drying. Underground walls can be built for resistance but it typically requires more attention to detail.

Like both of your wall options. Where we used to prefer SIPS for above grade walls we have been moving to huber's zip+R product for the walls but we have low minimum insulative sheathing requirements in the south. More northern climates may need more R value than the 1" available for that product.

I agree with your thinking on the attic but I find trusses to be generally less with most average sized builds. The higher costs come when we try to achieve code minimum or better levels of Rvalue with the spray foam. Most spray foam jobs are using less than code minimum. Vented attic with cheap cellulose can perform BUT you have to pay very careful attention to sealing the ceiling plane. This means avoiding recessed cans, keeping the attic access on an exterior gable and its best to drywall and tape the ceiling before doing any interior walls. This is all on top of meticulous sealing of any penetrations and absolutely no HVAC up there other than bath, dryer or kitchen exhaust.

Kind of confused about your foundation, radiant and north wall comments. Youre right to be concerned about finding an appropriate builder. Make sure they know about blower door testing and do it prior to drywall. Find out about their previous results and use it as a basis of comparison. One of the best things about air-sealing is that its easily measured and verified!

For air recovery, try searching ERV, HRV, or Lunos. Venmar is who we typically use mainly because of the local rep's excellent customer service. You could always go the cheap Panasonic bath fan route and they may have some cheap recovery units coming out now. Ultimate Air is another product I would look into. Try to get something with an ECM motor for better energy efficiency. The two numbers to look at are the recovery efficiency % and the watt usage of the fan. For comparison the Venmar with ECM uses about 14 watts while the typical PSC motor uses about 200.