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Anyone live in a double envelope home?

 
pioneer
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Looking for someone who lives in a double envelope home. I am trying to thermally model such a home so I know what method is required to reflect reality.

We are constructing such a home next year and we are looking to figure out how much insulation will be required where, how much ventilation is required, overhang required, etc ... Lots of stuff go into one of these homes for sure.

Currently using WUFI Passive and THERM for the bulk of estimations, not looking for certification but rather just a way to accurately model choices we make to our  model. But without an actual house to compare it to it will likely be hard to model accurately.

case3ZEDWUFIMODELING.jpg
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gardener
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Location: Ladakh, Indian Himalayas at 10,500 feet, zone 5
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Well, my house isn't exactly a double envelope, but it's entirely solar heated and the whole north side is what we call the thermal buffer zone, which I think is a similar idea. I'm sorry I don't have any technical specs for you, but I can share my experience from living in it.

The kitchen, bathing room, living room, bedrooms and little study or bedroom are in the south side of the house and as such are solar heated. The northern unheated buffer zone includes corridor, storerooms, stairs, and the two-story dry composting toilet. The upstairs cold corridor also has a washing machine and a handwashing sink outside the dry compost toilet room.

My contractor used only "straw clay" for insulation above the horizontal roof beams, and didn't insulate below the beams; insulated between the heated space and the buffer zone, but didn't insulate the outer walls of the buffer zone; and used single glazing on all the windows in it. Last winter the bottom of the corridor under the stairs did just touch freezing, but the upstairs corridor was a few degrees warmer, and the sink and washing machine had no trouble. This year hopefully the buffer zone will stay warmer, because we've put up white foam insulation mat on all the windows in the buffer zone. I hope to add roof insulation between the beams next year which I hope will also keep the house warmer.

In New Hampshire I think there are local habits and requirements for insulation that will be great. If I try to suggest that much insulation in the roof here people would be shocked and think it sounds completely unreasonable. I wish I could get good northeast US type insulation. Like, a foot thick, or R50. I just wish. My climate is high desert and good 10-15 degrees south of you (10,500 feet high and 34N), so the solar gain in winter is still pretty good, and being made of rammed earth my thermal mass is good. If only I could manage a LOT more insulation I think it would be a lot warmer in winter in this house.

The 3D picture below is not exactly what finally got built. We included an 18 inch overhang over both ground floor and upstairs on the south face, and all the upstairs windows on the south face are half-trombe wall, which in the 3d drawing is only shown on the leftmost window.

I insisted on single glazing on those upstairs south windows but maybe I regret it, because the bedrooms really do get damn chilly in the winter. Down in the low 50s F on January nights last year despite the wool curtains. Maybe even 40s. I don't want homemade double glazing because it gets moisture, dust, and insects inside, but if professionally made double glazing becomes available here I think I'll replace them. The east and west windows in the southern rooms are double glazed, but I wish we'd done double glazing on the windows of the buffer zone, too.
Solar-house-Ladakh-ground-floor-plan.jpg
Ground floor of rammed earth solar heated house in Ladakh
Ground floor of rammed earth solar heated house in Ladakh
Solar-house-Ladakh-upstairs-plan.jpg
Upstairs of rammed earth solar heated house in Ladakh
Upstairs of rammed earth solar heated house in Ladakh
Solar-house-Ladakh-with-greenhouse.jpg
House heated by attached greenhouse in Ladakh
House heated by attached greenhouse in Ladakh
 
steward
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I built and lived in an envelope house in northern Utah. The inner and outer envelope walls and ceilings were insulated as if they were stand alone houses. An insulated box, inside an insulated box with an airspace between them. There was a single wall on the east and west. A solarium on the south side. A 1 foot wide envelope on the north side, and between ceilings. The entire basement was part of the envelope.

South facing windows were vertical. Made from sliding glass door replacement panels, because they were the most affordable glass. No overhang. There were a few sliding glass doors between the solarium and the inner house.

 
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You might want to check out the comments by the author/owner of thenaturalhome.com. He thinks double envelopes are a bad idea. His basic ideas are sound and have held up for years.

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

"beware of envelope home and stick-frame architecture being sold as 'green building'

When examined from an indoor air quality perspective, many sustainable home design schemes are just plain old-fashioned wrong like the envelope home concept. Stick-frame wooden envelope homes allow heated/cooled air to loop around through the structure's walls. A cavity between inner and outer exterior walls is left open to act as a giant ventilation duct drafting passive solar heated air through it. Envelope homes are an extremely bad idea for your indoor air quality since there is absolutely no effective method to clean/sterilize this open 'duct area' between the walls. Mold, mildew, and the occasional dead mouse eventually renders an envelope home the distinction of being a very bad idea indeed. Envelope homes with fiberglass batt insulation are even worse. Impossible to clean without disturbing all that itchy fiberglass dust."

The idea for a double envelope home has been around for a very long time, but few have been built. That's a strong clue, as far as I can tell. I'd add that the extra expense of the second envelope will never pay off. But I'd sure like to hear about your project if you proceed with it.
 
author & steward
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Here's one in the Philippines at http://kotaronishiki.com/. It's called a passive solar house and utilizes double walls and roof as part of the overall strategy. The homeowner seems to think it's highly effective.
 
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I "grew up" in three improved versions of solar/envelope houses, helped my lifelong architect/builder friend build and design efficient houses over many decades and have been designing the "ultimate" envelope house for the last 10 years (but not building it).

I have learned:
    - literally everybody knows for certain that your ideas won't work, and
    - almost nobody has actually "mindfully" experienced any such proposed concept-homes.

Well, now that THAT is off my chest, I have learned:
    - Thicker walls work (my father's last house had 12" thick exterior walls, double studded with 12" bat fiberglass insulation. His goal was to light a candle in the fall and heat the home all winter in our northern-tier location.)
    - Triple-glazing works, especially when combined with exterior screens/shutters for summer heat and interior cellular shades for winter cold.
    - Frank Lloyd Wright was right about overhanging eaves (my father's version 2 house had 6-8 ft overhangs blocking summer direct sun but allowing winter horizontal sun fully across the living room to the opposite wall).
    - Trombe walls work, especially when the sun hits one side and a wood stove heats the inside.
    - Thermal switches for fans controlling semi-passive cooling of root cellars with outside night air work.
    - Attic exhaust fans controlling intake of cool night air resolves the "fresh air" paradox of excessive insulation and vapor barriers.
    - Envelope structures aren't all the same; hallways or sunrooms or enclosed porches as envelopes are good, sealed and inaccessible envelopes are not. (Use Hawaiian lanais as a model.)
    - Tinted, IR/UV filtering window films are effective when used with consideration of the direction that you wish heat to travel or be reflected (and must switch directions between summer and winter).
    - Outer envelope walls with "easy" ventilation options are good (all-window walls made of sliding glass doors are ideal for some sections).
    - Completely wood framed structures, including basement walls and floors are good (this idea courtesy of a WSU wood technology professor who showed me several farm homes built entirely of wood frame construction).
    - Sub-basement plenums with heat- or cold-storing rocks and controlled by ventilation fans are good.
    - Plenums using floor joist space are better than ductwork for ventilation.
    - Maintaining day/night room temperature "steady" is better than allowing cooling at night.
    - Plastic vapor barriers between ceiling rafters and sheetrock make the screws eventually slip  and cause the sheetrock to crash down on unsuspecting people reading magazines (this tip is not related to "efficiency").
    - Experiment with an "envelope" garage or shop buildings to validate your design with your locale.
    - My theoretical two-story Great Room octagon is all-glass with a 4' wide sunroom/porch made entirely of sliding-glass doors around the entire 360 degrees circumference. A mezzanine level provides an 8' wide "eave" for shade during summers so that zero sun hits the inner room yet winter sun can penetrate far into the room. The outer envelope is effectively an open screened porch in summer and a closed heat-trap in the winter. All glass walls have cellular top-down/bottom-up shades for controllable/directional insulation for all seasons. Note: This home is on an elevated and forested river-bank, so privacy is only an issue for intruders who penetrate the wild-rose thorns and juniper "fence line". Also, a biochar-producing steel fireplace/stove is set between the inner space and the outer envelope, contributing to carbon sequestration of my forest slash piles and ambiance, as well as creating soil amendments. The food-forest only has plums and apricots so far with two tomato plants and chives. But the compost pile is ripening...  Oh, and a simple composting plastic-bucket toilet from Walmart works, using only peat moss (to convince relatives before you get rid of the septic-tank and drain field).

I'm retired military and retired IT and am bound by my legacy  of genetic environmentalism with a twist of Eagle Scout-itis thrown in. Having moved 37 times in 47 years of marriage, I'm ready to settle down...  Though my current south-facing glass-walled great room along the river bank is "tolerable" for the time being...

And that is my two cents...


 
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When I was in Afghanistan the tent housing used the double envelope structure to limit solar gain and improve the efficiency of the heat and AC, but that was government housing intended to be temporary
 
pollinator
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I considered doing this....   Only on the inside of the home.

I was thinking of putting an insulated ice fishing tent inside my home for a place to sleep / compute.      Then only heat / cool this area with my mini split...        

As I think about it.   I could go triple layer a tent inside another tent......


Love the concept   if you lower the amount of space you have to heat / cool then you can be far warmer with less energy.
 
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After much research, 33 years in the construction business, growing up in Europe , the need to build a non toxic home, and lots of courses on building, we decided to build a concrete house in Hope, Maine for our daughter.  We are using Comfort Block a Genest Concrete product made in Sanford Maine.  They are based on a German design.   The house is small, 24'x35'.  The walls are 9' high and it took three guys in their 60's three and a half days to put up the walls.  The insulation is already embedded in the block.  The electrical channels inside and outside are part of the blocks as well.  They even have weep holes in case water ever does get in there.  We used triple pane windows from Pinnacle Windows.  If you call Genest, tell them that Crystal sent you.  They have a spec house you can look at that isn't far from NH and you are welcome to come to Hope.  What I like about it too is that we used stucco on the exterior and plaster on the interior.  If you have more time than money that is the way to go.  My husband and I did it ourselves and, frankly, we think the stucco looks professional even though we are amateurs.   The plaster on the inside was more difficult but that is because our daughter wanted us to use NH 3.5 lime plaster.  It is very pretty and durable but much more time consuming and difficult to use than the products that Genest recommend.

My brothers, who are also in construction, like the double wood walls but, unless every step along the way is done perfectly, there is too much opportunity for water to get in there and get trapped.  We saw way too many 10 year old houses that were built by other contractors that were completely rotted out.  A well designed and well built concrete house will last for centuries.

Good luck!

Crystal
 
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Check out Monolithic Dome Homes at:    https://www.monolithic.org/homes
These structures start with a "?rubberized canvas?" which is inflated after which an approx. 4" layer of foam is blown on the inside of the expanded half-sphere. After that process is completed and foam is cured re-bar hangers are inserted and then re-bar fitted vertically and horizontally on about a 9-12" grid. After the re-bar is set a light-weight concrete mixture is sprayed on the inside of the foam insulation to around a 3"to 4" thick layer.

Check out the web site for a TON of information about all of the How's and Why's, however, with the weatherproof "skin" and the insulation on the outside these homes are very good at maintaining temperatures, so good that the company usually tries to dissuade people from building fireplaces because of overheating possibilities.

 
Jesse Glessner
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I took time to review the information on the Monolithic Dome site and some things are hard to find on your first Navigation through the site. SO, I have added some specific links below to get you the the HOME area and to actually see Homes that have been built.

This link offers views of various builds of Dome Home plus much general information about designs, acquisition, financing, insuring, etc. The links further down are on the page, but may not be noticed for specific OFF-GRID LIVING ideas. ENJOY!

https://www.monolithic.org/homes/home

OFF-GRID Monolithic Homes

https://www.monolithic.org/in-the-media/living-off-the-grid-in-a-dome-home
https://www.monolithic.org/homes/featured-homes/off-grid-central-alberta-monolithic-dome
https://www.monolithic.org/homes/featured-homes/a-solar-equipped-monolithic-dome-in-illinois
 
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My aunt lives in Maine in a double envelope house. the original farmhouse was box in box, the later other side (a second house) used passive thermals to warm the whole house. Only a couple of days during the coldest part of the year do they use heating for the house. I can give you more details if you contact me
 
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We bought a home 2 yrs ago which is a double envelope home which also has 3 sides in the earth.  We were worried about possible mold etc and had it thoroughly checked out.  It was clean which was great as it was built in 1984.  It sits on a bluff above a river and has a fan that brings cool air off the river at night-which circulates to keep the home cool in summer.   It works well however when we get unusual hot weather (over 100 F) in consecutive days we use ceiling fans in the house. We have no other type of cooling.  As far as heating we do have an electric forced air heater if needed and also a woodburner which we use and works excellent.   The outer walls of the envelope are poured concrete and the south facing is all glass windows.

Our entire home is electric and water is from a well.

Our electric bill is low.  On average $52 per month give or take depending on the seasonal weather.

We were not looking for this type of home but we fell in love with this river property and gorgeous views. So we decided to take a leap and buy this unusual type of home.  We have not been disappointed in our decision.
 
pollinator
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The size of the eaves to cut entry of the sun through windows is called 'solar access' in Australia.
The dimensions alter for each location.
This link is to a fabulous site which talks about designing homes and lists a variety including passive solar.
There are many pages and I have taken you to the discussion about orientation of the home.
/passive-design/orientation
 
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I’ve lived in a double envelope home since 2015 and love it. We are looking to finish off another portion of the basement which is currently linked to the solarium and outer walls of the basement. Any suggestions on insulation and heating methods? Thinking we will need to not make any additional door ways or leave a draft between the hallway, but open to suggestions there too.
 
gardener
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Brittany Dixon wrote:I’ve lived in a double envelope home since 2015 and love it. We are looking to finish off another portion of the basement which is currently linked to the solarium and outer walls of the basement. Any suggestions on insulation and heating methods? Thinking we will need to not make any additional door ways or leave a draft between the hallway, but open to suggestions there too.


Hi Brittany, congratulations on your first post  If you look at the bottom of the page, there are links to similar posts. There may be something useful there.  Looking forward to seeing how your project progresses.
Cheers
 
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I currently have an envelope home. I don't have much advice but we moved here 6 months ago and the idea that it was energy efficient is so wrong. No air circulation and its either way too hot or extremely cold. We have been trying to think of ways to do away with the envelope areas of the home to make for less unused space.
 
pollinator
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I don’t have scientific data but after building a house with a outer envelope but I agree with my friend that there are better building methods. If I had the choice to build from scratch it would not be my first choice. He lives in a earth bermed dome with the mass as a stabilizing “thermal battery”.  But his is a mild temperate climate with the earth temperature around 55 degrees. I’m not sure how it would work in colder climates. The expense and quantity of materials for a envelope house concerns me. When I built in 2003 it seemed like a endless amount of lumber and I started feeling guilty about the trees. I can’t imagine doing that construction method now in 2021. I asked my friend how much he has invested in his earth bermed cement dome house after 45 years of living in it and he said $13,500 total! That’s amazing!. The monstrosity I built was probably $100,000 in materials. And that was after spending 3 years salvaging and upcycling materials. I figured out perhaps 50% of the house was up-cycled materials.  It took too long!. Three years of pulling nails. Never again! I don’t want to know how much it cost. I just know it was a lesson in what not to do for my low budget lifestyle. But I had two ungrateful stepchildren so needed a 3 bedroom house. So what else could I do!?
 
Burton Rosenberger
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UPDATE:

Its been a while, but we did find someone who was living in a poorly designed double envelope home (aka not modern with concerns addressed) ...

I spent a good week tweaking the WUFI models to see if we could reproduce the 2 years of data we were provided. I modeled their home and then would modify the assemblies and settings till I got what matched reality. In short, WUFI isn't capable of modeling these homes. The only thing I could do to make the numbers match up was to switch to a single envelop and make the walls R90 ... this on a building with exterior R19 walls. There were many methods I tried to model it correctly but nothing worked in away where I would be confident in "selling" the results if you will.

So we took our structure, modeled it in wufi, and ran it through as a single envelope home ... came out with equivalent 2.5 coords of wood a year required to do DHW + heating. So while we are leaving space in our floor plan for a future double envelope if required we are going to go forward with a hybrid design. We did install two massive earth tubes on either side of the building along with two internal tubes (TBZ tubes) to connect them in place of a crawlspace.

In version 1, (see attachment) on the west side of the building, the earth tubes will come into the sun room and the sun room will be used for the replacement air for the home. The sunroom here is smaller than the other side of the building. I believe it was like 22x8 and will also act as an airlock into the main part of the home. On the east side the sun room is much bigger. Its an odd shape though ... 33x30 with a garage cut out of that space at 17x20. It will be a sun room as well and also hold a sonnenhaus style drain back tank to act as a thermal mass for our recycled evacuated solar tubes with wood stove backup ... it will be used for DHW and HRH ... but I suspect with the HRH we will likely be running it in a closed loop given all the sun coming into the space.

This is going to be a multi unit place so it should be interesting to see how it works out. At the end of 2021 we had the site leveled, tubes in, all underground conduit in, FPSF* modified commercial scaled footers for the steel building in, and the ICF wall placed on top said footers. Later this year we are going to do the slab and start erecting the building if we can.  

V1_Basic_Floor_Plan_Base.png
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I bought an late 70s era double envelope passive solar home last year. I’ve paid more than I bought it for since then repairing it (and I guess building to my expensive no compromise taste too lol.)

Located east of Calgary Alberta the concept was a total failure for a few reasons, not least because the prior owner carried out zero maintenance.

I worked together with a contractor that had passing experience with net zero and passive house building. He handled mostly the exterior envelope, roof, windows, doors, siding, insulation etc. the scale of the windows alone on the south facing wall made DIY and saving money impossible. Managed to salvage more than 3/4 of the 26 massive 4x8ft windows that were already there.

The design was 2 level home with lower walkout in the hillside.
Double roof, double north wall and crawl space under the interior house along with a sunroom the size of a small townhouse created the interior air space. It was continuous. The floor of the sunroom has 4ft of sand below brick floor for thermal mass.

There were vents up in the attic operated by thermostat to release heat. And in August omg was it hot. Not much roof overhang.

Then winter hit. If it was -30C outside we had a whopping heat gain to -20C inside. Working right?

There was an insane number of electric baseboard heaters in the house. 18kw worth if I recall. Bills were massive. Also the sunroom was retrofitted with a propane furnace. All this stuff was really old and barely working so the design failure was probably evident the first winter it was ever occupied.

Obvious failures:
1. Cladding and insulation was carried out to typical building standards of the late 70s: tar paper on 1/4” cladding sloppy fibreglass insulation placement in ceiling and walls and little regard for vapor barrier sealing. In fact they used vapor barrier thinner than Saran Wrap in some spots.
2. Intake Vents on north wall. Plugged with matress foam and duct tape. Nice place for mice. Oh yeah, there was many days work shovelling mouse poop out of this leaky place.
3. Bathroom vents to attic space.
4. No air sealing between inner dwelling and sunroom.
5. Plumbing penetrations in floors on lower levels sealed with: masking tape!!!

The home had been built by some rich dude and no expense spared on stone work, carpentry, siding, landscaping. Nothing that matters to energy efficiency. The previous owner did not have the financial or physical wherewithal to maintain or improve. Lucky me were turning it in to our castle.

Improvements:
1. Geothermal heating for dhw and floor heating.
2. Extending south roof overhangs to shade. There was none at the mid level of the two story window wall. 4ft hip roof added there. This summer has seen the house a lot cooler than outside.
3. Replace all windows with all the latest greatest tech in windows. So t ask me what, at the moment I spec’d it I just said shut up and take my money!!! Also reduced the size of a few windows and had the east and west sides openable to allows a breeze.
4. Also windows used exterior grade windows between the inner living space and the sunroom to get better sealing.
5. Added 2 HRV systems to the interior portion. The layout is such that say kitchen and a few beds are on the west and some beds and baths are on the east and there’s very large common areas in between both up and down. This needing two HRV not one like normal people get in a brand new home.
6. Back north wall and attic gap are filled with insulation. The above grade portion of the north wall is now R100 of glass insulation and sealed very well. We also sealed the gap from below grade to prevent air moving from the crawl space up. Insulating the crawl space is a future project since it’s a pretty ugly and expensive job to only save a few watts. Also all the old exterior vents in the ceiling and back wall are sealed up.
2. Exterior is now clad with 1.5” eps and house wrapped to kingdoms come then steel siding. Steel roof. 17kw solar on garage roof. All the rain run off is ready to be collected but that’s a future project. Between house and garage there’s a lot of surface. I’m up in the air between cistern and pond but by this time you can imagine there’s not much money left.
3. Floor heating. Man oh man I don’t even want to get in to what I did right here Every trade from electrician to plumber to framer to the guy who sold me the tile is shaking their heads. It’ll work and it’s my house lol. RELAX! It heats up and holds heat really well and nothing is exploding and falling apart.
Anyway we’re still finishing the interior. We basically blasted the budget on the geo/solar/exterior and the in floor heating.
I have a regenerative farm to get building. I’ve been here a year and still had to buy food. That wasn’t part of the ambition.
 
John C Daley
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Geothermal heating for dhw


What is dhw please? thought bubble- domestic hot water?
You have been a busy person!
The improvements are impressive and you need to be complemented for going ahead with them.
When you want to think about collecting rainwater, look at the link in my signature, you may find it helpful
 
Lindsay Jamieson
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Burton Rosenberger wrote:UPDATE:

Its been a while, but we did find someone who was living in a poorly designed double envelope home (aka not modern with concerns addressed) ...

I spent a good week tweaking the WUFI models to see if we could reproduce the 2 years of data we were provided. I modeled their home and then would modify the assemblies and settings till I got what matched reality. In short, WUFI isn't capable of modeling these homes. The only thing I could do to make the numbers match up was to switch to a single envelop and make the walls R90 ... this on a building with exterior R19 walls. There were many methods I tried to model it correctly but nothing worked in away where I would be confident in "selling" the results if you will.

So we took our structure, modeled it in wufi, and ran it through as a single envelope home ... came out with equivalent 2.5 coords of wood a year required to do DHW + heating. So while we are leaving space in our floor plan for a future double envelope if required we are going to go forward with a hybrid design. We did install two massive earth tubes on either side of the building along with two internal tubes (TBZ tubes) to connect them in place of a crawlspace.

In version 1, (see attachment) on the west side of the building, the earth tubes will come into the sun room and the sun room will be used for the replacement air for the home. The sunroom here is smaller than the other side of the building. I believe it was like 22x8 and will also act as an airlock into the main part of the home. On the east side the sun room is much bigger. Its an odd shape though ... 33x30 with a garage cut out of that space at 17x20. It will be a sun room as well and also hold a sonnenhaus style drain back tank to act as a thermal mass for our recycled evacuated solar tubes with wood stove backup ... it will be used for DHW and HRH ... but I suspect with the HRH we will likely be running it in a closed loop given all the sun coming into the space.

This is going to be a multi unit place so it should be interesting to see how it works out. At the end of 2021 we had the site leveled, tubes in, all underground conduit in, FPSF* modified commercial scaled footers for the steel building in, and the ICF wall placed on top said footers. Later this year we are going to do the slab and start erecting the building if we can.  



It’s good you can start new. See my retrofit description of a failed design.
 
Lindsay Jamieson
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John C Daley wrote:

Geothermal heating for dhw


What is dhw please? thought bubble- domestic hot water?
You have been a busy person!
The improvements are impressive and you need to be complemented for going ahead with them.
When you want to think about collecting rainwater, look at the link in my signature, you may find it helpful



Yes domestic hot water. Jargon learned on the path.
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