New off-grid home build -- passive cooling & materials

A couple of people asked for more specifics on a new build 1100sq off-grid house in the Ozarks. I designed the house and spec'd all the materials however a builder is doing all the construction. I will see it for the first time when I move in August

The style and functionality basically mirrors a 1930s Arkansas farmhouse designed to be heated/cooled without any power whatsoever. The floorplan is designed for one adult and a couple of large dogs plus the occasional guest. Instead of modern farmhouse I am going for haunted farmhouse and since there was a dilapidated 1930s farmhouse on the 30 acre property I was able to have the old doors, windows and hardware salvaged to give the new house an authentic old-house vibe.

It has a 6kW Victron solar system with 15Kw battery (not grid tied). There will be a 400 gallon rain water storage system though it is on city water (drilling a well was not practical in that region). There is also a 500 gal propane tank.

For cooling in 100+ degree summers the house has:
-- 8' overhang porch on the south side
-- 9' ceilings
-- Windows/doors aligned to allow a direct path of air north/south and east/west
-- Working louvered shutters on the east/west to block morning/evening sun
-- Closed floorplan kitchen to allow cooking/baking/canning without heating up the whole house
-- Operational transoms above all family room doors for airflow when doors are closed
-- Whole house fan in family room for rapid air changes in the morning/evening
-- Insulated ceiling with a walk-in attic

For heating in winters that can dip below zero:
-- Closed floorplan to focus heat in the main living space (family room and bedroom)
-- 2x6 exterior walls with mineral wool insulation
-- Direct vent propane heaters in family room and bedroom
-- Jotul F 602 V2 wood stove with cooktop in family room
-- Interior glass storm windows (for 90 yr old restored windows)
-- Glass storm/security doors to protect/insulate old Craftsman exterior doors
-- PEX pipes to prevent bursting in cold weather (this was the builder's idea)
-- Slab foundation with 1/4th inch foam and plywood underlayment to warm/soften vinyl sheet flooring. Would have preferred hardwood but vinyl was more practical.
-- Off-grid propane range (Kodiak), on demand propane water heater, propane dryer etc...

Since there is no HVAC system interior humidity levels will be high at times from open windows, showers, cooking etc... so selecting materials that allow the moisture to escape from inside the wall cavities was very important. I had done prior research on insulating 100 year old houses and sadly many old houses have been lost after being "upgraded" with modern insulation leading to rapid mold and rot. I ended up selecting all pre-1930 building materials since they have stood the test of time for 100+ years. Avoid house wrap and spray foam insulation! Materials for house included:

-- Sheet rock on the interior
-- Mineral wool insulation (dries out quickly, fire proof)
-- Plywood (dries faster than OSB)
-- Roofing Felt/Tar Paper sheathing, non-synthetic (no vapor barrier/wrap, seams are not taped)
-- A rain screen (thin furring strips to create an air gap between the sheathing and the siding)
-- Pine board and batten siding
-- I did go with fiberglass insulation above the ceiling along with modern roofing materials since water cannot get trapped in the attic.

If folks use a builder I would strongly suggest having phase inspections done by a third party inspector. It costs very little, provides piece of mind, and can save you a fortune later. Plus since I am a female with zero building experience if there was a problem it wouldn't just be me and my "layman's opinion" telling the builder how to do his job, it would be on the advice of a seasoned professional. Building can be stressful even when things go well; avoid petty ego battles and change orders.

Looking good. Watching. We are non grid and looking to improve cooling for our summer cottage.

So not even a mini split for summer cooling and dehumidification? Why?

For the deep deep south [Houston] dehumidification is key both for general comfort and prevention of mold growth. If you can limit air leakage, then bring in fresh air through an exchanger with chiller, you should be able to control the humidity using minimal power.

What is the ground temperature? My preference would be an earth berm or underground structure. Would work best in extreme climates like Dallas that get really hot and cold. Use the earth for thermal mass, then insulate a couple of feet down.

Love it! I too suggest a mini split as a nice option for summer heat. You don’t have to use it.

I will need to look into your methods of insulating as I am considering foam between studs and exterior sheathing etc.

I am definitely bookmarking this. Please update progress and when it’s done!

1201 said:

So not even a mini split for summer cooling and dehumidification? Why?

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I live in middle Georgia now and have not used A/C for 5 years. People think they need it because they use it constantly and are not acclimated to the hotter temps. Though grant it if the temp drops below 70 I am reaching for a sweater.

I did get a portable a/c unit for the new house mainly because I have 14 year old dogs and worry excessive heat triggering heart problems though the new house is much better insulated, has shutters and a whole house fan so it should be MUCH cooler than the house I am in now.

Nan_wpg said:

Looking good. Watching. We are non grid and looking to improve cooling for our summer cottage.

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A whole house fan and shading the windows would probably give you the most bang for your buck. The ventilation in my current house isn't that great, even with fans running all night the interior is warmer than the outside night time air. A whole house fan will do a complete air change in 3-5 minutes which makes a huge difference.

Delmar said:

For the deep deep south [Houston] dehumidification is key both for general comfort and prevention of mold growth. If you can limit air leakage, then bring in fresh air through an exchanger with chiller, you should be able to control the humidity using minimal power.

What is the ground temperature? My preference would be an earth berm or underground structure. Would work best in extreme climates like Dallas that get really hot and cold. Use the earth for thermal mass, then insulate a couple of feet down.

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That is all true and I did look into earth berm houses years ago. It is a neat concept but likely would have been cost-prohibitive and a bit too risky/experimental for me. Prior to 1960 all houses were designed without HVAC systems and those houses didn't develop mold problems even in Houston.

I am a prepper so it is all about redundancy, if a system fails I want a sustainable plan B that doesn't require outside expertise or equipment.

Hopefully this isn’t too “all over the place”:

Your 8’ overhang - south wall is for sun blocking? Are there louvered shutters on the south windows? Or just E/W?

Your N wall has a 4’ overhang…. Are the N and S walls rainscreened? Or just the E/W walls with no overhang.

When you say whole house fan is that the fan in the middle of the ceiling (big fan) that pulls the air from the home and into,the attic to,exhaust (and consequently pulling in cooler air from the outside?)

@Nan_wpg Yes the 8' overhang on the south side is to block the sun. Shutters on the east/west are to block the morning and evening sun though I put them on all the windows for privacy and because they look nice. You can also use awnings or even heavy curtains to block the sun coming in windows.

All four sides of the house have a rain-screen. Even though rain only hits the east/west sides indoor humidity may cause moisture to build up in the north/south walls and the rain screen helps with that. It also helps to prevent the pine siding from rot. How old is your cottage? If it is pre-1960 it probably has similar features already.

I went with an attic fan (QuietCool 3081 Energy Saver which uses 285 watts on high and 80 watts on low). You can run the fan on high for 10-15 minutes to flush out the hot air or run it on low for hours to create a breeze. If you have a modern sealed structure (with house wrap etc...) then it can raise the indoor humidity which can be problematic though opening a window does the same thing. Some styles allow venting through an exterior wall if the attic is not practical.

I made a video on passive cooling methods few years ago and you may find it helpful. Many people have features like double hung windows designed for passive cooling in their homes now but they never learned how to use them.

S610 said:

Prior to 1960 all houses were designed without HVAC systems and those houses didn't develop mold problems even in Houston.

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However homes of that era had little to no insulation and the walls were vented well. Once you start sealing the envelop you also seal in the moisture.

Delmar said:

However homes of that era had little to no insulation and the walls were vented well. Once you start sealing the envelop you also seal in the moisture.

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Yes exactly. That is why the envelope isn't sealed. It is plywood with tar paper layered over it. The seams are not taped and there is no vapor barrier so hopefully there will be sufficient air flow. The walls are insulated but with mineral wool which is stiff and won't compress or hold onto moisture.

Worse case scenario, I might have to drill some weep holes through the plywood to allow more ventilation from the outside. After reading your post I realized it would be pretty easy to drill a couple of discrete holes in the sheet rock to check the humidity in wall cavities once in a while.

What a great thread. Would love a video tour of the place and specifically the power room and the solar panels.

I like your style. Nice place.

What is the seasonal weather like there?

In my area we have mostly cool cloudy wet months starting late October through marck/april. High 20s to low 40s at night November through feb/march. June to august is dry and 70s-100 degree highs.

S610 said:

@Nan_wpg Yes the 8' overhang on the south side is to block the sun. Shutters on the east/west are to block the morning and evening sun though I put them on all the windows for privacy and because they look nice. You can also use awnings or even heavy curtains to block the sun coming in windows.

All four sides of the house have a rain-screen. Even though rain only hits the east/west sides indoor humidity may cause moisture to build up in the north/south walls and the rain screen helps with that. It also helps to prevent the pine siding from rot. How old is your cottage? If it is pre-1960 it probably has similar features already.

I went with an attic fan (QuietCool 3081 Energy Saver which uses 285 watts on high and 80 watts on low). You can run the fan on high for 10-15 minutes to flush out the hot air or run it on low for hours to create a breeze. If you have a modern sealed structure (with house wrap etc...) then it can raise the indoor humidity which can be problematic though opening a window does the same thing. Some styles allow venting through an exterior wall if the attic is not practical.

I made a video on passive cooling methods few years ago and you may find it helpful. Many people have features like double hung windows designed for passive cooling in their homes now but they never learned how to use them.

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Interesting video. We are likely replacing windows in our cabin. Double hung makes sense.

Our cabin was rebuilt in 1984. 2 x 4 construction, pink insulation. Vapor barber on the inside, and “sheathing” is ranchwall (what Americans call t100 or something like that).

Wood stove for heat. No awnings.

At my house we put screens on the outside of our windows to block the sun before it hits the glass. It’s made a difference.

Did you consider a cold roof? Same concept as a rain screen. It’s another roof deck with air space allowing air flow to disapate heat.

As for your attic fan do you leave all the windows open or do you open the window where you want “the breeze”? I’d imagine if all the windows were open you’d just have less breeze in each window, but regardless a cooler home.

Does the fan exhaust into the attic, or “through” the attic and directly outside?

RyGuy said:

What is the seasonal weather like there?

In my area we have mostly cool cloudy wet months starting late October through marck/april. High 20s to low 40s at night November through feb/march. June to august is dry and 70s-100 degree highs.

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Hot summers (humid and sometimes 100+ degrees) and cold winters. In most of the South we don't really have spring, it goes from freezing at night to 85 degree days very quickly. It only snows once every year or two but I am also from the West Coast originally and have never lived in cold weather. Fortunately the builders are originally from Michigan so they know how to build for the cold.

Nan_wpg said:

Did you consider a cold roof? Same concept as a rain screen. It’s another roof deck with air space allowing air flow to disapate heat.

As for your attic fan do you leave all the windows open or do you open the window where you want “the breeze”? I’d imagine if all the windows were open you’d just have less breeze in each window, but regardless a cooler home.

Does the fan exhaust into the attic, or “through” the attic and directly outside?

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I have never heard of a "cold roof" though the house has a full well ventilated attic and the floor of the attic is insulated so it will buffer the roof heat from the house.

The attic fan vents directly into the attic space (which has soffet vents and ridge vents to provide plenty of escape routes for the hot air). You can see it in the pic below, the fan is the green part which makes it quieter since it is a few feet from the ceiling vent.

You typically open a couple of windows run the fan whenever it is cooler outside than inside; you always have to have some cracked/open windows when running else it will wear out the fan and definitely don't turn it on accidentally when you are burning your wood stove. Usually folks run it at dusk/night or early morning to cool things off as much as possible including the walls then you seal up the house (close all the windows) to keep the cool air inside for most of the day. When the house gets stuffy in the late afternoon you can open a couple of windows on the north side and run it again.

Attic fans were very popular in the 50's and 60's and they work well, they went out of style when air conditioning became common. Using window screens that filter dust/pollen is a good idea to prevent it from being sucked inside.

There are DOE “Cool Roof” certified paints that have published reflectivity and emissivity ratings.

Note the Henry products that are generally available to normal people at Home Depot perform pretty well.

I’ve put the elastomeric paint (not the silicone) on several roofs and shipping containers. It’s been doing well for over 20 years. Goes on easy.

https://downloads.energystar.gov/bi/qplist/roofs_prod_list.pdf

The Henry stuff doesn’t stay brilliant white. If that color bothers you. It gets dirty and blends better though a little less efficient.

Bluedog225 said:

There are DOE “Cool Roof” certified paints that have published reflectivity and emissivity ratings.

Note the Henry products that are generally available to normal people at Home Depot perform pretty well.

I’ve put the elastomeric paint (not the silicone) on several roofs and shipping containers. It’s been doing well for over 20 years. Goes on easy.

https://downloads.energystar.gov/bi/qplist/roofs_prod_list.pdf

The Henry stuff doesn’t stay brilliant white. If that color bothers you. It gets dirty and blends better though a little less efficient.

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Wonder if it helps reflect light for roof mounted solar panels too? I went with a plain galvanized colored roof thinking it would reflect some light/heat.

I will keep that roof paint in mind!

Plain galvanized or galvalume emisivity and reflectivity values are published. They are not bad. Esp. If you clean once in a while. Much better than a dark roof.

They may be on that big pdf but I can’t search it on the iPad. Maybe compare “ash gray”.

White would help with roof mounted biracial. But you have to have them raised quite a bit.

Bluedog225 said:

Plain galvanized or galvalume emisivity and reflectivity values are published. They are not bad. Esp. If you clean once in a while. Much better than a dark roof.

They may be on that big pdf but I can’t search it on the iPad. Maybe compare “ash gray”.

White would help with roof mounted biracial. But you have to have them raised quite a bit.

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I debated whether I should have gone with a dark roof so it blends into the woods better. Glad to know the lighter roof was a good choice.

Though no one, even the neighbors, seem to know it is there so I guess it is camouflaged pretty well.

It is far too late to make any changes to this project so I will be interested to see how it comes out.
First off, has an angle calculation been made for the south overhang for passive solar heating in the winter? In the high summer with sun angle at around 29 degrees in your location you would want the entire south wall shaded to the bottom, but in winter with a sun angle closer to 44 degrees you can allow the sun to warm that wall and even the interior through the windows IF the overhang height and length are strictly controlled.
I can appreciate the use of period doors and windows for aesthetics but if the glass, at least, isn't updated you are going to have horrible thermal transfer.
A lot of old houses from this time period were built with lathe and plaster interior. The better built ones had a brick exterior. Even though there is no insulation in the walls, there is significant thermal mass to even out temperature changes in a structure without having forced air ventilation. The "thermos bottle" design with a largely sealed environment, timber frame, clapboard (and later siding) exterior, drywall interior, and insulation largely came about after WW2 in an effort to reduce building costs for a country that had a high demand for single family dwellings. This design was only viable because electricity was available to drive forced air ventilation. There is an interesting back story there, but the point I am getting to is that with modern knowledge it appears you have chosen a combination of some of the worst materials choices from both time periods. I'm not trying to be mean, I'm trying to share knowledge.
I believe the true road to comfortable off grid living is a design that reduces necessary energy inputs to the minimum possible while still staying comfortably livable. Those designs exist, they have been experimented with for decades now, and are fairly known quantities. The keywords you want to research will be: thermal mass, passive solar, earthship.
Please see the following video about compressed earth block structures, but keep in mind this applies to multiple methods of using natural material thermal mass building. It is a long video but if you are interested in efficient structure design it is worth your time.
The video includes references to research done by professors of engineering and architecture at both University of Texas and University of Oklahoma, if you want to dig deeper.
I applaud heartily your advice about getting N3P (neutral third party) inspections done. You can save around 20% acting as your own general contractor BUT if you aren't an expert in all phases and types of construction being used then it is wise to spend some of those savings on experts to come in and note the corners that are being cut ESPECIALLY on rural property that may not have a formal permitting and inspection process.

What a pointless and long winded post.

Op, you did good.

I guess someone didn't read the original post very well. Especially the part about "Interior glass storm windows."

@Snaketzu I am really glad you weren't trying to be mean! And yes, I realize there will be virtually no passive heating. I had read about the ideal overhang height/length based on the windows for passive heating and decided I wanted a decent sized covered back porch more (plus the old windows are too small to capture much).

Most southern farmhouses had wood construction, not brick. The overall layout is based on the classic "center hallway" Southern farmhouse design. The old windows were reglazed and retain as much of the original wavy glass as possible. Tempered glass interior storm windows will be used in the winter to add an air pocket and stop leakage. Likewise the old doors, which also have a lot of glass will be protected by a glass storm/security doors.

I want to capture the look and feel of an early 20th century Southern vernacular farmhouse NOT a 1970s earth berm hippy house or a hideously modern house with lots of glass to optimize passive heating.