Additional Passive Cooling Strategies for Hot Climates

Windcatchers have been employed for thousands of years to cool buildings in hot climates. The windcatcher is able to chill indoor spaces in the middle of the day in a desert to frigid temperatures.

The following list includes dozens of low tech, low cost ways to cool buildings in hot climates passively without electricity or machinery, i.e., passive cooling or natural cooling. This list is in addition to the 11 or so simple passive cooling techniques that I talked about in my video the other day. Altogether there are over 50 practical methods for cooling your home sustainably. Despite all these wonderful methods, most people – at least in North America – live in poorly insulated boxy houses with costly, wasteful air conditioners. This is one example of “ignorance is not bliss”.
– night cooling: open the windows at night to let in cooler, fresher air.
– roof vents for improved ventilation. This could include a ridge vent and cupola.
– gable vents on gable end walls
– adequately shaded clerestory windows
– smaller windows on the east and west to prevent overheating (if the walls aren’t shaded)
– louvers and vents
– well located doors
– 50-100% more or larger windows on the leeward side than the windward side to help hot air to escape
– earth berming with moist vegetation such as grass
– keeping vegetation moist around the house to help cool the breezes (the yard)
– planting trees to funnel air toward your house
– plant trees that don’t block breezes
– wing wall to direct cool breezes into the home
– building on stilts
– stack effect: multi-story designs can be very effective at encouraging natural convection
– open plan living areas that encourage air circulation
– narrow floorplans
– orientation to catch breezes more effectively
– location: breezy locations near lakes, etc.
– outdoor living areas
– porches/verandas that shade the walls
– shaded, high thermal mass walls such as earthbags, adobe, etc.
– windscoop/windcatcher (with possible addition of a water element)
– evaporative cool wall such as double terra-cotta brick walls (low fired brick) filled with moist sand
– Venturi effect
– solar chimney: chimney designed to heat air and draw air from the house
– atrium or sunroom: can act like a solar chimney if properly designed
– basement: upper floors draw cool air upwards from the basement
– cool pantry and rootcellar
– well, open air cistern or underground water canal in the basement
– earth tubes in dry climates where mold is not a problem and digging is fairly easy
– roof insulation and reflective roof insulation
– fly roof (secondary roof over the main roof)
– green roof/living roof
– soffit vents and baffles between rafters to improve roof ventilation
– light roof color that reflects sunlight
– manmade water feature such as a lily pond on the windward side
– awnings (if you don’t have large roof overhangs)
– inner courtyard/open atrium
– pergolas and trellises to shade walls
– minimize sun reflection and re-radiation from surrounding environment: plants versus gravel or pavement
– blinds: close if sunlight is entering window
– avoid skylights unless openable and tinted
– smooth plaster reflects more light than textured plaster

Note: This is just a list of practical cooling strategies. There are plenty of ‘yeah, buts’ you should be aware of to prevent problems. There isn’t time or space here to cover everything. A fair amount of research is required to learn the details so you can optimize the passive cooling design for your home and building site.

Image source: Wiki – Windcatchers (good info on windcatchers)
Good reference with more details: Passive Cooling at House-Energy.com

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Cordwood Construction on Gravel Bag Foundation

Demonstration wall showing cordwood stacked on earthbag bag foundation (click to enlarge)

Demonstration wall showing cordwood stacked on earthbag bag foundation (click to enlarge)

There are a lot of little details you can search on the Internet. This is just a basic introductory video to show you the cordwood/earthbag concept. What I like to do is have the mortar recessed slightly. It looks a little better if the wood is protruding slightly. You smooth this out. The mix is very similar — it’s basically cob. You could also call it earthen mortar.

Here is my general impression of cordwood construction. It’s extremely beautiful. It’s very practical in certain areas where you have an abundant wood supply. But it’s very labor intensive. Earthbag is several times faster. So it’s very slow. What I would recommend for most people is maybe just use it around a doorway, an entryway, because it’s very beautiful. Maybe around your fireplace, something like this, because it’s very beautiful. You can search the Internet and see some really beautiful examples of cordwood construction.

You can watch almost 100 videos at Earthbag Natural Houses YouTube channel. Each step of instruction, including how to make gravel bag foundations, is shown in detail.
Earthbag Instructable: steo-by-step earthbag building instructions

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Low Cost Products for Weatherizing Your Home

Seal gaps around doors, windows, outlets, pipe penetrations and other openings with caulk.

Weatherstripping doors and windows can reduce drafty air in your home and lower utility bills.

Door seals or door sweeps with rubber or felt seals block drafts at the bottom of doors.

“Weatherization facts:
– Low income families will realize greater comfort and additional disposable income, saving over $400 in reduced energy costs (at current prices) the first year. This equates to a 23% reduction in primary heating and cooling fuel costs.
– Taken together every $1 invested in the weatherization program returns $2.72 in energy and non-energy related benefits.
– Some of the largest returns are from the easiest projects including weatherstripping doors and windows, caulking exterior cracks and replacing door sweeps and door bottoms.
– Reducing energy demand decreases the environmental impacts of energy production.”

Source: Weatherization Facts
Image source: Green World 365
Image source: DIY Life
Image source: Soundproofing.org

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PAHS Earthbag House Near Completion

PAHS hyperadobe earthbag house by Earthen Hand Natural Building (click to enlarge)

“Earthen Hand Natural Building recently has created an 800 sf earthbag house on the Olympic Peninsula in Washington state. Passive Annual Heat Storage (PAHS) design features were used in this building, giving it the ability to heat and cool itself passively using the earth beneath the building and the walls themselves as a battery of heat. This technique has been around a long time and has produced some amazing results. This building will also incorporate a south-facing greenhouse, greywater system, and solar.

A standard rubble trench foundation with gravel-filled poly bags was used, and the mesh bags or ‘hyperadobe’ were used in the majority of the wall. We used individual bags and not continuous bag on this project. These bags are similar to onion bags and they allow the fill to squish out of the tiny holes so that the clay of one bag sticks to the others around it with considerable strength. The hyperadobe technique eliminates the need for using barb wire, and instead we added borax-soaked bamboo stakes in every bag for earthquake insurance.

PAHS design involves the addition of sloping underground sheets of plastic diverting all water away from the base of the building, which keeps the soil around and under the building dry. Because it is dry we can store the excess summertime heat in the soil to be released in winter. Two air tubes wind underneath the berm that is built around the house. The air is moved by convection and the tubes bring in cool fresh air in the summer and warm fresh air in the winter.”

PAHS Principles Explained
PAHS Earthbag House

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Underground Houses

Underground houses by Vetsch Architektur

Modern, sustainable underground home

Hebridean Earth House

“Underground living refers simply to living below the ground’s surface, whether in naturally occurring caves or in built structures.

Underground homes are an attractive alternative to traditionally built homes for some house seekers, especially those who are looking to minimize their home’s negative impact on the environment. Besides the novelty of living underground, some of the advantages of underground houses include resistance to severe weather, an exceptionally quiet living space, an unobtrusive presence in the surrounding landscape, and a nearly constant interior temperature due to the natural insulating properties of the surrounding earth. The greatest draw for most, however, is the energy efficiency and environmental friendliness of such houses. Because of the stable subsurface temperature of the Earth, heating and cooling costs are often much lower in an underground house than in a comparable above-ground house. When combined with solar design, it is possible to eliminate energy bills entirely. Initial building costs are also often exceptionally low, as underground building is largely subtractive rather than additive, and because the natural materials displaced by the construction can be recycled as building materials. However, underground living does have certain disadvantages, such as the potential for flooding, which in some cases may require special pumping systems to be installed.”

Source: Wiki
Image source: Erdhaus
Image source: Home-02
Image source: Hebridean Earth House

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Earth-sheltered Homes

Earth covered farm homes in Keldur, Iceland. These were built in 1193, and are supposedly the oldest buildings in Iceland. (click to enlarge)

Earth-sheltered home

Earth-sheltered home

“Earth sheltering is the architectural practice of using earth against building walls for external thermal mass, to reduce heat loss, and to easily maintain a steady indoor air temperature. Earth sheltering is popular in modern times among advocates of passive solar and sustainable architecture, but has been around for nearly as long as humans have been constructing their own shelter.

The expression earth-sheltering is a generic term, with the general meaning: building design in which soil plays an integral part.

Definition of earth-sheltering: A building can be described as earth-sheltered if its external envelope is in contact with a thermally significant volume of soil or substrate (where “thermally significant” means making a functional contribution to the thermal effectiveness of the building in question.)

There may be said to be three forms of earth-sheltered building:
– earth-covered
– earth-bunded [I call this earth bermed.]
– subterranean

The benefits of earth sheltering are numerous. They include: taking advantage of the earth as a thermal mass, offering extra protection from the natural elements, energy savings, providing substantial privacy, efficient use of land in urban settings, shelters have low maintenance requirements, and earth sheltering commonly takes advantage of passive solar building design.

The Earth’s mass absorbs and retains heat. Over time, this heat is released to surrounding areas, such as an earth shelter. Because of the high density of the earth, change in the earth’s temperature occurs slowly. This is known as ‘thermal lag.’ Because of this principle, the earth provides a fairly constant temperature for the underground shelters, even when the outdoor temperature undergoes great fluctuation. In most of the United States, the average temperature of the earth once below the frost line is between 55 and 57 degrees Fahrenheit (13 to 14 degrees Celsius). Frost line depths vary from region to region. In the USA frost lines can range from roughly 20 inches to more than 40 inches. Thus, at the base of a deep earth berm, the house is heated against an exterior temperature gradient of perhaps ten to fifteen degrees, instead of against a steeper temperature grade where air is on the outside of the wall instead of earth. During the summer, the temperature gradient helps to cool the house.

The reduction of air infiltration within an earth shelter can be highly profitable. Because three walls of the structure are mainly surrounded by earth, very little surface area is exposed to the outside air. This alleviates the problem of warm air escaping the house through gaps around windows and door. Furthermore, the earth walls protect against cold winter winds which might otherwise penetrate these gaps.”

Source: Wiki
Image source: Wiki
Image source: Earth-sheltered Homes (good summary of earth-sheltered homes)
Image source: Earth-sheltered Homes

From Earth-sheltered Homes by Rob Roy:
“Back in the ’70s, earth-sheltered housing enjoyed great popularity, thanks in part to the energy crisis resulting from the 1973 oil embargo. Adventurous builders and researchers explored various forms of earth-sheltered building, from underground excavated spaces to surface-level buildings with earth piled in berms against their walls. People searching for alternatives to conventional building showed that sheltering a building with earth could reduce energy costs for both heating and cooling by half or more — at little or no increased expense… An earth-bermed house can reap about 95 percent of the energy advantages of a fully underground home, and adding an earth roof, or living roof, further promotes planetary health by “greening” the house’s footprint.”
Read the full article at Mother Earth News

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It Can’t Possibly Be Worth It

Rob Roy’s earth-sheltered cordwood home

“More than a third of the average American’s after-tax income is devoted to shelter, usually rent or mortgage payments. If a person works from age 20 to age 65, it can be fairly argued that he or she has put in 15 years (20 in California) just to keep a roof over their head. With a piece of land, six months’ work, and — say — $35,000, he (or she) and his family could have built his own home.

To save 14½ years of work, you cannot afford not to build, even if it means losing a job while you do it. Granted, the land (and the $35,000) has to come from somewhere, but this amount is no more (and probably no less) than the down payment on a mortgaged contractor-built home, and about half the cost of a new double-wide mobile home (figuring either option as being about the same square footage as an earth-sheltered home).

So… why don’t more people do it? Is it really worth giving up 15+ years of your life (and I’d say for many people, more) to pay off the house you live in just to save yourself the effort of having to do it yourself? Surely it can’t be that a life of 9-to-5 indentured servitude is so wonderful that one can’t give up a summer or three building a house like the one above, which I believe came in at about $20,000… And with an increasing percentage of people defaulting on their mortgages and losing all of those years, even on a risk management level it seems completely nonsensical.”

Source: I Need More Life

“An earth-sheltered, earth-roofed home has the least impact upon the land of all housing styles, leaving almost zero footprint on the planet.

Earth-Sheltered Houses is a practical guide for those who want to build their own underground home at moderate cost. It describes the benefits of sheltering a home with earth, including the added comfort and energy efficiency from the moderating influence of the earth on the home’s temperature (keeping it warm in the winter and cool in the summer), along with the benefits of low maintenance and the protection against fire, sound, earthquake, and storm afforded by the earth. Extra benefits from adding an earth or other living roof option include greater longevity of the roof substrate, fine aesthetics, and environmental harmony.”
Earth-Sheltered Houses by Rob Roy

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Withyfield Cottage and the Woodsman’s Cottage

Withyfield Cottage by Ben Law

Withyfield Cottage interior by Ben Law

More work by Ben Law. His ideas are spreading throughout the region. The video below shows his finished home before he built the addition.

“Beautiful, sustainable, luxury holiday accommodation. Located on a working dairy farm on the edge of the South Downs National Park, this unique roundwood timber, straw bale and cedar shingle holiday cottage is the perfect spot to escape and unwind.
Inspired and built by Ben Law and his team (as seen on Channel 4’s Grand Designs) the cottage is a testament to contemporary green building practice. Supremely comfortable, beautifully furnished and well equipped yet made by local craftsmen using local materials.”

Source: Withyfield Cottage

The Woodsman’s Cottage

“This video from Grand Designs on British TV was voted the most popular show ever by viewers, and apparently Kevin McCloud’s favorite also. Ben Law’s house has been described as possibly the most sustainable house anywhere. It’s built almost entirely with reject wood culled from the local forest: bowed or leaning trees for the crucks, wavy slab wood siding from milling lumber, and coppicing. All this left over ‘waste wood’ from standard log milling operations is typically burned or left to rot. Ben stacked straw bales around the outside of the timber frame for superinsulation.”

Ben Law Woodsman
Woodland House book
Previous blog post: Ben Law’s Woodland Home
Cruck Frame Houses

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Zero Energy Earth Home in Texas?

Kelly and Owen,
I’d like to thank you for all of the wonderful information you have offered for free to the world! I’ve been following along for about a year now and it just keeps getting better and better.

I have a question about insulation and thermal mass. I live in Austin Texas and our summer nights are a lot of times only 20 degrees cooler than the day time high. Which that day time high can get to over 110F. If I build with only earth/adobe filled bags, I don’t think that the house would be very comfortable during the summer months. I’m planning on rebuilding a small dilapidated shed in about a year using the hyperadobe method. The shed will have plumbing and electrical. Basically I’m going to build it just like I would build a house for our family to live in full time. This is going to be a proof of concept to show my lovely wife that it’s not a bad idea and that a house built in this fashion can look professional.

So my question is, how would you go about insulating a building built with the hyperadobe method, or would you build using a different method?

Thank you for any information!
Mike

Hi Michael,
I just looked up what the year-round underground temperature is in Austin, TX, and noticed that it is 71 degrees F. You couldn’t ask for a nicer temperature to live in! A substantially bermed or underground home in that locality could easily become a zero energy home, as far as heating and cooling goes.

You are right that a solid adobe-walled home there would be too hot in the summer for sure. Yes, it can be insulated, either with exterior insulation, or by filling the bags with an insulating material, and this would help keep the interior more comfortable…but you are still going to need air conditioning most likely.

If it were me, I’d go underground!
Kelly

[Owen: This can include building above grade with earth berming/earth sheltering to reduce the risk of flooding.]

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Straw/Clay Mixer

Straw/Clay Mixer

“Rather than laboriously tossing clay slip with straw by hand to make light clay straw for finishing the stuffing of the bale walls, we used this mixer to speed up the process. We could mix large batches of light clay straw in a short amount of time as well as maintain a consistent amount of clay and moisture on the straw.
Two people load the mixer at one end with straw and clay slip. The clay slip gets mixed beforehand in buckets. It is a combination of water and either bagged clay or soil with a certain clay content.
The long barrel of the mixer is sloped downwards away from the end that gets loaded, and the straw and clay slip are tossed together as they move down the length of the mixer.”

Source: TRC Timberworks & Natural Homes

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