Heat and Humidity with Natural Buildings

Dan Chiras has been involved in natural and alternative building since 1994 and lives in an off-grid passive solar/solar electric home in the foothills of the Rockies. His house is built from straw bales, rammed earth tires, and numerous green building materials and is powered entirely by wind and solar energy. Dan is author of The Natural House: A Complete Guide to Healthy, Energy-Efficient, Environmental Homes, published by Chelsea Green; and numerous articles on natural building and sustainable design, which have appeared in Mother Earth News, Natural Home, and The Last Straw. Dan embraces a comprehensive systems approach to building that offers a wide range of benefits to people, the planet, and our economy. He will field general questions on natural building and offers consultation on project design and construction, as well as lectures and workshops on various aspects of natural and sustainable design and construction.

Questions and Answers

Q: I'm having my home built currently, and have taken steps to reduce the overall energy consumption expected (eg using LED lightings, Solar Water Heating and Solar Panel etc). As I'm from the tropical country of SINGAPORE, we experience high humidity levels all year round (RH of >70% is guaranteed). Are there any natural ways of 'De-Humidification' ?

A: I am not aware of any ways to reduce humidity levels inside a home naturally, other than preventive measures, such as reducing the number of indoor plants and cooking with lids on pots and pans. You can also eliminate internal sources by installing quiet, energy-efficient exhaust fans in bathrooms, and using them when people take baths or showers. Exhaust vents over stoves also help to reduce moisture produced when cooking food. As you probably know, using ceiling fans, which are very energy efficient, helps to keep people cool in a hot, humid climate.

Q: I am very interested in sustainable housing in the future, but am unsure of which type for my location. I live the southeastern part of Louisiana. Basically, wet, rainy, humid, hot, mildew, etc. Does straw bale homes mold/rot in wet climates? Which method would you suggest for my location/conditions?

A: (Kelly) I think the best way to stay cool in a hot, humid climate is to dig into the ground, or berm the earth up around the house and have a well insulated roof. Strawbales don't do well if they get wet, so they wouldn't be my first choice for your climate, although there are some successful strawbale houses in very wet places, like in the Northwest. For underground building, I would suggest building with a material that is basically unaffected by a damp environment, such as earthbags filled with earthen materials or using masonry materials.

Response: Digging into the ground is not going to work. We live in basically a swamp environment. That's why we bury our dead above ground. There's basically nothing but water a few feet down. I will keep into mind the earthbags & masonry materials, above earth though.

A: (Kelly) If the water table is that high, then rather than digging into the ground, simply build above ground and berm the earth around and possibly over the house. There are many ways to do this.

Q: I am dreaming of building a house with my own hands, on a nice small part of my sister's 40 acre farm in Baton Rouge, louisiana. My major problems are: Mosquitos...I want a nice outdoor living space, without a boxy screen porch look. I looked into adobe, etc. and you say almost all these materials retain, or let moisture in,it is constantly humid and rains a lot here. Third, I want to use a very small budget, say up to $10,000, and build it myself, (a little help when needed). I am a young single mom, I am fit and enjoy physical labor, I also like grappling with structural challenges, (I am studying for a degree in architecture), so do you have any suggestions for building materials, etc.?

A: (Kelly) Most natural building materials can be used in humid, rainy climates, as long as properly designed and crafted. You might like to take a look at the video I made about building our earthbag/papercrete home (available at the store), since it would give you an idea of what is entailed in this sort of building, which can be done quite cheaply.

Q: My husband and I are planning to build a home.We are not sure which would be the best material to use. We live in Uruguay. The winter months are very rainy and the average temp. is 35f and there is a lot of wind. The summer months are warm with the average temp. at 85f . Our biggest problem is the rain, most houses have a lot of humidity in the walls and ceilings and clothes get moldy. In the area we live in the ground stays wet for a while after rainfall. We would love to build an adobe or sand bag home but it doesn't seem practical for the area. Any suggestions?

A: (Kelly) I always suggest looking for building materials that are as local in origin as possible. Most methods of alternative and natural building can and are used in very damp climates; it is mostly a matter of planning the construction to deal with this issue. For instance, straw bale, adobe, cob, etc., all require roofs with large overhangs, or even wrap around porches, to keep the bulk of the moisture off the walls. Earthbags buildings, depending on what the bags are filled with, might stand up better in very wet climates. Dealing with the humidity in the air is a concern no matter what the house in made of. It might be necessary to employ some sort of dehumidifier in the house in some circumstances. In general, materials that don't tend to hold moisture would probably be the best choice, so earthbags filled with gravel for instance might work, especially if the gravel is packed well enough to be stable in the bags, and yet was loose enough to provide air spaces to provide insulation in the walls.

Q: I was wondering what the best alternative building process would be best for the area I live in in central Kentucky. I have done a lot of internet research and cannot find a technique suitable completely for this area with it's hot humid summers. Winters are not terribly bad, but I guess you could say I live in a pretty temperate area (winter and summer about equal). I have looked into strawbale, but I am concerned about the humidity. I have also looked into cob construction, but am concerned about r-factors and our wet, cloudy winters. I am definitely going to use a passive solar design. There is no information whatsoever on alternative building in the mid-eastern states. Any suggestions?

A: (Kelly) It sounds like heat and humidity are your biggest concerns, and I probably would not choose straw bales to build with either, because of moisture concerns. I feel that the best way to deal with the heat is to dig into the ground, either completely or partially, so that you can take advantage of all that cool earth to keep you comfortable. Digging in mandates working with materials that can withstand that sort of environment, so I would look at the use of earthbags, lightweight concrete, or masonry materials for the part of the structure that is actually adjacent to the earth. For the above-ground portions of the house, good insulation is the key. Cordwood would be a good choice, but other combinations of materials could also work. You want to have plenty of thermal mass on the inside, and good insulation on the outside. I am an advocate of hybrid building that uses a variety of materials in the best way.

Q: I have a couple of questions regarding Adobe, rammed earth and straw/mud construction. Here's my situation: I have a lot for a house in Lee County (Lehigh Acres), FL -Gulf Side- and I'm interested in building a Spanish style home on it. The land is un-cleared (bushes and trees) and I'm wondering how well Adobe-built homes would fare in the hurricane-prone, damp climate of southwest Florida? I'm an ex-snowboard industry guy who's had his fill of toxic materials and I find that even today's modern builders are using toxic stuff! I'd like to build my own place and the charm, earth-friendliness of the Adobe and natural construction homes really feel right Now, I'm ready for the "reality" or downside of this construction... Is this feasible in the area I am considering? I've just started my research and your site has been great!

A: Adobe might work okay in Florida, but I have some concerns to share with you. On its own, adobe will not withstand driving rains. The walls will wash away. To protect it from driving rain, you would want to design the home correctly -- that is, install adequate overhangs and pay attention to a host of other details outlined in my book, The Natural Plaster Book (Chapter 3 covers design). Further protection would be provided by applying a lime plaster finish coat rather than an earthen plaster finish coat. Lime plaster withstands driving rain very well and is very popular in wet climates!

That said, there are other concerns that you should be aware of. As you know, adobe is a high mass exterior wall. I would be leery of having that much thermal mass in the exterior walls of a house in such a hot, humid climate. Here's the reason why: As you probably know, adobe works well in hot, arid climates (deserts). The thick exterior mass walls accumulate heat (from the outside) during the day, but if the walls are thick enough, the heat cannot migrate into the interior of the house. When the sun sets in a hot, arid climate outside temperature plummets and heat accumulated in exterior walls dissipates into the atmosphere. This serves to keep the house cool all summer long.

In a hot, humid climates, however, nighttime temperatures during the cooling season (spring, summer, and fall) don't fall appreciably. Thus, heat gained by the exterior walls during the days tends to accumulate and can radiate into the interior of the house. This makes adobe a bad choice unless...you insulate the walls against external heat gain...say by building a double adobe wall with an air space between the interior and exterior courses of adobe block (something I explain in my book, The Natural House. See the chapter on adobe construction). You may want to consider other options...for example, straw bale, or straw-clay.

Q: Funny you should mention straw-bale construction; after I sent you the email regarding the Adobe question, I discovered the Straw-bale construction method and the apparent ease of building and awesome insulating characteristics! Could I be right in assuming that a straw-bale home could have the charm and appealing look of an Adobe home, but be better all around?

A: Strawbale has a lot going for it, especially the insulation. If you put an earthen plaster on it, the appearance can be similar to adobe. The walls go up fast, but after that, there is still a lot of work to finish, and the details need to be done right to avoid moisture in the walls. I suggest thoroughly learning about this method of construction before you attempt it, and Dan's book is a good start.

Q: What type of building materials and style(s)do you suggest for hot, raining, and humid climates. Mold and fungi can be a big problem in such a climate.

A: (Kelly) I have never lived in this sort of climate, so I don't have direct experience to draw on. In general though, I would say that the use of materials that are not subject to rot or harboring molds would be appropriate. These materials might include most earth-based techniques (adobe, cob, rammed earth, earthbags), bamboo, stone, etc. The use of strawbales or wood could be possible if special care is taken to keep it as dry as possible (good foundations off the ground and roofs with substantial eaves), and they are allowed to breath fully.

I would seriously look at the vernacular architecture of that locality to see what has been effective in the past. I would also consider various underground schemes, as long as drainage problems can be mitigated. Digging into the ground can buffer hot temperatures and make for a very comfortable environment.

Q and A (Kelly) We are looking to build in Auckland, New Zealand which is wet and humid and prone to earth quakes. Auckland also rains throughout the year so finding a long stretch of dry weather to build may be an issue. I love earth homes and soft curves. Rammed earth looks too flat planed for interesting design, ie you are limited to flat walls and corners. Mud bricks looks like too much work (I have helped to make thousands of bricks for a friend and wouldn't do it again). How would straw bale go in a wet climate?

Strawbale homes do fine in damp climates as long as care is taken to keep the bales dry while building, and a good raised foundation and roof overhangs are provided. It is best to use a breathable plaster on the bale walls so that they can dry out if they do get wet.

I love the flexibility of design with earth bags, but I doubt I'd find somebody to build. Also I don't know how open to new designs the Auckland council is.

Yes, earthbag building is rather new, so few builders or building departments are familiar with the technique.

Any thoughts and suggestions as to what we should be thinking about? Also I am starting from scratch but passionate about learning as much as possible.

In a rainy climate, one approach that works well is to build a timber-frame and roof structure first, so that you can work in any weather on the rest of the house. Such a frame can then be in-filled with most any other material, such as strawbales, cordwood, cob, earthbags, stones, etc. Your best choice of these materials would depend on the climate...whether you need to insulate against extremes in temperature. This approach also has the advantage that this type of construction usually satisfies the requirements of most building departments regarding the safety of the structure.

Q: We are using clay blocks and lime finish (the walls are breathable) would this dictate a particular type of heating that we can use in the buildings?

A: The heating system should not be affected by the use of lime finish but by the climate (how hot and cold it gets) and the type of wall. If you are building in a cold climate, clay brick can result in a very cold home, unless the brick walls are insulated on the inside. If you are in a hot climate, the structure can get very hot unless the walls are extremely thick or are well insulated.


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