Uninsulated Thermal Mass Walls in a Hot Climate

I recently got this email from Steven Green:

“I built a 10 meter earthbag roundhouse with the open air patio in Chaing Rai, Thailand. I bought the plans from Owen Geiger. In the cold season it is OK, a bit stuffy but warmer than outside. But now I’m suffering in the hot season. In the day it reached 100 degrees but it is cooler at night… but unfortunately I’m not able to enjoy this coolness because the house stores all the heat of the day.

I got a sheet metal overhang on the first level and a sheet metal roof on the patio, and the walls are rendered with lime stone plaster. However we poured concrete for the roof/ceiling so I guess that was the mistake. I tried a ceiling vent and a wall vent… nothing but hot air blowing around. I have louvered windows above each door and window… don’t seem to do anything at all.

I’m a bit depressed… all this work at a big cost (much more than anticipated) in the land of smiles… to be suffocated in my own house at night and day when I close the windows. Right now it’s 5 am and the air is cool and fresh, but I have to go outside to enjoy it, so I’m still homeless even with a home. Do I really have to buy an aircon unit to survive here? That would defeat the whole purpose of the earthbags, right? Any useful ideas?”So I answered, “What you describe is the classic result of building a solid thermal mass building in a climate with temperatures that get too hot too much of the time. The only real way to fix this is to insulate the house on the outside somehow. Then it will be the most comfortable house in your neighborhood. I live in a old adobe house that I insulated on the outside and now it is extremely comfortable all year round. I’m not sure what is available in Thailand to do this, but it would be the best solution to your predicament.”

Steven responded, “It sounds like a good idea, but I have 3 doors and 7 windows; shall I just insulate around the doors and windows? OK, I guess the overhang that keeps the walls shady all day is a no go because the heat creeps up underneath them. 109 F. real feel today. What can I put in the bags if I build another wall outside the existing one?”

Then I wrote: “Yes, it is mainly the bag walls that need to be insulated; insulating the doors and windows to some extent could also help.”

“I just looked up the average annual temperature in Bangkok and it is 85 degrees F., so your walls have probably settled to about that temperature, or perhaps warmer in the warm season. Since it cools down during the night, you can open the windows to ventilate the house at night and close it up during the heat of the day, and that might help. Otherwise, your only other recourse would be air conditioning to cool the space down. If you resort to this, at least the insulated thermal mass walls will make it much more efficient, because they will hold the cooler temperature.”

“There are some ways to passively cool a living space through the use of passing air over pools of water, but this only works in fairly arid climates and I expect that Thailand is too humid for evaporative cooling to be very effective.””Possible Insulating earthbag fill materials include rice hulls, lightweight volcanic stone, shredded styrofoam, and perlite.”

Steven responded: “It’s brutal here.100 degrees really feels like 109 degrees, with no air movement…  very very humid. And to make matters worse, they burn plastic and leaves roadsides, mountainsides, and more. I am in the house right now, I had to leave my bedroom and move the mattress to other side of house. All doors are open and all windows are open, all louvered windows above each door and window are open.  I have 4-5  fans running now and nothing helps at all… it is so hot here.  And let me tell you if I walk outside it’s a lot cooler than it is inside my earthbag house. Any more ideas?So I wrote, “I still think that what I outlined earlier is your best bet, although it could take months for the mass walls to cool down much. Your house looks beautiful, by the way.”

If anybody else has any advice for Steven, he might appreciate it.

20 thoughts on “Uninsulated Thermal Mass Walls in a Hot Climate”

  1. How about switching the roof to clay tiles, in a light colour if available. I suspect it’s the sheet metal roof. It is horrible for the kind of temps we get here. I hope you resolve the overheating issues with your home, because it really is lovely.

  2. Hello Steve, did you manage to solve the over heating problem in your home? I do not have a solution but I am planning on building a house of similar design in Jamaica but I am worried about the overheating problems you have raised.

    • No not yet. But Im working on it! Using wood, I built an overhang in the front of the house covering the concrete slab however low on money this year because my flight was cancelled on 1 April and lost 7 months of work on Marthas vineyard…..So no roof as of yet. But will use local bamboo and split it in half and use it as roofing material maybe shingles or long stalks cut in half overlapping to direct the rain. But I have to wait for the end of the dry season so I don’t have to cure all the bamboo with chemicals against bugs. Now it’s the end of the rainy season ; bugs eat bamboo during this time.
      I posted my problem during the burning season here..which I was locked down in during covid. Weather’s a bit better now.
      I’m sure that covering the concrete slab and painting the roof a lighter color will help tremendously.
      Now we are approaching the cooler season and for a month or two the rainy season has rendered a better quality of life and air levels are 23 instead of 150 -375..,yikes.
      The burning season was a horrible first time experience for me. Even now if I get my neighbors to recycle
      and stop burning plastic I will be styling, but that will take some doing.

      Using earthbag will make the house strong, materials are cheaper rv value not the greatest, but I’m planning maybe to cover the outside with some form of insulation maybe like 5 inch cut logs and branches that will give it an extra protection against the sun

      For now I open windows at night allow cool air to pass in .

      Believe me in the daytime after closing windows against sun and heat in the late morning the house is so much cooler inside. So ya, earthbag are worth doing, you just have to find ways to block the sun…

      Best wishes and best of luck.Steven

  3. I want to echo all the great comments which include:

    – Shade over the house
    – Insulation (especially of the roof)
    – Use of rice husks instead of earth in earthbag construction can improve the situation dramatically

    Also, some of this can be done mathematically in advace. Start with the the comfort envelope and then calculate based on actual climate. I suggest doing this for both highs and lows, and then choose which do you prefer in terms of discomfort (would you rather be too hot or too cold?).


    For places like Chiang Rai which can be very hot, having an uninsulated earthbag construction, even if the sun is kept off of the entire structure (and roof), is not viable. If it gets up to 35c in the day and 25c at night, then the thermal mass temperature will be around 30c (this varies of course based on weather conditions and length of daylight). 30c is not so comfortable unless the relative humidity is 10% or less.

    Add to this direct sunlight (especially on a dark-colored roof, without insulation) and it will never be comfortable. Even with an insulated roof, or complete shade from the sun, it is still not very viable.

    The other factor is that in places like Chiang Rai, many months of the year the air polution is quite bad with high AQI, therefore the ability to use fans and ventillation for cooling is constrained.

    In this case, one needs to be able to close one’s windows and doors in order to run air purifiers and have any effect on lowering the AQI.

    Therefore a highly insulated house is really the only choice available, or the mandatory use of air conditioners to keep the place cool).

    Even the largest cob building (Dingle Dell) is wrapped in polystyrene for insulation purposes — see starting at 29 minutes: https://www.dailymotion.com/video/x6eue6e

    Once a building gets insulated to that degree, it needs an HRV/ERV system (also shown in the Dingle Dell video starting at 31 minutes, linked above).

  4. Your house is beautiful – and I agree with the already-posted comments. In addition, would it change the appearance too much (or help at all) to add louvered shutters for the open 2nd level – maybe with lightweight insulation in the shutters? Maybe the shutters could have Thai carving on them? I really like the idea of a living roof – maybe with succulents (i don’t know if those are available in Thailand) – and more plants around – maybe with a small recycling water feature? Such a pretty house, though! I miss Owen Geiger – but so glad that Kelly Hart is continuing the website/blog.

  5. Previous comments have really good ideas. Plus, consider berming part of the walls with earth. Run a humidifier 24/7. Lighten the color of the roof and add vegetation along the walls. Any combination of these remedies should make a difference. Good Luck!

  6. Hello Steve. I had a very similar problem here in the philippines until last week. Basically, it’s the same here as the Thai climate. This is how I solved the problem. It starts with keeping the sun off your house and the hot winds out of your house. First, let’s deal with the sun.

    1. Extra shading. Plant lots of bamboo or other stuff to block the sun from hitting all parts of your house.

    2. I see i your photo you have lovely roof, shading / awnings. Paint it all white with solar reflective paint. Home Pro and all good stores in Thailand should stock it. If they don’t stock it buy Boysen or Davies water-based elastomeric paint. ‘Rain Shine ROS 100′ is very good too… again water-based Paint the entire house white. It will make a massive difference… and it’ll remind you of a wedding cake! Sorted!


    3. If you have concrete pathways or anything else near the house similar to concrete consider the likelihood of thermal gain and radiant heat being carried by winds from the material and straight into your house. Cover them with turf, or remove them entirely or place shades over them. Sail shades, i’d personally recommend. Even makeshift with tarpaulin as a temporary measure will be good enough until you get the real thing… but strong winds will be a constant battle for tarpaulin. Perhaps use multiple layers of tightly knitted netting like you sometimes see used in supermarket car parks to shade customers’ vehicles.

    4. Buy a load of caulking sealer to close all gaps in windows and doors to keep out the hot air during the day. I realise you have louvre windows too – keep them closed during the day and fully open during the night. Consider purchasing double or triple glazed windows too.

    5. During the worst summer months, hose the place down to reduce thermal gain. No joke. It’s not a long term sustainable solution but I did it 3 times a day during the 47 degrees heat we had here a few weeks ago. Extreme measures, yes, but it worked.

    All of the above will make a positive difference. Guaranteed!

    • Thank You for your advice,I’m very happy to get some feedback. Internet was out for 3 days here; but now I realize that the concrete slab in front of the home is a bad idea but after you mentioned it ,I decided to turn it into an above ground pool for exercise and against the sun reflecting.
      The outdoor upstairs patio is a mind boggler,
      As to what material to enclose it in..concrete will make it an oven bamboo won’t last , metal is an idea a gambion rock wall another..I also agree with the roof paint ,. The supplier told me brown was a cool color maybe took it wrong and used it but it is hot.

  7. I live in a building made of bags of rice husks (hulls) covered with an earth plaster in Chiang Dao, northern Thailand.. my neighbour lives in an adobe building. These buildings breathe and have to be managed. We close our buildings in the early morning when it is cool and by the time the afternoon sun hits, just one speed of fan in my room and it is super comfortable. In the early evening we open up to let the cool breezes come into the rooms, and at night I again just use minimum speed on my fan and usually use a thin blanket… I would be happy to share info and experience with Steven! BTW I am selling up here and planning to build nearby with some new ideas that I hope will make my house even cooler!

  8. Sorry to hear about your troubles. Perhaps get rid of the concrete roof slab (heat sink) and install a living roof? I think you have enough rain there to keep it going? On really hot days any excess water in the roof should evaporate and take the heat away with it….not an expert, but I did install a living sedum roof on my earth bag roundhouse, plus 15 cms of rockwell insulation. This is the UK, so a very different climate to yours, but it keeps it pretty well insulated against extremes of heat and cold in my temperate climate.

    Wishing you the best…don’t give up!

  9. I was considering building the same exact home and model that you built, including a concrete top floor. Here in the Philippines it is just about as hot and humid as in Thailand. The temperature of my well water is a constant 82 degrees.

    My current home that I rent is made of concrete block which is the most common building material here. Concrete homes too are hot, but I managed to cool the home down by keeping the walls shaded by growing trellised vines such as grapes and bougainvilleas. Also I planted some moringa and ipil-ipil trees that are fast growing to shade parts of the roof. This shade has made a considerable difference in making this home more tolerable.

    The reason for my choice of a round earth bag home is it’s stability and strength in earthquakes and typhoons. I’d consider having a double roof and be sure it is white, that too may help keep things cooler. Perlite is cheap and readily available here. I could get it delivered custom pre-bagged.

    Have you considered sleeping on the second floor, though you’d need mosquito netting, do you think that would be any cooler? Perhaps have a 10 foot overhang and make it a double duty porch around the house?

    Does the opening on the roof help with heat dissipation?

    Thank you for posting your experience, you just saved me a ton of money and tears for a hot home that I probably could not sell if I needed to leave.

  10. In warm climates, it’s always a good idea to use white roof metal. This can make a BIG difference with indoor temperatures. White reflects more sunlight, and therefore, heat.

  11. Shade on the sunny side, use moringa trees? Trellises on the building with vines for shade creating a cool environment.

  12. I would say, get rid of all, at least 90%, of that paving/gravel surrounding the house. All it’s doing is reflecting the heat into the walls, and plant some quick growing, big-leafed plants/trees as close to the house as practicable and get some climbers growing on the walls – not actually on the walls, (because, earthbags) but on trellises 10-20-cm away from the walls, the gap provides a bit of a breezeway.
    Get rid of the dark brown tin roofing and replace it with a much lighter colour.
    Good luck.

  13. I am soon to build a cob hybrid house in Lucerne Valley, CA which is in the High Desert portion of the Mojave Desert.
    I am building on a hillside with a cliff as the north wall and the east and west walls sloping up the hillside.
    Only the south wall is going to built from the ground to the roof.
    It has a base of rock three feet thick and 2-3- feet high with 48″ of straw bale over that with a 6″ coat of cob inside and outside. The top two feet will be just cob 24″ thick and 12′ of that vertical space will be mostly windows.
    Three of the walls have literally a mountain behind them which is good insulation.
    The south wall is where I am really stacking the deck to insulate.
    I’ll let you know in two years if the inside temperature is the constant 65 degrees I expect it to be.

  14. you need ice bags.
    have you considered solar extraction fans in the ceiling.keep the doors shut shut as much as possible and suck the heat out, cause a draught from the slits in the bottom of the house, get it moving.

  15. Your home is gorgeous! Sorry to hear the heat is miserable. Have you looked into earth tubes? I remember learning about them in school many years ago, but have never used them. Here is an intro video–https://www.youtube.com/watch?v=l4nMsHqCTeI I hope you find a solution asap!


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