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Building modified Trombe wall — How to stop heat from sinking into foundation?

albion10 | Posted in Green Building Techniques on

Howdy planning a modified trombe wall but wondering how to stop the heat from migrating threw the 8 ” stem wall an down into the foundation an soils of the crawl space. Is there a method of installing say a 2″ isolation foam wedge to isolate the wall above the main floor ?

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  1. Expert Member
    ARMANDO COBO | | #1

    It would help if you have a detail we can see. Is the trombe wall on top of the stem wall or on top of a concrete slab? Is it a slab on grade? Monolithic or three pour foundation? Is the slab and stem wall detached? Usually trombe walls are set 1’-2’ away from the south facing window. Where is your location or climate zone? What are its dimentions and material the trombe wall is to be build? Is it a closed or open system? Is it mechanically aided or passive? Has the foundation and/or floor system already built or are you on the design stage?

  2. GBA Editor
    Martin Holladay | | #2

    No one builds Trombe walls any more, for good reasons. The investment in materials will never yield a reasonable return in energy savings. There are lots of measures you can employ to save energy in your home that make more sense. Start with air sealing measures, better insulation, and high-quality windows -- forget the Trombe wall.

    If, however, you can't resist experimenting, there are ways of insulating a concrete wall so that it doesn't lose heat to the earth. It's even possible to install foam under the footing of your wall if you want to. More information here: Foam Under Footings.

  3. albion10 | | #3

    Thank you for your responses. First in the planning stage was considering extending the concrete stem wall 4 foot above the first floor to act as a heat sink and store then release heat into the room. The cost of extending the wall will be next to nothing as will do work my self and its a 10 foot long wall.. Unlike a true trombe wall this wall will be the opposite wall of the room not right next to the glass. So i was thinking of an isolation foam wedge at the sub foor level in the cement to stop heat sink.
    Reducing the chance of over heating due to a large southern exposure is my reasoning for the trombe wall. Always a good idea to reduce air infiltration and better windows are a small help. Going with an air infiltration rated glazing or .1 . Thanks again for your responses.

  4. Expert Member
    ARMANDO COBO | | #4

    If I understand correctly, you are building a Mass Wall, which is very different than a Trombe Wall. Both walls have kind of similar purposes, but they are different applications, and as such they require different design principles.
    Both Mass and Trombe walls store thermal energy to be release at a slower rate, but that energy is released in very different ways. In a Mass wall, it is released to the inside and outside at the same time, and the temperature differences dictates the rate of heat transfer to both sides. In a Trombe wall, which is inside the building enclosure, all the heat is release to the inside of the building. A passive system can work well in small buildings, but in large buildings unless they are mechanically aided, it will make room temperatures too uneven to be comfortable. I’ve seen too many homes in the Southwest with Trombe/Mass walls that are a complete failure, and IMO, a waste of resources.
    I’ve designed Trombe walls that are a closed systems. The walls are contained between floor to ceiling, and both sides. One side has a door or passage way that you can enter to clean the windows from time to time. The walls have an opening(s) at the bottom, and a dedicated ducted fan to the plenum of the air handler, so the warm air is distributed to other rooms in the building, and controlled by a thermostat. I have not designed homes with a Mass wall only, but I imagine you could install a dedicated ducted fan located high on a wall or ceiling, to the plenum as well,
    Either way, even when they are done right, they are difficult to control and homeowners need to be open to life and comfort adjustments. Also, the thickness of a mass wall need to be calculated correctly, as it may release heat too soon or too late. The Anasazi and Pueblo people in NM and the Southwest knew that a thousand or so years a go.
    I should mention to include Passive Solar principles in the house design. You do not want to heat a Mass or Trombe wall in the middle of summer. Also, if done correctly, you could help cool a house in the summer days after cool evenings.

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