Bill Tucker

To C. Letellier: thank you very much for your post. I was intrigued by the different thermal properties of marble chips vs. gravel in order to extend the number of days of heat storage. However, I have come to learn that in high humidity environments such as where I will be building, disease-promoting organisms thriving on the gravel is a threat. I will be incorporating Healthy House elements into my design so this particular health risk trumps the storage advantages. I wanted to stay away from (the more efficient) water as storage because I am concerned by leaks over time. However, I may end up designing an in-ground storage area which slopes away from the house if leaks ever do occur. Thank you again for your interest!

Thank you for your reply, Rebecca. I hope you enjoy Ladakh, which I have never visited, but I could never seem to get enough of the delicious Kerala food when visiting there!

Re opening up the house, I do not intend to exceed Brian's glass-to-floor ratio. And I envision a vine-covered trellis to block summer and fall sun. What I meant about opening the house up was sliding glass walls such as these: http://www.nanawall.com/ I feel that there must be a reasonable, cost-effective alternative to sealing oneself off from the outside. Air-conditioning has only been around for about 50 or so years...

I particularly appreciate your comments about cement and stone floors, the apparent materials of choice for thermal mass. And yes, I definitely prefer the thermal mass approach and see that Ladakh weather is harsher than where I intend to build, so their bulding experience is important.

Rebecca, thank you for your post. And Brian Knight! I appreciate your humor, have read your articles and even discussion threads, including those with Ted Clifton (ref. the upper-floor slab), which prompted me to visit him personally two months ago. (I live abroad, but perhaps I could interest you in getting together for coffee or lunch this October ...) I totally appreciate the thinking behind and success of the "insulate (very!) tight ventilate right" school of thought and have read about heating homes via body heat. Very impressive. My challenge, though, is that I ALSO want to open the house up to the lovely outdoors (e.g. Nana-type doors). I'm not sure the two design concepts are compatible but am definitely open to wise voices of experience. Yes re the thermal slab and the windows, and my exploration of gravel/marble includes strategies for passive cooling. I agree with you that humidity is my greatest challenge to address passively. Have you seen the Leaf House desiccant waterfall out of UMD? Not totally passive but very interesting. And I keep thinking that Vanderbilt and his summer guests were somehow ok without air conditioners and dehumidifiers. There MUST be strategies which work.

Rebecca, covenants I will have to follow disallow earthen buildings but I do appreciate their thermal properties combined with low-embodied energy. Good for you and again, thank you for your comment.

Finally, sincere kudos to PERMIES for helping me make these connections!!

Thank you for your prompt and very useful input, Miles. I had read the UNESCO document and am STILL trying to work through the formulae to figure out how much stone I will need. I had not seen the "Which Rocks Absorb Heat" article, which is clearer than others I have read. And I will look further into marble heaters! What I like about gravel (and marble?) storage is that the heating part can be totally passive, and the stone can be used for cooling too.

The "Which Rocks Absorb Heat" article mentions that two types of rocks may be best for a given application. That is precisely what I am trying to explore, but I can't find anything about good combinations, or even where such a configuration has been tried, if anywhere. That makes this search fun. The concept of two types of stone with different thermal characteristics makes good intuitive sense to me, but I struggle with interpreting the tables showing material density, heat capacity, thermal conductivity, etc. Are there any Science Teachers out there who can help?

Thank you again, Miles. I was very pleasantly surprised to see a notification from Permies that a reply had been posted!

I am planning on building a passive solar home and am considering a gravel bed for heat storage during the winter. My understanding is that gravel is "efficient" in that it heats up quickly during sunny days, which I believe also means that it will radiate out its heat quickly as well. To extend gravel bed heat storage over a greater number of sunless days, deeper gravel beds are needed. So I thought of marble as an alternative to deeper gravel beds. I believe marble takes longer to heat up ("Why does marble always feel cool?", etc.) but also longer to cool down, meaning it would store heat for more sunless days. Is this correct? Would it make sense to have TWO beds - one gravel and one marble - which would complement each other in terms of thermal properties? I have not been able to find any literature about this anywhere and I don't understand the thermal conductivity equations. Thank you all for any help.