Lightweight Thermal Mass

An oxymoron?  I'm designing a house for my son.  I want to see if it is possible to insulate under the wooden floor with vermiculite and achieve solar heat storage on the south facing wall.  There will be floor to ceiling (almost) windows via French doors on the S, SW, and W facing walls of the octagonal wooden 'yurt'.

Even if we don't get it to throw a ton of heat back on winter evenings, can we make the house more heat efficient vs conventional methods?

Thanks heaps,

I think it would be difficult. Most things that absorb heat well, tend to be dense and heavy. You could maybe look at some of the phase change materials that are used in greenhouses.

I guess I would be curious, why the lightweight requirement? Will this yurt be moved around a lot? Could you accomplish the same end result of a more comfortable interior by using more insulation vs actual heat storage?

Hi, Nissa

I don't have any knowledge on vermiculite though these threads might help you or others that might be interested in using vermiculite in passive solar:

https://permies.com/t/42722/Passive-Solar-House-design-Cloudy

https://permies.com/t/103389/PAHS-AGS-style-heating-cooling#851904

Is your octagonal design more like a yurt (tent) or more like a hogan house (adobe and wood)?

For a small space and portability, what about water? A row of jugs, preferably dark coloured, would work pretty well and when it comes time to move, you just tip them out and refill at the new site.

Or you could have boxes filled with sand.

Matt McSpadden wrote:I think it would be difficult. Most things that absorb heat well, tend to be dense and heavy. You could maybe look at some of the phase change materials that are used in greenhouses.

I guess I would be curious, why the lightweight requirement? Will this yurt be moved around a lot? Could you accomplish the same end result of a more comfortable interior by using more insulation vs actual heat storage?

Lightweight because we're wanting to build on piers rather than laying a slab, if possible.

Good questions.  Thanks!

I't s actually a modified Coperthwaite yurt.  Because we want taller windows and French doors on the southern-most sides, we're modifying the first floor to have straight side rather than slanted.  

Amy Gardener wrote:Is your octagonal design more like a yurt (tent) or more like a hogan house (adobe and wood)?

We're planning to collect rainwater from the roof (preferably a living one).

Phil Stevens wrote:For a small space and portability, what about water? A row of jugs, preferably dark coloured, would work pretty well and when it comes time to move, you just tip them out and refill at the new site.

Or you could have boxes filled with sand.

So I've decided to go with really good insulation and a Walker continental rocket cooker/mass heater.  It's rated to heat 1200 sq ft and we're under that.  I'm considering hempwool insulation at this time.  I'm also considering transoms over the doors for better airflow when the doors are closed.  If at all possible, I'll use pocket French doors on those rooms that need doors, except for maybe the bathroom.  That will probably get a solid door. :).

Thanks for your input everyone!

The answer is NO.  Mass is mass and you want as much of it as possible.

If you are building a Walker cookstove, you will obviously be giving that area a substantial foundation. If you wanted mass spread over/in the floor, that can give a good amount without stressing any one support too much. Vermiculite would be insulation and not mass. You could put down a layer of vermiculite topped with gravel or other mass material (as long as you protect the vermiculite from damp, as it will wick water and reduce its insulating ability.)