Natural Adobe “Thermal Mass”

Credit: National AtlasPassive solar design has nothing to do with high technology or blue panels.  It is an ancient understanding which used to be practiced in home building everywhere  outside the tropics – until cheap energy made it less essential.

Today passive solar is undergoing a renaissance as we come to terms with the cost of our dependence on fossil and other fuels.  People are beginning to understand that we can live much more independently and comfortably by reviving some of these ancient understandings.

Passive solar design requires 3 or 4 things:  1) solar gain, 2) thermal mass, 3) insulation, and sometimes 4) convection.  Most people understand solar gain – getting the sun to shine into enough windows to gain heat – and insulation – which must be on the outside of the house when working with thermal mass.  Convection means the movement of air, so that the heat doesn’t accumulate in one portion of the house.  And thermal mass – that’s what most people need help understanding, even though it’s a fairly simple concept.

Some things exposed to heat absorb the heat better than other things, for instance, bricks and stones will be hotter after exposure to sun than wood will be.  Other thermal mass materials are concrete, containers of water, cast iron, and adobe.  When a home has substantial thermal mass inside it, and it gains heat in any manner – solar, fireplace, furnace – the heat will be absorbed into the thermal mass in the home, and it will be held there indefinitely.

On the other hand, if a home has little or no thermal mass, then the heat stays in the air, and sometimes the air can become too hot for comfort.  And the heat can be very easily lost when a door or window is opened – wasting it.

Two important things happen when a home has thermal mass absorbing the heat:  1) the air temperature will not skyrocket or make the house or room too hot to use, and 2) the absorbed heat will be released slowly only after the air temperature has fallen.  Both the daytime heat and the nighttime cold are moderated.  Wild swings of 50-60 degrees in a day can be radically moderated to mild swings approaching zero, depending on how much thermal mass is involved.

This home has had 2 tons of adobe brought in, plus bricks, cast iron, and tile. Sometimes when others complain of hot days or cold, I don’t even need to turn on the swamp cooler or furnace!

IMG_3429 cropOf all the materials that provide thermal mass, adobe is the most ancient, inexpensive, and fun to use.

The current American renaissance of “natural plaster” is simply a refined version of adobe – each of the elements is simply sifted through a fine screen for a smooth finish.  This is applied over ordinary adobe, which is used to create the overall shape or the sculpture.

Other natural elements are often added to modern mixes, including shredded newspaper (for fiber which helps knit it together), wheat paste (for the hardening glue), borax (to inhibit mold), earth pigments (for color), additional clay (for color and stickiness), glass sand (for brightening), mica (for sparkle), etc.

IMG_3371   This “Grandmother tree” has a full moon behind one fin

This younger tree disguises a buttress, and appears to dance:tree cropped

And all the doors and windows are framed with arches, breaking the standard rectilinear design of most homes:IMG_3401

But the main purpose, beyond this fun, is thermal mass – 2 tons – which keeps the home warmer in winter and cooler in summer, naturally.