This article discusses the design details, color, coating of a mass wall intended to absorb and store solar heat for a passive solar energy home.

Page top photo: interior of a passive solar home in Mexico.

Notice the small windows around the wall tops, avoiding excessive heat gain in summer. Photos by D Friedman.

Accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Coating, Color, Design for Thermal Mass Wall for Passive Solar Design

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Topic: Use of Drywall over Masonry Block Thermal Mass Wall

Question: what's the impact on thermal mass if we cover a masonry block wall with drywall - glued to the block?

In a passive solar home I am building, the entire first floor is enclosed by vermiculite-filled, 10-inch concrete block externally insulated by 2-inch thick polystyrene insulating board.

I am inquiring about the efficiency of covering the interior surface of the masonry block thermal mass wall with drywall that would be attached directly to the block by adhesive.

Will solar-gain heat be absorbed by the drywall and thereby conducted to and stored in the underlying masonry wall? -- David Kallett, Pompton Lakes NJ

Photo: solid brick walls of this New York City apartment were covered by glued-on drywall directly bonded to the brick, retaining much of the building's thermal mass.

This apartment is discussed also at PASSIVE SOLAR PERFORMANCE PROBE

Answer:

If the thermal mass walls are intended to absorb and store solar heat, the wall surface should have high absorptance (a dark color) and conductivity that equals or exceeds that of the storage materials themselves (the concrete block) so that heat will flow into the thermal storage wall at least as fast as if the wall were left uncovered.

You mention that most of the walls will not receive direct sunshine (see our photo at page top), but will absorb heat from the room air. In this case the color of the surface [of walls not receiving direct sunlight] has little importance in the heat gain and storage of the mass wall.

Plaster on the block wall would be your best bet, since its internal properties are about the same as concrete block, and it would bond tightly and continuously to the block.

Gypsum board is almost as conductive as concrete block (k = 4.4 vs. 5.0 for concrete block).

[See THERMAL MASS in BUILDINGS].

More important, however, is the bonding of the gypsum board or drywall to the block wall.

Gluing in the typical fashion (beads of glue applied with a caulking gun) will leave air spaces that will impede the heat flow from the drywall into the block wall.

So if you can't plaster the block wall, how about just painting it?

By the way, directly irradiated mass is several times more effective than convectively coupled mass - or in simple terms, a thermal mass block wall that receives direct sunlight is several times more effective than thermal mass walls that do not.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

The link to the original Q&A article in PDF form immediately below has been preceded by an expanded/updated online version of this article.

• Mass-Wall Finishes - Q&A on use of drywall over a block wall used for thermal mass storage in passive solar energy design - PDF version, use your browser's back button to return to this page
  

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Continue reading at FLOOR COVERING for OVER THERMAL MASS SLABS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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THERMAL MASS WALL DESIGN at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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