BUILDING

Or more about hydraulic lime, the construction and the comfort of Hartman Place

The Romans perfected the use of hydraulic lime; the Pantheon in Rome is the icon today of a lime concrete building that has stood since the 1st Century A.D. with little maintenance. Unfortunately, the building knowledge that created the Pantheon was lost during the Dark Ages and was just beginning to be understood again by mid-1800, when Portland cement was discovered. This new binder replaced the use of hydraulic lime by the early to mid 20th century in developed countries worldwide, although to this day some countries continue to use lime as a building material binder.  In France, two companies never quit making Natural Hydraulic Lime and they both export this material to the United States.  Even with shipping, this material carries a much smaller carbon footprint than Portland cement.

The case for lime was underscored by a unique combining of the two building materials at Fort Washington, just south of D.C., built to defend our capital in 1824. Originally, it was constructed using stone and brick with lime mortars, but in the late 1950’s, Portland cement mortar was used to repair a portion of the fort wall. Unexpectedly, less than 50 years later, the Portland repair fell off the fort wall while the lime portion stood strong. This stark illustration demonstrated the longevity of lime and the relative obsolescence of Portland cement.

At Hartman Place we are working with a team of engineers and materials specialists from Scotland, experts in the use of hydraulic lime, as well as a historic mason from Virginia, to develop a wall system composed of natural lime concrete blocks. This wall will be 24 inches thick; inside blocks will be filled with hydraulic lime concrete for a mass wall effect; the rest of the wall will be filled with a perlite and lime mix for insulation, forming a thermal break for the mass wall. Because of the porous properties of the lime binder, this wall will provide superior indoor air qualities. As the air vapor transfers through the wall, there will be no need for the trapping vapor barriers added to most new buildings. The interior and exterior finish will in most cases be lime plaster or stucco finish, painted with either a lime paint or a mineral paint that allows for the flow of vapors, but also inhibits the flow of water through to the inside. Natural lime plasters can be finished in many wonderful warm finishes and textures.

Heating and cooling at Hartman Place also has Roman roots. Roman hypocaust heating systems used radiant heating coupled with building mass to maintain comfort in the cold northern European climates. Turkish aristocracy channeled cool stream water through their palace walls to provide effective cooling during the warm summers. These two systems used building mass and radiant heat transfer systems to create effective indoor comfort conditions, and were constructed and designed over two millennia ago. Melding these old ideas with new technology, Hartman Place will use radiant tubes in the concrete floors and concrete ceilings with heated or cooled water from ground source heat pumps. Ground source heat pumps (GSHPs) are electrically powered systems that tap the stored energy of the greatest solar collector in existence: the earth. These systems use the earth's relatively constant temperature to provide heating, cooling, and hot water. These heat pumps offer high efficiency and low operating cost.