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The Mansion at Filoli is Cool, Daddy-o


By Joan Jordan, Chair of Garden Lecture Series and Co-chair of Self-guided Docent Committee


THE HOUSECome in and cool off in the mansion at Filoli. When the temperature rises above 90 degrees in the amazing gardens on the property, come inside to cool off.  That’s not what one normally expects – usually summer temperatures outside, with a breeze, are cooler than a brick house with no air conditioning. At Filoli, there can be as much as a 20 degree temperature difference between the formal sunken garden and the first floor of the house. It’s cool – literally, not just esoterically. The country house of stately proportions and more than 54,000 sq feet on three floors has a heating system but no cooling aids anywhere in the house.

In the 21st Century, we take temperature control for granted – flip a switch and pick your degree of heating or cooling. That was not available in 1914 when the house was planned. No major modifications have been made to the system and yet, the interior of the historic rooms offer cool respite from the California summer.

The other mystery which surprises visitors is why there are no falling bricks or major cracks in the brick exterior of the building. Why not? The San Andreas Fault runs right through the property, roughly 180 meters (600 feet) from the Georgian mansion.

The 1989 Loma Prieta earthquake rocked the Bay Area and wrecked havoc with brick buildings in San Francisco Filoli House experienced minimal damage. Bricks don’t flex when the earth shakes. Especially if they are under the pressure of holding up a roof or wall, their mortar cracks and breaks apart quickly. Yet, Filoli mansion stands proudly. Why? Why did the Bourn family build in an earthquake prone area after seeing what happened to San Francisco in 1906? The Bourns returned from Europe in 1906 to see their beloved city in ruins – what hadn’t fallen, burned.

Part of it is that they didn’t understand earthquakes like we do today. The exact causes of earthquakes were not known at the time. But, what was known, was that steel superstructures fared better in earthquakes. The bricks of Filoli are not truly structural but are instead a facing on the building. Therefore, the bricks are under very little downward pressure. Pressure would make their mortar rigid enough to crack when the earth moves. The genius of the design was to build the huge home with large open spaces for entertaining with the use of a STEEL superstructure.  

After the Loma Prieta earthquake Bay Area owners of unreinforced masonry (brick) buildings were required to retrofit their structures by adding a steel frame or reinforcing the walls in other -read expensive – ways. Not Filoli. The original  design from early 20th Century is generally what is recommended today. Although a retrofit was undertaken in 1993 and 1994, very few additional steel beams were found to be needed. Most of the retrofit involved the inside corners of the courtyard walls and the basement foundations.   

Huge steel girders rise on either side of the mansion and meet in the 11,000sq ft. attic. Climbing steep stairs from the third floor to the contiguous attic feels like traveling back through time. But then you’re greeted with the thoroughly modern sight of black steel beams that hold up the house! Mr. Bourn is famously quoted as wanting a garden that would be ‘interesting in 100 years’. It is likely that not only the garden, but the house will survive another century.

So that makes the forward thinking design ‘cool’ but how does that contribute to lower the temperature? The exterior brick facings are generally 13 inches thick.  The interior lath and plaster walls are anywhere from 6 to 18 inches away from the brick due to the structural steel I-beams. Another stroke of genius – the ‘dead’ space  provides plenty of space for all sorts of conduits. Electrical wiring, telephone wires, computer or television cabling, plumbing and heating pipes all pass through the space perfectly. Anything the 20th C. demanded, the generous space provided. AND the air space helps insulates the interior against extreme temperatures. Very cool, indeed. Mechanical necessities are hidden, which makes the rooms infinitely more gracious and the natural air conditioning keeps visitors comfortable.  

Cool, Daddy-o