About the House: Unreinforced Masonry and the Craftsman Home

By Matt Cantor
Thursday January 07, 2010 - 08:48:00 AM
The Craftsman Bungalow often found in Berkeley poses hazards in earthquake country.
Matt Cantor
The Craftsman Bungalow often found in Berkeley poses hazards in earthquake country.

It’s a good thing there are no dead-animal right’s groups or I’d surely be hiding in my home most of the time, because there’s nothing I enjoy more than beating a dead horse. 

The main issue I should like to beat to the ground today is that long-expected earthquake that has yet to hit our Terra Haute Cuisine of Berkeley, California.  

Based on their design, houses vary a lot in the way they will respond to earthquakes. We are clearly making very substantial headway in the varied areas of code enforcement, design education and manufacturing, but that only speaks to newer homes. We are graced with a splendid landscape of older homes in this Arcadia of ours, and among these are homes that possess special vulnerabilities to earthquake movement. One type, that I happened to see the other day is not uncommon (at least locally) and worthy of some discussion. 

This house is a type of Craftsman Bungalow, but all Craftsman Bungalows do not share these features. Nonetheless, much of what I have to say will apply to this lovely style of house. 

If you drive through the streets of the East Bay, particularly in the older neighborhoods, you’ll periodically spot a house that has stone or brick columns in the front and a long sweeping porch roof that will cross and extend past a large front porch. These often sport a stone foundation below the porch and also have, with few exceptions, a stone or brick chimney (usually stone or stone-faced).  

These houses have never (I said never) been hit by an earthquake of any significant size. For some of you this will be repetition, but it’s critical to understand that our area has seen only minor temblors in the last 141 years and that includes both the Loma Prieta (1989) and the 1906 earthquake in San Francisco. While the ’06 was fairly large in San Francisco, there wasn’t much damage over here. Actually, the last “big one” in 1868 did quite a bit of damage and there were relatively few building standing here at that time.  

So when we’re looking at stone pillars on a building from 1908 and marveling at their condition, we should keep in mind that a one minute event that will likely occur in the next few years will do what nothing over the last 100 years could do. 

Mortared stone or brick (referred to in the parlance as unreinforced masonry, or URM) is particularly vulnerable to the shaking and vibration of large-scale earthquakes. Past earthquakes have provided loads of evidence defending this notion. If your front porch and a large portion of your roof is supported by a pair or set of mortared stone columns, it is nearly certain that these will be in a state of collapse after the next earthquake. This is not the case for many other styles of buildings, including many that date from the same era. This is a special class.  

Some buildings from this period, many of them bungalow style, have stone or brick foundations and we all know that these are similarly unreliable. While a house may not collapse as a result of a collapsed brick foundation, it may be unmanageably expensive to pick up this house, move it back to its original location and install a foundation beneath it after the damage has been done. You might just find yourself walking away with a small fraction of its former value as compensation. Not to mention that you’ll be one of the half million refugees that are expected in the wake of Upheaval Alice. 

An additional issue with most of the early buildings of the East Bay (again, subject of past discussion at this birdcage liner) is that brick was the preferred material for chimneys and flues, and this means that virtually all of these houses will experience falling (or flying) brick as these tall narrow stacks shake violently apart. Now, many chimneys are located along the perimeter of the house and mount to the exterior of framed walls, which means that they these will do relatively small amounts of damage to these houses and their occupants. But many early 20th-century houses contain brick flues that are entirely within the framed structure.  

Many of these are paired flues that served two adjacent functions; one serves as a stove vent and the other as a flue for a coal burner or fireplace (most were for coal). Since most of these serve no practical function today and will certainly make a helluva mess (and perhaps do real harm to occupants) when Alice hits, it’s best to remove these. At very least, take a good look at these, discuss them with your family and be prepared to move away from them when an earthquake starts. Consider that the removal of items like this can open up storage area, decrease the likelihood of leaks in subsequent roofs and increase your choices during kitchen remodeling. 

A house that lacks these areas of URM is nearly certain to have a better time of it during a large earthquake. Such a house is also much more likely to provide you with that green tag, allowing you to stay put afterwards (a red tag sends you to your in-laws and all that bad food).  

If you have a porch of the kind I’ve described, there are fixes but they’re not cheap. As one of the Faithful, I cannot, in good conscience, condone a major design and appearance change for these homes so I feel obliged to start with the fix that I firmly believe in. Stone or brick columns can be replaced with steel reinforced concrete ones clad in stone or brick facings just thick enough to pull of the illusion. Modern houses that have “stone” columns are virtually always of this kind. For real authenticity, one can even saw the existing stone or brick into the thin slices on a tile or lapidary saw so that the color and patterns match other remaining parts of the house. 

If a stone or brick foundation supports the porch or other parts of the house, and one is sufficiently devoted, the same facing trick can be performed. But I would only bother in cases where the front footing is tall and clearly visible from the street. 

In the case of columns or footings, an engineer is the person to talk with, in part because there may be other issues to tackle while you’re at it. In the case of our huge front porch roof, the columns may need to be built to manage substantial swaying forces in addition to simple “gravity” loads. This is likely to include the use of heavy hardware as well as a wide and deep base capable of resisting overturning forces. 

Once in a great while, I see a grand dame from 1905, of just the kind I’m describing, that has been similarly transformed and, for me, it’s very exciting (I don’t get out much). Because my love of these houses is so great and my belief in what this earthquake will do, is so firm, it just makes me want to hug the person that had the vision and spent the money to save another work of art. If you own such a house, think hard on these things. I’m saving a hug for you too.