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Dear Family and Friends, This is the second of the three-part series of Protecting Your Home From Earthquakes. Part 2 focuses on non-structural areas that may need attention. For the most part, a preventative measure will be simpler and cheaper than structural supports. Many you'll be able to complete in 15 minutes or less, but with chimney bracing, you may want to call in a professional. CHIMNEYS Santa Claus might have a wee problem sliding down this chimney! Most brick chimneys built prior to 1970 lack adequate steel reinforcing and metal strapping. These two modifications typically reduce serious damage. In a violent earthquake, it's common for chimneys located on outside walls to crack at the roof line. The portion which extends beyond the roof line is most vulnerable. As a general rule, the taller, more slender chimney, is most susceptible to quake damage. In some cases, the entire chimney can peel away from the side of the home or crash through the roof. If a chimney is still standing after an earthquake, it can present a major safety hazard. Check the chimney for cracks and weak mortar after a shaker and before using it. Any crack wider than the edge of a dime or an Australian 5 cent coin is serious. Mortar between bricks should not scrape away easily with a metal tool. An unreinforced brick chimney in Kelso damaged during the 1949 Olympia quake. This chimney twisted on a mortar joint. (Photo from Edwards, 1951). UNREINFORCED CHIMNEYS Even if your chimney is in good condition, it may still be at risk, especially if it is tall and slender. Some chimneys have metal straps that hold them to the side of the home. Carefully inspect these fastenings. They should be in good condition with no evidence of poor workmanship or rust. If you are uncertain about what you see, consult with a professional engineer. The engineer may recommend adding a brace between the top portion of the chimney and the roof. You may also need to use metal straps at several points to anchor the chimney to the home. When a chimney is to be replaced because of structural damage, there are two alternatives to consider: 1. Replace entire structure with a new reinforced brick chimney including building a new reinforced concrete foundation. 2. Replace the existing brick chimney down to the shoulder with a new lightweight prefabricated metal flue system with a wood enclosure. UH-OH Chimneys are built with tons of brick and mortar which can crash through the roof into the house or down to the ground injuring people and "remodeling" vehicles. Though this chimney damage was due to a tornado, it illustrates the hazard presented should the brick and mortar give way. BRACING THE CHIMNEY Check to see if your chimney is both reinforced and strapped. Straps are usually visible in the attic and should be nailed or bolted to the ceiling framing or blocking. However, a structural engineer should be consulted for this project. We have to agree especially in light of conflicting information from respected sources on how to secure the chimney. The difference of opinion has to do with tying the chimney to the roof. The Army Corp. of Engineers advises against doing this saying it can cause the chimney to fall through the roof as a unit rather than shatter in smaller pieces. The photo on the right is an example of a chimney braced to the roof. WHERE TO REINFORCE A CHIMNEY Metal straps are an excellent way to brace and stabilize a chimney. For a secure chimney three sets of opposing straps should be installed and one at the chimney top. Alternately the Corp. recommends that the ceiling surrounding the chimney be reinforced with 3/4" plywood nailed to ceiling joists. Additional structural work may be needed like blocking between the joists or using additional hold downs on corners of the building. A professional can best supply the specifics. On the flip side of the roof issue, EQE International, a two-decade old consulting and engineering firm specializing in structural and seismic engineering says just the opposite. "Masonry chimneys should be reinforced with steel and tied to the roof and upper floor framing with steel straps to make them more earthquake-resistant."2 NOTE: Wood blocking should be added to joists underneath metal straps. So bottom line, once you've done the preliminary checking, consult a structural engineer for advice. Continue © Text and Graphics, 2001 Stan and Holly Deyo, except where otherwise credited